LM317 Regulator Test Circuit
Circuit :  Abu-Hafss, Pakistan
Email  :   Email


Description
This is both a useful and very handy test circuit for quickly diagnosing faulty regulator IC's. In addition, Abu has a novel and innovative solution to quickly connect all 3 regulator pins - just by using an 8 pin DIL socket.

Notes
Recently, I had to face a lot of frustration and wasted 5 days because of fake LM317 regulators (5 pcs) I received. So I decided to make a simple tester.

Here is simple but handy testing circuit for LM317 adjustable voltage regulator IC. I am sure it can be used to test other similar ICs like LM117, LM138, LM338 etc.

The circuit is pretty straightforward. The circuit is based on normal configuration of adjustable voltage regulator.

A DPDT switch is used to connect the ADJ pin of the IC to either ground or to the resistor R1. When connected to ground, the output should be at the lowest level around 1.2V and when connected to R1 the output should be the maximum level (around 7.5V for 9V input). Next, LM741 is used to compare the output with a preset voltage level.

When the DPDT switch is in X position the ADJ pin is connected to ground and the (-)ve input of 741 is connected to R4. The potential divider R3+R4 gives about 1.37V at (-)ve input of 741 which is compared with the output from the Voltage Regulator IC. In this case it should be about 1.2V which less than 1.37V hence the output of 741 remains low and the green LED glows. If for some reason the output from the voltage regulator IC is more than 1.37V the output of 741 goes high and the red LED lights up, indicating malfunction of the v/reg IC.

When the DPDT switch is in XX position the ADJ pin is connected to R1 and the (-)ve input of 741 is connected to R5. The potential divider R3+R5 gives about 8.1V at (-)ve input of 741 which is compared with the output from the Voltage Regulator IC. In this case it is should be about 7.5V which less than 8.1V hence the output of 741 remains low and the green LED glows. If for some reason the output from the voltage regulator IC is more than 8.1V the output of 741 goes high and the red LED lights up, indicating malfunction of the v/reg IC.

If none of the LEDs glows, it indicates that input pin and ADJ pin of the voltage regulator IC is short because the +9V are connected to ground via ADJ pin.

An 8-pin DIL IC socket or simply a 3-pin female connector may be used to hold the voltage regulator IC for testing.

Circuit Exchange International Return to Test Gear http://www.zen22142.zen.co.uk