Re: Recent s.s.t.c. work

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

"Gates" always blew a little above 50V when I used to destroy things 
specifically testing for that...  And I tested thousands...  They all 
make the gate oxide layers the same...

But a transorb directly from gate to source (gate to emitter ;-))) 
will fix that problem right there without any worry.  Unless you try 
something really odd, the dV/dT will never be high enough to get past 
the transorb.  30V is a nice voltage for them,  That gives 20V of 
margin for them to kick in if something really fast comes along.  A 
gate drive voltage of 25 volts should turn on a device to the point 
where more voltage just does not matter any more.  Thus, I drive to 
25V and protect at 30V...

The spec of 15 or 20V for gate drive just is not quite enough for 
"us" ;-)))  But past 25V, the silicon just gives up and more voltage 
is just waisted in gate capacitance charging energy...

Cheers,

        Terry


At 03:39 PM 11/29/2005, you wrote:
> Hey Ken,
>
> I'd be hesitant to come to that conclusion. IGBT gates can go pretty 
> freaking high before they fail (I have tested mine to 50v, and 
> remember an application not saying 50% survival was at 70-80v!), and 
> the gate shorts out when the CE is overvolted, or the device 
> overheats as well. How high were you running the gate voltage?
>
> It can be frustrating when you think you fixed a problem, and it 
> happens again. You don't want to lose any more motivation!
>
> Good luck,
>
> Jimmy
>
> On 11/29/05, Tesla list <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx> wrote:
> Original poster: "K. C. Herrick" <<mailto:kchdlh@xxxxxxx>kchdlh@xxxxxxx>
>
> Just to assure some of you that I've not totally given up yet...
>
> As I've mentioned before, I find that at my advanced age I'm losing
> the motivation to continue "making things"--as I have been doing for
> ~70 years.  So I haven't done anything further yet on trying to find
> the source of the problem with my new s.s.t.c.  I think that I have
> set the peak gate voltage too high, and consequently shorted the gate
> of one of the bricks.  I can readily reduce that by 5V and I have 2
> more good bricks; it's just a matter of getting around to it.
>
> Finn Hammer mentioned potential problems with putting the primary
> inside the secondary, as I have done.  I think my solution to that
> would be to raise up the entire secondary so that the bottom of it
> was more or less at the top of the primary winding.  Then, add an
> auxiliary secondary, of sufficiently larger diameter, aligned with
> the primary and of more or less the same height.  That way, I keep
> all the existing hardware and only have to fabricate the relatively
> simple auxiliary coil and its former.
>
> So the steps I need to take are clear.  I'll likely get to them some
> time after the holdiays are over.
>
> Ken Herrick