LM317-10A-1.2 to 30 V power supply advices

bertus

Joined Apr 5, 2008
20,573
Hello,

As dd told you, better use a PNP transistor as pass transistor.
This picture from the hamradio magazine " FUNK Amateur march 2016" shows you the effect of using the PNP pass transistor:

Pass_transistor_on_regulatos.jpeg

Sorry for the german text, but the images are clear.

Bertus
 

Marcus2012

Joined Feb 22, 2015
383
Hello,

As dd told you, better use a PNP transistor as pass transistor.
This picture from the hamradio magazine " FUNK Amateur march 2016" shows you the effect of using the PNP pass transistor:
Bertus
I've seen that 7805 pass PNP diagram before in the datasheet for the 78xxs and I couldn't figure out why that PNP doesn't have a base resistor. It seemed a bit odd but I figured there was something I didn't understand.
 

ronv

Joined Nov 12, 2008
3,770
I've seen that 7805 pass PNP diagram before in the datasheet for the 78xxs and I couldn't figure out why that PNP doesn't have a base resistor. It seemed a bit odd but I figured there was something I didn't understand.
I've seen that 7805 pass PNP diagram before in the datasheet for the 78xxs and I couldn't figure out why that PNP doesn't have a base resistor. It seemed a bit odd but I figured there was something I didn't understand.
I'm guessing your worried about the base current? The 317 acts as the base resistor. The circuit has no short circuit protection anymore as it is. You could add a little resistor in the base to current limit the transistor again.
 
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