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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Use the diode test function on your DMM. This puts 1mA through the probes and reads the voltage hat appears between them. A good transistor should look like two diode junctions. So with the + prong on the base, you should read about 0.5 to 0.7V when the - prong is on the emitter, and about the same if you move the - prong to the collector. All other combinations of probes should read overrange. (ie the same display you see when the probes are not connected to anything on the resistance ranges)
I forgot to mention, that is for a NPN transistor: for a PNP you should reverse the red and black prongs.
If you see a very low voltage when testing between any pins, the transistor is dead. Continuity across all points means it is melted into a lump internally
Registered Member #32
Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549
What Steve said ^^^
If you're having trouble with killing 2N3055s in a flyback circuit or something, try to get hold of another transistor like the MJ10012. The MJ10012 is awesome. In Australia it costs ~$12 from Jaycar so it's more expensive than a 2N3055 but it's likely you'll kill your flyback before you kill a transistor like that. You can use it for ignition coils, too.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I killed one overheating it at 40 volts (feedback flyback driver) Flyback made some nice arcs, fat and hot (melted steel wool rapidly, wires also got burning, lots of current in the arc)
At 20 volts im now using 2SB863 (can be bought for 1/6 price of 2N3055, PNP, 10 amperes 160 volts) and tortured it for long, it didnt blow or even heat that much that it cannot be touched (about 40 - 50 degrees max)
Registered Member #229
Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
I am using two KD502 in parallel in my twinflyback, for 36 VDC input. There are a few transistor choices for simple high power driver as MJ series. If you know another good parts just post here.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I was wondering if with some re-dos maybe power mosfet or IGBT could be used, with the same feedback method I found one incredibly cheap transistor, 2SB863, PNP in my country costs like a LED but ratings are 10A 160V, lots can be stacked if necessary.
I tried it to drive flybacks, preforms very well and for now its my 'top' bipolar transistor
Registered Member #123
Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162
Hi, As all have said the transistor would seem dead. Depending on the application you may want a higher voltage or current rating. if switching a transformer with a single transistor then voltage rating will be of highest importance. If driving say resistive load then you may not have current rating. However you only asked how to test one and haven't said if you even used it at all What's the application out of interest? Colin
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Dead power transisitor?
