Inverters to power fluorescent lamps from low voltage DC
Introduction:
------------
This is a collection of non-intelligent (at least for now) inverter circuits
for operating fluorescent or other similar devices from low voltage DC power
sources. These designs - mostly obtained by reverse engineering commercial
camping lanterns, power inverters, and the like - are all very basic circuits
which use simple oscillators, easy to obtain or construct transformers, and
common power semiconductors.
These designs can easily be modified for other purposes such as powering
photoflash or signal strobes and HeNe lasers.
Additional circuits will be added as they become available. Contributions
are welcome.
Super simple inverter:
---------------------
This circuit can be used to power a small strobe or fluorescent lamp. It will
generate over 400 VDC from a 12 VDC, 2.5 A power supply or an auto or marine
battery. While size, weight, and efficiency are nothing to write home about -
in fact, they are quite pitiful - all components are readily available (even
from Radio Shack) and construction is very straightforward. No custom coils
or transformers are required. If wired correctly, it will work.
Output depends on input voltage. Adjust for your application. With the
component values given, it will generate over 400 V from a 12 V supply and
charge a 200 uF capacitor to 300 V in under 5 seconds.
For your less intense applications, a fluorescent lamp can be powered directly
from the secondary (without any other components). This works reasonably well
with a T5-13W or T8-15W bulb but Q1 does get quite hot so use a good heat sink.
C1 1 uF D2 1N4948 R2
+------||------+ T1 1.2KV PRV 1K 1W
| | +-----|>|-----/\/\---+------o +
| R1 4.7K, 1W | red ||( blk |
+-----/\/\-----+------+ ||( |
| yel )||( +_|_ C2
+ o----------------------------------+ ||( --- 300 uF
| red )||( - | 450 V
| +--------------+ ||( |
| Q1 | ||( blk |
6 to 12 | |/ C +--------------------+------o -
VDC, 2A +----| 2N3055 Stancor P-6134
D1 _|_ |\ E 117 V Primary (blk-blk)
1N4007 /_\ | 6.3 VCT Secondary (red-yel-red)
| |
- o------------+------+
Notes on super simple inverter:
------------------------------
1. Construction can take any convenient form - perf board, minibox, etc.
Make sure the output connections are well insulated.
2. C1 must be nonpolarized type - not an electrolytic.
3. D1 provides a return path for the base drive and prevents significant
reverse voltage on the B-E junction. Any 1 A or greater silicon diode
should be fine.
4. C2 is shown as typical energy storage capacitor for strobe applications.
5. D2 should be a high speed (fast recovery) rectifier. However, for testing,
a 1N4007 should work well enough. R2 limits surge current through D2.
6. The polarity of the input with respect to the output leads is important.
Select for maximum voltage by interchanging the black output wires.
7. Mount Q1 (2N3055) on a heat sink if continuous operation is desired. It
will get warm. Any general purpose NPN power transistor should work. For
PNP types, reverse the the polarities of the power supply and D1, and
interchange one set of leads (where a diode is used for DC output).
8. Some experimentation with component values may improve performance for
your application.
9. When testing, use a variable power supply so you get a feel for how much
output voltage is produced for each input voltage. Component values are
not critical but behavior under varying input/output voltage and load
conditions will be affected by R1 and C1 (and the gain of your particular
transistor).
10. WARNING: Output is high voltage and dangerous even without large energy
storage capacitor. With one, it can be lethal. Take appropriate
precautions.
11.
| | |
---+--- are connected; ---|--- and ------- are NOT connected.
| | |
Low power fluorescent lamp inverter 1:
-------------------------------------
The circuit below was reverse engineered from a model number FL-12 'Made
in Hong Kong' battery (8 AA cells) or 12 V wall adapter powered portable
fluorescent lamp. The bulb is an F8-T5.
This design can easily be modified for many other uses at lower or higher
power. Note that its topology is similar to that of the circuit described
in the section: "Super simple inverter".
C2 .01 uF
+------||------+ T1 3
| | +------------+-+
| R1 1.5K | 4 o ||( | |
+-----/\/\-----+------+ ||( +---+
| 15T F )||( | |
| 1 )||( | | FL1
+ o-----+----------|---------------------+ ||( O 350 T | | F8-T5
| | )||( | |
| | 20T D )||( | |
| R2 / 2 )||( | |
| 68 \ +-------+------+ ||( +---+
6 to 12 _|_ C1 / Q1 | | ||( | |
VDC --- 100 uF | | | +---+--------+-+
| 16 V | |/ C | |
| +----| 5609 +---------------+
| C3 _|_ |\ E NPN O = Output
| .027 uF --- | D = Drive
| | | F = Feedback
- o-------+----------+------+
Notes on low power fluorescent lamp inverter 1:
----------------------------------------------
1. T1 is an E-core ferrite transformer. The core is 5/8" x 3/4" x 3/16"
overall. The outer legs of the core are 3/32" thick. The central leg is
3/16" square. The square nylon bobbin has a diameter of 5/16". There is
no visible spacer between the cores but I did not disassemble to confirm.
The 350T O (Output) is wound first followed by the 25T D (Drive) and 18T F
(Feedback) windings. There should be a strip of mylar insulating tape
between each of the windings.
The number of turns were estimated without disassembly as follows:
* The resistances of each of the windings was measured to determine the
arrangement of the transformer.
* The inverter was run at just enough input voltage for it to oscillate
(so the load of the fluorescent tube would not affect the readings) and
the voltages on all 3 windings were measured on an oscilloscope.
From this, the ratios for the windings were determined.
* An estimate was made of the number of turns likely to be on the Drive
winding based on other similar designs. The number of turns on the
other windings were calculated based on the turns ratios. Wire size
is probably #36 AWG.
2. The transistor was marked 5609 which I could not cross to anything. I
would guess that a general purpose medium power transistor like a 2N3053
or ECG24 would be suitable. For PNP types, reverse the polarities of the
power supply and C1.
Since it is very low power, no heat sink is used in this lamp. However,
for other applications, one may be needed.
3. Some experimentation with component values may improve performance for
your application.
4. When testing, use a variable power supply so you get a feel for how much
output voltage is produced for each input voltage. Component values are
not critical but behavior under varying input/output voltage and load
conditions will be affected by C2, C3, R1, R2, the number of turns on each
of the windings of T1, and the gain of your particular transistor.
5. WARNING: Output is high voltage and dangerous. Take appropriate
precautions.
6.
| | |
---+--- are connected; ---|--- and ------- are NOT connected.
| | |
Low power fluorescent lamp inverter 2:
--------------------------------------
The circuit below is the type used in inexpensive fluorescent camping lanterns.
It will drive T5-4W to T5-13W tubes depending on input voltage. The power
source can be a 4 to 9 V 2 A power supply (depending on the size of your lamp)
or a suitable battery pack. This design was reverse engineered from a random
commercial unit of unknown manufacture.
o T1
+ o----+---------+-------------------+
| | )|:| o C2
| S1 | D 20T )|:| +-------||-----+-+
| Start |- #26 )|:|( .022 uF | |
| | )|:|( 600 V +---+
| | +-------+ |:|( | |
| R2 \ | |:|( O 250T | |
| 270 / | o |:|( #32 | | FL1
| \ +------|-------+ |:|( | | T5 lamp
+_|_ C1 | | | F/S 7T )|:|( | |
--- 100 uF | | | #32 )|:| +-------+ | |
- | 16 V +----|------|---+---+ | +---+
| | | | | | |
| | | +-----------------|------+-+
| | +-----------+ |
| S2 | | | | O = Output
| _|_ Off | |/ C | | D = Drive
+-- --+--------+----| Q1 | | F/S = Feedback/starting
| | | |\ E 2SC1826 _|_ D2 |
| \ _|_ | /_\ 1N4007 |
| R1 / D1 /_\ | | |
| 220 \ 1N4148 | | | |
| | | | | |
o-----+-----+--------+------+-----------+---------+
The approximate measured operating parameters are:
Lamp type V(in) I(in) starting/running
-------------------------------------------------------------
T5-4W 3 V .9/.6 A
4 V 1.1/.7 A
5 V 1.3/.8 A
T5-6W 4 V 1.1/.8 A
5 V 1.2/.9 A
6 V 1.4/1.0 A
T5-13W 6 V 1.6/.95 A
7 V 1.7/1.0 A
8 V 1.8/1.2 A
9 V 2.1/1.3 A
No, this circuit does not have over 100% efficiency (the power input is less
than the tube wattage ratings). Obviously, the tubes are not being run at
their full rated power (I have not measured output V and I).
Notes on low power fluorescent lamp inverter 2:
-----------------------------------------------
1. Construction can take any convenient form - perf board, minibox, etc.
Make sure the output connections are well insulated.
2. T1 is assembled on a square nylon bobbin, 3/8" cubed. Wind the 250T O
(Output) first, insulate with mylar tape, 20T D (Drive) next, and 7T F/S
(Feedback/Starting) last. Observe directions of windings as indicated by
the dots (o). The number of turns for the O winding was estimated based
on measured winding resistance, wire size, and the dimensions of the bobbin.
The core is just a straight piece of ferrite 1/4" x 1/4" x 1-3/8" It is
fully open - there is no gap.
3. Any general purpose reasonably high gain NPN power transistor should work.
For PNP types, reverse the polarities of the power supply, C1, D1, and D2.
Use a good heat sink for continuous operation at higher power levels (6 V
input or above). The type used (2SC1826) was a replacement after I fried
the unidentified transistor originally installed.
4. Pushbutton switches are used to control operation. S1 (Start) provides
initial base drive to the transistor via the Feedback/Starting winding of
T1 until the tube arc is established. At that point, feedback is sustained
via current flowing through the tube. S2 (Off) shorts the base of the
transistor to ground to stop the oscillator.
Like a regular manual start preheat fluorescent fixture, the start switch,
must be depressed until the lamp comes on at full brightness indicating that
the filaments are adequately heated.
5. Some experimentation with component values may improve performance for
your application.
6. When testing, use a variable power supply so you get a feel for how much
output voltage is produced for each input voltage. Component values are
not critical but behavior under varying input/output voltage and load
conditions will be affected by R1 and R2 (during starting in particular),
the number of turns on each of the windings of T1, and the gain of your
particular transistor.
7. WARNING: Output is high voltage and dangerous. Take appropriate
precautions.
8.
| | |
---+--- are connected; ---|--- and ------- are NOT connected.
| | |
Archer mini flashlight fluorescent lamp inverter:
------------------------------------------------
The circuit below was reverse engineered from the Archer model number 61-3724
mini fluorescnet/incandescent flashlight combo (no longer in the Radio Shack
catalog). The entire inverter fits in a space of 1-1/8" x 1" x 3/4". It is
powered by 3 C size Alkaline cells and drives a T5-4W tube.
This design can easily be modified for a many other uses at lower or higher
power.
o T1
+ o----+----------+----------------+ o
| | )|:| +--------------+-+
| \ D 28T )|:|( | |
| R1 / #26 )|:|( +---+
| 560 \ +---------+ |:|( | |
| / | |:|( O 315T | | FL1
| | | o |:|( #32 | | T5-4W
| +------|---------+ |:|( | |
| | | )|:|( +---+
+_|_ C1 | | F 28T )|:|( | |
--- 47 uF | | #32 )|:| +--------------+-+
- | 16 V | | +---+
| | | Q1 | O = Output
| | C \| | D = Drive
| C2 _|_ |---+ F = Feedback/Starting
| .022 uF --- E /| |
| | | _|_ C3
| | | --- .022 uF
| | | |
o-----+----------+------+-----+
Notes on Archer mini flashlight fluorescent lamp inverter:
---------------------------------------------------------
1. T1 is an E-core ferrite transformer. The core is 5/8" x 3/4" x 3/16"
overall. The outer legs of the core are 1/8" thick. The central leg
is 3/16" square. The square nylon bobbin has a diameter of 5/16". There
is a .020" gap (spacer) in between the two halves of the E-core.
The 315T O (Output) is wound first followed by the 28T D (Drive) and 28T F
(Feedback) windings. There should be a strip of mylar insulating tape
between each of the windings.
The number of turns were estimated without disassembly as follows:
* The wire sizes were determined by matching the diameters of the visible
ends of the wire for each winding to magnet wire of known AWG.
* The number of turns in the Output winding was determined based on its
measured resistance, core diameter, and the wire gauge tables.
* A 50 KHz .1 V p-p signal was then injected into the Feedback winding.
The amplitudes of the resulting outputs from the Drive and Output
windings were then measured. From these, the ratios of the number of
turns were calculated.
2. The transistor was totally unmarked. Any general purpose reasonably
high gain NPN power transistor should work. For PNP types, reverse the
polarities of the power supply and C1.
Since it is very low power, no heat sink is used in the Archer flashlight.
However, for other applications, one may be needed.
3. Some experimentation with component values may improve performance for
your application.
4. When testing, use a variable power supply so you get a feel for how much
output voltage is produced for each input voltage. Component values are
not critical but behavior under varying input/output voltage and load
conditions will be affected by C2 and C3, the number of turns on each of
the windings of T1, and the gain of your particular transistor.
5. WARNING: Output is high voltage and dangerous. Take appropriate
precautions.
6.
| | |
---+--- are connected; ---|--- and ------- are NOT connected.
| | |
Energizer mini flashlight fluorescent lamp inverter:
---------------------------------------------------
The circuit below was reverse engineered from the Energizer model number
unknown (worn off) mini fluorescent/incandescent flashlight combo. The entire
inverter fits in a space of 1-1/8" x 1-1/8" x 3/4". It is powered by 4 AA
size Alkaline cells and drives a F4-T5 tube.
