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


von Kayham (Guest)


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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

von Martin (Guest)


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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

von Kayham (Guest)


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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.

Can someone enlight me please?

Thanks

von Esko (Guest)


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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.

von Martin (Guest)


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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_current_waveform_18F5EAD9-CA6B-5E4E-250950656C4D83E6.JPG

von Kayham (Guest)


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Ah OK, makes sense.

Greetings Kayham

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