Hello,
I'm about to make a regulated power supply using a LM317 and a pass power transistor. I had seen circuits like this:
However, why not to just remove R1 and change R2 for a direct connection? To me it seems like the regulator would try to keep the output voltage, modifying the current thru the transistor's base. It's also more straightforward.
Probably there's something i'm not seeing, but why to use R1 and R2? To me it seems like the circuit would run just fine without them.
I built the circuit in a protoboard, and the only ill effect seems to be that the power supply output voltage goes up (1V approx) with no load. Probably this is because the ADJ current of the regulator is forcing the transistor to conduct. Any load (for example: a led using 20ma current) would lower the voltage to normal levels.
I'm about to make a regulated power supply using a LM317 and a pass power transistor. I had seen circuits like this:
However, why not to just remove R1 and change R2 for a direct connection? To me it seems like the regulator would try to keep the output voltage, modifying the current thru the transistor's base. It's also more straightforward.
Probably there's something i'm not seeing, but why to use R1 and R2? To me it seems like the circuit would run just fine without them.
I built the circuit in a protoboard, and the only ill effect seems to be that the power supply output voltage goes up (1V approx) with no load. Probably this is because the ADJ current of the regulator is forcing the transistor to conduct. Any load (for example: a led using 20ma current) would lower the voltage to normal levels.