# Lm317 problem

With the adjust pin grounded the output voltage is around 1.3 volts for the lm317 chip that I am using, however if I draw a current of around 120mA in this condition the output falls to 0.3 volts, below 120mA the output is stable at 1.3 volts. the readings are being taken right at the output pin, the input voltage is well over 7 volts, does this mean my lm317 is blown?

Thanks.

Have you looked at the datasheet? If that is the only thing that is connected to the ADJ pin... that might be your problem. You need feedback for the voltage reference.

This part is not designed to have its ADJ pin held to GND potential with no other connections.

Is this on a heatsink? If not it could be the thermal limit operating. If its properly heatsunk and dropping out at 0.13A, its sounds like its fried.

You can use the device with the adjust pin grounded just fine.

[ Quick thought - you do have the decoupling caps on input and output? They are required... ]

waqaszahid: Does this mean my lm317 is blown?

It could be. Was it working before? Show us a circuit diagram.

If it was working before, and if you have a bunch of spare LM317, then pop in a new one and see what happens.

waqaszahid: With the adjust pin grounded the output voltage is around 1.3 volts for the lm317 chip that I am using, however if I draw a current of around 120mA in this condition the output falls to 0.3 volts, below 120mA the output is stable at 1.3 volts. the readings are being taken right at the output pin, the input voltage is well over 7 volts, does this mean my lm317 is blown?

You can safely ground the Adj pin of an LM317 and have it's reference voltage on the output (~1.25volt).

If the LM317 can sustain >120mA depends on it's input voltage and heatsinking. With e.g. 12volt input, almost 11volt * 0.12A = 1.3watt is dissipated in the chip. It will likely shut down without a heatsink. Leo..

P.S. I assume you have the right smoothing caps on input and output (see datasheet).