Comments on: 12V 15A voltage regulator

By: Jonathan

Jonathan — Sat, 16 Apr 2011 22:48:23 +0000

At .5A throught 7815, R1 will see a 1.1V drop (discounting base current through 2955s), which will put about .5V across each emitter resistor – (.5V/.22ohm)X 5 = 11.5A or so – pretty close! The precise voltages vary a bit, and so do the actual resistances and gains, so not bad. If you used a 12V transformer, it puts out maybe 17-18V no load, so if you load it down, the voltage from the bridge will drop below a regulatable level. You have to balance desired output V&A against starting V&A and minimize the difference while maintaining a few volts for regulation buffer, thereby reducing waste heat (and keeping the 2955s cooler!)

By: Seetharaman

Seetharaman — Sat, 16 Apr 2011 10:47:18 +0000

I have tried up to 10 Amps. using < 500mA through 7815 and R1 as 2.2 ohms with 5 TIP2955s on the same IC's heat sink and emitter resistance of 0.22 ohms 2 watts each. Filter 5 X 4700uF 25volts.

By: Jonathan

Jonathan — Sat, 16 Apr 2011 07:01:33 +0000

Has anyone tried this circuit? Probably didn’t work, because R1 is too small. Try about 1.2 ohms, instead: at 1 amp, it will put 1.2 V across the emitter resistor and E-B junction
(.5V across the emitter resistors for 5A each)at 1amp limit
through the IC. If T1 is 15V no load, there will be less waste heat: you’re gonna need a BIG heatsink either way. C1
can be anything over 20,000 MFD, swap C2 with C3, and F1 isn’t needed at all.