Any one knows that how to identify the base, emitter and colletor of an transistor by an simple multimeter??

Answer 1

as an electronics hobbyist, here's my procedure for identifying common transistors. first try to determine the base by trial and error, interchanging + and - leads of your multimeter, set multimeter to diode test, or if no function of diode test set range to around 2k ohms. you can determine the base by measuring resistance , with one lead of your tester connected to one leg of transistor and measure the second leg by connecting the second lead of your tester, note if there is resistance reading, if there is a reading then note it, note also the polarity of the tester lead connected. if no reading or infinity then reverse your leads. if after reversing it is still infinity then these two leads are the collector and emitter. so now you had identified the base, which was not connected. now connect your positive lead of your tester(this is for npn test) to the last leg which was identified as base, and connect the negative lead to any leg and note your reading, then transfer that negative lead to the other leg of the transistor and note again your reading. you can now compare your reading and you can notice a slight difference in ohms, the reading with lower resistance with respect to your base is the collector and the higher one is the emitter. for pnp transistors, you will connect the negative lead of your tester to the identified base, and procedure will be the same. always remember that the collector will register a lower resistance compared to the emitter. testing some transistors with an internal damper diode connected between collector and emitter is misleading, so its better to read datasheets.

Answer 2

Most multimeters put a + on the red lead when measuring ohms. If the transistor is npn, then, a red on the base creates a forward diode drop (low resistance) to both the emitter and the collector. If Pnp, the black on the base will do this.
The other polarity will read extremely high resistance.

It is not possible to distinguish the collector and emitter without more work With power transistors, the collector will be connected to some thermal mass, (the case) because that's where the heat is generated.

The b-e diode will have a 5-7 volt reverse breakdown, while the b-c diode will be much larger. Most multimeter's can not detect this without more instrumentation.
p.s. it is not good to reverse breakdown the b-e diode on low noise transistors.

Answer 3

Transistor Legs

Answer 4

Think of the transistor as two diodes. One is the base/emitter diode, the other is the base/collector diode. An NPN one has both diode anodes at the base. A PNP one has both diode cathodes at the base. The majority of analogue multimeters have the negative of their internal batteries appear on the positive probe and vice versa.

Answer 5

If it's a plastic transistor you can only identify the Base because the emitter and collector will give similar forward resistance readings on the multimeter (used on ohms range).

Answer 6

Set up a circuit with a power source that is not too strong to overwhelm them. Start at zero with each wire. Measure what will come out with the others. If you put the power source at the emitter, and slowly increase the voltage, the base will send out electrons first. Gradually increase the voltage and at 1.5 volts approx the collector will emit.

Answer 7

Set MM to resistance. Probes onto two leads. If hi R then reverse probes. If still hi R then they are the collector & emitter.

Answer 8

Find a part number on the device, then spend 5 minutes looking up a data sheet for it on the 'Net.

Doug