Re: A s.s. head-scratcher

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Ken,

I read somewhere (can't recall where) that IGBT's failed with open 
gates with the oddest of causes during a lab performing IGBT testing. 
What was interesting is this particular failure was caused by C-E 
short circuit testing. Surprised the people doing the testing and 
probably anyone who read the article.

I personally have only shorted FETs and IGBTs, but I guess there are 
some situations (di/dt) that can do odd things. My point is that the 
gate opening is apparently possible. From your description, the gate 
open would certainly cause what your seeing.

Take care,
Bart

Tesla list wrote:

> Original poster: Ken or Doris Herrick <kchdlh@xxxxxxxxx>
>
> Steve Ward et al-
>
> This one stumps me but perhaps not someone else:  I'm implementing 
> my push-pull s.s. primary circuit, using two Powerex CM300DY-24H IGBTs.
> Previously it appeared to function but not satisfactorily so I've 
> redesigned and rebuilt the drivers.  Waveforms now, right at the 
> IGBT gates, appear perfect.  However...  The IGBTs will conduct no 
> current; nada, zip, neither of them.  Nothing within them is 
> shorted, per my ohmmeter, and the gate:emitter nodes are "open" per 
> the ohmmeter.
>
> In order to accommodate my revised driver circuit, which has 
> back:back zener protection, I had carefully removed the 10K 
> resistors that were protecting the gates.  Was I not careful enough, 
> do you suppose?
> Could the gates have actually opened up within the packages?  >Both< 
> of them??  Not hardly, I should think: they'd be shorted, if 
> anything.  Does anyone have a clue, before I have to un-mount them & 
> jury-rig a test-setup?
>
> Ken Herrick