Problem with LM317 voltage regulation.

Thread Starter

vinay sv

Joined Nov 16, 2020
hello guys, I am very new to electronics where I have designed the LM317 power regulator for my led power driver project and the output voltage has been set for 10volts of 500ma where I am getting around 2.4v as output and my input voltage is 13v my circuit diagram is pasted below and please someone tells me where I have made a mistake.



Joined Mar 14, 2008
How did you get those values for LR1 and LR2?
Typically LR1 is set to 120 ohms (so that regulation is maintained even with no load).
Since the LM317 maintains a constant 1.25V between the output and the Adj pin, the current through LR1 would be 10.4mA.
To get 10V out, this current must generate 10V-1.25V = 8.75V across LR2 (the current through LR1 must also flow through LR2 since the Adj pin draws negligible current).
So LR2 then equals 8.75V / 10.4ma = 840 ohms.

Try those values and see what output you get.


Joined Oct 11, 2019
if you Google LM317 resistor calculator. It can be a quick way to double check the maths. Also L3 is providing current limiting not constant current. So if your just powering some LEDs that's fine, if your powering a high current led. Look up constant current lm317. In which you will need a 2.5ohm 1watt resistor.