How to get more output current out of your regulator

[ambulancevoice]

if you notice anything wrong with this etc please tell me
http://www.aronnelson.com/gallery/main.php/v/ambulancevoice/100_1149.JPG.html
http://www.aronnelson.com/gallery/main.php/v/ambulancevoice/100_1151.JPG.html
http://www.aronnelson.com/gallery/main.php/v/ambulancevoice/100_1152.JPG.html

[km-r]

it looks fine to me.

my method is quite the same but im using an NPN power tranny as series element. tapping the Base to the output of the regulator. i also bump up the regulator with one diode to compensate for the VBE. but my actual prototype has a trimmer on the output of the regulator and the base connected to the wiper of the trimmer, the other end on the trim goes to ground. this way i can adjust the voltage.

[George Giblet]

FYI, the PNP versions is a better method.

In the NPN method:
- the Vbe drop depends on output current and the compensator diode current is more or less constant.  That means the load regulation is much poorer.
- the compensated diode is at a different temperature to the pass transistor so the output voltage drifts with load (as the pass transistor heats up)
- the drop-out voltage is increased
- the short circuit current isn't limited

[The Tone God]

Silly question, why don't you just use a regulator with a higher current rating and not screw around with all those extra parts and added complexity ?

Andrew

[George Giblet]

> Silly question, why don't you just use a regulator

There's many reasons and as time goes on the right decisions change.  The made-up version uses easy to get parts and you might have these in your junk box.  The availability of the high current regulators varies and so does the cost.   Some of those high-current regulators have high Junction to case thermal resistance, so using a transistor with a low thermal resistance could help reduce the size of the heatsink.  Separating the transistor and high current parts can reduce drift.

[Sir H C]

My only issue with the PNP version is stability of the circuit.  It could scream like a banshee if not properly compensated.

[Minion]

I have made a 24v 4a PSU useing a LM317 and a Tip36 PNP and it worked great and there were only 3 extra parts (2 power resistors and a PNP Power Transistor) ....I use it in a small 10w Class A single ended amp I built, ...

Cheers

[ambulancevoice]

well, the most current out of a regulator that i could get here is 1A
4A would be nice

[Minion]

If you look at the Second Picture labeled "LM317 Voltage Regulator with Pass transistor" in this doc it will show you have to make a High current Adjustabe regulator....

http://www.ee.teihal.gr/labs/electronics/web/downloads/LM317T_Variable_Voltage_Regulator.pdf


Remember to use a Heatsink on both the reg and Trans....

Cheers