RE: drsstc - catastrophic failure! And Thor

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Original poster: "jimmy hynes by way of Terry Fritz <teslalist-at-qwest-dot-net>" <chunkyboy86-at-yahoo-dot-com>

Hi,

One of the coolest things about OLTCs is that they are so simple. Designing 
a resonant power supply would ruin that aspect of it. You could easily 
convert it to a boost converter instead. If I remember correctly, the IGBT 
you killed was because of this "problem", when you weren't quenching at the 
first notch. With lower charging inductance, 1kv should be easy.  The peak 
current would not rise too much either.  unless the inaccuracies are really 
bad, you could just add a few extra IGBTs that you would have used in the 
resonant power supply.

Do you know what is causing the inconsistant charging voltage? how bad is 
it?  Are you planning on using the same secondary and toroid?


Original poster: "Stephen Conner by way of Terry Fritz "

At 07:21 28/04/03 -0600, you wrote:
 >Original poster: "by way of Terry Fritz "
 >
 >
 >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 ra! n 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/isola! tion electronics
with a pair of TC442x type driver chips and a sin gle 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.





Jimmy