Inductor Core Material

Depends on what you're doing with it!

Try a Vishay Dale IH10BQ101K at Mouser.

try getting a small ferrite size of your little finger sizw , wind cable sheathed wire of small dia wire with few strands on the same, the two ends of the wire should be connected in line with your ckt, if ur not satisfied wid the o/p include more ferrites of same combination in series with your ckt.

Grain-oriented (GO) silicon steel probably best.

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Define small.

The laws of physics will determine the right size.

What are trying to reject?

Have you seen this or similar? http://users.catchnet.com.au/~rjandusimports/tut_6.html

Filter blocks are used at the AC entry of all commercial and technical equipment. They are catalog items from all maior electrical houses, as Arrow, Newark or Mouser. They are the smallest possible, while still fullfilling its function and maintain safety standards. While not advisable, you can do in a homebuilt, as you like. In commercial equipment, for safety and liability reasons iury-rigged solutions are not permitted.

If you do not have space in the equipment, you can insert one, or a back to back pair in the AC cable, in the fashion PC printer outrigger power supplies are inserted into the AC line. Easy, and in most places I know, permitted.

You did not tell us what exactly you want to do.

If you want to improve your sine-shape you should prefer iron powder cores in the low frequency range. If you want to reduce EMI at higher frequencies then ferrite materials are the better choice.

Another point of view is whether you want to reduce differential or single ended spikes or harmonics. If your surrounding is sensitive for radiation your choice should be a ring core. Regard the saturation of the material - the higher the saturation the lower the µ and the Al-values and the higher the dimension which is a design conflict.

On WE-ONLINE.COM you find a lot of cores and a product selector software to determine the filter characteristics.

Another hint for magnetics development is never to develop from smaller to bigger size but always from bigger to smaller size when the function of big is ok.

Regards Uwe

Thank you for your input.

The inductor is for suppressing EMI at around a few hundred khz, the inductor current is at mains supply 50 Hz.

The normal core materials used is powdered iron which will result in very bulky choke. I am thinking whether using silicon steel which has high Bmax will result in smaller size. Is this type material still effective in suppressing at a few hundred kHz? Also, is air gap necessary?

What has your personal research suggested?

You had asked for a 100 to 200uH inductor, which is a fairly high value for a 5A current, if small is important. You'll be following the choke with a little RF filter capacitor (often called the "X" capacitor), right, say 0.1uF? Since 200uH and 0.1uF are resonant at about 36kHz, this would provide an attenuation of (f_H/f_L)², or about 30x at 200kHz.

But I wonder if you're trying to suppress the EMI noise from a switching converter that's running near 200kHz? That would be the switching-noise repetition frequency, visible with an oscilloscope. But it's likely that you actually have a periodic set of RF ringing or similar noise every 5us, but with a 2.5 to 10MHz ringing frequency. This would mean that you can filter it with an RF filter.

For example, if your filter is resonant at 250kHz, it would provide 100x or higher attenuation at 2.5MHz. This means that L = 1 / C (2∏ f_L)² = 4uH would be adequate. Given a 5 or 10A rating, that's a very simple problem, compared to 100 to 200uH. You could use one of my favorites, little 07HCP series radial-lead chokes (datasheet link) made by Fastron and sold by Mouser.

For example, the 07HCP-4R7M-50 (Mouser link) is a 4.7uH choke with a 5.4A saturation current, selling for 79 cents.

BTW, often the RFI noise from a switching regulator is common-mode, or ground noise. This is best dealt with a common-mode choke, which is actually a trick: a series-connected transformer that cancels the noise. This will also have some leakage inductance, filling the role of the inductor we were talking about above. But before I go on about that, maybe you can let us know a bot more about your problem.

The EMI is coming from AC mains chopping by triac, the chopping is to achieve variable dimming for lighting. Is this type EMI Common mode? In these products, the Earth line is usually not available, so , common mode choke solution is not possible.

The Worst measured EMI is at around 150 to 300 kHz.

Common and differential mode filtering does not depend on the ground wire. It takes only two: hot and return. And it is not simply chokes. Google or bing "dimmers filtered" and you get many pages listed. Buy some, and replace the bothersome ones. You will not be able to design one on the kitchen table.