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camera flash transistor keeps blowing

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teslacoolguy

Fri Mar 14 2008, 03:06AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
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Posts: 792

i am trying to make a multi camera flash device that puts out a enormus amount of light for a split second so i banked up 4 xenon tubes from disposable cameras along with a 200uf flash cap instead of 120uf and after playing with it for a while i got it to work well but it would keep blowing the transistor tht is used to oscillate the inverter transformer. Why is it doing this and how do you think i can fix this problem?

uzzors2k

Fri Mar 14 2008, 03:31PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Try disconnecting the charger before firing, it's is good practice anyway. I'm not too familiar with camera-chargers, but since they don't seem to use mechanical switching there must be some silicon somewhere which controls the switching process. 4 xenon tubes VS 1 should have ~1/4 of the resistance, so the increased peak current might be the problem.

teslacoolguy

Fri Mar 14 2008, 05:49PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

disconnecting the power from the charger before i triggered it worked. Now i have to design a circut that cuts the power to the flash unit a couple ms before the flash triggers via a scr then returns power to the flash unit and then triggers the scr again to start the recharge so any suggestions on how to do that will be appereciated.

this is the sequence that i need. power off then around 1ms later scr on for 1ms and power stays off through the entire time the scr is on so 4ms then power turns back on and 1ms later the scr turns on for 1ms to start the recharge and the power stays on to recharge the unit and then when i push the button not holding it down the process starts all over. i was thinking of using a small pic connected to a 4017 chip but i think there are better ways.

flannelhead

Fri Mar 14 2008, 06:32PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

teslacoolguy wrote ...

i am trying to make a multi camera flash device that puts out a enormus amount of light for a split second so i banked up 4 xenon tubes from disposable cameras along with a 200uf flash cap instead of 120uf and after playing with it for a while i got it to work well but it would keep blowing the transistor tht is used to oscillate the inverter transformer. Why is it doing this and how do you think i can fix this problem?

Strange problem...

Uzzors wrote ...

Try disconnecting the charger before firing, it's is good practice anyway. I'm not too familiar with camera-chargers, but since they don't seem to use mechanical switching there must be some silicon somewhere which controls the switching process. 4 xenon tubes VS 1 should have ~1/4 of the resistance, so the increased peak current might be the problem.

The triggering done with a trigger transformer. The trigger transformer generates a pulse of some kV which ionizes the gas in the tube. Then the 200V in the caps have free way to go. So there should be no silicon in the trigger circuitry.

As Uzzors said, it could be the 1/4 of the normal resistance which caused the transistor death. I've never had a problem with a single flash tube and 480uF@330V. You should also try paralleling the caps, it should increase the brightness.

Backyard Skunkworks

Fri Mar 14 2008, 08:29PM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

Maybe your best bet is finding some other way of ionizing the Xenon tube, after all these cameras are built for taking 27 pictures and have the bare minimum of beefy-ness required. I've even had some charging circuits fail during normal use of the camera!

The caps are pretty versitile but the charing circuitry just isnt built for anything more then a few mA at 330 volts and a 10kV pulse.

Speaking of camera inverters I did a little experiment and a few of these things in parallel using NiMH batteries is enough voltage and current to electrolyze tap water, although its pretty slow.

Tesladownunder

Sat Mar 15 2008, 12:28PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

I used a camera circuit in my Candy Box HV.
I had figured the load would be too much for the existing transistor and I substituted it for a BD140. Been reliable for years running 3V of alkaline batteries (instead of the designed 1.5V). I have used a heat sink so I guess the BD140 might have been getting warm.

TDU

Conundrum

Sat Mar 15 2008, 08:54PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

yep, those transistors work just fine when used normally, but it looks like they can't handle anything more than a momentary overload. I learned this the hard way when building a 6 inverter HV generator and blew out 4 pairs (!) the first time I attempted to draw sparks.

For future reference, I had to put resistors in the grounds from each CCFL transformer to get around this.

-A

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