Re: Transistor Veb rating... plus Patent Update


"Tony Williams" <tonyw@xxxxxxxxxxxxxxxxxxx> wrote in message
news:4eb5f29538tonyw@xxxxxxxxxxxxxxxxxxxxxx
In article <mjVAh.11264$Zl6.10855@xxxxxxxxxxxxxxxxxxxx>,
Genome <mrspamizgood@xxxxxxxxxxx> wrote:

Anyway, as I mention on the first page, I'm bothered about the
Veb rating of the transistor in the IGBT. I've had a 'touch'
from a semiconductor manufacturer and this problem has been
mentioned. The concern is the figure itself and possible
reliability issues when driving the device as I have suggested,
they have no long term figures for this kind of operation.......

I notice that the mosfet in the IGBT is turned Off,
before the -20A applied.

It might be useful to have a look at keeping the
mosfet On, apply the -20A, then turn the mosfet Off.
This sequence holds the base of the pnp at a known
low impedance 0V whilst its emitter is taken negative.

Also clamp the IGBT so that the -20A does not take
it, say, more than 0.7V below 0v. The maximum Veb
is then defined.

Hmm... reminiscent of commutating an SCR.

--
Tony Williams.

In the original setup, on the first page this is the case. That worked for
the particular arrangement I had at that time and it was the simplest to
implement. The patent application does mention the fact that relative timing
of the drive waveforms may need adjusting.

On the new page, with the new PFC circuit, I had to provide drive waveforms
that do what you describe to achieve the effect.

http://www.genomerics.org/patent/newpfc.html

On the first page the turn off current source is -20.1A so only 100mA is
available to turn the device off. Clamping the device with a diode would
mean that you don't provide sufficient reverse bias to remove the stored
charge.

'Hmm... reminiscent of commutating an SCR.'

There was mention of that but I sort of discounted it. I suppose they might
be concerned that if what I am proposing for an IGBT has already been done
with SCRs then the patent might not be valid on the grounds of obviousness.
OTOH if it were so obvious because it is done with SCRs why is it not being
done with IGBTs?

Thanks

DNA


.

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