Testing Transistors in Circuits with Multimeters, and Curve Tracer

The transistor is a small semiconductor device that can be damaged if connected incorrectly. The transistor may also be damaged if a higher current or voltage is given at the input. It is suggested to test the transistor. The transistor burning effect can be observed by looking at the circuit. Testing transistors in circuits with multimeters is a good idea if no visual effect can be seen on the circuit board.

Depending upon the digital multimeter functionality, the transistor can be checked for its working in the form of a pass and fail. Other multimeters can also test the gain of the transistor by setting it to the hFE mode.

The transistor can also be checked with an ohmmeter and curve tracer. The ohmmeter checks the connectivity of the two terminals. Where the curve tracer uses different current, and voltage points to draw the VI characteristics of the transistor.

testing transistors in circuit with multimeter-min — Testing Transistors in Circuit with a Multimeter

Steps for Testing Transistors in Circuits with Multimeters

Follow the following steps for a testing transistor in a circuit with a multimeter.

Disconnect

Disconnect the transistor you want to test from the circuit board. Otherwise, the multimeter may be damaged and the correct result will not show up.

Inserting transistor

If your digital multimeter has a transistor testing port, use it. And insert the transistor into the dedicated port for transistor testing. Insert the transistor according to the notation of NPN or PNP. If there is no port for the transistor, test the transistor with an ohmmeter instead.

Testing Transistors in Circuits with Multimeters — Inserting the transistor into the Transistor Testing Port

Mode setting

Now rotate the knob to correctly set the mode to test the transistor. Use the symbol of hFE to obtain the gain of the transistor.

Reading

At this stage, the digital multimeter screen will read the gain of the transistor. If the reading is not showing up, change the configuration of the transistor from E-B-C configuration to B-C-E.

testing transistors port in multimeter-min — NPN and PNP port different configurations

Testing Transistors with an Ohmmeter

Testing a transistor with an ohmmeter is the old way of testing the transistor. The ohmmeter testing of the transistor has two PN junctions base-emitter and base-collector. Treating these two junctions like individual diodes may help in determining the working of the transistor.

Steps for Testing a Transistor with an Ohmmeter

First of all, make sure to remove the transistor from the circuit.

Step 1: Base-Emitter check

For the NPN transistor, connect the positive lead to the base and the negative to the emitter of the transistor. A good transistor must show connectivity. And vice versa for the PNP transistor.

For the NPN transistor, now reversing the leads, i.e., connecting the positive to the emitter and negative to the base of the transistor. In this case, there will be no connectivity for a good transistor.

Testing transistors with ohmmeter — Testing a Transistor with an Ohmmeter

Step 2: Base-collector check

For the NPN transistor, connect the positive lead to the base and the negative lead to the collector. A good transistor must show connectivity. And vice versa for the PNP transistor.

For the NPN transistor, now reversing the lead i.e., connecting the positive lead to the collector and negative lead to the base of the transistor. A good transistor must show no connectivity.

testing transistors with curve tracer — Testing Transistor with Curve Tracer

Testing Transistor with Curve Tracer

A curve tracer is like an oscilloscope with different features like time sampling, list sweep, and multichannel sweep. Curve tracers are used to analyze the diode, transistors, and thyristors, etc. Use the proper setting to set the voltage and analyze the collector current. Similarly, use the different base currents to analyze the collector current and draw the VI characteristics curves.