How to check that whether the lead of a transistor is emitter or collector?

Question

how to check that whether the lead of a transistor is emitter or collector.......

1. without a multimeter.

2. with a multimeter.

thnx

Answer 1

I already answered this.

Best way is to get a copy of the data sheet and look at it. You will need it if you plan on using the transistor in any kind of circuit.

To use an ohmmeter to check leads is almost impossible, a) as there are too many combinations possible, and b) C-B and E-B junctions look the same to an ohmmeter.

However, metal can (TO5, TO18) transistors do have a standard. Look at it with the can away from you. Starting at the tab and moving clockwise, the leads are E B C.

TO3 power devices also have a standard. The case is C. The other 2, you'll have to look up, I don't recall.

For plastic devices, there are usually two or more standards, so you have to look them up.

.

Answer 2

Simply measure the emitter-base breakdown voltage. It will be about 5V for the emitter-base, and about 30V or more for the collector-base. You need a 30V power supply and a multimeter. Or you could use a curve tracer.

You could also measure hfe. This will be a hundred or so with the collector and emitter correctly connected, about 3 with them reversed. Either use a tranisitor tester or improvise one with your power supply and multi meter.

Be careful not to damage the transistor as you perform these tests.

The base is easy to identify with an ohm meter. The base-emitter junction and the base-collector junction both appear as diodes, thus identifying the base pin.