Re: Terry's DRSSTC - Odd IGBT damage??

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Stork,

At 11:16 AM 2/3/2005, you wrote:
> Terry,
>
> Your probably right about the reverse diodes.  Check a good IGBT and see 
> what voltage the reverse diode conducts then check to see if your driver 
> reverse diode conducts at the same voltage or is shorted or open.    Do it 
> with DC and also at operating frequency.
>
> > I am thinking the anti-parallel diodes have gone away.  Strange since one 
> > would think the IGBTs themselves would get beat up from tiny dead times 
> > and fast switching rather than the separate diodes....
> > So I am going to switch out the set of IGBTs and see if it all returns to 
> > normal.  If so, I will have the die checked to find what blew up.
>
> stork

There coming out anyway ;-))  I think I know what happened....

It was that 2000V/uS voltage rise across the diode's capacitance.  If they 
are say 50pF gate capacitance diodes, that gives a 100mA reverse junction 
current!  The diodes can do maybe 700 amps forward, but nil 
backward...  The forced reverse current wiped them out.  According to IR, 
the super high dV/dT will get the IGBTs too with time.  The IGBTs also have 
lots of similar junctions that don't like that stuff...  My observation 
that the noise seems to be getting worse is probably true and indicting 
that an explosion is eminent.  In this pulsed low duty cycle low current 
situation, I was probably able to crunch them all without doing instant 
catastrophic damage.  I will see if I can get photos of the odd damage once 
I get them apart.  That should be really cool!  I would guess the junctions 
got damaged and then the diodes blew out, but I think that would have blown 
them apart too.?.?

That is good news since "I did it" ;-))  I just won't run them without the 
dead time anymore.  They switch really fast all by themselves but they just 
can't be forced to switch faster...

> I know you have other immediate coil issues now, but if you have a chance 
> could you share your fiber optic control system and how it connects to and 
> controls your microprocessor?

The schematic is at:

http://drsstc.com/~terrell/schematics/PulseContoller.gif

http://drsstc.com/~terrell/schematics/Controller.gif

Pages 11 and 20 of:

http://drsstc.com/~terrell/datasheets/FiberReceiver-5988-3624EN.pdf

Just the digital versions of my old fiber optic probe opto stuff...

Dan Wrote:

> Huey with all the waveforms.
>
> LETS SEE SOME ARCS!!!!  :)
>
> Dan

Your talking to the guy that has been asked what the sparks looked like and 
I said, "I don't know, I was watching the scope" :o)))  I have to say I do 
like watching arcs more on a scope or in a computer model more than real 
life ;-))  But no worries, I run the box with the cover on now and all the 
tests and experiments to bring just the box up are wrapping up!  Weather is 
nice outside these days too so just in time!!

Cheers,

        Terry