Some explanation about transister

[firoz.raj]

Can anyone tell me ?how should i idetify transister type ?i simple want to know .from the board.it is pnp transister or npn transister physically.Kindly let me know the idea.Any help woud be highly appreciated.

 

[phyzguy]

Try this link.

http://tritium.fis.unb.br/Fis3Exp/fcim.csdc.com/fcimis/compid/semi/tashome.html

 

[vk6kro]

Transistors have numbers on them. Something like C115 may mean 2SC115, so you could look that up on Google.

Transistors test like two diodes joined together at one end. You test with the "diode" function of a digital multimeter, not the "ohms" function which is usually too low a voltage to turn on diodes.
If the "diodes" appear to be joined at the anodes, then it is a NPN transistor. If they are joined at the cathodes, it is a PNP transistor. The pin where they appear to join is the base of the transistor.

You can sometimes do this when the transistor is still on the board and it is also an excellent test for faulty transistors. Shorted or open diodes may mean a faulty transistor, but other components on the board may give a false impression of this.

If you can remove the transistors from the board, most digital multimeters would have a "hfe" type gain test. You can safely put the device into this in different ways until it gives good gain. Then you will know the pin connections and if the transistor is faulty or not.