Testing of Transistor with Multimeter

Testing of Transistor with Multimeter

Different types of transistor tester instrument are used to check the transistors. Of these, the quick test transistor tester is used to test the contact transistor in the circuit. Some other transistors have to be ejected from the tester to test the transistor. By measuring the junction resistance of the transistor with all these service type transistor testers, a short circuit or open circuit is detected between the base collector and the emitter.

With this, leakage current is also detected between the junctions. In addition, the transistors can also be tested with an ordinary multimeter. To test the transistor with a multimeter, use the following method.

Any transistor (P.N.P or N.P.N) has two junctions. One base collector junction and the other base emitter junction. Each transistor employs two diodes. The base common in the P.N.P transistor acts like the cathode and the base common in the N.P.N transistor acts as the common anode.

P.N.P Transistor Testing: Sets the multimeter in the range of resistance. Now, connect the positive lead of the multimeter to the base and the negative lead to the collector, in this case the base collector junction will be in reverse bias so that no current will flow in the circuit and the multimeter will show the maximum resistance. The same situation will be achieved by connecting negative lead emitter and positive lead base.

PNP Transistor Testing

When the leads of the meter are reversed ie on the negative base and on the positive collector or ammeter, then in this situation both junctions fall in the forward bias. Causing maximum current to flow in the circuit. And the multimeter shows the least resistance. Now, connect the negative lead on the collector of the transistor and the positive lead on the ammeter.

In this case, one of the two diodes of the transistor stays in the reverse bias, so that the meter displays the maximum resistance. The above position will be obtained even after changing the leads of the multimeter, in all the above situations, if the multimeter displays different readings than this, the transistor will be faulty.

N.P.N Transistor Testing: In N.P.N Transistor, base P type material and collector emitter are made of N type material. Therefore, when the positive lead of the multimeter is connected to the base and the negative lead to the collector or ammeter, both junctions are in the forward bias. That is why in this case the multimeter shows the following resistance, then the transistor is correct otherwise bad. Because in this case high resistance means that the junction is open.

NPN Transistor Testing

If the leads of the multimeter are replaced, that is, the negative lead is placed on the base and the positive on the Emitter or collector then the meter will show high resistance. If the multimeter is somehow connected between the emitter and collector of the transistor, the high resistance should be displayed only if the transistor will OK . If low resistance is attained, then the collector emitter junction will be short, causing the transistor to be defective.

As you see above the transistor Testing is approximately similar to diode.

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