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ADP1048 Killing FETs

Question asked by mark-arnott on Jun 23, 2015
Latest reply on Jun 24, 2015 by LtCommData

Hi,

 

We are using the ADP1048 in an odd application that requires minimal output capacitance. We are building an underwater LED driver that is pressure compensated, as a result we cannot have big caps on the output. We don't have very much space to work with and don't have any input line filtering.

 

We are running the ADP1048 in interleaved mode. Our system goes from 200-300VDC and 100-240VAC. It is designed to output 500W.

On DC our system works fine. On AC above 208V it runs fine as well.

 

When running on 120VAC the ADP1048 has trouble staying stable at 500W. The output flickers a lot. The problem is exaggerated when we run with a couple 100' of extension cords.

 

I scoped the VAC pin and it is getting really bad noise on the input. I added a RC filter and it helped reduce the input noise so it will run. The problem is now I keep getting Fast OCP faults. Every so often when the board is turned on one of the switching FETs will blow.

 

My questions are:

 

- Does adding RC on the VAC detection pin cause a phase shift that is causing the PFC logic to fail and as a result kill the switching FETs? If so can this phase shift be accounted for in software?

- Does the ADP1048 have problems running on long extension cords? Does the voltage drop across the cord and added inductance hurt the PFC operation?

- The OCP fault detection doesn't always protect the FETs even when set at the lowest debounce setting. Would using higher current rated FETs prevent them from blowing?

 

Thanks,

Mark

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