Discussion in 'General Electronics Chat' started by Mazaag, Apr 26, 2007.

  1. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
    Hey guys,
    I have a bunch of Darlington Pairs lying around, and a bunch of NPN transistors too, but i'm not sure if they are burnt out or not....

    any quick tests? I have a multimeter (obviously) and a few resistors and stuff lying around...

    thanks guys
  2. Salgat

    Active Member

    Dec 23, 2006
    A quick test is to check the resistance across Collector Base, Collector Emittor, and Base Emittor. CB is reverse biased(in normal operation), BE is forward biased, and CE shouldn't allow any current to flow when the Base isn't active. Check for shorts or opens. Remember, in normal operation for NPN transistors the collector is attatched to Vcc, base is tied to a positive value of your choice, and the emittor is grounded.
  3. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    here's another way or explanation.

    remember that a transistor is actually 2 diodes configured back to back, hence it can be check accordingly. to test a transistor for a short or open, just connect the positive lead of the ohmmeter (R x 100) to the base and the negative lead to the emitter of an npn transistor. it is now forward biased resulting in a low resistance reading. reversing the leads will reverse bias the emitter/base regions and the result will show a high resistance reading. likewise the base/collector regions are check the same way. remember that a low/high resistance reading should always take place. 2 highs indicates an open transistor; 2 lows indicates a shorted transistor.

    another way to determine the quality of the transistor is to 1st locate the collector/emitter leads. place 1 lead of the ohmmeter on the emitter and 1 on the collector. this will result to some kind of a reading. now short the the base lead to the emitter; the resistance on the scale should increase. when the base lead is shorted to the collector the resistance reading should decrease.

    on how to identify the transistor legs please refer to my previous post.