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Old 1st January 2012, 01:47 PM   #1
godfrey is offline godfrey  South Africa
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Default Interesting BJT failure mode...

It was a low voltage, high current PNP transistor used as the output device in the dimmer circuit for my son's car's dashboard lights. Testing with a multimeter suggests the base is now shorted to the collector and the emitter is totally open circuit.

Some previous owner had screwed up the wiring and connected the output directly to ground, so cause of death will have been overcurrent or overheating. There's no external signs of damage though (like a burned/exploded case).

Is this in any way normal? Seems weird to me!
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Old 1st January 2012, 02:56 PM   #2
Elvee is offline Elvee  Belgium
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Originally Posted by godfrey View Post

Is this in any way normal? Seems weird to me!
Hi Godfrey,

It looks normal to me: first, the junction was melted into a short by the overload, and then the emitter bonding wire acted as a fuse, leaving just B and C shorted
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Old 1st January 2012, 09:55 PM   #3
godfrey is offline godfrey  South Africa
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Thanks, that makes sense.
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