![]() With the switch closed both lamps are on. Note that NPN transistors have low resistances where PNP have high, and vice versa.įigure 2. Many meter have a position marked with a diode symbol which must be selected when checking transistors or diodes. Note that for this to work the internal battery of the meter must supply a voltage high enough to overcome the forward resistances of the transistors. You should now be able to identify the base connection and then decide if the transistor is OK. If you cant find the data then measure between the three connections in both directions. If youĭon't know the transistor connections consult a data book. It should read high resistance in both directions. Now measure the resistance between emitter and collector. If they were both low before they should now both be high. If they were both high before they should now be both low. The results should be the opposite of those obtained before. Now reverse the leads and repeat the procedure. The readings should both be the same, either both high resistance or both low resistance. ![]() Touch the other lead first onto the collector lead and then onto the emitter lead. With the meter set to measure ohms, clip one meter lead to the base connection of the transistor. This test can detect only two types of faults: shorted and open. If the voltage drop between any of the terminals is not equal to the expected voltage, then the transistor is not functioning properly. So, the ideal voltage should be between 0.4 to 0.9 volts.Ĭollector and emitter: Now touch the red and black probe to the collector and base terminal, respectively.įor both NPN and PNP transistors, the multimeter should display ‘OL’.įor both NPN and PNP transistors, the multimeter should display ‘OL’. So, there should be an open circuit, and the multimeter should display ‘OL’ or ‘1’.įor a PNP transistor, this is the forward bias configuration of the collector-to-base PN junction. Red touching the collector and black touching the base terminal.įor an NPN transistor, this is the reverse bias configuration of the base-to-collector PN junction. So, there should be an open circuit, and the multimeter should display ‘OL’ or ‘1’.Ĭollector and base: Swap the probes. So, the ideal voltage should be between 0.4 to 0.9 volts.įor a PNP transistor, this is the reverse bias configuration of the collector-to-base PN junction. So, the ideal voltage should be between 0.4 to 0.9 volts.īase and collector: Touch the red probe to the base terminal and the black probe to the collector terminal.įor an NPN transistor, this is the forward bias configuration of the base-to-collector PN junction. So, there should be an open circuit, and the multimeter should display ‘OL’ or ‘1’.įor a PNP transistor, this is the forward bias configuration of the emitter-to-base PN junction. Red touching the emitter and black touching the base terminal.įor an NPN transistor, this is the reverse bias configuration of the base-to-emitter PN junction. So, there should be an open circuit, and the multimeter should display ‘OL’ or ‘1’.Įmitter and base: Swap the probes. So, the ideal voltage should be between 0.4 to 0.9 volts.įor a PNP transistor, this is the reverse bias configuration of the emitter-to-base PN junction. ![]() How to test an NPN transistor using a multimeterīase and emitter: Touch the red probe to the base terminal and the black probe to the emitter terminal.įor an NPN transistor, this is the forward bias configuration of the base-to-emitter PN junction. Only when you know which terminal is which, continue with the next step. Look at the datasheet for the pinout or search on Google, ‘xxxxx pinout’. The next step is to identify its terminals. Find out if it is an NPN type or a PNP type. Look at the part number printed on the transistor casing and search for it on Google. Step 1: Identify the transistor type and its pinout If the voltage drops between any of the terminals deviates from the value given above, the transistor is most likely bad.įor a step-by-step guide on testing the transistor using a multimeter, keep reading. Voltage between NPN transistor PNP transistor Base and Emitter 0.4V to 0.9V OL Emitter and Base OL 0.4V to 0.9V Base and Collector 0.4V to 0.9V OL Collector and Base OL 0.4V to 0.9V Collector and Emitter OL OL Emitter and Collector OL OL Expected voltage across terminals during NPN & PNP transistor testing. Compare the values with the readings given below. Measure the voltage drop between every pair of terminals in diode test mode- B and E, B and C, E and B, C and B, and C and E. Test analysis How to test a transistor with a multimeter?.Step 2: Set the multimeter in the diode mode.Step 1: Identify the transistor type and its pinout.How to test a transistor with a multimeter?.
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