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Electronics => Electronics => Topic started by: ed1380 on March 18, 2007, 02:10:19 PM

Title: Test mosfets
Post by: ed1380 on March 18, 2007, 02:10:19 PM
How do I test one. I only have a multi test and other simple stuff? I think when I was unsoldering them I burned them.
Title: Re: Test mosfets
Post by: trigger on March 18, 2007, 02:26:07 PM
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm

first hit on google search
Title: Re: Test mosfets
Post by: ed1380 on March 18, 2007, 04:22:39 PM
no diode test range available. will it work with 9 volts?
I bet it's dead since I touched up on them, and unsoldering them with took some time with a 150w gun.
Title: Re: Test mosfets
Post by: ed1380 on March 19, 2007, 06:26:42 PM
How do I know if it's a voltage regulator or mosfet. I looked at pics and they look similar.
Title: Re: Test mosfets
Post by: trigger on March 19, 2007, 07:23:30 PM
MOSFETs are pretty heat sensitive. If you didn't heat sink it, you might have fried it. 

You should be able to tell it's a mosfet or a voltage regulator by the part number. Just type the part number into digikey and see what comes up.
Title: Re: Test mosfets
Post by: ed1380 on March 23, 2007, 07:04:30 PM
Thanks. that helped. worked for 2 of the 3
I still couldn't find what this was. Heres a pic of whats on it. Looks like 2 diodes to me
Title: Re: Test mosfets
Post by: trigger on March 23, 2007, 07:33:15 PM
Thanks. that helped. worked for 2 of the 3
I still couldn't find what this was. Heres a pic of whats on it. Looks like 2 diodes to me

Yes, it's probably an NPPN or PNNP transistor (P & N refer to doped regions), which is effectively two diodes stuck together.  So it's got to be a multijunction transistor.  I think it's probably used for transient voltage suppression because I've seen this circuit symbol elsewhere.  Another multijunction transistor, the thyristor for example, is an NPNP (so two diodes stuck together, facing same direction). 

I couldn't find an exact match, but here's an example of a slightly different circuit: 

(http://www.ce-mag.com/ARG/01SprCE_136a.jpg)