RE: drsstc - catastrophic failure! And Thor

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 07:21 28/04/03 -0600, you wrote:
>Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><Marco.Denicolai-at-tellabs-dot-com>
>
>I suggest you to use my approach:
>- measure with reduced input voltage
>- find the spikes and transients (e.g. on Vcc, Vge, etc.)
>- develop solutions to reduce them at a minimum
>
>This way you'll have "things in order" also for full power or, at least,
>as good as you possibly can get.

I totally agree that this is a great way to do things. If you apply full 
power and there's something wrong with the circuit, it usually just goes up 
in smoke. At reduced voltage, the thing will probably hold together long 
enough for you to look at waveforms and see what the problem is. I ran my 
first OLTC attempts off 30V. Straight away I could see that the waveforms 
sucked and I knew what needed work.

 > Did you read the description of my last
 > development on Thor's power supply (i.e. the revision B stuff at
 > www.iki.fi/dncmrc)?

I've been following the Thor power supply thing with great interest. The 
reason is that I need a charge circuit for the OLTC that charges to an 
accurate voltage. So I can push the IGBTs to the max without blowing them 
up. The ordinary DC resonant charge circuit isn't predictable enough. Plus, 
it can't generate more than twice the DC bus voltage. I hope to have 1200V 
IGBT bricks so I need about 1kV. A mini version of the Thor power supply 
that gives about 1kW -at- 900-1000V would be ideal. Plus it would be a great 
challenge... I've never built a big off-line switcher and I'm frankly 
scared of the things 8--at-

If I built it, I would replace all the gate drive/isolation electronics 
with a pair of TC442x type driver chips and a single gate drive transformer 
with 4 secondaries, like in a full-bridge SSTC. I can do this because I 
don't need the multi-module thing.

I would also change the current limiting circuit- I believe the circuit 
Marco originally used could cause second breakdown in the IGBTs, because it 
clamps the current instead of feeding back to the controller chip and 
ending the pulse.

I'd appreciate any comments from the original inventor :)

Steve C.