Re: [TCML] gate drive issues

[Bert Hickman <bert.hickman@xxxxxxxxxx>]

Hi John,

It looks like you're seeing the superimposed combination of the gate 
signal and common-mode coming from the high-current primary circuit. I 
would suspect its an artifact of your measurement setup. Are you using a 
wideband CT to get an isolated gate current measurement? If so, you may 
be getting some induction effects from the strong primary field. Does 
the shape of the waveform change if you reroute the coax cable from the 
CT or the change the orientation of the CT relative to the primary 
circuit/winding? What happens if you simply place the CT in the same 
position with NO wire inside the core?

Bert
--
Bert Hickman
Stoneridge Engineering
http://www.capturedlightning.com
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John Forcina 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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