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Re: Smokin' gate drive chips on DRSSTC-2 board

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Scott,

At 12:40 AM 12/5/2004, you wrote: 
Terry -

I am building (3) of Dan McCauley's DRSSTC driver boards, and the first one
I powered up (with no gate drive transformer connected) instantly let out a
small wisp of smoke from one of the driver chips  ......


I see.  I bet they need a load to run right.


Curiously, I was ramping up input power with a variac, and if I recall this
happened at about 80 or 90 VAC input. I think it was U36 that suddenly got
hot and emitted a very thin thread of smoke. I instantly cut power, checked
everything out, installed some small inductors across the gate driver
outputs to simulate the load of a transformer, and re-applied power. Despite
the initial wisp of smoke, U36 appears to operate normally now, and drives a
real gate drive transformer just fine. If I recall, the output waveforms
were somewhat irregular until I install a load across the driver outputs.

If the internal transistors cross conducted or oscillated that would make sense. The power supplies current limiting save them from actually being destroyed. They just got real hot.


Here's a related question: Dan has used a pair of 10uF tantalum coupling
caps (10uF @ 35V, C45 & C46) in series with the gate drive transformer
primary windings. I'm not sure I understand how a polarized capacitor is
appropriate for this particular application. Any concerns? Would a
non-polarized, low-inductance polypropylene film cap be a better choice?

I think they block DC voltage from pumping a lot of current in the transformer if the thing is not oscillating. The caps would normally charge in only one direction and discharge through the transformer so they would be perfectly fine as is.


Regards,
Scott Hanson

PS - Any intention of buying some more of your power supply boards and
offering them to the List members who are building up Dan's driver boards?
I'm sure there would be some level of interest ......

I have one extra bare board and a few parts to it here if anyone wants it (say $50). They are sort of pricey due to their size and low quantity purchases. I am not in the selling stuff mood but the art is at:

http://hot-streamer.com/TeslaCoils/MyCoils/DRSSTC/DRSSTCpower-01.pcb

Cheers,

        Terry