Winning LM317 and unexpected voltage.

[Zero999]

I'm puzzled as to why there are quite a few schematics as the LM317 with PNP power transistors, but none mention the existence of poor voltage regulation. That's not to say your wrong, I just haven't come across the negative reports of the circuit at the top of this thread, my opening post. I would try the PNP transistor driving the NPN to see if I can build this layout. Thanks for posting it.

My comments were aimed at Terry Bytes, hence the quote.

There's nothing wrong with using the LM317 to drive PNP transistors. It works by sensing the current going into the LM317 and switching on the PNP transistor, once its base-emitter voltage is exceeded, which normally happens at around 0.6V, which corresponds to about 700mA, with a 10R resistor.

The issue is connecting the output of the LM317, to an emitter follower, as per Terry Byte's schematic, which results in poor regulation, because the voltage drop of the emitter follower varies, depending on the load current and temperature. The circuit I posted doesn't have this issue, because the emitter of the NPN BJT is connected directly to the LM317's well-regulated output and its base is driven by a PNP transistor, which is switched on, by the voltage dropped across a sense resistor in series with the LM317's input.

[davelectronic]

I've been having issues with the homebrew Manhattan style strip board ( first picture ) but I will try the PNP driving an NPN transistor, not to far in the future.