SMPSU IC explosion... (UC3844)

[Jules Richardson]

Tony Duell wrote:
>> Tony Duell wrote:
>>>> Random failure of the weekend was a UC3844 IC in a switchmode power supply - 
>>>> with a very loud bang, the entire top of the chip blew off, but there's no 
>>>> *obvious* sign of any other failure within the supply.
>>> This deos not mean there are no other component failurs. This sort of 
>>> thing is very common actially.
>> I must have been lucky... all the ones I've had to fix before have had failed 
>> in other ways...
> 
> You have been very lucky. 

Until now :)

> I have never had a chopper transistor fail open-circuit.

casualties so far are both choppers (IRF740's), the UC3844, and a couple of 
resistors (they were hidden by the heatsink before; rather obviously cremated 
now I've removed it!)

The UC3844's current sense line got a blast of mains down it which is what 
killed it...

I'll test other components in the area though in case they've failed with no 
visible effects.

cheers

Jules