[R-390] OT: Pass Transistor Question

[Barry]

>A few weeks ago, I mentioned I wanted to build a regulated, low-voltage 
>power supply that uses an LM317 with some pass transistors to enable it to 
>handle a larger current than the LM317 can handle.  The circuit uses a 
>2N2905 to drive a 2N3055 in a "pass transistor" configuration around the 
>LM317 and the circuit description states it's capable of delivering up to 3 
>amps in this configuration.
>
> I have a transformer with a 6-amp capacity and I would like the power 
> supply to deliver up to 5 (maybe all 6 amps) if I want.  Is it possible to 
> put another 2N3055 in parallel with the one in the circuit allowing thus 
> allowing the pass transistors to deliver the extra amperage.  Will this 
> work?
>
> I ran across something like it here:
>
> http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm
>
> (Scroll down to the middle of the page).  The two 2N3055s are paralled and 
> have 0.1-ohm resistors in the emitter lines.  Not sure what these 
> equalizing resistors do, but perhaps that's all I need to add?
>
> By the way, the original circuit is on page 127 of the 1978 ARRL handbook.
>
> Thanks guys for the OT help.
>
> Barry

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?

Thanks again,
Barry - N4BUQ