Author Topic: Mystery transistors, jfets, and fet test circuits.  (Read 1361 times)

Thecomedian

Mystery transistors, jfets, and fet test circuits.
« on: June 06, 2013, 01:33:31 PM »
Are there any circuits which can determine NPN from PNP from FET, or which can tell whether a transistor is simply a FET or not without damaging non-fet transistors?

I have a few TO-92 (in appearance) packages, with absolutely no markings on them, in gray color. touching the two out leads with probes reveals a ~4.7k resistance. Reversing the leads shows ~4.7k. This implies a a through circuit, and the resistance value is about what I would expect from a FET (their internal resistance is supposed to range from 4k-12k), while the middle lead has 4+Mohm resistance to either outer lead, in either probe alignment.

Are these fets? How could I safely test their properties (gain, max volts, max amps) if so? Is it just something you need to know their maker and data sheet for?
If I can solve the problem for someone else, I've learned valuable skill and information that pays me back for helping someone else.

nocentelli

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squeeze on the back and never open it up again

Thecomedian

Re: Mystery transistors, jfets, and fet test circuits.
« Reply #2 on: June 06, 2013, 01:55:54 PM »
Time to save a little extra cash this month, lol.
If I can solve the problem for someone else, I've learned valuable skill and information that pays me back for helping someone else.

artifus

Re: Mystery transistors, jfets, and fet test circuits.
« Reply #3 on: June 06, 2013, 01:58:27 PM »
i don't have the link i'm afraid but search youtube - i saw some vid demonstrating how to use a multimeter for a more educated guess sometime ago.

Thecomedian

Re: Mystery transistors, jfets, and fet test circuits.
« Reply #4 on: June 06, 2013, 02:25:17 PM »
the funny thing is that they were lying on the carpet and they still work. I'll have to take more ASD precaution until I know whether my mystery bags full are FET or NPN.

Im also guilty of getting a large bag of Tin Can Op amps and handling them freely when I didn't know what they were months ago  :icon_redface:

This is inspiring me to create a test circuit with some op-amp sockets for tin can and see if I can come up with some sort of pattern for figuring out what the IC is and who made it.
« Last Edit: June 06, 2013, 02:32:05 PM by Thecomedian »
If I can solve the problem for someone else, I've learned valuable skill and information that pays me back for helping someone else.