Transistor testing

[Dr.james]

hi i am new to electronics and i want to learn electronics very well, so my first question is how to test a transistor? I know absolutely nothing about electronics!. Help me

 

[duffy]

The first and most useful thing is to look at the transistor-diode equivalent test. A bipolar transistor will look like two diodes in the following configuration:

So use the diode setting on your meter. With the black lead on the base of a PNP, you should see about .7V on the Emitter and Collector. Then reverse the two leads and it should read open both ways. For an NPN, use the red (+) lead on the base to see the .7V.

Read the number off the transistor and use the internet to find out what kind it is, and where the base, emitter and collector leads are located.

 

[Dr.james]

thanx Duffy, and are you talking about testing a transistor that is working in a powered circuit(a biased transistor?)? If so can you tell me how to test another transistor that is not powered (not biased) or not connected into a circuit?

 

[duffy]

This IS for testing a transistor that is not wired into anything. You have a multimeter, right? See that diode symbol on there? That's the setting you want to use. Touch the test leads together and it should read "0" (or "Shrt"). Open should blink a number, or read "OPn". On a good diode, or these transistors, it will read about "0.7".

 

[ericgibbs]

hi,
Perhaps this image will make the testing clearer.

 

[audioguru]

I have used thousands of transistors, never burnt one out and never tested one to see if it is bad.
I have never bought cheap counterfeit Chinese transistors from E-Bay.

A transistor fails if your circuit exceeds its voltage rating, exceeds its current rating or exceeds its power (heating) rating.

 

[Dr.james]

so if i tested an NPN from "B" to "E" and "B" to "C", then does it show the "0.7" in both ways? I have just tested a Bc548 transistor from base to emitter and base to collector, and it shows "760" in diode test, and shows nothing when test from E to C and reverse. Can u pls tell me what does it mean?

 

[Brevor]

so if i tested an NPN from "B" to "E" and "B" to "C", then does it show the "0.7" in both ways? I have just tested a Bc548 transistor from base to emitter and base to collector, and it shows "760" in diode test, and shows nothing when test from E to C and reverse. Can u pls tell me what does it mean?

That means the transistor is good.

 

[Dr.james]

but duffy said it should read about 0.7, what is it?

 

[Boncuk]

but duffy said it should read about 0.7, what is it?

0.7V or 700mV. It's the same.

Boncuk

 

[duffy]

Yes, it's reading 760 mv, or .76V, so it's fine.

By the way, like audioguru, I never bother to test new components or ones removed from working equipment, and have never had a bad one. You get bad ones when you do something that exceeds the ratings. It's important to point this out because I have known a couple of people who just test parts all the time and never build anything - I don't understand this trap, but please don't fall into it.

 

[flat5]

The diode test on a multi-meter is a resistance test expressed in ohms.
(am I wrong here?)

.7 volts would not be a resistance. It is a voltage. Things are getting confused here.
Especially for a beginner.
Just saying...

 

[audioguru]

The diode test on a multi-meter is a resistance test expressed in ohms.
(am I wrong here?)

.7 volts would not be a resistance. It is a voltage. Things are getting confused here.
Especially for a beginner.
Just saying...

Wrong.
The diode test on a multimeter sends a current and shows the forward voltage of the diode (about 0.7V for an ordinary diode and 1.8V for a red LED).

 

[Dr.james]

okey, so what reading may i read on the multimeter if i tested a transistor that is burnt? I mean what is the result for a bad transistor?

 

[audioguru]

if a transistor is burnt out then either it is blown open and never conducts or it is melted and is shorted.

 

[Dr.james]

ok.. And is it possible to test any kinds of transistors using this method? Eg.powertransistor

 

[duffy]

You can read bipolars this way, power and otherwise, but not fet's. Are you interested in building something?

 

[Dr.james]

You can read bipolars this way, power and otherwise, but not fet's. Are you interested in building something?

ow yeah, and what is bipolar and Fet? Thnx duffy

 

[audioguru]

ow yeah, and what is bipolar and Fet?

I guess you did not bother to look up TRANSISTOR in a book or in Google.

 

[duffy]

https://en.wikipedia.org/wiki/Transistor