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bridge rectifier blowing up

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geek12

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Someone designed a circuit some years ago which employs a rectifier (half wave rectification) switched by a Solid state relay and fed to resistive load. The system was working fine for some time but now we are noticing diode blown up badly. I started investigating and thought coz diode was burnt it could be temperature related problem so found that amibent and surface temperature was well above 80C.But I believe rectifer which we are using can withstand 150c. Any idea why a rectifier will blow up (seriously burnt) without blowing any fuses? Also would it make any difference where the connections are made ? Any suggestions are welcome?
 

Sounds like thermal wear of the device. It causes failure of the join between rectifier chip and connecting metal.
If you accept the limited lifetime, replace with a rectifier of the same type, otherwise use one with a considerable
higher current rating.
 

Well I don't know if it is thermal breakdown or any other cause I want to look at all possibilities. But higher current rating device won't help if it is thermal issue. Do we have some MTBF type calculations for Diode based on temperature? I don't see we exceed temperature ever above it's rated value we are only taking about 7-8A when it is rated for 25A at 55C. Now the question is if it is rated for 25A at 55C when will breakdown if we operate at say 90C with 7 A current?
 

Based on the few informations you gave originally, it can be only a guess.

You have been asking a particular question, and I tried to answer it. The assumption is however, that "burnt without blowing any fuses" has a meaning, in other words, that if the rectifier fails short circuit, the fuse would blow.

I agree, that 1/3 rated current sounds like a gentle mode of operation. But for power semiconductors, there's always thermal wear. It depends very much on the rectifier type and it's operation condidtions. In addition, some connection methods, e.g. faston connectors, have a high likelihood to fail at increased temperatures,
 

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