This design is very similar to the Archer model (see the section: "Archer mini
flashlight fluorescent lamp inverter", but eases starting requirements by
actually heating one of the filaments of the T5 lamp. Thus, a lower voltage
transformer can be used.
o T1 o
+ o----+----------+--------+-------------------+ |:| +----------------+
| | C4 _|_ )|:|( H 16T #32 |
| \ 1000 --- D 32T )|:| +--------------+ |
| R1 / pF | #26 )|:|( | |
| 360 \ +-------------------+ |:|( +---+
| / | |:|( | |
| | | o |:|( O 160T | | FL1
| +--------|-------------------+ |:|( #32 | | F4-T5
| | | )|:|( | |
+_|_ C1 | | F 16T )|:|( +---+
--- 47 uF | | #26 )|:|( | |
- | 16 V | | Q1 +---+ |:| +--------------+-+
| | | MPX9610 |
| | C \| R2 | O = Output
| C2 _|_ |---+---/\/\--- D = Drive
| .047 uF --- E /| | 22 F = Feedback
| | | _|_ C3 H - Heater (filament)
| | | --- .01 uF
| | | |
o-----+----------+--------+-----+
Notes on Energizer mini flashlight fluorescent lamp inverter:
------------------------------------------------------------
1. T1 is an E-core ferrite transformer. The core is 1/2" x 5/8" x 3/16"
overall. The outer legs of the core are 3/32" thick. The central leg
is 3/16" square. The square nylon bobbin has a diameter of 5/16". There
is a .010" (estimate) gap (spacer) in between the two halves of the E-core.
The 160T O (Output) is wound first followed by the 16T H (Heater), 32T D
(Drive), and 16 T F (Feedback) windings. There should be a strip of mylar
insulating tape between each of the windings.
The number of turns were estimated after unsoldering the transformer from
the circuit board as follows:
* The wire sizes were determined by matching the diameters of the visible
ends of the wire for each winding to magnet wire of known AWG.
* The number of turns in the Output winding was determined based on its
measured resistance, core diameter, and the wire gauge tables.
* A 100 KHz .1 V p-p signal was then injected into the Drive winding. The
amplitudes and phases relationship of the resulting outputs from the
Feedback, Heater, and Output windings were then measured. From these,
the ratios of the number of turns and winding start/end were determined.
2. The transistor was an MPX9610. I was not able to locate specs for this
part number but a transistor like a 2N3053 or ECG24 should work. For PNP
types, reverse the polarities of the power supply and C1.
Since it is very low power, no heat sink is used in the Energizer
flashlight. However, for other applications, one may be needed.
3. Some experimentation with component values may improve performance for
your application.
4. When testing, use a variable power supply so you get a feel for how much
output voltage is produced for each input voltage. Component values are
not critical but behavior under varying input/output voltage and load
conditions will be affected by C2 and C3, the number of turns on each of
the windings of T1, and the gain of your particular transistor.
5. WARNING: Output is high voltage and dangerous. Take appropriate
precautions.
6.
| | |
---+--- are connected; ---|--- and ------- are NOT connected.
| | |
Medium power fluorescent lamp inverter:
--------------------------------------
This circuit is capable of driving a variety of fluorescent lamps from a 3 to
12 V, 2 to 3 A DC power supply, or auto or marine battery. With appropriate
modifications (if needed) it may be used for other applications like powering
an electronic flash or HeNe laser tube. The transformer will need to be custom
wound (by you) but this is not really difficult - just slightly time consuming
for the 600 turn O (Output) winding if you don't have a coil winding machine.
I have used it on fluorescent tubes of many sizes: F6-T5, F13-T5, F15-T12,
and F20-T12. The arc will be sustained with the filaments hot on an input
as low as about 3.5 to 4 V (with a new tube) but during starting, an input
voltage of about 5 or 6 V may be needed until the filaments are hot enough
to sustain the arc at the lower voltage.
+Vcc
o Q1 +----------------+
| | )|:|
+ B |/ C )|:|
L1 |:|( +------| 2N3055T )|:| C1
24T |:|( | |\ E D 15T )|:| +----------||---------+-+
#22 |:|( | | #26 )|:|( .0039 uF | |
+ | -_- )|:|( 600 V +---+
| | )|:|( | |
+--|-------------------------+ |:|( | |
| | Q2 _-_ )|:|( | | FL1
| | | )|:|( O 600T | | F5 lamp
| | B |/ E D 15T )|:|( #32 | |
| | ----| 2N3055T #26 )|:|( | |
| | | |\ C )|:|( | |
| | | | )|:|( | |
| | | +----------------+ |:|( +---+
| | | |:|( | |
| | -----------------------+ |:| +---------------------+-+
| | F 10T )|:|
| | #32 )|:|
| | +---------+ |:|
| | | F 10T )|:| T1
| | | #32 )|:|
| +-------------------------+
| |
| R1 | R2
+----------/\/\/\--+--/\/\/\--+
220 22 _|_
1 W 2 W -
The switching frequency is about 21 KHz and varies less than 5 percent over
the range of a lighted bulb (it is significantly different with no load).
The approximate measured input voltage and current are:
V(in) I(in) F13-T5 I(in) F20-T12
----------------------------------------------------
3 V - 1.37 A
4 V 1.76 A 1.52 A (SV)
5 V 1.80 A (SV) 1.60 A
6 V 1.90 A 1.65 A
7 V 1.96 A (FB) 1.70 A
8 V 2.02 A 1.80 A
9 V 2.16 A 1.90 A
10 V 2.33 A 2.05 A (FB)
11 V - 2.30 A
12 V - 2.60 A
Note: SV = Starting Voltage (current is lower), FB = Full Brightness.
Notes on medium power fluorescent lamp inverter:
-----------------------------------------------
1. T1 is an E-core ferrite transformer. Once complete, the cores are installed
on the bobbin with a 2 mm gap. Some experimentation with the core gap may
be needed to optimize performance for a given lamp type and input voltage.
Each E core is 1" x 1/2" x 1/4" overall. The outer legs of the core are
1/8" thick. The central leg is 1/4" square. The square nylon bobbin has
a diameter of 5/16" and length of 3/8".
The 600T O (Output) is wound first followed by the 15T D (Drive) and 10T F
(Feedback) windings. For convenience, wind the D and F windings bifiler
style (the two wires together). Determine the appropriate connections
with an ohmmeter (or label the ends). The centertaps are brought out to
terminals. Try to distribute the O winding uniformly across the entire
bobbin area by winding it in multiple layers. This will assure that no
wires with a significant voltage difference are adjacent. There should be
a strip of insulating tape between the O and the other windings.
2. L1 isolates the power supply. It is 24 turns of #22 wire wound on a 1/4"
ferrite core. The inverter works fine without L1 but seems to have a tad
more strength at low voltage with it.
3. The transistors are 2N3055T (TO220 package) types but are not critical.
However, I expect that some faster switching transistors would run cooler.
Any high gain fast switching NPN power transistor should work. For PNP
types, reverse the polarity of the power supply.
For operation above about 6 V, a pair of good heat sinks will be required.
4. Some experimentation with component values may improve performance for
your application.
5. When testing, use a variable power supply so you get a feel for how much
output voltage is produced for each input voltage. Component values are
not critical but behavior under varying input/output voltage and load
conditions will be affected by C1, the number of turns on each of the
windings of T1, the gap of the core of T1, and the gain of your particular
transistor.
6. WARNING: Output is high voltage and dangerous. Take appropriate
precautions.
7.
| | |
---+--- are connected; ---|--- and ------- are NOT connected.
| | |
Basic 200 W power inverter:
--------------------------
This circuit was reverse engineered from a Tripp-Lite "Power-Verter" Model
PV200 DC to AC Inverter - typical of those used for camping or boating
applications where the only source of power is an auto or marine battery.
This particular model is rated 200 W continuous. There is no regulation or
precise frequency control.
Modifications for higher or lower output voltage are easily achieved. For
example, a fast cycle strobe requiring 330 VDC, would only require using three
times the number of turns on the Output winding and the addition of a bridge
rectifier to charge the energy storage capacitor(s). Alternatively, the
inverter could be used as-is with the addition of a voltage tripler. A tripler
rather than doubler is needed because of the squarewave output. (The RMS and
peak voltages are the same so you don't get the boost of 1.414 as you do with
the sinusoidal waveform from the power company.)
3 o
+12 VDC +--------+--------------+ ||
o | | )||
| |/ C _|_ C1 )||
S F1 20 A +------| Q1 --- 10 uF 31T D )|| 2
| | |\ E -_|_ 160 V #13 )|| +---------o AC Hot
\ S1 | &nb
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DC-Output, Constant Wattage 12 Volt Mercury Ballast!
Please read this article in its entirety before constructing this.
CAUTION - The following material gets quite technical at times, the device below makes high voltages that can kill you, and if things go wrong it is easy to make lots of smoke, custom and/or homebrew ferrite core inductors are necessary, this circuit can be abusive to mercury lamps, mercury lamps should be in suitable enclosed fixtures in case they explode. I recommend this as a project only for those with prior electronic project and electronic repair experience.
Corrections, additions, and questions to (don@misty.com). DO NOT use this with metal halide or sodium lamps, since these lamps do not like DC and metal halide lamps are less tolerant of constant-wattage warmup than mercury lamps.
Below is a schematic for a DC output, nearly constant wattage circuit to power mercury vapor lamps from 12 to 14 volts DC. The overvoltage detection/handling circuit is shown separately below the main portion of this schematic for clarity, but must be included. See the component descriptions following the schematics for values and descriptions.
See other instructions following the component descriptions. It is important to test for proper operation and proper power output.
This electronic ballast will give a mercury vapor lamp nearly constant wattage despite variations in the voltage across the lamp. This will give the lamp excessive current during warmup, when the voltage across the lamp is less. An advantage of this is accelerated warmup of the lamp. A disadvantage is overheating of the electrodes, especially the positive electrode. Expect some significant discoloration around the positive electrode, which will partially evaporate after several minutes to an hour of use fully warmed up. Some permanent discoloration will remain.
I have found this discoloration quite severe with the Philips 40/50 watt mercury lamp, but quite tolerable with 100 and 175 watt lamps. Please beware that after the positive electrode has been abused a few times with constant wattage warmup, it is likely to never work well in the future as a negative electrode.
B+ B+
^ ^
| |
D1 V >
- > Rsense
| >
| +--------------------------------------+ To Overvoltage
| | B+ ) +-->Sense Circuit
> > ^ ) L1 |
R1a> >R1b 330k > ) |
> > +--VVVV------+ > | Dout | L2
| | | | >2.2k +--->|----+--UUUU----+
| | | |\ +-+ __________ | | |
+----|--+------|+ \ | | | / === Cf |
| | | >--+-|2 | | |D | |
| +---------|- / | | 555 | | | Q1 | |
> > |/ +-|6 3|___| |S | (lamp)
R1c> >R1d 339 |__________| \ | |
> > | | |
| | Gnd Gnd Gnd
Gnd Gnd
| |
--+-- is connected; --|-- is not connected.
| |
555 Connections not shown:
Pin 1 - B+.
Pin 8 - Gnd.
Pin 4 - Connect a .1 uF capacitor fvrom this pin to Gnd.
Pin 7 - Do not connect to anything.
Pin 5 - Connect as directed below in the overvoltage sensing circuit.
Not shown: Power supply bypass capacitors. I recomend at least .1 uF across
the power pins of each IC, as well as at least 1 uF per output watt of
tantalum plus 10 uF per watt of electrolytic capacitor(s) across the power
supply, as close to the sense resistor and mosfet source(s) as possible.
Overvoltage sensing circuit:
B+
^
| +--------------------------->From output filter capacitor Cf
> |
1K > >
| >470K (determines voltage limit) (560k at your risk for more voltage)
V > 470k (hysteresis)
D3 - | +-------VVVV-+
| | | |\ |
+----|----+----|+ \ |
| | | >--+--->To Pin 5 of the 555
| +---------|- /
| | |/
Z1 V > 339
- > 10K
| >
| |
Gnd Gnd
Important component descriptions:
555 - I recommend the National Semiconductor LM555. Digi-Key sells this. Other 555's often do not work as well in ultrasonic circuits where a response lag around a microsecond can change things - at best, this can affect the power regulation.
339 - This is a 339 comparator. This is a quad comparator, only two of the four comparator sections are used. Other comparators will probably work if they can source and sink _at least_ 5 milliamps and preferably 10. Please note that the 339 is an "open-collector" type, requiring the pullup resistors (2.2K) from their outputs to B+. Most other comparators do not need this. I do NOT recommend op-amps, since they will respond more slowly.
Rsense - use approx. .06 ohm for a 100 watt mercury lamp. Change this inversely with lamp wattage for other wattage lamps. Wirewound is OK - I have tried this, and the inductance is not enough to mess things up too badly. Nichrome wire is OK - but solders with some difficulty if bright and shiny and free of oxide (scrape any off), and not at all where oxide is present.
D1 - Any ordinary rectifier diode.
D3 - I recommend putting an LED here to keep the voltage at the comparator noninverting input well below B+ should the supply voltage drop really low for any reason. Otherwise, comparators may act strangely.
Dout - This must be a high speed type, and should be rated to continuously handle the current obtained from dividing the lamp wattage by 12 volts. Fast diodes don't handle the peak current of the output pulses from L1 as well as ordinary rectifiers do.
Cf - If this circuit operates at several kilohertz or higher, I recommend approx. .1 to .15 microfarad multiplied by the lamp wattage in watts. For a 100 watt lamp, use 10 to 15 uF.
