• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

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

Status
Not open for further replies.

athlon11

New Member
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 ?

WITHOUT HAVING THE DATABOOK NEAR TO YOU. please help, explain properly, am not that expert.

thank u in adv.
 

induction1

New Member
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.
 

mechie

New Member
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.
 

Attachments

pebe

Member
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.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top