# Forum: Analog Circuits Active PFC in a 24V (Truck/Bus) network?

 Author: Kayham (Guest) Posted on: 2011-05-24 01:08

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Hello,

when I was seaching for infos on how to use a standard Computer
in a truck or bus, I came across the "active PFC" and read,
that I should use it in DC/DC converters to, to avoid the high
switching frequencies on the bordnet.

Can someone tell me, which PFC chip I should use for it and
maybe some links to application notes and schematics?

Thanks Kayham

 Author: Martin (Guest) Posted on: 2011-05-24 08:53

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I think that makes no sense. PFC means power factor correction, and for
a power factor you need alternating current. But in a 24V net, you have
DC current.
To reduce high switching currents, you just need a good filtering, so
input capacitors and inductors must be well chosen.

Regards,

Martin Antoni

 Author: Kayham (Guest) Posted on: 2011-05-24 11:59

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This is one of the source where I found the thing with the DC PFC:

http://www.smps.us/power-supply.html

The PFC is AFTER the rectifier, hence on the DC side.

Thanks

 Author: Esko (Guest) Posted on: 2011-05-24 13:36

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> I think that makes no sense. PFC means power factor correction,
> and for  power factor you need alternating current.
He is right.

 Author: Martin (Guest) Posted on: 2011-05-24 17:03

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After the rectifier, you have also a alternating current, but only with
positive sign. And then, the current is drawn sinusodial, to match it
with the input voltage. This current is then stored in a 'big'
capacitor, which is in input to the next switching converter.

In this picture, you see the current, which matches in average a sinus

http://cr4.globalspec.com/PostImages/200911/PFC_cu...

 Author: Kayham (Guest) Posted on: 2011-05-24 18:55

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Ah OK, makes sense.

Greetings Kayham

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