L2 - Resonant frequency between L2 and Cf should be a fraction of the operating frequency of the main circuit, generally near a kilohertz, maybe as low as several hundred Hz. This indicates a few millihenries for a 100 watt lamp. This inductor should not saturate at twice the normal lamp current. I also recommend having an ohm or two of resistance in series with the lamp. The inductor should be ferrite core to get the eddy current losses down while having a reasonable size and weight and number of turns.
Alternatively, you can use a resistor with a value of 800 ohms divided by the lamp wattage in watts. This would be 8 ohms for a 100 watt lamp. This would give a gentler warmup that is not hard on the lamp's electrodes, but will waste at least 4 percent of your power when the lamp is warmed up. This resistor can get as much as 60 percent of the output power during warmup.
L1 - Must not saturate with 1.33 times the ratio of lamp wattage to supply voltage, plus allowance for losses and errors and tolerances. Ontime will be typically 2/3 of (inductance * average current / supply voltage). Average current is the ratio of wattage to supply voltage, plus a bit more for losses, and will be close enough to .09 amp for each watt of lamp wattage at 12-13 volts. That means the inductance in microhenries would be 180-200 times the desired ontime in microseconds, divided by the lamp wattage in watts. I recommend an ontime around 30-40 microseconds. This would result in an inductance in microhenries of 6000 to 8000, divided by the lamp wattage in watts, for 12-13 volts. This inductor must have a ferrite core.
A few guidelines formulas for home-winding inductors on ferrite cores:
1. Flyback transformer cores are OK.
2. Maximum peak magnetic flux should not exceed 4,000 Gauss - preferably not exceed 3,000 Gauss. Even less if the core is made of "3B7" ferrite. Magnetic flux in gauss is one tenth of 4pi times the current in amps times the number of turns divided by the effective air gap in centimeters. Or, that's 4pi * N * amps / effective gap in millimeters. Effective gap is close enough to twice the physical air gap, since in most cores the magnetic flux flows through two gaps. The separation between two core halves will be the half-gap. If you want to figure the effective gap more exactly (generally not necessary), add to the efective gap the ratio of the total route length of an average line of flux to the permeability of the core material (typically a couple thousand).
3. Inductance in nanohenries is 4pi times the square of the number of turns, times the cross section area of the center leg of the core (cross section of the core period for toroids and C-C cores such as flyback transformer cores) in square centimeters, divided by the effective gap in centimeters.
In the 100 watt version I built and tested, L1 consists of 20 turns of 12-gauge wire on a ferrite E-E core with a center leg cross section area of approx. 1.8 square centimeters. The half-gap is approx. .8 millimeter, so the effective gap is .16 centimeter. This would make the inductance 56 microhenries (I did not actually measure this). With the 12 amp peak current, the magnetic flux would be nearly 1900 Gauss - nowhere near the limits of 3B7, 3C8, nor any common flyback transformer ferrite. The theoretical ontime with 12 volts across this inductor during the on-time and current increasing from 6 to 12 amps would be 28 microseconds. My actual ontime is longer.
Q1 - I recommend a paralled bank of IRF730 or IRF740 power MOSFETs. Use maybe 16 IRF730's or 8 IRF740's in parallel for a 100 watt mercury lamp. Since a 555 comfortably drives half of this at ultrasonic frequencies (I don't know yet about more), I recommend one 555 per 50 watts of mercury lamp. Connect all 555's in parallel, that is, connect all corresponding pins together - with the exception of Pin 3. Each Pin 3 drives a separate sub-bank of four IRF740's or eight IRF730's. Connect all drains together and all sources together. Connect all gates together within each sub-bank.
Please use some heat sinking. The IRF730 MOSFETs will be dissipating nearly half a watt each (twice this for IRF740's), which can make them get quite warm if they are close together without a heat sink. Their "on" resistance increases with temperature, which may cause "thermal runaway" if they get too warm.
R1a, R1b, R1c, R1d - These should be 10K 1 percent resistors. Do not put these anywhere where any heat source would heat them too unequally. Moderate heating is OK if all four of these are heated nearly equally.
Important Testing Information:
When you are ready to operate this circuit, use a 120 volt incandescent lamp instead of a mercury lamp. The incandescent lamp should have a rated wattage 1.5 to 2 times that of the mercury lamp. Apply power - the lamp should glow. It should glow much more brightly than it does with 12 volts, but dimmer than it does with 120 volts.
So far, so good? Monitor the voltage across the sense resistor (Rsense, the really low value one) with an oscilloscope. The waveform should be a triangle wave and the voltage across this resistor should have a minimum near .4 volt and a maximum near .8 volt. The average should be close to the voltage across the diode D1 that is in series with R1a.
If the voltage across Rsense is too low, add a small amount of extra resistance in series with R1a. If this voltage is too high, add a small amount of extra resistance in series with R1b.
If the average voltage is OK but the voltage does not swing enough (stays far within the range of 2/3 to 4/3 the average), replace the 330k resistor with one of a lower value. If this voltage swings far outside the range of 2/3 to 4/3 of the average, replace this resistor with a higher value one. If the waveform's shallower slopes (increasing current) get steeper as current increases, than the inductor is saturating. You may be able to fix this by replacing the 330k resistor with a higher value one to decrease the current range. Otherwise, you need to increase the gap in L1 or otherwise rebuild it.
If you feel comfortable enough with this circuit to do so, you can change the 330k resistor to adjust the oscillation frequency or to reduce switching losses or for whatever other purpose. Just be sure the inductor is not saturating and the minimum voltage across the sense resistor is not too low - if the minimum voltage hits zero without the "on" cycle being restarted, you get nothing out.
Is everything checking out OK at this point?
If so, then use a 120 volt incandescent lamp (or combination of lamps in parallel) of rated wattage equal to that of the mercury lamp that you will use. Apply power. The lamp should get rated power. You can measure the voltage across it with a DC voltmeter. Be sure the brightness is close to that of the same lamp getting 120 volts, in case anything strange is going on.
If the lamp is being overpowered, add a small resistance in series with R1b.
If the lamp is being underpowered, add a small resistance in series with R1a.
Major output power adjustments would need a different sense resistor - change this inversely with the desired change in wattage.
Verify that the voltage waveform across the sense resistor remains good after adjusting the output power.
Is everything still checking out OK at this point?
If things are still good, operate this electronic ballast with no load at all, while monitoring the voltage across the output filter capacitor. There should be a bleeder resistor around a megohm or so across the output for this. The voltage quickly rise to 300 volts or so. If it goes much higher (anywhere near or over 400 volts), immediately shut this circuit down. Repair the overvoltage handling circuit.
If the overvoltage handling circuit is working properly, the output voltage should rise quickly to approx. 300 volts, then the circuit should automatically shut down, then restart after the output voltage bleeds down a couple percent.
If repairs were necessary, be sure no mosfets heat up unusually during operation.
Is everything still checking out OK at this point?
If things are OK at this point, then you can use a mercury vapor lamp. It is preferred with some mercury lamps to make the shell of the base positive and the tip contact negative. If the socket has a white wire and a black one, make the white one positive and the black one negative. If you have a brass screw and a silver-colored screw, make the silver-colored one positive and the brass one negative. Polarity may be important for continued reliable operation of the starting electrode inside the arc tube of the mercury lamp. Making the electrode closer to the starting electrode positive may cause the lamp to deteriorate in a way that impairs starting.
Please note that full normal lamp life is unlikely since whichever electrode in the arc tube is positive will be trashed by just a few constant-wattage warmups.
Please note that wattage will vary roughly proportionately with supply voltage. By "constant wattage", I am referring to wattage not varying much with the voltage across the lamp.
DC-Output, Constant Wattage 12 Volt Mercury Ballast!
Please read this article in its entirety before constructing this.
CAUTION - The following material gets quite technical at times, the device below makes high voltages that can kill you, and if things go wrong it is easy to make lots of smoke, custom and/or homebrew ferrite core inductors are necessary, this circuit can be abusive to mercury lamps, mercury lamps should be in suitable enclosed fixtures in case they explode. I recommend this as a project only for those with prior electronic project and electronic repair experience.
Corrections, additions, and questions to (don@misty.com). DO NOT use this with metal halide or sodium lamps, since these lamps do not like DC and metal halide lamps are less tolerant of constant-wattage warmup than mercury lamps.
Below is a schematic for a DC output, nearly constant wattage circuit to power mercury vapor lamps from 12 to 14 volts DC. The overvoltage detection/handling circuit is shown separately below the main portion of this schematic for clarity, but must be included. See the component descriptions following the schematics for values and descriptions.
See other instructions following the component descriptions. It is important to test for proper operation and proper power output.
This electronic ballast will give a mercury vapor lamp nearly constant wattage despite variations in the voltage across the lamp. This will give the lamp excessive current during warmup, when the voltage across the lamp is less. An advantage of this is accelerated warmup of the lamp. A disadvantage is overheating of the electrodes, especially the positive electrode. Expect some significant discoloration around the positive electrode, which will partially evaporate after several minutes to an hour of use fully warmed up. Some permanent discoloration will remain.
I have found this discoloration quite severe with the Philips 40/50 watt mercury lamp, but quite tolerable with 100 and 175 watt lamps. Please beware that after the positive electrode has been abused a few times with constant wattage warmup, it is likely to never work well in the future as a negative electrode.
B+ B+
^ ^
| |
D1 V >
- > Rsense
| >
| +--------------------------------------+ To Overvoltage
| | B+ ) +-->Sense Circuit
> > ^ ) L1 |
R1a> >R1b 330k > ) |
> > +--VVVV------+ > | Dout | L2
| | | | >2.2k +--->|----+--UUUU----+
| | | |\ +-+ __________ | | |
+----|--+------|+ \ | | | / === Cf |
| | | >--+-|2 | | |D | |
| +---------|- / | | 555 | | | Q1 | |
> > |/ +-|6 3|___| |S | (lamp)
R1c> >R1d 339 |__________| \ | |
> > | | |
| | Gnd Gnd Gnd
Gnd Gnd
| |
--+-- is connected; --|-- is not connected.
| |
555 Connections not shown:
Pin 1 - B+.
Pin 8 - Gnd.
Pin 4 - Connect a .1 uF capacitor fvrom this pin to Gnd.
Pin 7 - Do not connect to anything.
Pin 5 - Connect as directed below in the overvoltage sensing circuit.
Not shown: Power supply bypass capacitors. I recomend at least .1 uF across
the power pins of each IC, as well as at least 1 uF per output watt of
tantalum plus 10 uF per watt of electrolytic capacitor(s) across the power
supply, as close to the sense resistor and mosfet source(s) as possible.
Overvoltage sensing circuit:
B+
^
| +--------------------------->From output filter capacitor Cf
> |
1K > >
| >470K (determines voltage limit) (560k at your risk for more voltage)
V > 470k (hysteresis)
D3 - | +-------VVVV-+
| | | |\ |
+----|----+----|+ \ |
| | | >--+--->To Pin 5 of the 555
| +---------|- /
| | |/
Z1 V > 339
- > 10K
| >
| |
Gnd Gnd
Important component descriptions:
555 - I recommend the National Semiconductor LM555. Digi-Key sells this. Other 555's often do not work as well in ultrasonic circuits where a response lag around a microsecond can change things - at best, this can affect the power regulation.
339 - This is a 339 comparator. This is a quad comparator, only two of the four comparator sections are used. Other comparators will probably work if they can source and sink _at least_ 5 milliamps and preferably 10. Please note that the 339 is an "open-collector" type, requiring the pullup resistors (2.2K) from their outputs to B+. Most other comparators do not need this. I do NOT recommend op-amps, since they will respond more slowly.
Rsense - use approx. .06 ohm for a 100 watt mercury lamp. Change this inversely with lamp wattage for other wattage lamps. Wirewound is OK - I have tried this, and the inductance is not enough to mess things up too badly. Nichrome wire is OK - but solders with some difficulty if bright and shiny and free of oxide (scrape any off), and not at all where oxide is present.
D1 - Any ordinary rectifier diode.
D3 - I recommend putting an LED here to keep the voltage at the comparator noninverting input well below B+ should the supply voltage drop really low for any reason. Otherwise, comparators may act strangely.
Dout - This must be a high speed type, and should be rated to continuously handle the current obtained from dividing the lamp wattage by 12 volts. Fast diodes don't handle the peak current of the output pulses from L1 as well as ordinary rectifiers do.
Cf - If this circuit operates at several kilohertz or higher, I recommend approx. .1 to .15 microfarad multiplied by the lamp wattage in watts. For a 100 watt lamp, use 10 to 15 uF.
L2 - Resonant frequency between L2 and Cf should be a fraction of the operating frequency of the main circuit, generally near a kilohertz, maybe as low as several hundred Hz. This indicates a few millihenries for a 100 watt lamp. This inductor should not saturate at twice the normal lamp current. I also recommend having an ohm or two of resistance in series with the lamp. The inductor should be ferrite core to get the eddy current losses down while having a reasonable size and weight and number of turns.
Alternatively, you can use a resistor with a value of 800 ohms divided by the lamp wattage in watts. This would be 8 ohms for a 100 watt lamp. This would give a gentler warmup that is not hard on the lamp's electrodes, but will waste at least 4 percent of your power when the lamp is warmed up. This resistor can get as much as 60 percent of the output power during warmup.
