[R-390] OT: Pass Transistor Question

[James A. (Andy) Moorer]

Barry, the problem is that the votage from the base to the emitter varies a 
lot from transistor to transistor, even when they are all 3055's. The 
collector current depends exponentially on this VBE, so tiny changes in VBE 
make big changes in collector current. The end result is that one transistor 
often gets all the current and the others get little - this is called 
"current hogging". The resistors can either be in the base circuit or the 
emmitter circuit. If they are in the base circuit, they have to be larger by 
a factor of beta (maybe 100 or so). The resistor has the effect of 
equalizing the base currents, and thus the collector currents.

James A. (Andy) Moorer
www.jamminpower.com

----- Original Message ----- 
>
> Hmmm.  I backed up a page or two (p. 124) in the ARRL Handbook and it 
> discusses parallel pass transistors, specifically 2N3055's.  I'm still 
> wondering what the equalizing resistors do.  Anyone care to explain?
>