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Old 20th January 2007, 11:46 PM   #1
borges is offline borges  Norway
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Location: Oslo, Norway
Default AC filter for PSU

I'm designing a new PSU for a CD player of mine. One of the things I want to do is put in an AC filter so that it may pass required government testing and also give the transformers cleaner AC.

One option is to buy a module:
Click the image to open in full size.
(The image comes from Elfa and is their product number 69-667-17.)

On the picture, the R is a VDR, voltage dependant resistor, sort of like an AC zener that gets lower impedance at higher voltages. The Cx and Cy caps I have also figured out.

But what are the inductors for? At Elfa they have different rated AC filter modules, the higher the rated AC current, the smaller the inductor.

If I want to build a discrete filter (the module is a bit pricy, the one with a fuse built in is very pricy), what sort of inductors should I use? And how should I choose the component values for 115V rather than 230V?


Cheers,
BÝrge
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Old 22nd January 2007, 05:13 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
a 110/120Vac version needs double the current capacity.
The VDR can be chosen to suit 135Vac.
Use a real X rated (between lines) capacitor.
Use real Y rated (line to earth) capacitors.

The toroid inductor allows balanced current to flow easily (one current flowing in and one curent flowing out).
It attenuates unbalanced (common mode) current (both trying to flow in together) that is often the form of line interference.
This toroid is the part that most limits the current capacity of the filter.

Some users report that the inductor affects the sound of the downstream components. A few report it ruins the sound.
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Old 23rd January 2007, 02:10 PM   #3
borges is offline borges  Norway
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Join Date: Dec 2003
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Thanks Andrew,

What might be the cause of the toroidal transformer being audible? I'd think it would rather be a good thing since it lessens the load of the mains transformer. With the toroid maintaining balanced current and the VDR preventing spikes, isn't that way better than noen of the above?

Cheers,
BÝrge
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Old 31st January 2007, 12:12 AM   #4
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Are these what you have in mind??
Corcom Search Results for 20VK1
Visit Corcom, the world leader in EMI/RFI filters and other filter technology and filtering solutions ... 1 matching item(s) found. Click on any of the buttons for more information

www.cor.com/results.asp?Catalog=20VK1 ∑ Cached pa

I have a few 10VK1's and a few 20VK1's e-mail me I frequently send packages to Akrehamn Norway.
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Old 31st January 2007, 01:22 PM   #5
borges is offline borges  Norway
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Join Date: Dec 2003
Location: Oslo, Norway
Yes, this is the sort of thing I'm looking for. For the longest time I wanted to build the whole thing on my own, but I ended up with a module which integrates the mains connector and filter.

Thanks,
BÝrge
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