Quote:
Originally Posted by TonyDuell
Now use the Hfe range. You know which the base lead is, connect that to the 'b' hole of the test socket. Try the other 2 leads each way round in the 'e' and "c' sockets. One way will give a much higher reading than the other (for the 2N3906 I've just tried it was around 200 one way, 3 the other). The connection that gives the higher reading is the right one, you have the collector in 'c', etc.
|
I have seen a trick used to quickly identify the C from the E with a meter, Though the meter must be a type with an Rx10k range and a 22.5V battery, like the Hioki A-10. It is based on the fact that the typical zener voltage of the B-E is around 7v for a silicon signal transistor, and usually much higher for the B-C. So the B-E conducts with both meter polarities on the B-E connections but only one way on the B-C connection.
However, I've never thought this was a good idea because each time the B-E is zenered, it slightly degrades the transistor's hfe, without altering the transistor's other parameters (the mechanism of this effect has been the subject of some good research papers by Motorola). I have experimented with this effect as a tool to hfe match transistor pairs, its very real.
I have seen it claimed (by Audiophiles) that due to coupling capacitors to bipolar OP amps, when the power is switched on and off, that the input transistors b-e 's get zenered, slowly degrading the OP amp performance. I haven't bought into this notion completely, but I guess its possible.