LM317 constant current load

constant-currentlm317load

Would this work as a constant current load since I don't have a high power pot?
Is there a better way to do it?

schematic

simulate this circuit – Schematic created using CircuitLab

Best Answer

You're loading the 1.25V output of the LM317 with a transistor- it won't work very well. It will burn the pot out if you turn it up all the way.

I assume you're trying to draw a constant current from V1.

One method is to use an op-amp such as 1/2 an LM358:

schematic

simulate this circuit – Schematic created using CircuitLab

With the values shown, it will allow a current from 0-1A to be drawn from V1. R1 will dissipate up to 1W, and Q2 will dissipate most of the rest of the power- up to 2.7W for the values shown.

R2 is a voltage divider that provides an adjustable 0-1V signal on the non-inverting input. R4 provides a bit higher maximum output voltage from OA1. Q1 and Q2 form a darlington pair. R1 is the current sense resistor.