At 10:44 AM 4/12/01 -0400, Dan Michaels wrote: >Vasile wrote: > >In my opinion HOW to do this is very interesting, but the result > >is a toy. I can't imagine who will use this tool. Here every > >child know to handle with a digital multimeter and find quickly what have > >in his hands, a npn, a pnp or a fet... > >And a digital multimeter is cheapest than a pic based tool ( even 12c509 ) > >and can do more things. > > > >Can you easily identify a MOSFET or SCR with a DMM, or do a >dynamic check on a semi device? MOSFET - easy to do. Here is how I do it: Set meter to diode test mode. Moisten fingertip slightly, touch all 3 leads together. You want to remove any residual gate charge. Touch meter leads to S & D backwards (+ to S for a N channel device). If you don't know if it is a N or P channel device, this test will tell you. You should see a normal Si diode drop (0.6V or so) in the reverse direction. This is the internal substrate diode. If no reading either direction, either you are on the gate terminal or the device is open. Very low reading in both directions: FET is shorted. Now hold or clip the appropriate meter lead to the S lead (normal mode). In other words, if you have a N channel FET, clip the - lead to the source. Touch the + lead to D. You should see no conduction. Now lift the + lead from D, touch it to G, then touch and hold the + lead on D again. You should now see conduction, with very low voltage drop. Continue to hold the leads on the FET to see if the voltage drop changes: this gives a good idea of how good the gate insulation is. The 1st step of the test weeds out shorted FETs quickly as well as identifying the polarity. It will also help you identify the leads (S,G, D) if you are not sure. The 2nd step of the test makes sure that the FET is really off, then uses the open circuit voltage from the meter to apply charge to the gate (which looks like a capacitor), then checks to make sure the charge turned on the FET. It also identifies FETs with defective gate insulation (the gate charge leaks away quickly). It takes longer to read this than to actually do the test. I've taught this to many broadcast engineers over the years to help them test the output FETs in AM broadcast transmitters. It does provide a very quick GO - NO GO test! dwayne Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 17 years of Engineering Innovation (1984 - 2001) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads