Holley 4 Brrl gm ecm

[ECMnut at aol.com]

Grumpy & I were talking about this..
I was thinking putting something like a LM1939
where the smoked driver is in his last 7749... 
 Is there something better ?
Thanks,
Mike V      (EE challenged)

In a message dated 5/22/00 11:52:50 AM Eastern Daylight Time, 
garwillis at msn.com writes:

> Now in a Darlington, as much as they want to make the final driver
>  devices one single transistor for this reason, beyond a certain size,
>  you get *localized* current hogging (hot spots) in that one largo
>  transistor, so they rely on the uniformity of multiple transistors
>  within the same die, and they DO parallel up transistors. Either way,
>  it's quite possible for some of those to blow open, leaving you with not
>  much of an overall big driver anymore. I've seen pix of failed large
>  bipolar devices covered with bomb craters; the device still passed
>  current, but the gain was pretty low. :)  Same thing would happen if as
>  Chris suggested, the final driver totally failed open, and the predriver
>  was still intact and able to conduct thru the base-emitter of the final.
>  You end up with a whimp of a transistor.
>  
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