[R-390] OT: Pass Transistor Question

Barry n4buq at knology.net
Tue Oct 14 20:18:52 EDT 2008


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 



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