L1 - Must not saturate with 1.33 times the ratio of lamp wattage to supply voltage, plus allowance for losses and errors and tolerances. Ontime will be typically 2/3 of (inductance * average current / supply voltage). Average current is the ratio of wattage to supply voltage, plus a bit more for losses, and will be close enough to .09 amp for each watt of lamp wattage at 12-13 volts. That means the inductance in microhenries would be 180-200 times the desired ontime in microseconds, divided by the lamp wattage in watts. I recommend an ontime around 30-40 microseconds. This would result in an inductance in microhenries of 6000 to 8000, divided by the lamp wattage in watts, for 12-13 volts. This inductor must have a ferrite core.
A few guidelines formulas for home-winding inductors on ferrite cores:
1. Flyback transformer cores are OK.
2. Maximum peak magnetic flux should not exceed 4,000 Gauss - preferably not exceed 3,000 Gauss. Even less if the core is made of "3B7" ferrite. Magnetic flux in gauss is one tenth of 4pi times the current in amps times the number of turns divided by the effective air gap in centimeters. Or, that's 4pi * N * amps / effective gap in millimeters. Effective gap is close enough to twice the physical air gap, since in most cores the magnetic flux flows through two gaps. The separation between two core halves will be the half-gap. If you want to figure the effective gap more exactly (generally not necessary), add to the efective gap the ratio of the total route length of an average line of flux to the permeability of the core material (typically a couple thousand).
3. Inductance in nanohenries is 4pi times the square of the number of turns, times the cross section area of the center leg of the core (cross section of the core period for toroids and C-C cores such as flyback transformer cores) in square centimeters, divided by the effective gap in centimeters.
In the 100 watt version I built and tested, L1 consists of 20 turns of 12-gauge wire on a ferrite E-E core with a center leg cross section area of approx. 1.8 square centimeters. The half-gap is approx. .8 millimeter, so the effective gap is .16 centimeter. This would make the inductance 56 microhenries (I did not actually measure this). With the 12 amp peak current, the magnetic flux would be nearly 1900 Gauss - nowhere near the limits of 3B7, 3C8, nor any common flyback transformer ferrite. The theoretical ontime with 12 volts across this inductor during the on-time and current increasing from 6 to 12 amps would be 28 microseconds. My actual ontime is longer.
Q1 - I recommend a paralled bank of IRF730 or IRF740 power MOSFETs. Use maybe 16 IRF730's or 8 IRF740's in parallel for a 100 watt mercury lamp. Since a 555 comfortably drives half of this at ultrasonic frequencies (I don't know yet about more), I recommend one 555 per 50 watts of mercury lamp. Connect all 555's in parallel, that is, connect all corresponding pins together - with the exception of Pin 3. Each Pin 3 drives a separate sub-bank of four IRF740's or eight IRF730's. Connect all drains together and all sources together. Connect all gates together within each sub-bank.
Please use some heat sinking. The IRF730 MOSFETs will be dissipating nearly half a watt each (twice this for IRF740's), which can make them get quite warm if they are close together without a heat sink. Their "on" resistance increases with temperature, which may cause "thermal runaway" if they get too warm.
R1a, R1b, R1c, R1d - These should be 10K 1 percent resistors. Do not put these anywhere where any heat source would heat them too unequally. Moderate heating is OK if all four of these are heated nearly equally.
Important Testing Information:
When you are ready to operate this circuit, use a 120 volt incandescent lamp instead of a mercury lamp. The incandescent lamp should have a rated wattage 1.5 to 2 times that of the mercury lamp. Apply power - the lamp should glow. It should glow much more brightly than it does with 12 volts, but dimmer than it does with 120 volts.
So far, so good? Monitor the voltage across the sense resistor (Rsense, the really low value one) with an oscilloscope. The waveform should be a triangle wave and the voltage across this resistor should have a minimum near .4 volt and a maximum near .8 volt. The average should be close to the voltage across the diode D1 that is in series with R1a.
If the voltage across Rsense is too low, add a small amount of extra resistance in series with R1a. If this voltage is too high, add a small amount of extra resistance in series with R1b.
If the average voltage is OK but the voltage does not swing enough (stays far within the range of 2/3 to 4/3 the average), replace the 330k resistor with one of a lower value. If this voltage swings far outside the range of 2/3 to 4/3 of the average, replace this resistor with a higher value one. If the waveform's shallower slopes (increasing current) get steeper as current increases, than the inductor is saturating. You may be able to fix this by replacing the 330k resistor with a higher value one to decrease the current range. Otherwise, you need to increase the gap in L1 or otherwise rebuild it.
If you feel comfortable enough with this circuit to do so, you can change the 330k resistor to adjust the oscillation frequency or to reduce switching losses or for whatever other purpose. Just be sure the inductor is not saturating and the minimum voltage across the sense resistor is not too low - if the minimum voltage hits zero without the "on" cycle being restarted, you get nothing out.
Is everything checking out OK at this point?
If so, then use a 120 volt incandescent lamp (or combination of lamps in parallel) of rated wattage equal to that of the mercury lamp that you will use. Apply power. The lamp should get rated power. You can measure the voltage across it with a DC voltmeter. Be sure the brightness is close to that of the same lamp getting 120 volts, in case anything strange is going on.
If the lamp is being overpowered, add a small resistance in series with R1b.
If the lamp is being underpowered, add a small resistance in series with R1a.
Major output power adjustments would need a different sense resistor - change this inversely with the desired change in wattage.
Verify that the voltage waveform across the sense resistor remains good after adjusting the output power.
Is everything still checking out OK at this point?
If things are still good, operate this electronic ballast with no load at all, while monitoring the voltage across the output filter capacitor. There should be a bleeder resistor around a megohm or so across the output for this. The voltage quickly rise to 300 volts or so. If it goes much higher (anywhere near or over 400 volts), immediately shut this circuit down. Repair the overvoltage handling circuit.
If the overvoltage handling circuit is working properly, the output voltage should rise quickly to approx. 300 volts, then the circuit should automatically shut down, then restart after the output voltage bleeds down a couple percent.
If repairs were necessary, be sure no mosfets heat up unusually during operation.
Is everything still checking out OK at this point?
If things are OK at this point, then you can use a mercury vapor lamp. It is preferred with some mercury lamps to make the shell of the base positive and the tip contact negative. If the socket has a white wire and a black one, make the white one positive and the black one negative. If you have a brass screw and a silver-colored screw, make the silver-colored one positive and the brass one negative. Polarity may be important for continued reliable operation of the starting electrode inside the arc tube of the mercury lamp. Making the electrode closer to the starting electrode positive may cause the lamp to deteriorate in a way that impairs starting.
Please note that full normal lamp life is unlikely since whichever electrode in the arc tube is positive will be trashed by just a few constant-wattage warmups.
Please note that wattage will vary roughly proportionately with supply voltage. By "constant wattage", I am referring to wattage not varying much with the voltage across the lamp.
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@yeming
再來一個DC-Output,ConstantWattage12VoltMercuryBallast!Pleasereadthisarticleinitsentiretybeforeconstructingthis.CAUTION-Thefollowingmaterialgetsquitetechnicalattimes,thedevicebelowmakeshighvoltagesthatcankillyou,andifthingsgowrongitiseasytomakelotsofsmoke,customand/orhomebrewferritecoreinductorsarenecessary,thiscircuitcanbeabusivetomercurylamps,mercurylampsshouldbeinsuitableenclosedfixturesincasetheyexplode.Irecommendthisasaprojectonlyforthosewithpriorelectronicprojectandelectronicrepairexperience.Corrections,additions,andquestionsto(don@misty.com).DONOTusethiswithmetalhalideorsodiumlamps,sincetheselampsdonotlikeDCandmetalhalidelampsarelesstolerantofconstant-wattagewarmupthanmercurylamps.BelowisaschematicforaDCoutput,nearlyconstantwattagecircuittopowermercuryvaporlampsfrom12to14voltsDC.Theovervoltagedetection/handlingcircuitisshownseparatelybelowthemainportionofthisschematicforclarity,butmustbeincluded.Seethecomponentdescriptionsfollowingtheschematicsforvaluesanddescriptions.Seeotherinstructionsfollowingthecomponentdescriptions.Itisimportanttotestforproperoperationandproperpoweroutput.Thiselectronicballastwillgiveamercuryvaporlampnearlyconstantwattagedespitevariationsinthevoltageacrossthelamp.Thiswillgivethelampexcessivecurrentduringwarmup,whenthevoltageacrossthelampisless.Anadvantageofthisisacceleratedwarmupofthelamp.Adisadvantageisoverheatingoftheelectrodes,especiallythepositiveelectrode.Expectsomesignificantdiscolorationaroundthepositiveelectrode,whichwillpartiallyevaporateafterseveralminutestoanhourofusefullywarmedup.Somepermanentdiscolorationwillremain.IhavefoundthisdiscolorationquiteseverewiththePhilips40/50wattmercurylamp,butquitetolerablewith100and175wattlamps.Pleasebewarethatafterthepositiveelectrodehasbeenabusedafewtimeswithconstantwattagewarmup,itislikelytoneverworkwellinthefutureasanegativeelectrode. B+ B+ ^ ^ | |D1V > - >Rsense | > | +--------------------------------------+ ToOvervoltage | | B+ ) +-->SenseCircuit > > ^ )L1 |R1a> >R1b 330k > ) | > > +--VVVV------+> | Dout | L2 | | | |>2.2k +--->|----+--UUUU----+ | | | |\ +-+ __________ | | | +----|--+------|+\ || | / ===Cf | | | | >--+-|2 | ||D | | | +---------|-/ || 555 | || Q1 | | > > |/ +-|6 3|___||S | (lamp)R1c> >R1d 339 |__________| \ | | > > | | | | | Gnd Gnd Gnd Gnd Gnd | |--+--isconnected;--|--isnotconnected. | |555Connectionsnotshown:Pin1-B+.Pin8-Gnd.Pin4-Connecta.1uFcapacitorfvromthispintoGnd.Pin7-Donotconnecttoanything.Pin5-Connectasdirectedbelowintheovervoltagesensingcircuit.Notshown:Powersupplybypasscapacitors.Irecomendatleast.1uFacrossthepowerpinsofeachIC,aswellasatleast1uFperoutputwattoftantalumplus10uFperwattofelectrolyticcapacitor(s)acrossthepowersupply,asclosetothesenseresistorandmosfetsource(s)aspossible.Overvoltagesensingcircuit: B+ ^ | +--------------------------->FromoutputfiltercapacitorCf > |1K> > | >470K(determinesvoltagelimit)(560katyourriskformorevoltage) V > 470k(hysteresis)D3- | +-------VVVV-+ | | | |\ | +----|----+----|+\ | | | | >--+--->ToPin5ofthe555 | +---------|-/ | | |/Z1V > 339 - >10K | > | | Gnd GndImportantcomponentdescriptions:555-IrecommendtheNationalSemiconductorLM555.Digi-Keysellsthis.Other555'softendonotworkaswellinultrasoniccircuitswherearesponselagaroundamicrosecondcanchangethings-atbest,thiscanaffectthepowerregulation.339-Thisisa339comparator.Thisisaquadcomparator,onlytwoofthefourcomparatorsectionsareused.Othercomparatorswillprobablyworkiftheycansourceandsink_atleast_5milliampsandpreferably10.Pleasenotethatthe339isan"open-collector"type,requiringthepullupresistors(2.2K)fromtheiroutputstoB+.Mostothercomparatorsdonotneedthis.IdoNOTrecommendop-amps,sincetheywillrespondmoreslowly.Rsense-useapprox..06ohmfora100wattmercurylamp.Changethisinverselywithlampwattageforotherwattagelamps.WirewoundisOK-Ihavetriedthis,andtheinductanceisnotenoughtomessthingsuptoobadly.NichromewireisOK-butsolderswithsomedifficultyifbrightandshinyandfreeofoxide(scrapeanyoff),andnotatallwhereoxideispresent.D1-Anyordinaryrectifierdiode.D3-IrecommendputtinganLEDheretokeepthevoltageatthecomparatornoninvertinginputwellbelowB+shouldthesupplyvoltagedropreallylowforanyreason.Otherwise,comparatorsmayactstrangely.Dout-Thismustbeahighspeedtype,andshouldberatedtocontinuouslyhandlethecurrentobtainedfromdividingthelampwattageby12volts.Fastdiodesdon'thandlethepeakcurrentoftheoutputpulsesfromL1aswellasordinaryrectifiersdo.Cf-Ifthiscircuitoperatesatseveralkilohertzorhigher,Irecommendapprox..1to.15microfaradmultipliedbythelampwattageinwatts.Fora100wattlamp,use10to15uF.L2-ResonantfrequencybetweenL2andCfshouldbeafractionoftheoperatingfrequencyofthemaincircuit,generallynearakilohertz,maybeaslowasseveralhundredHz.Thisindicatesafewmillihenriesfora100wattlamp.Thisinductorshouldnotsaturateattwicethenormallampcurrent.Ialsorecommendhavinganohmortwoofresistanceinserieswiththelamp.Theinductorshouldbeferritecoretogettheeddycurrentlossesdownwhilehavingareasonablesizeandweightandnumberofturns.Alternatively,youcanusearesistorwithavalueof800ohmsdividedbythelampwattageinwatts.Thiswouldbe8ohmsfora100wattlamp.Thiswouldgiveagentlerwarmupthatisnothardonthelamp'selectrodes,butwillwasteatleast4percentofyourpowerwhenthelampiswarmedup.Thisresistorcangetasmuchas60percentoftheoutputpowerduringwarmup.L1-Mustnotsaturatewith1.33timestheratiooflampwattagetosupplyvoltage,plusallowanceforlossesanderrorsandtolerances.Ontimewillbetypically2/3of(inductance*averagecurrent/supplyvoltage).Averagecurrentistheratioofwattagetosupplyvoltage,plusabitmoreforlosses,andwillbecloseenoughto.09ampforeachwattoflampwattageat12-13volts.Thatmeanstheinductanceinmicrohenrieswouldbe180-200timesthedesiredontimeinmicroseconds,dividedbythelampwattageinwatts.Irecommendanontimearound30-40microseconds.Thiswouldresultinaninductanceinmicrohenriesof6000to8000,dividedbythelampwattageinwatts,for12-13volts.Thisinductormusthaveaferritecore.Afewguidelinesformulasforhome-windinginductorsonferritecores:1.FlybacktransformercoresareOK.2.Maximumpeakmagneticfluxshouldnotexceed4,000Gauss-preferablynotexceed3,000Gauss.Evenlessifthecoreismadeof"3B7"ferrite.Magneticfluxingaussisonetenthof4pitimesthecurrentinampstimesthenumberofturnsdividedbytheeffectiveairgapincentimeters.Or,that's4pi*N*amps/effectivegapinmillimeters.Effectivegapiscloseenoughtotwicethephysicalairgap,sinceinmostcoresthemagneticfluxflowsthroughtwogaps.Theseparationbetweentwocorehalveswillbethehalf-gap.Ifyouwanttofiguretheeffectivegapmoreexactly(generallynotnecessary),addtotheefectivegaptheratioofthetotalroutelengthofanaveragelineoffluxtothepermeabilityofthecorematerial(typicallyacouplethousand).3.Inductanceinnanohenriesis4pitimesthesquareofthenumberofturns,timesthecrosssectionareaofthecenterlegofthecore(crosssectionofthecoreperiodfortoroidsandC-Ccoressuchasflybacktransformercores)insquarecentimeters,dividedbytheeffectivegapincentimeters.Inthe100wattversionIbuiltandtested,L1consistsof20turnsof12-gaugewireonaferriteE-Ecorewithacenterlegcrosssectionareaofapprox.1.8squarecentimeters.Thehalf-gapisapprox..8millimeter,sotheeffectivegapis.16centimeter.Thiswouldmaketheinductance56microhenries(Ididnotactuallymeasurethis).Withthe12amppeakcurrent,themagneticfluxwouldbenearly1900Gauss-nowherenearthelimitsof3B7,3C8,noranycommonflybacktransformerferrite.Thetheoreticalontimewith12voltsacrossthisinductorduringtheon-timeandcurrentincreasingfrom6to12ampswouldbe28microseconds.Myactualontimeislonger.Q1-IrecommendaparalledbankofIRF730orIRF740powerMOSFETs.Usemaybe16IRF730'sor8IRF740'sinparallelfora100wattmercurylamp.Sincea555comfortablydriveshalfofthisatultrasonicfrequencies(Idon'tknowyetaboutmore),Irecommendone555per50wattsofmercurylamp.Connectall555'sinparallel,thatis,connectallcorrespondingpinstogether-withtheexceptionofPin3.EachPin3drivesaseparatesub-bankoffourIRF740'soreightIRF730's.Connectalldrainstogetherandallsourcestogether.Connectallgatestogetherwithineachsub-bank.Pleaseusesomeheatsinking.TheIRF730MOSFETswillbedissipatingnearlyhalfawatteach(twicethisforIRF740's),whichcanmakethemgetquitewarmiftheyareclosetogetherwithoutaheatsink.Their"on"resistanceincreaseswithtemperature,whichmaycause"thermalrunaway"iftheygettoowarm.R1a,R1b,R1c,R1d-Theseshouldbe10K1percentresistors.Donotputtheseanywherewhereanyheatsourcewouldheatthemtoounequally.ModerateheatingisOKifallfouroftheseareheatednearlyequally.ImportantTestingInformation:Whenyouarereadytooperatethiscircuit,usea120voltincandescentlampinsteadofamercurylamp.Theincandescentlampshouldhavearatedwattage1.5to2timesthatofthemercurylamp.Applypower-thelampshouldglow.Itshouldglowmuchmorebrightlythanitdoeswith12volts,butdimmerthanitdoeswith120volts.Sofar,sogood?Monitorthevoltageacrossthesenseresistor(Rsense,thereallylowvalueone)withanoscilloscope.Thewaveformshouldbeatrianglewaveandthevoltageacrossthisresistorshouldhaveaminimumnear.4voltandamaximumnear.8volt.TheaverageshouldbeclosetothevoltageacrossthediodeD1thatisinserieswithR1a.IfthevoltageacrossRsenseistoolow,addasmallamountofextraresistanceinserieswithR1a.Ifthisvoltageistoohigh,addasmallamountofextraresistanceinserieswithR1b.IftheaveragevoltageisOKbutthevoltagedoesnotswingenough(staysfarwithintherangeof2/3to4/3theaverage),replacethe330kresistorwithoneofalowervalue.Ifthisvoltageswingsfaroutsidetherangeof2/3to4/3oftheaverage,replacethisresistorwithahighervalueone.Ifthewaveform'sshallowerslopes(increasingcurrent)getsteeperascurrentincreases,thantheinductorissaturating.Youmaybeabletofixthisbyreplacingthe330kresistorwithahighervalueonetodecreasethecurrentrange.Otherwise,youneedtoincreasethegapinL1orotherwiserebuildit.Ifyoufeelcomfortableenoughwiththiscircuittodoso,youcanchangethe330kresistortoadjusttheoscillationfrequencyortoreduceswitchinglossesorforwhateverotherpurpose.Justbesuretheinductorisnotsaturatingandtheminimumvoltageacrossthesenseresistorisnottoolow-iftheminimumvoltagehitszerowithoutthe"on"cyclebeingrestarted,yougetnothingout.IseverythingcheckingoutOKatthispoint?Ifso,thenusea120voltincandescentlamp(orcombinationoflampsinparallel)ofratedwattageequaltothatofthemercurylampthatyouwilluse.Applypower.Thelampshouldgetratedpower.YoucanmeasurethevoltageacrossitwithaDCvoltmeter.Besurethebrightnessisclosetothatofthesamelampgetting120volts,incaseanythingstrangeisgoingon.Ifthelampisbeingoverpowered,addasmallresistanceinserieswithR1b.Ifthelampisbeingunderpowered,addasmallresistanceinserieswithR1a.Majoroutputpoweradjustmentswouldneedadifferentsenseresistor-changethisinverselywiththedesiredchangeinwattage.Verifythatthevoltagewaveformacrossthesenseresistorremainsgoodafteradjustingtheoutputpower.IseverythingstillcheckingoutOKatthispoint?Ifthingsarestillgood,operatethiselectronicballastwithnoloadatall,whilemonitoringthevoltageacrosstheoutputfiltercapacitor.Thereshouldbeableederresistoraroundamegohmorsoacrosstheoutputforthis.Thevoltagequicklyriseto300voltsorso.Ifitgoesmuchhigher(anywherenearorover400volts),immediatelyshutthiscircuitdown.Repairtheovervoltagehandlingcircuit.Iftheovervoltagehandlingcircuitisworkingproperly,theoutputvoltageshouldrisequicklytoapprox.300volts,thenthecircuitshouldautomaticallyshutdown,thenrestartaftertheoutputvoltagebleedsdownacouplepercent.Ifrepairswerenecessary,besurenomosfetsheatupunusuallyduringoperation.IseverythingstillcheckingoutOKatthispoint?IfthingsareOKatthispoint,thenyoucanuseamercuryvaporlamp.Itispreferredwithsomemercurylampstomaketheshellofthebasepositiveandthetipcontactnegative.Ifthesockethasawhitewireandablackone,makethewhiteonepositiveandtheblackonenegative.Ifyouhaveabrassscrewandasilver-coloredscrew,makethesilver-coloredonepositiveandthebrassonenegative.Polaritymaybeimportantforcontinuedreliableoperationofthestartingelectrodeinsidethearctubeofthemercurylamp.Makingtheelectrodeclosertothestartingelectrodepositivemaycausethelamptodeteriorateinawaythatimpairsstarting.Pleasenotethatfullnormallamplifeisunlikelysincewhicheverelectrodeinthearctubeispositivewillbetrashedbyjustafewconstant-wattagewarmups.Pleasenotethatwattagewillvaryroughlyproportionatelywithsupplyvoltage.By"constantwattage",Iamreferringtowattagenotvaryingmuchwiththevoltageacrossthelamp.
