Inductor selection criteria 3

[ohmrun]

I need to select an inductor to be used in a 10 kHz circuit. It will be used in a series resonant circuit where the A.C. current can be as high as 200 mA. I notice that most of the inductors of the type I would like to use have a D.C. current rating. There will be no D.C. current flowing in this circuit. However, the A.C. current exceeds the D.C. current rating. Will this be a problem?

 

[electricuwe]

If you load the inductor with an AC current higher than the DC rating you will have higher losses in the winding and in the core even if additional losse due to skin and proximity effect and hysteresis losses are neglected. You didn't state the inductance and the type of winding you are talking about but I guess you will see smoke coming out of the inductor very soon.

 

[ohmrun]

I wanted to use a 4.7 mH coil Toko 181LY-472J. The test frequency is 50 kHz with Q minimum of 100. The rated DC current is 40 mA. The appealing characteristics of this coil is that it is magnetically shielded and it is small, 10.5 mm od and 14 mm tall.

 

[electricuwe]

I wouldn't even try it !

 

[ohmrun]

Any suggestions?

 

[electricuwe]

Some components used for separating frequencies in loudspeaker-arrangements might be suitable for your application, since in this application inductors work in the frequency and power range you need.

If you can not find one there the easiest way is to wind one yourself on a ferrite core.

 

[jmarko]

Hello, Mryan!
Just explanation, why producers if inductors give data of saturation current in DC value (despite that in real circuits usually appears AC signal): it is much easier to measure inductance with small AC signal, superimposed to large DC signal, when measuring saturation values - and these measurements are pretty identical like if it was pure large AC signal applied. Data for saturation DC current is then equal to maximum (peak) value of AC current thrue inductor.
And as you know, if current exceeds saturation limit value, inductance of inductor with core starts to decrease.
Best regards, Jmarko

 

[RomanM]

Try following this link, it is to an app note on Linear Technology's site.

http://www.linear.com/pub/document.html?pub_type=app&document=90

They specialize in switching regulators and I've found this particular app note #19 as especialy helpful.

Good example on page 4

Good Luck