How to Test a Transistor Using a Digital Multimeter

Basically a transistor is nothing but two pn-junctions connected back to back. By examining both the junctions (Emitter-Base junction and Collector-Base junction) with the help of a digital multimeter, we can comment on the functionality of the transistor.

The test of the transistor is based on the principle of pn-junction biasing, i.e., when a forward bias is applied to the pn-junction (by connecting positive terminal to the p-region and negative terminal to the n-region), the junction allows current to through it. When the reverse bias applied to the junction, it behaves as an open circuit.

NPN Transistors are widely used. We can test an NPN transistor by testing the junction's continuity in the forward bias and reverse bias mode. In the same manner, we can test a PNP transistor too.

Step by Step Testing of NPN Transistor

• Set the digital multimeter to Diode or Continuity range.

• Connect the Positive probe (Red coloured) of multimeter to the base terminal of the transistor.

• Connect the negative or common probe (Black coloured) of multimeter to the emitter terminal. The multimeter should give some reading.

• Connect the negative or common probe (Black coloured) of multimeter to the collector terminal. Again, the multimeter should give some reading.

• Now, connect the negative or common probe of multimeter to the base terminal of the transistor.

• Connect the positive probe of multimeter to the emitter terminal. This time, the multimeter should read open circuit.

• Connect the positive probe of multimeter to the collector terminal. Again, the multimeter should read open circuit.

• Now, connect the negative probe of the meter to the emitter and the positive probe to the collector. The meter should read open circuit in this case.

• Also, connect the positive probe of the meter to emitter and the negative probe to the collector. Again, the meter should read open circuit.

• If the transistor passes all the tests then, it is functional and all the junctions are in healthy condition.

Manish Kumar Saini

Published on 26-May-2021 14:45:25

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