Re: [TCML] gate drive issues

[Steve Ward <steve.ward@xxxxxxxxx>]

John,

I dont think you linked to the most important picture:

https://secure.flickr.com/photos/forcijo/7799111918/in/photostream/

which to me looks characteristic of partial discharges.

But maybe you arent worried about that anymore??  What exactly is your
concern?  I see there is significant droop on what you claimed was a
gate drive waveform.  That could just be poor measurement technique.

Please clarify!

Steve

On Sat, Sep 29, 2012 at 1:14 AM, John Forcina <forcijo10@xxxxxxxxx> wrote:
> Hey guys, so i am nearing completion on a new large CM600 based DRSSTC and
> i am encountering this strange problem that i just cant wrap my head
> around.  I suspect that i could have partially damaged igbt's however i am
> hoping that is not the case.   I am experiencing a very strange problem
> with my gate drive waveforms.  As i increase my bus voltage the gate drive
> waveforms seem to get worse and worse and it seems to be directly
> proportional to primary current although they look pretty nasty to begin
> with.  Here is a scope capture of primary current vs the waveforms of one
> of the gates.
> https://secure.flickr.com/photos/forcijo/8034549201/in/photostream  Here is
> a similar capture that shows primary GDT waveforms vs the waveforms at one
> of the gates
> https://secure.flickr.com/photos/forcijo/8034549201/in/photostream
>
> This whole situation gets worse and worse the more i crank up the bus
> voltage but strangely i am still getting pretty good output waveforms
> https://secure.flickr.com/photos/forcijo/8034761102/in/photostream/ aside
> from the initial cycle which has some weird oscillations going on
> https://secure.flickr.com/photos/forcijo/8034764783/in/photostream/  Yet
> another oddity is when i synthesize feedback from a signal generator (when
> there is no actual current flowing through the system) all the waveforms
> look quite alright.  This is another thing that makes me suspect they are
> they igbt's themselves but i am pretty stumped.  If anybody has any ideas
> of what the problem is i am experiencing that would be greatly appreciated.
>
> John.
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