Pi filter for power supply

[steven_first_2001]

Hello everyone. I am working on making a high current dc power supply and I need to make a Pi filter for it but I am stuck. I am using a 24VDC (34Vac pk-pk) 10A transformer (running at 60Hz) and this will be ran to a regulator circuit but first it must be filtered. I need a hand designing the filter so that it runs with minimum ripple. I can not find any information on how to properly use a Pi filter for this application! I know the basics of simple filters and all but I just don’t know what affect the inductor and cap are supposed to have on one another in this configuration. I know I am NOT looking for the resonant frequency to be 60Hz seeing that would defeat the purpose of the filter… If anyone can help me out with designing this and maybe explain the operation and mathematical aspects of the Pi filter, I would be very grateful.

Steven

 

[Nigel Goodwin]

This is the 21st century, nor the early part of the 20th century! - PI filters haven't been used hardly at all for many decades - and for a 10A one you would be talking a LOT (and I mean a LOT) of money for a suitable choke.

All you need is a good sized electrolytic capacitor - as has been mentioned a lot recently, a 'rule of thumb' is 1uF per mA - so a minimum of 10,000uF, and preferably more (say two or three in parallel, this will help with ESR and ripple current).

 

[dknguyen]

Isn't the LC-DC link in a motor drive just a big pi filter?

But yeah, I wouldn't worry about it too much. Just get a big cap, and stick whatever inductor (that can handle the current) if you really want one.

 

[Hero999]

It really depends on what ripple current you require.

Inductors make good filters for high currents but the large chokes can be expensive and will result in a large voltage drop. A toroidal transformer primary is the only suitable thing I can think of, choose a lower voltage transformer as possible.

 

[PCBONEZ]

This is the 21st century, nor the early part of the 20th century! - PI filters haven't been used hardly at all for many decades - and for a 10A one you would be talking a LOT (and I mean a LOT) of money for a suitable choke.

That's a load of rot.

With the exception of very cheap ones every PC PSU I've ever seen has between 1 and 3 PI filters, and I've probably seen 100's by now.

For than matter, most good video cards have one or two.
.
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[JimB]

With the exception of very cheap ones every PC PSU I've ever seen has between 1 and 3 PI filters, and I've probably seen 100's by now.

For than matter, most good video cards have one or two.

For 10 amps at 60/120hz ripple?

Yeah right!

By the way, nice resurection of a five year old thread!

JimB

 

[dr pepper]

I'm with Jim and Nige on this one, I've a couple of valve amps that use chokes in the dc rail, but nothing since the 50's