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再來一個DC-Output,ConstantWattage12VoltMercuryBallast!Pleasereadthisarticleinitsentiretybeforeconstructingthis.CAUTION-Thefollowingmaterialgetsquitetechnicalattimes,thedevicebelowmakeshighvoltagesthatcankillyou,andifthingsgowrongitiseasytomakelotsofsmoke,customand/orhomebrewferritecoreinductorsarenecessary,thiscircuitcanbeabusivetomercurylamps,mercurylampsshouldbeinsuitableenclosedfixturesincasetheyexplode.Irecommendthisasaprojectonlyforthosewithpriorelectronicprojectandelectronicrepairexperience.Corrections,additions,andquestionsto(don@misty.com).DONOTusethiswithmetalhalideorsodiumlamps,sincetheselampsdonotlikeDCandmetalhalidelampsarelesstolerantofconstant-wattagewarmupthanmercurylamps.BelowisaschematicforaDCoutput,nearlyconstantwattagecircuittopowermercuryvaporlampsfrom12to14voltsDC.Theovervoltagedetection/handlingcircuitisshownseparatelybelowthemainportionofthisschematicforclarity,butmustbeincluded.Seethecomponentdescriptionsfollowingtheschematicsforvaluesanddescriptions.Seeotherinstructionsfollowingthecomponentdescriptions.Itisimportanttotestforproperoperationandproperpoweroutput.Thiselectronicballastwillgiveamercuryvaporlampnearlyconstantwattagedespitevariationsinthevoltageacrossthelamp.Thiswillgivethelampexcessivecurrentduringwarmup,whenthevoltageacrossthelampisless.Anadvantageofthisisacceleratedwarmupofthelamp.Adisadvantageisoverheatingoftheelectrodes,especiallythepositiveelectrode.Expectsomesignificantdiscolorationaroundthepositiveelectrode,whichwillpartiallyevaporateafterseveralminutestoanhourofusefullywarmedup.Somepermanentdiscolorationwillremain.IhavefoundthisdiscolorationquiteseverewiththePhilips40/50wattmercurylamp,butquitetolerablewith100and175wattlamps.Pleasebewarethatafterthepositiveelectrodehasbeenabusedafewtimeswithconstantwattagewarmup,itislikelytoneverworkwellinthefutureasanegativeelectrode. B+ B+ ^ ^ | |D1V > - >Rsense | > | +--------------------------------------+ ToOvervoltage | | B+ ) +-->SenseCircuit > > ^ )L1 |R1a> >R1b 330k > ) | > > +--VVVV------+> | Dout | L2 | | | |>2.2k +--->|----+--UUUU----+ | | | |\ +-+ __________ | | | +----|--+------|+\ || | / ===Cf | | | | >--+-|2 | ||D | | | +---------|-/ || 555 | || Q1 | | > > |/ +-|6 3|___||S | (lamp)R1c> >R1d 339 |__________| \ | | > > | | | | | Gnd Gnd Gnd Gnd Gnd | |--+--isconnected;--|--isnotconnected. | |555Connectionsnotshown:Pin1-B+.Pin8-Gnd.Pin4-Connecta.1uFcapacitorfvromthispintoGnd.Pin7-Donotconnecttoanything.Pin5-Connectasdirectedbelowintheovervoltagesensingcircuit.Notshown:Powersupplybypasscapacitors.Irecomendatleast.1uFacrossthepowerpinsofeachIC,aswellasatleast1uFperoutputwattoftantalumplus10uFperwattofelectrolyticcapacitor(s)acrossthepowersupply,asclosetothesenseresistorandmosfetsource(s)aspossible.Overvoltagesensingcircuit: B+ ^ | +--------------------------->FromoutputfiltercapacitorCf > |1K> > | >470K(determinesvoltagelimit)(560katyourriskformorevoltage) V > 470k(hysteresis)D3- | +-------VVVV-+ | | | |\ | +----|----+----|+\ | | | | >--+--->ToPin5ofthe555 | +---------|-/ | | |/Z1V > 339 - >10K | > | | Gnd GndImportantcomponentdescriptions:555-IrecommendtheNationalSemiconductorLM555.Digi-Keysellsthis.Other555'softendonotworkaswellinultrasoniccircuitswherearesponselagaroundamicrosecondcanchangethings-atbest,thiscanaffectthepowerregulation.339-Thisisa339comparator.Thisisaquadcomparator,onlytwoofthefourcomparatorsectionsareused.Othercomparatorswillprobablyworkiftheycansourceandsink_atleast_5milliampsandpreferably10.Pleasenotethatthe339isan"open-collector"type,requiringthepullupresistors(2.2K)fromtheiroutputstoB+.Mostothercomparatorsdonotneedthis.IdoNOTrecommendop-amps,sincetheywillrespondmoreslowly.Rsense-useapprox..06ohmfora100wattmercurylamp.Changethisinverselywithlampwattageforotherwattagelamps.WirewoundisOK-Ihavetriedthis,andtheinductanceisnotenoughtomessthingsuptoobadly.NichromewireisOK-butsolderswithsomedifficultyifbrightandshinyandfreeofoxide(scrapeanyoff),andnotatallwhereoxideispresent.D1-Anyordinaryrectifierdiode.D3-IrecommendputtinganLEDheretokeepthevoltageatthecomparatornoninvertinginputwellbelowB+shouldthesupplyvoltagedropreallylowforanyreason.Otherwise,comparatorsmayactstrangely.Dout-Thismustbeahighspeedtype,andshouldberatedtocontinuouslyhandlethecurrentobtainedfromdividingthelampwattageby12volts.Fastdiodesdon'thandlethepeakcurrentoftheoutputpulsesfromL1aswellasordinaryrectifiersdo.Cf-Ifthiscircuitoperatesatseveralkilohertzorhigher,Irecommendapprox..1to.15microfaradmultipliedbythelampwattageinwatts.Fora100wattlamp,use10to15uF.L2-ResonantfrequencybetweenL2andCfshouldbeafractionoftheoperatingfrequencyofthemaincircuit,generallynearakilohertz,maybeaslowasseveralhundredHz.Thisindicatesafewmillihenriesfora100wattlamp.Thisinductorshouldnotsaturateattwicethenormallampcurrent.Ialsorecommendhavinganohmortwoofresistanceinserieswiththelamp.Theinductorshouldbeferritecoretogettheeddycurrentlossesdownwhilehavingareasonablesizeandweightandnumberofturns.Alternatively,youcanusearesistorwithavalueof800ohmsdividedbythelampwattageinwatts.Thiswouldbe8ohmsfora100wattlamp.Thiswouldgiveagentlerwarmupthatisnothardonthelamp'selectrodes,butwillwasteatleast4percentofyourpowerwhenthelampiswarmedup.Thisresistorcangetasmuchas60percentoftheoutputpowerduringwarmup.L1-Mustnotsaturatewith1.33timestheratiooflampwattagetosupplyvoltage,plusallowanceforlossesanderrorsandtolerances.Ontimewillbetypically2/3of(inductance*averagecurrent/supplyvoltage).Averagecurrentistheratioofwattagetosupplyvoltage,plusabitmoreforlosses,andwillbecloseenoughto.09ampforeachwattoflampwattageat12-13volts.Thatmeanstheinductanceinmicrohenrieswouldbe180-200timesthedesiredontimeinmicroseconds,dividedbythelampwattageinwatts.Irecommendanontimearound30-40microseconds.Thiswouldresultinaninductanceinmicrohenriesof6000to8000,dividedbythelampwattageinwatts,for12-13volts.Thisinductormusthaveaferritecore.Afewguidelinesformulasforhome-windinginductorsonferritecores:1.FlybacktransformercoresareOK.2.Maximumpeakmagneticfluxshouldnotexceed4,000Gauss-preferablynotexceed3,000Gauss.Evenlessifthecoreismadeof"3B7"ferrite.Magneticfluxingaussisonetenthof4pitimesthecurrentinampstimesthenumberofturnsdividedbytheeffectiveairgapincentimeters.Or,that's4pi*N*amps/effectivegapinmillimeters.Effectivegapiscloseenoughtotwicethephysicalairgap,sinceinmostcoresthemagneticfluxflowsthroughtwogaps.Theseparationbetweentwocorehalveswillbethehalf-gap.Ifyouwanttofiguretheeffectivegapmoreexactly(generallynotnecessary),addtotheefectivegaptheratioofthetotalroutelengthofanaveragelineoffluxtothepermeabilityofthecorematerial(typicallyacouplethousand).3.Inductanceinnanohenriesis4pitimesthesquareofthenumberofturns,timesthecrosssectionareaofthecenterlegofthecore(crosssectionofthecoreperiodfortoroidsandC-Ccoressuchasflybacktransformercores)insquarecentimeters,dividedbytheeffectivegapincentimeters.Inthe100wattversionIbuiltandtested,L1consistsof20turnsof12-gaugewireonaferriteE-Ecorewithacenterlegcrosssectionareaofapprox.1.8squarecentimeters.Thehalf-gapisapprox..8millimeter,sotheeffectivegapis.16centimeter.Thiswouldmaketheinductance56microhenries(Ididnotactuallymeasurethis).Withthe12amppeakcurrent,themagneticfluxwouldbenearly1900Gauss-nowherenearthelimitsof3B7,3C8,noranycommonflybacktransformerferrite.Thetheoreticalontimewith12voltsacrossthisinductorduringtheon-timeandcurrentincreasingfrom6to12ampswouldbe28microseconds.Myactualontimeislonger.Q1-IrecommendaparalledbankofIRF730orIRF740powerMOSFETs.Usemaybe16IRF730'sor8IRF740'sinparallelfora100wattmercurylamp.Sincea555comfortablydriveshalfofthisatultrasonicfrequencies(Idon'tknowyetaboutmore),Irecommendone555per50wattsofmercurylamp.Connectall555'sinparallel,thatis,connectallcorrespondingpinstogether-withtheexceptionofPin3.EachPin3drivesaseparatesub-bankoffourIRF740'soreightIRF730's.Connectalldrainstogetherandallsourcestogether.Connectallgatestogetherwithineachsub-bank.Pleaseusesomeheatsinking.TheIRF730MOSFETswillbedissipatingnearlyhalfawatteach(twicethisforIRF740's),whichcanmakethemgetquitewarmiftheyareclosetogetherwithoutaheatsink.Their"on"resistanceincreaseswithtemperature,whichmaycause"thermalrunaway"iftheygettoowarm.R1a,R1b,R1c,R1d-Theseshouldbe10K1percentresistors.Donotputtheseanywherewhereanyheatsourcewouldheatthemtoounequally.ModerateheatingisOKifallfouroftheseareheatednearlyequally.ImportantTestingInformation:Whenyouarereadytooperatethiscircuit,usea120voltincandescentlampinsteadofamercurylamp.Theincandescentlampshouldhavearatedwattage1.5to2timesthatofthemercurylamp.Applypower-thelampshouldglow.Itshouldglowmuchmorebrightlythanitdoeswith12volts,butdimmerthanitdoeswith120volts.Sofar,sogood?Monitorthevoltageacrossthesenseresistor(Rsense,thereallylowvalueone)withanoscilloscope.Thewaveformshouldbeatrianglewaveandthevoltageacrossthisresistorshouldhaveaminimumnear.4voltandamaximumnear.8volt.TheaverageshouldbeclosetothevoltageacrossthediodeD1thatisinserieswithR1a.IfthevoltageacrossRsenseistoolow,addasmallamountofextraresistanceinserieswithR1a.Ifthisvoltageistoohigh,addasmallamountofextraresistanceinserieswithR1b.IftheaveragevoltageisOKbutthevoltagedoesnotswingenough(staysfarwithintherangeof2/3to4/3theaverage),replacethe330kresistorwithoneofalowervalue.Ifthisvoltageswingsfaroutsidetherangeof2/3to4/3oftheaverage,replacethisresistorwithahighervalueone.Ifthewaveform'sshallowerslopes(increasingcurrent)getsteeperascurrentincreases,thantheinductorissaturating.Youmaybeabletofixthisbyreplacingthe330kresistorwithahighervalueonetodecreasethecurrentrange.Otherwise,youneedtoincreasethegapinL1orotherwiserebuildit.Ifyoufeelcomfortableenoughwiththiscircuittodoso,youcanchangethe330kresistortoadjusttheoscillationfrequencyortoreduceswitchinglossesorforwhateverotherpurpose.Justbesuretheinductorisnotsaturatingandtheminimumvoltageacrossthesenseresistorisnottoolow-iftheminimumvoltagehitszerowithoutthe"on"cyclebeingrestarted,yougetnothingout.IseverythingcheckingoutOKatthispoint?Ifso,thenusea120voltincandescentlamp(orcombinationoflampsinparallel)ofratedwattageequaltothatofthemercurylampthatyouwilluse.Applypower.Thelampshouldgetratedpower.YoucanmeasurethevoltageacrossitwithaDCvoltmeter.Besurethebrightnessisclosetothatofthesamelampgetting120volts,incaseanythingstrangeisgoingon.Ifthelampisbeingoverpowered,addasmallresistanceinserieswithR1b.Ifthelampisbeingunderpowered,addasmallresistanceinserieswithR1a.Majoroutputpoweradjustmentswouldneedadifferentsenseresistor-changethisinverselywiththedesiredchangeinwattage.Verifythatthevoltagewaveformacrossthesenseresistorremainsgoodafteradjustingtheoutputpower.IseverythingstillcheckingoutOKatthispoint?Ifthingsarestillgood,operatethiselectronicballastwithnoloadatall,whilemonitoringthevoltageacrosstheoutputfiltercapacitor.Thereshouldbeableederresistoraroundamegohmorsoacrosstheoutputforthis.Thevoltagequicklyriseto300voltsorso.Ifitgoesmuchhigher(anywherenearorover400volts),immediatelyshutthiscircuitdown.Repairtheovervoltagehandlingcircuit.Iftheovervoltagehandlingcircuitisworkingproperly,theoutputvoltageshouldrisequicklytoapprox.300volts,thenthecircuitshouldautomaticallyshutdown,thenrestartaftertheoutputvoltagebleedsdownacouplepercent.Ifrepairswerenecessary,besurenomosfetsheatupunusuallyduringoperation.IseverythingstillcheckingoutOKatthispoint?IfthingsareOKatthispoint,thenyoucanuseamercuryvaporlamp.Itispreferredwithsomemercurylampstomaketheshellofthebasepositiveandthetipcontactnegative.Ifthesockethasawhitewireandablackone,makethewhiteonepositiveandtheblackonenegative.Ifyouhaveabrassscrewandasilver-coloredscrew,makethesilver-coloredonepositiveandthebrassonenegative.Polaritymaybeimportantforcontinuedreliableoperationofthestartingelectrodeinsidethearctubeofthemercurylamp.Makingtheelectrodeclosertothestartingelectrodepositivemaycausethelamptodeteriorateinawaythatimpairsstarting.Pleasenotethatfullnormallamplifeisunlikelysincewhicheverelectrodeinthearctubeispositivewillbetrashedbyjustafewconstant-wattagewarmups.Pleasenotethatwattagewillvaryroughlyproportionatelywithsupplyvoltage.By"constantwattage",Iamreferringtowattagenotvaryingmuchwiththevoltageacrossthelamp.
