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Ed Aho
12-12-2013 02:53 AM

Active or Passive PFC for front end?

I have a design that does not have a PF requirement, but I am considering using active PFC to lower harmonics thus EMI filter requirements. There is also the benefit of making the second stage (an isolated DC/DC converter) an easier design by providing a regulated input. I think there is also the benefit to lower current inrush.

Is this too much complexity versus simply using a bridge rectifier capacitor to make the DC voltage and design the EMI filter and isolated DC/DC converter appropriately? The bulk capacitors will have to be derated for a higher voltage - which adds to the cost and complexity (I can not use aluminum electrolytic capacitors).

Have I summed up the trade-offs? Any suggestions or comments?
12-12-2013 05:04 AM
Top #2
Mau Pham
12-12-2013 05:04 AM

Your scheme of

"simply using a bridge rectifier capacitor to make the DC voltage"

is not passive PFC at all. In fact, it doesn't provide any PFC.

However, you might be able to avoid the cost of PFC if it's not required. If you can tolerate that the input current would be spiky instead of a smooth sine wave in phase with the input voltage. Balance Dollars with Sense!
12-12-2013 07:15 AM
Top #3
Darrell Hambley P.E.
12-12-2013 07:15 AM
Ed, I'm curious - You mentioned 400Hz so that indicates it could be airborne but there's not a requirement for PFC so is this for a military power supply? Then you mentioned that you need a lagging power factor. Is this in your customers spec that it must be lagging?
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