Harold

Doesn't answer all your questions, but International Rectifier App note
AN-983 gives a good explanation of how an IGBT works
(www.irf.com/search/).

Ron

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 Ron Kreymborg                   Computer Systems Manager
 Monash University               CRC for Southern Hemisphere Meteorology
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On Tue, 11 Nov 1997, Harold Hallikainen wrote:

>         I've been looking for a way to get around the saturation voltage
> of triacs and have considered FETs and IGBTs for AC switching.  It SEEMS
> to me that the saturation voltage on an IGBT is going to be higher than
> that of a FET.  I view an IGBT as a sort of darlington with an FET as the
> first transistor.  Is this correct?  If so, the input FET can go to a
> source-drain short and we still need 700 mV or so on the collector to
> turn on the base.  Seems that directly driving the gate of a FET would
> give us lower voltage drop (just due to Rds on).
>         In AC applications, I've thought of putting two FETs in series
> and using the intrinisic diodes to steer the current into the appropriate
> FET.  Again, we'll lose about 700 mV across the diode of the FET that is
> being bypassed.  It seems that the voltage drop will be approaching that
> of a triac, and we have increased circuit conplexity to boot!
>
> Harold
>