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再來一個DC-Output,ConstantWattage12VoltMercuryBallast!Pleasereadthisarticleinitsentiretybeforeconstructingthis.CAUTION-Thefollowingmaterialgetsquitetechnicalattimes,thedevicebelowmakeshighvoltagesthatcankillyou,andifthingsgowrongitiseasytomakelotsofsmoke,customand/orhomebrewferritecoreinductorsarenecessary,thiscircuitcanbeabusivetomercurylamps,mercurylampsshouldbeinsuitableenclosedfixturesincasetheyexplode.Irecommendthisasaprojectonlyforthosewithpriorelectronicprojectandelectronicrepairexperience.Corrections,additions,andquestionsto(don@misty.com).DONOTusethiswithmetalhalideorsodiumlamps,sincetheselampsdonotlikeDCandmetalhalidelampsarelesstolerantofconstant-wattagewarmupthanmercurylamps.BelowisaschematicforaDCoutput,nearlyconstantwattagecircuittopowermercuryvaporlampsfrom12to14voltsDC.Theovervoltagedetection/handlingcircuitisshownseparatelybelowthemainportionofthisschematicforclarity,butmustbeincluded.Seethecomponentdescriptionsfollowingtheschematicsforvaluesanddescriptions.Seeotherinstructionsfollowingthecomponentdescriptions.Itisimportanttotestforproperoperationandproperpoweroutput.Thiselectronicballastwillgiveamercuryvaporlampnearlyconstantwattagedespitevariationsinthevoltageacrossthelamp.Thiswillgivethelampexcessivecurrentduringwarmup,whenthevoltageacrossthelampisless.Anadvantageofthisisacceleratedwarmupofthelamp.Adisadvantageisoverheatingoftheelectrodes,especiallythepositiveelectrode.Expectsomesignificantdiscolorationaroundthepositiveelectrode,whichwillpartiallyevaporateafterseveralminutestoanhourofusefullywarmedup.Somepermanentdiscolorationwillremain.IhavefoundthisdiscolorationquiteseverewiththePhilips40/50wattmercurylamp,butquitetolerablewith100and175wattlamps.Pleasebewarethatafterthepositiveelectrodehasbeenabusedafewtimeswithconstantwattagewarmup,itislikelytoneverworkwellinthefutureasanegativeelectrode. B+ B+ ^ ^ | |D1V > - >Rsense | > | +--------------------------------------+ ToOvervoltage | | B+ ) +-->SenseCircuit > > ^ )L1 |R1a> >R1b 330k > ) | > > +--VVVV------+> | Dout | L2 | | | |>2.2k +--->|----+--UUUU----+ | | | |\ +-+ __________ | | | +----|--+------|+\ || | / ===Cf | | | | >--+-|2 | ||D | | | +---------|-/ || 555 | || Q1 | | > > |/ +-|6 3|___||S | (lamp)R1c> >R1d 339 |__________| \ | | > > | | | | | Gnd Gnd Gnd Gnd Gnd | |--+--isconnected;--|--isnotconnected. | |555Connectionsnotshown:Pin1-B+.Pin8-Gnd.Pin4-Connecta.1uFcapacitorfvromthispintoGnd.Pin7-Donotconnecttoanything.Pin5-Connectasdirectedbelowintheovervoltagesensingcircuit.Notshown:Powersupplybypasscapacitors.Irecomendatleast.1uFacrossthepowerpinsofeachIC,aswellasatleast1uFperoutputwattoftantalumplus10uFperwattofelectrolyticcapacitor(s)acrossthepowersupply,asclosetothesenseresistorandmosfetsource(s)aspossible.Overvoltagesensingcircuit: B+ ^ | +--------------------------->FromoutputfiltercapacitorCf > |1K> > | >470K(determinesvoltagelimit)(560katyourriskformorevoltage) V > 470k(hysteresis)D3- | +-------VVVV-+ | | | |\ | +----|----+----|+\ | | | | >--+--->ToPin5ofthe555 | +---------|-/ | | |/Z1V > 339 - >10K | > | | Gnd GndImportantcomponentdescriptions:555-IrecommendtheNationalSemiconductorLM555.Digi-Keysellsthis.Other555'softendonotworkaswellinultrasoniccircuitswherearesponselagaroundamicrosecondcanchangethings-atbest,thiscanaffectthepowerregulation.339-Thisisa339comparator.Thisisaquadcomparator,onlytwoofthefourcomparatorsectionsareused.Othercomparatorswillprobablyworkiftheycansourceandsink_atleast_5milliampsandpreferably10.Pleasenotethatthe339isan"open-collector"type,requiringthepullupresistors(2.2K)fromtheiroutputstoB+.Mostothercomparatorsdonotneedthis.IdoNOTrecommendop-amps,sincetheywillrespondmoreslowly.Rsense-useapprox..06ohmfora100wattmercurylamp.Changethisinverselywithlampwattageforotherwattagelamps.WirewoundisOK-Ihavetriedthis,andtheinductanceisnotenoughtomessthingsuptoobadly.NichromewireisOK-butsolderswithsomedifficultyifbrightandshinyandfreeofoxide(scrapeanyoff),andnotatallwhereoxideispresent.D1-Anyordinaryrectifierdiode.D3-IrecommendputtinganLEDheretokeepthevoltageatthecomparatornoninvertinginputwellbelowB+shouldthesupplyvoltagedropreallylowforanyreason.Otherwise,comparatorsmayactstrangely.Dout-Thismustbeahighspeedtype,andshouldberatedtocontinuouslyhandlethecurrentobtainedfromdividingthelampwattageby12volts.Fastdiodesdon'thandlethepeakcurrentoftheoutputpulsesfromL1aswellasordinaryrectifiersdo.Cf-Ifthiscircuitoperatesatseveralkilohertzorhigher,Irecommendapprox..1to.15microfaradmultipliedbythelampwattageinwatts.Fora100wattlamp,use10to15uF.L2-ResonantfrequencybetweenL2andCfshouldbeafractionoftheoperatingfrequencyofthemaincircuit,generallynearakilohertz,maybeaslowasseveralhundredHz.Thisindicatesafewmillihenriesfora100wattlamp.Thisinductorshouldnotsaturateattwicethenormallampcurrent.Ialsorecommendhavinganohmortwoofresistanceinserieswiththelamp.Theinductorshouldbeferritecoretogettheeddycurrentlossesdownwhilehavingareasonablesizeandweightandnumberofturns.Alternatively,youcanusearesistorwithavalueof800ohmsdividedbythelampwattageinwatts.Thiswouldbe8ohmsfora100wattlamp.Thiswouldgiveagentlerwarmupthatisnothardonthelamp'selectrodes,butwillwasteatleast4percentofyourpowerwhenthelampiswarmedup.Thisresistorcangetasmuchas60percentoftheoutputpowerduringwarmup.L1-Mustnotsaturatewith1.33timestheratiooflampwattagetosupplyvoltage,plusallowanceforlossesanderrorsandtolerances.Ontimewillbetypically2/3of(inductance*averagecurrent/supplyvoltage).Averagecurrentistheratioofwattagetosupplyvoltage,plusabitmoreforlosses,andwillbecloseenoughto.09ampforeachwattoflampwattageat12-13volts.Thatmeanstheinductanceinmicrohenrieswouldbe180-200timesthedesiredontimeinmicroseconds,dividedbythelampwattageinwatts.Irecommendanontimearound30-40microseconds.Thiswouldresultinaninductanceinmicrohenriesof6000to8000,dividedbythelampwattageinwatts,for12-13volts.Thisinductormusthaveaferritecore.Afewguidelinesformulasforhome-windinginductorsonferritecores:1.FlybacktransformercoresareOK.2.Maximumpeakmagneticfluxshouldnotexceed4,000Gauss-preferablynotexceed3,000Gauss.Evenlessifthecoreismadeof"3B7"ferrite.Magneticfluxingaussisonetenthof4pitimesthecurrentinampstimesthenumberofturnsdividedbytheeffectiveairgapincentimeters.Or,that's4pi*N*amps/effectivegapinmillimeters.Effectivegapiscloseenoughtotwicethephysicalairgap,sinceinmostcoresthemagneticfluxflowsthroughtwogaps.Theseparationbetweentwocorehalveswillbethehalf-gap.Ifyouwanttofiguretheeffectivegapmoreexactly(generallynotnecessary),addtotheefectivegaptheratioofthetotalroutelengthofanaveragelineoffluxtothepermeabilityofthecorematerial(typicallyacouplethousand).3.Inductanceinnanohenriesis4pitimesthesquareofthenumberofturns,timesthecrosssectionareaofthecenterlegofthecore(crosssectionofthecoreperiodfortoroidsandC-Ccoressuchasflybacktransformercores)insquarecentimeters,dividedbytheeffectivegapincentimeters.Inthe100wattversionIbuiltandtested,L1consistsof20turnsof12-gaugewireonaferriteE-Ecorewithacenterlegcrosssectionareaofapprox.1.8squarecentimeters.Thehalf-gapisapprox..8millimeter,sotheeffectivegapis.16centimeter.Thiswouldmaketheinductance56microhenries(Ididnotactuallymeasurethis).Withthe12amppeakcurrent,themagneticfluxwouldbenearly1900Gauss-nowherenearthelimitsof3B7,3C8,noranycommonflybacktransformerferrite.Thetheoreticalontimewith12voltsacrossthisinductorduringtheon-timeandcurrentincreasingfrom6to12ampswouldbe28microseconds.Myactualontimeislonger.Q1-IrecommendaparalledbankofIRF730orIRF740powerMOSFETs.Usemaybe16IRF730'sor8IRF740'sinparallelfora100wattmercurylamp.Sincea555comfortablydriveshalfofthisatultrasonicfrequencies(Idon'tknowyetaboutmore),Irecommendone555per50wattsofmercurylamp.Connectall555'sinparallel,thatis,connectallcorrespondingpinstogether-withtheexceptionofPin3.EachPin3drivesaseparatesub-bankoffourIRF740'soreightIRF730's.Connectalldrainstogetherandallsourcestogether.Connectallgatestogetherwithineachsub-bank.Pleaseusesomeheatsinking.TheIRF730MOSFETswillbedissipatingnearlyhalfawatteach(twicethisforIRF740's),whichcanmakethemgetquitewarmiftheyareclosetogetherwithoutaheatsink.Their"on"resistanceincreaseswithtemperature,whichmaycause"thermalrunaway"iftheygettoowarm.R1a,R1b,R1c,R1d-Theseshouldbe10K1percentresistors.Donotputtheseanywherewhereanyheatsourcewouldheatthemtoounequally.ModerateheatingisOKifallfouroftheseareheatednearlyequally.ImportantTestingInformation:Whenyouarereadytooperatethiscircuit,usea120voltincandescentlampinsteadofamercurylamp.Theincandescentlampshouldhavearatedwattage1.5to2timesthatofthemercurylamp.Applypower-thelampshouldglow.Itshouldglowmuchmorebrightlythanitdoeswith12volts,butdimmerthanitdoeswith120volts.Sofar,sogood?Monitorthevoltageacrossthesenseresistor(Rsense,thereallylowvalueone)withanoscilloscope.Thewaveformshouldbeatrianglewaveandthevoltageacrossthisresistorshouldhaveaminimumnear.4voltandamaximumnear.8volt.TheaverageshouldbeclosetothevoltageacrossthediodeD1thatisinserieswithR1a.IfthevoltageacrossRsenseistoolow,addasmallamountofextraresistanceinserieswithR1a.Ifthisvoltageistoohigh,addasmallamountofextraresistanceinserieswithR1b.IftheaveragevoltageisOKbutthevoltagedoesnotswingenough(staysfarwithintherangeof2/3to4/3theaverage),replacethe330kresistorwithoneofalowervalue.Ifthisvoltageswingsfaroutsidetherangeof2/3to4/3oftheaverage,replacethisresistorwithahighervalueone.Ifthewaveform'sshallowerslopes(increasingcurrent)getsteeperascurrentincreases,thantheinductorissaturating.Youmaybeabletofixthisbyreplacingthe330kresistorwithahighervalueonetodecreasethecurrentrange.Otherwise,youneedtoincreasethegapinL1orotherwiserebuildit.Ifyoufeelcomfortableenoughwiththiscircuittodoso,youcanchangethe330kresistortoadjusttheoscillationfrequencyortoreduceswitchinglossesorforwhateverotherpurpose.Justbesuretheinductorisnotsaturatingandtheminimumvoltageacrossthesenseresistorisnottoolow-iftheminimumvoltagehitszerowithoutthe"on"cyclebeingrestarted,yougetnothingout.IseverythingcheckingoutOKatthispoint?Ifso,thenusea120voltincandescentlamp(orcombinationoflampsinparallel)ofratedwattageequaltothatofthemercurylampthatyouwilluse.Applypower.Thelampshouldgetratedpower.YoucanmeasurethevoltageacrossitwithaDCvoltmeter.Besurethebrightnessisclosetothatofthesamelampgetting120volts,incaseanythingstrangeisgoingon.Ifthelampisbeingoverpowered,addasmallresistanceinserieswithR1b.Ifthelampisbeingunderpowered,addasmallresistanceinserieswithR1a.Majoroutputpoweradjustmentswouldneedadifferentsenseresistor-changethisinverselywiththedesiredchangeinwattage.Verifythatthevoltagewaveformacrossthesenseresistorremainsgoodafteradjustingtheoutputpower.IseverythingstillcheckingoutOKatthispoint?Ifthingsarestillgood,operatethiselectronicballastwithnoloadatall,whilemonitoringthevoltageacrosstheoutputfiltercapacitor.Thereshouldbeableederresistoraroundamegohmorsoacrosstheoutputforthis.Thevoltagequicklyriseto300voltsorso.Ifitgoesmuchhigher(anywherenearorover400volts),immediatelyshutthiscircuitdown.Repairtheovervoltagehandlingcircuit.Iftheovervoltagehandlingcircuitisworkingproperly,theoutputvoltageshouldrisequicklytoapprox.300volts,thenthecircuitshouldautomaticallyshutdown,thenrestartaftertheoutputvoltagebleedsdownacouplepercent.Ifrepairswerenecessary,besurenomosfetsheatupunusuallyduringoperation.IseverythingstillcheckingoutOKatthispoint?IfthingsareOKatthispoint,thenyoucanuseamercuryvaporlamp.Itispreferredwithsomemercurylampstomaketheshellofthebasepositiveandthetipcontactnegative.Ifthesockethasawhitewireandablackone,makethewhiteonepositiveandtheblackonenegative.Ifyouhaveabrassscrewandasilver-coloredscrew,makethesilver-coloredonepositiveandthebrassonenegative.Polaritymaybeimportantforcontinuedreliableoperationofthestartingelectrodeinsidethearctubeofthemercurylamp.Makingtheelectrodeclosertothestartingelectrodepositivemaycausethelamptodeteriorateinawaythatimpairsstarting.Pleasenotethatfullnormallamplifeisunlikelysincewhicheverelectrodeinthearctubeispositivewillbetrashedbyjustafewconstant-wattagewarmups.Pleasenotethatwattagewillvaryroughlyproportionatelywithsupplyvoltage.By"constantwattage",Iamreferringtowattagenotvaryingmuchwiththevoltageacrossthelamp.
