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New in your chat, Basic Question: How to...??

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athlon11

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I'm completly new in the world of electronics, trying to learn, intrested very.

I have a transistor:
1- how to know if its working? by measuring, how to measure using VMM, how to which pin is the E,C,B?

2- how to know the type of it NPN, PNP ?

take the number off of your tranny and type it into any search engine. you'll find data sheet links easily that will answer most of your q's. there are also data sheet sites, but i don't know them off hand.

Testing a Transistor

That tutorial confuses me !

If you consider a transistor as two back-to back diodes then you can use a meter to test most types for simple go/no-go operation.
Just test both 'diodes' for conducting in one direction only - totally open circuits are no good and shorted both ways are failures.
If there is a short from collector to emitter then something is wrong as well.

The attached diagram shows (top) the theory book drawing of a transistor
(middle) a more accurate 'construction' drawing
(lower) an equivalent circuit.

BUT note that some devices (darlington, UJT, weird stuff) can't be tested like this.

The equivalent circuit is just as the meter sees the transistor, in reality there is only three layers of silicon (ignore rare germanium devices) N-P-N and the equivalent circuit thinks there are four N-P-P-N; this is why two diodes don't work as a transistor :!:

Also note that in reality the emitter is a bigger lump than the collector, they cannot be swapped for each other for this reason.

A diode test will let you find the base lead and seperate NPN from PNP, faulty from good but it is guesswork which lead is emitter and which is collector; if you are really desperate/indifferent then the lowest forward-bias voltage will suggest the base-emitter junction.

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Re: Testing a Transistor

mechie said:
A diode test will let you find the base lead and seperate NPN from PNP, faulty from good but it is guesswork which lead is emitter and which is collector; if you are really desperate/indifferent then the lowest forward-bias voltage will suggest the base-emitter junction.
You can tell the emitter from the collector because the base/emitter junction will zener at about 6v when reverse biassed.

Use about a 12v supply with current limited with a 1K resistor as a test source.

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