Class D output filter coil - diyAudio
 Class D output filter coil
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 22nd March 2012, 03:31 PM #1 diyAudio Member   Join Date: Mar 2012 Location: Arnhem Class D output filter coil Hey DAers, I'm currently trying to learn something about coilcores in outputfilters. I'm having a 1500W in 4 ohm Subwoofer, (120V single supply) My output filter is constructed out 47uH coils and 1u5F capacitors. Where do I find information about calculting the saturation etc.? Or how can I choose wisely?
 22nd March 2012, 03:41 PM #2 diyAudio Member     Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina An important data is frequency, voltage and current in the inductor. Normally a N27 material go well up to 100KHz, but usually higher frequencies requieres lower permeability ferrites, NOT GAPPED, and more turns than lower freq. There are several interesting in the web. I can send a copy of ones that helped in my design. __________________ Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001. Argentine Ham Radio LW1DSE since 1987.
 22nd March 2012, 03:43 PM #3 diyAudio Member   Join Date: Oct 2008 with those kinds of currents, air-core would be the safest...only issue is kind of a large leakage field...but maybe you can put it someplace it wouldn't matter so much, or use a toroidal winding geometry around an air core. If you did it as a solenoid, then 92 turns on a 1" diameter cylinder that is 4 inches long gives 47.5 micro-Henries. Here's the solenoid equation, due to Wheeler: L=n^2*r^2/(9*r+10*l), where L is inductance in micro-Henries. r is radius in inches l is the length in inches n is the number of turns
diyAudio Member

Join Date: Mar 2011
Quote:
 Originally Posted by Blackdrake Hey DAers, I'm having a 1500W in 4 ohm Subwoofer, (120V single supply)
A bridge?
And if you already have it running , whats the problem?
What cores do you have?

diyAudio Member

Join Date: May 2004
Location: Budapest
Quote:
 Originally Posted by Blackdrake Hey DAers, I'm currently trying to learn something about coilcores in outputfilters. I'm having a 1500W in 4 ohm Subwoofer, (120V single supply) My output filter is constructed out 47uH coils and 1u5F capacitors. Where do I find information about calculting the saturation etc.? Or how can I choose wisely?
An example for 1 kW:
ucd 25 watts to 1200 watts using 2 mosfets
+ 1 info: saturation current= ~250 A*turn/mm for MnZn ferrites.

I recommend a big, gapped ferrite, stranded wire, keep distance from gap with wire! Iron powder can be also good, but generally harder to get the proper one (with low permeability and low loss).

Low permeability ferrite? What material? NiZn? Totally unsuitable (max 0.2 T)!
Air core? Induction heater!

diyAudio Member

Join Date: Mar 2012
Location: Arnhem
Quote:
 Originally Posted by Dimonis A bridge? And if you already have it running , whats the problem? What cores do you have?
I have the bridge working but without the filter, simply cause I do not know jet which kind of coilcore to choose

Fullbridge 1500W (4 ohm)
It's a subwoofer --> 10 - 200 Hz

Last edited by Blackdrake; 23rd March 2012 at 07:40 AM.

diyAudio Member

Join Date: Mar 2012
Location: Arnhem
Quote:
 Originally Posted by Osvaldo de Banfield An important data is frequency, voltage and current in the inductor. Normally a N27 material go well up to 100KHz, but usually higher frequencies requieres lower permeability ferrites, NOT GAPPED, and more turns than lower freq. There are several interesting in the web. I can send a copy of ones that helped in my design.
Would be great if you could send me copies, thanks

 23rd March 2012, 12:58 PM #9 diyAudio Member     Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina Filter Try "sloa119.pdf" in the Texas Instrument web page. It´s too big to attach. __________________ Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001. Argentine Ham Radio LW1DSE since 1987.
diyAudio Member

Join Date: Mar 2011
Quote:
 Originally Posted by Blackdrake I have the bridge working but without the filter, simply cause I do not know jet which kind of coilcore to choose Fullbridge 1500W (4 ohm) It's a subwoofer --> 10 - 200 Hz
How can it work without an inductor?
You are cheating somewhere ?

OK, you need the inductor with such values : 47uH , 30Amp (120V/4oHm) , withstanding frequency above 200kHz
I can suggest EDT59 core from Epcos , RM14 core from Epcos and T157-2 ring core.
Attached Images
 etd59.JPG (91.2 KB, 350 views) rm14.JPG (90.4 KB, 337 views) T157-2.JPG (102.0 KB, 332 views)

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