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Old 22nd March 2012, 03:31 PM   #1
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Default 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?
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Old 22nd March 2012, 03:41 PM   #2
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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.
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Old 22nd March 2012, 03:43 PM   #3
djoffe is offline djoffe  United States
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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
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Old 22nd March 2012, 03:47 PM   #4
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Inductor Design Software



RF Design Software
Download


--Filesize ~1.5 MB

Click Here to Download
Inductor Design Software 2010 (MicroRelease_March2010.exe)



Download


--DOS version
--Filesize ~400K

Click Here to Download
RF Design Software (Toroid.zip)
Micrometals, Inc. has thoroughly reviewed this design software and the equations utilized to calculate the suggested windings and believe the information to be accurate. It is important to note that the default settings can be altered and unacceptable designs generated. Before using this product, the buyer agrees to determine suitability of the product for their intended use or application. Micrometals shall not be liable for any loss or damage, including but not limited to incidental or consequential damages as a result of the use of this software.

Micrometals will gladly offer engineering assistance and provide samples to aid in your core selection, please do not hesitate to contact your local representative or the factory directly.

The updated version offered here includes new materials.

Micrometals Inductor Software is a flexible user friendly tool designed to assist in the selection of iron powder cores. The software file size is 1.5 MB.

The user will have the opportunity to select from five different inductor applications:

1) Design of DC output inductors Differential mode inductors

2) Design of controlled swing inductors where the inductance does not exceed a maximum value at reduced current.

3) Design of wide swing inductors utilizing a composite core of ferrite and iron powder.

4) Design of a power factor boost or buck inductor, commonly referred to as a PFC choke.

5) Design of 60 Hz dimmer inductor

6) Design of a Resonant Converter Inductor

The program accepts user defined design requirements in terms of required inductance, dc resistance, dc bias current and applied ac voltage. The user has the option of specifying core geometry (i.e. Toroid, E-Core or Ferrite/Iron Powder Composite), specific core materials or all materials, metric units or English units, maximum window fill factor, temperature rise, ambient temperature, etc.

This program will automatically calculate the smallest core size possible and will display;

1) Micrometals Part Number

2) Approximate unit price

3) Core AL Value

4) Required Number of Turns

5) Wire Size

6) Percent Window Fill

7) DC Winding Resistance

8) B ac

9) Percent Initial Permeability

10) Core Loss

11) Copper Loss

12) Temperature Rise.

In addition, new features alow the user to analyze specific designs as well as check the core's operating temperature vs. time for thermal aging analysis of designs.

The software allows the design engineer to quickly work up multiple design solutions based on user specified electrical requirements which all can easily printed for hard copies. Designs can also be saved to a file by using the 'F' key.

The following are definitions of the units utilized by the design software:

Unit

Description

Defined
AL


Inductance Rating


Nanohenries per turn squared (nH/N2)
Price


US Dollars


Approximate value at 2,500 pieces
RDC


DC Resistance


Ohms
BAC


Peak AC Flux


Gauss
P FE


Core Loss


Watts
P CU


Copper Loss


Watts
T Rise


Temperature Rise


Degrees Celsius

The design program is automatically set to default to an ambient temperature of 25°C in free standing air with maximum temperature rise of 40°C.

Micrometals Inductor Software is a flexible user friendly tool designed to assist in the selection of iron powder cores. The software is a DOS based program with a file size of 250KB.This version "2000b" of the design software is for 'beta' release only.

Please contact Micrometals if you require technical support regarding the use of this software or our product line. Micrometals will also gladly offer sample cores to assist in your core selection.
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Old 22nd March 2012, 04:49 PM   #5
Dimonis is offline Dimonis  Russian Federation
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Quote:
Originally Posted by Blackdrake View Post
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?
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Old 22nd March 2012, 08:46 PM   #6
Pafi is offline Pafi  Hungary
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Location: Budapest
Quote:
Originally Posted by Blackdrake View Post
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!
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Old 23rd March 2012, 07:37 AM   #7
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Quote:
Originally Posted by Dimonis View Post
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.
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Old 23rd March 2012, 07:38 AM   #8
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Quote:
Originally Posted by Osvaldo de Banfield View Post
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
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Old 23rd March 2012, 12:58 PM   #9
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Default Filter

Try "sloa119.pdf" in the Texas Instrument web page. It´s too big to attach.
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Old 23rd March 2012, 02:48 PM   #10
Dimonis is offline Dimonis  Russian Federation
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Quote:
Originally Posted by Blackdrake View Post
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.
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File Type: jpg etd59.JPG (91.2 KB, 275 views)
File Type: jpg rm14.JPG (90.4 KB, 261 views)
File Type: jpg T157-2.JPG (102.0 KB, 256 views)
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