Introduction: How to Test Bipolar Transistors If You Have an Analog Multimeter
More by the author:
About: Do-It-Yourself electronic projects I've made. Read it, Learn it, Use it....spread the word!
We know how transistor works but some of us doesn't really know how to test the component itself. Nowadays, most Digital Multimeters have sockets provided to test them, but what will you do if you have those old Analog/Needletype ones? This is a simple way to do it.
Step 1: Basic Configuration
Bipolar transistors has 3 pins, The Emitter(E), Base (B) and the Collector (C) which is usually connected to the casing for most Power transistors (TO-3 casing). It can be categorized into two, NPN and PNP configuration, see figure 2. This test is based on the theory that a transistor is like two diodes connected together, see figure 1.
Step 2: For PNP Transistors
1. Set your Analog Multimeter to Ohmmeter X1 Ohm Scale.
2. Connect the Negative Probe (Black) to Emitter and the Positive Probe (Red) to the Base. The needle should deflect to the right side,reading less than 100 ohms.
3. Now invert the probe connections to the Emitter for the Red Probe and to the Base for Black. The Needle should not deflect.
5. Invert the probes again, Black to the Base and the Red probe to the Collector. The Needle should not move.
2. Connect the Negative Probe (Black) to Emitter and the Positive Probe (Red) to the Base. The needle should deflect to the right side,reading less than 100 ohms.
3. Now invert the probe connections to the Emitter for the Red Probe and to the Base for Black. The Needle should not deflect.
- If the results are the same as above, your Emitter-Base junction is OK.
5. Invert the probes again, Black to the Base and the Red probe to the Collector. The Needle should not move.
- If results are the same as above, your Base-Collector junction is Ok.
Step 3: For NPN Transistors
1. Set your Analog Multimeter to Ohmmeter X1 Ohm Scale.
2. Connect the Negative Probe (Black) to Base and the Positive Probe (Red) to the Emitter. The needle should deflect to the right side,reading less than 100 ohms.
3. Now invert the probe connections to the Base for the Red Probe and to the Emitter for Black. The Needle should not deflect.
5. Invert the probes again, Red to the Base and the Black probe to the Collector. The Needle should not move.
2. Connect the Negative Probe (Black) to Base and the Positive Probe (Red) to the Emitter. The needle should deflect to the right side,reading less than 100 ohms.
3. Now invert the probe connections to the Base for the Red Probe and to the Emitter for Black. The Needle should not deflect.
- If the results are the same as above, your Emitter-Base junction is OK.
5. Invert the probes again, Red to the Base and the Black probe to the Collector. The Needle should not move.
- If results are the same as above, your Base-Collector junction is Ok.
Step 4: Detecting Defective Transistors
1. If their is no resistance between any of the pairs during test (needle goes all the way to the right) for all the steps. The transistor is shorted.
2. If for all the steps, no needle deflection occured, the transistor is open.
2. If for all the steps, no needle deflection occured, the transistor is open.