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再來一個DC-Output,ConstantWattage12VoltMercuryBallast!Pleasereadthisarticleinitsentiretybeforeconstructingthis.CAUTION-Thefollowingmaterialgetsquitetechnicalattimes,thedevicebelowmakeshighvoltagesthatcankillyou,andifthingsgowrongitiseasytomakelotsofsmoke,customand/orhomebrewferritecoreinductorsarenecessary,thiscircuitcanbeabusivetomercurylamps,mercurylampsshouldbeinsuitableenclosedfixturesincasetheyexplode.Irecommendthisasaprojectonlyforthosewithpriorelectronicprojectandelectronicrepairexperience.Corrections,additions,andquestionsto(don@misty.com).DONOTusethiswithmetalhalideorsodiumlamps,sincetheselampsdonotlikeDCandmetalhalidelampsarelesstolerantofconstant-wattagewarmupthanmercurylamps.BelowisaschematicforaDCoutput,nearlyconstantwattagecircuittopowermercuryvaporlampsfrom12to14voltsDC.Theovervoltagedetection/handlingcircuitisshownseparatelybelowthemainportionofthisschematicforclarity,butmustbeincluded.Seethecomponentdescriptionsfollowingtheschematicsforvaluesanddescriptions.Seeotherinstructionsfollowingthecomponentdescriptions.Itisimportanttotestforproperoperationandproperpoweroutput.Thiselectronicballastwillgiveamercuryvaporlampnearlyconstantwattagedespitevariationsinthevoltageacrossthelamp.Thiswillgivethelampexcessivecurrentduringwarmup,whenthevoltageacrossthelampisless.Anadvantageofthisisacceleratedwarmupofthelamp.Adisadvantageisoverheatingoftheelectrodes,especiallythepositiveelectrode.Expectsomesignificantdiscolorationaroundthepositiveelectrode,whichwillpartiallyevaporateafterseveralminutestoanhourofusefullywarmedup.Somepermanentdiscolorationwillremain.IhavefoundthisdiscolorationquiteseverewiththePhilips40/50wattmercurylamp,butquitetolerablewith100and175wattlamps.Pleasebewarethatafterthepositiveelectrodehasbeenabusedafewtimeswithconstantwattagewarmup,itislikelytoneverworkwellinthefutureasanegativeelectrode. B+ B+ ^ ^ | |D1V > - >Rsense | > | +--------------------------------------+ ToOvervoltage | | B+ ) +-->SenseCircuit > > ^ )L1 |R1a> >R1b 330k > ) | > > +--VVVV------+> | Dout | L2 | | | |>2.2k +--->|----+--UUUU----+ | | | |\ +-+ __________ | | | +----|--+------|+\ || | / ===Cf | | | | >--+-|2 | ||D | | | +---------|-/ || 555 | || Q1 | | > > |/ +-|6 3|___||S | (lamp)R1c> >R1d 339 |__________| \ | | > > | | | | | Gnd Gnd Gnd Gnd Gnd | |--+--isconnected;--|--isnotconnected. | |555Connectionsnotshown:Pin1-B+.Pin8-Gnd.Pin4-Connecta.1uFcapacitorfvromthispintoGnd.Pin7-Donotconnecttoanything.Pin5-Connectasdirectedbelowintheovervoltagesensingcircuit.Notshown:Powersupplybypasscapacitors.Irecomendatleast.1uFacrossthepowerpinsofeachIC,aswellasatleast1uFperoutputwattoftantalumplus10uFperwattofelectrolyticcapacitor(s)acrossthepowersupply,asclosetothesenseresistorandmosfetsource(s)aspossible.Overvoltagesensingcircuit: B+ ^ | +--------------------------->FromoutputfiltercapacitorCf > |1K> > | >470K(determinesvoltagelimit)(560katyourriskformorevoltage) V > 470k(hysteresis)D3- | +-------VVVV-+ | | | |\ | +----|----+----|+\ | | | | >--+--->ToPin5ofthe555 | +---------|-/ | | |/Z1V > 339 - >10K | > | | Gnd GndImportantcomponentdescriptions:555-IrecommendtheNationalSemiconductorLM555.Digi-Keysellsthis.Other555'softendonotworkaswellinultrasoniccircuitswherearesponselagaroundamicrosecondcanchangethings-atbest,thiscanaffectthepowerregulation.339-Thisisa339comparator.Thisisaquadcomparator,onlytwoofthefourcomparatorsectionsareused.Othercomparatorswillprobablyworkiftheycansourceandsink_atleast_5milliampsandpreferably10.Pleasenotethatthe339isan"open-collector"type,requiringthepullupresistors(2.2K)fromtheiroutputstoB+.Mostothercomparatorsdonotneedthis.IdoNOTrecommendop-amps,sincetheywillrespondmoreslowly.Rsense-useapprox..06ohmfora100wattmercurylamp.Changethisinverselywithlampwattageforotherwattagelamps.WirewoundisOK-Ihavetriedthis,andtheinductanceisnotenoughtomessthingsuptoobadly.NichromewireisOK-butsolderswithsomedifficultyifbrightandshinyandfreeofoxide(scrapeanyoff),andnotatallwhereoxideispresent.D1-Anyordinaryrectifierdiode.D3-IrecommendputtinganLEDheretokeepthevoltageatthecomparatornoninvertinginputwellbelowB+shouldthesupplyvoltagedropreallylowforanyreason.Otherwise,comparatorsmayactstrangely.Dout-Thismustbeahighspeedtype,andshouldberatedtocontinuouslyhandlethecurrentobtainedfromdividingthelampwattageby12volts.Fastdiodesdon'thandlethepeakcurrentoftheoutputpulsesfromL1aswellasordinaryrectifiersdo.Cf-Ifthiscircuitoperatesatseveralkilohertzorhigher,Irecommendapprox..1to.15microfaradmultipliedbythelampwattageinwatts.Fora100wattlamp,use10to15uF.L2-ResonantfrequencybetweenL2andCfshouldbeafractionoftheoperatingfrequencyofthemaincircuit,generallynearakilohertz,maybeaslowasseveralhundredHz.Thisindicatesafewmillihenriesfora100wattlamp.Thisinductorshouldnotsaturateattwicethenormallampcurrent.Ialsorecommendhavinganohmortwoofresistanceinserieswiththelamp.Theinductorshouldbeferritecoretogettheeddycurrentlossesdownwhilehavingareasonablesizeandweightandnumberofturns.Alternatively,youcanusearesistorwithavalueof800ohmsdividedbythelampwattageinwatts.Thiswouldbe8ohmsfora100wattlamp.Thiswouldgiveagentlerwarmupthatisnothardonthelamp'selectrodes,butwillwasteatleast4percentofyourpowerwhenthelampiswarmedup.Thisresistorcangetasmuchas60percentoftheoutputpowerduringwarmup.L1-Mustnotsaturatewith1.33timestheratiooflampwattagetosupplyvoltage,plusallowanceforlossesanderrorsandtolerances.Ontimewillbetypically2/3of(inductance*averagecurrent/supplyvoltage).Averagecurrentistheratioofwattagetosupplyvoltage,plusabitmoreforlosses,andwillbecloseenoughto.09ampforeachwattoflampwattageat12-13volts.Thatmeanstheinductanceinmicrohenrieswouldbe180-200timesthedesiredontimeinmicroseconds,dividedbythelampwattageinwatts.Irecommendanontimearound30-40microseconds.Thiswouldresultinaninductanceinmicrohenriesof6000to8000,dividedbythelampwattageinwatts,for12-13volts.Thisinductormusthaveaferritecore.Afewguidelinesformulasforhome-windinginductorsonferritecores:1.FlybacktransformercoresareOK.2.Maximumpeakmagneticfluxshouldnotexceed4,000Gauss-preferablynotexceed3,000Gauss.Evenlessifthecoreismadeof"3B7"ferrite.Magneticfluxingaussisonetenthof4pitimesthecurrentinampstimesthenumberofturnsdividedbytheeffectiveairgapincentimeters.Or,that's4pi*N*amps/effectivegapinmillimeters.Effectivegapiscloseenoughtotwicethephysicalairgap,sinceinmostcoresthemagneticfluxflowsthroughtwogaps.Theseparationbetweentwocorehalveswillbethehalf-gap.Ifyouwanttofiguretheeffectivegapmoreexactly(generallynotnecessary),addtotheefectivegaptheratioofthetotalroutelengthofanaveragelineoffluxtothepermeabilityofthecorematerial(typicallyacouplethousand).3.Inductanceinnanohenriesis4pitimesthesquareofthenumberofturns,timesthecrosssectionareaofthecenterlegofthecore(crosssectionofthecoreperiodfortoroidsandC-Ccoressuchasflybacktransformercores)insquarecentimeters,dividedbytheeffectivegapincentimeters.Inthe100wattversionIbuiltandtested,L1consistsof20turnsof12-gaugewireonaferriteE-Ecorewithacenterlegcrosssectionareaofapprox.1.8squarecentimeters.Thehalf-gapisapprox..8millimeter,sotheeffectivegapis.16centimeter.Thiswouldmaketheinductance56microhenries(Ididnotactuallymeasurethis).Withthe12amppeakcurrent,themagneticfluxwouldbenearly1900Gauss-nowherenearthelimitsof3B7,3C8,noranycommonflybacktransformerferrite.Thetheoreticalontimewith12voltsacrossthisinductorduringtheon-timeandcurrentincreasingfrom6to12ampswouldbe28microseconds.Myactualontimeislonger.Q1-IrecommendaparalledbankofIRF730orIRF740powerMOSFETs.Usemaybe16IRF730'sor8IRF740'sinparallelfora100wattmercurylamp.Sincea555comfortablydriveshalfofthisatultrasonicfrequencies(Idon'tknowyetaboutmore),Irecommendone555per50wattsofmercurylamp.Connectall555'sinparallel,thatis,connectallcorrespondingpinstogether-withtheexceptionofPin3.EachPin3drivesaseparatesub-bankoffourIRF740'soreightIRF730's.Connectalldrainstogetherandallsourcestogether.Connectallgatestogetherwithineachsub-bank.Pleaseusesomeheatsinking.TheIRF730MOSFETswillbedissipatingnearlyhalfawatteach(twicethisforIRF740's),whichcanmakethemgetquitewarmiftheyareclosetogetherwithoutaheatsink.Their"on"resistanceincreaseswithtemperature,whichmaycause"thermalrunaway"iftheygettoowarm.R1a,R1b,R1c,R1d-Theseshouldbe10K1percentresistors.Donotputtheseanywherewhereanyheatsourcewouldheatthemtoounequally.ModerateheatingisOKifallfouroftheseareheatednearlyequally.ImportantTestingInformation:Whenyouarereadytooperatethiscircuit,usea120voltincandescentlampinsteadofamercurylamp.Theincandescentlampshouldhavearatedwattage1.5to2timesthatofthemercurylamp.Applypower-thelampshouldglow.Itshouldglowmuchmorebrightlythanitdoeswith12volts,butdimmerthanitdoeswith120volts.Sofar,sogood?Monitorthevoltageacrossthesenseresistor(Rsense,thereallylowvalueone)withanoscilloscope.Thewaveformshouldbeatrianglewaveandthevoltageacrossthisresistorshouldhaveaminimumnear.4voltandamaximumnear.8volt.TheaverageshouldbeclosetothevoltageacrossthediodeD1thatisinserieswithR1a.IfthevoltageacrossRsenseistoolow,addasmallamountofextraresistanceinserieswithR1a.Ifthisvoltageistoohigh,addasmallamountofextraresistanceinserieswithR1b.IftheaveragevoltageisOKbutthevoltagedoesnotswingenough(staysfarwithintherangeof2/3to4/3theaverage),replacethe330kresistorwithoneofalowervalue.Ifthisvoltageswingsfaroutsidetherangeof2/3to4/3oftheaverage,replacethisresistorwithahighervalueone.Ifthewaveform'sshallowerslopes(increasingcurrent)getsteeperascurrentincreases,thantheinductorissaturating.Youmaybeabletofixthisbyreplacingthe330kresistorwithahighervalueonetodecreasethecurrentrange.Otherwise,youneedtoincreasethegapinL1orotherwiserebuildit.Ifyoufeelcomfortableenoughwiththiscircuittodoso,youcanchangethe330kresistortoadjusttheoscillationfrequencyortoreduceswitchinglossesorforwhateverotherpurpose.Justbesuretheinductorisnotsaturatingandtheminimumvoltageacrossthesenseresistorisnottoolow-iftheminimumvoltagehitszerowithoutthe"on"cyclebeingrestarted,yougetnothingout.IseverythingcheckingoutOKatthispoint?Ifso,thenusea120voltincandescentlamp(orcombinationoflampsinparallel)ofratedwattageequaltothatofthemercurylampthatyouwilluse.Applypower.Thelampshouldgetratedpower.YoucanmeasurethevoltageacrossitwithaDCvoltmeter.Besurethebrightnessisclosetothatofthesamelampgetting120volts,incaseanythingstrangeisgoingon.Ifthelampisbeingoverpowered,addasmallresistanceinserieswithR1b.Ifthelampisbeingunderpowered,addasmallresistanceinserieswithR1a.Majoroutputpoweradjustmentswouldneedadifferentsenseresistor-changethisinverselywiththedesiredchangeinwattage.Verifythatthevoltagewaveformacrossthesenseresistorremainsgoodafteradjustingtheoutputpower.IseverythingstillcheckingoutOKatthispoint?Ifthingsarestillgood,operatethiselectronicballastwithnoloadatall,whilemonitoringthevoltageacrosstheoutputfiltercapacitor.Thereshouldbeableederresistoraroundamegohmorsoacrosstheoutputforthis.Thevoltagequicklyriseto300voltsorso.Ifitgoesmuchhigher(anywherenearorover400volts),immediatelyshutthiscircuitdown.Repairtheovervoltagehandlingcircuit.Iftheovervoltagehandlingcircuitisworkingproperly,theoutputvoltageshouldrisequicklytoapprox.300volts,thenthecircuitshouldautomaticallyshutdown,thenrestartaftertheoutputvoltagebleedsdownacouplepercent.Ifrepairswerenecessary,besurenomosfetsheatupunusuallyduringoperation.IseverythingstillcheckingoutOKatthispoint?IfthingsareOKatthispoint,thenyoucanuseamercuryvaporlamp.Itispreferredwithsomemercurylampstomaketheshellofthebasepositiveandthetipcontactnegative.Ifthesockethasawhitewireandablackone,makethewhiteonepositiveandtheblackonenegative.Ifyouhaveabrassscrewandasilver-coloredscrew,makethesilver-coloredonepositiveandthebrassonenegative.Polaritymaybeimportantforcontinuedreliableoperationofthestartingelectrodeinsidethearctubeofthemercurylamp.Makingtheelectrodeclosertothestartingelectrodepositivemaycausethelamptodeteriorateinawaythatimpairsstarting.Pleasenotethatfullnormallamplifeisunlikelysincewhicheverelectrodeinthearctubeispositivewillbetrashedbyjustafewconstant-wattagewarmups.Pleasenotethatwattagewillvaryroughlyproportionatelywithsupplyvoltage.By"constantwattage",Iamreferringtowattagenotvaryingmuchwiththevoltageacrossthelamp.
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