Re: FET vs IGBT thoughts

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 21:39 08/04/03 -0600, you wrote:
>Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
>
>Hi All,
>
>I thought I would just mention why IGBTs are preferred over FETs where 
>high currents are concerned.
>
>FETs basically look like say 0.1 ohm resistors when they are turned full 
>on where IGBTs look more like a diode.  Up to say 10 amps, there is not 
>much difference.  However, if we run say 200 amps through them there is a 
>giant difference!!
>Lets put some "real" current through them like 200 amps ;-))
>
>The FET now has 200 amps at 200 x 0.1 = 20 volts for a stunning 4000 watts 
>of heat!!

I ought to mention that when FETs are driven much above their datasheet 
drain current rating, they go "into saturation" (terminology is other way 
round compared to bipolar transistors) and start to look like a constant 
current source. This is what lets stereo amp manufacturers build 
"short-circuit proof" amps with them. It also means that you'd never get 
200 amps through that FET however hard you tried. Unless it was a 200 amp 
FET of course, good luck trying to buy one of those.

Steve C.