EE help needed: Need to build a filter

[RU482]

I need to build a filter that will help combat coducted emissions. My problem frequencies are between 150Khz and 2.5Mhz. The line that I need to filter is an AC power source line that is fused/breaker'd at 20A / 120VAC.

I'm in the process of building a prototype of this filter, but I need some help honing in on the inductor/capacitor values I need to knock down those frequencies. Does anyone have any input or direction to some resources that could help?

 

[AbsolutDealage]

I'm a little rusty on filter design, but I have a small suggestion for you: why don't you just build a low pass instead of a band pass? There's no real reason I can think of to pass freq's above 250MHz, unless I'm missing something....

 

[sgtroyer]

So if all you want to do is get rid of high frequency emissions, can't you use an RF choke? I think it's basically a magnet that you wrap the wire around, but I'm fuzzy on the details. This, I think, is done quite commonly, for that very reason.

If you do want to make a filter, though...

Sounds like your filter doesn't need to be very sharp, it can roll off slowly. So a simple first order RC should do it for you. You shouldn't need any inductors. Be sure that your R can handle large amounts of power, and your C can handle large amounts of voltage. You should be able to work out the actual amounts.

I'm not really familiar with power delivery type electronics, so I can only offer limited help. See if you can find a relevant textbook. Horowitz and Hill's "Art of Electronics" is a good general guide to back of the envelope electronics, but ideally you could find a book that talks about power delivery stuff. Browse the nearest University's engineering library.

And be careful. 120VAC is a much harsher teacher than 5VDC.

 

[blahblah99]

What you need is an AC line filter to filter out the high frequencies. You can buy commercially available units or make your own consisting of an LC circuit.