Re: Interupting xenon flash current ?

Jim Thompson To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx posted to
sci.electronics.design:

On Wed, 05 Dec 2007 12:52:21 -0500, Mike <nomtrxspam@xxxxxxxxxxx>
wrote:

I was reading about how autoexposure and speed flash units work and
found out that in modern units IGBTs are used to turn off the tube
current at the proper time. I scrounged up the parts to flash a tube
and measured the current pulse during discharge. For my test setup I
measured the the current peak to be about 1900A and am fairly
certain that number is pretty close. The current was above 1000A for
about 6us and still at 300A after 200us then finally decayed to 0
after about 600us. How is it possible for any reasonably
priced/sized IGBT to survive under that kind of stress? I was going
to try interupting the pulse, but the only IGBT I have is one I took
from a dead microwave oven inverter and it's only rated at 150A for
1ms. My test setup isn't all that powerful, only about 37J (600uf
flash cap charged to 350v). I'm also curious about why it takes 20us
from the time of the HV trigger to the time the tube starts to
conduct. It may not be, but that just seems like and
awfully long time. Not enough trigger voltage maybe? Also, it takes
another 15us for the current to reach it's peak. Unfortunately I
don't have any data for the flash tube. It is fairly large, 80mm
long and 8mm dia. The trigger is a thin wire spirally wrapped the
entire length of the tube.

Mike


If there is no absolute truth then nothing can be known.

I did that in the '60's, but used an SCR, read my patent at...

http://analog-innovations.com/SED/Pat-3496411.pdf

...Jim Thompson

So basically you are commutating the flashtube with the SCR instead of
another SCR?

.

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