Can off-the-shelf inductor handle skin effect loss? 1

[grigson]

Hello

Please could you tell if an off-the-shelf inductor will be ok for our requirement?

Eg will this inductor be ok….
2209-RC (47uH from Bourns.com)

http://www.bourns.com/data/global/p...w.bourns.com/data/global/pdfs/2200_series.pdf

It is the output inductor on a half-bridge smps.

It will see a Max current of following

Average current = 4 Amps.
RMS current = 4.4 Amps.
Peak current = 6.7 Amps

Ripple frequency = 111KHz.

The di is quite high (5.1Amps)
i.e. 5.1 Amps at the switching frequency (111KHz)

We need a high ripple in the inductor to improve our transient response.

Will an off-the shelf inductor with a single winding be ok, or will we need to custom build, with multiple strand conductors to mitigate skin effect?

 

[IRstuff]

Have you run a skin effect calculation? There are tons of such calculators on the web.

http://www.calculatoredge.com/electronics/skin effect.htm

Unless someone here magically knows how the rest of your circuit works, how is anyone going to know whether you can tolerate the skin effect?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[grigson]

Hi the Coilcraft calculator for their PCV-0-473-05L (47u, 6A) inductor gave an AC loss of just 43mW for these conditions...which seems incredibly low to me...and i wonder if it is a mistake on the calculator?

http://www.coilcraft.com/apps/loss/loss_2.cfm

 

[Comcokid]

The problem with many off-the-shelf inductors is that the current ratings are for the inductor at room temperature, immediately after the current is applied. But once the inductor heats up, it may be close to saturating as the typical heat-rise at the rms current is 40C. Additionally, some maufacturers specify the saturation current as the current at which the inductance has changed 10%. Others as the current at a 40% change, which would be very deep into saturation.

Now, as for an inductor on the output what you are trying to create is DC, and as such you don't generally wind it for skin effect as you want to attenuate any higher frequency components. It's the same situation for inductors on an input filter - you are not trying to pass the high frequency but [/i]attenuate[/i] it. Although the attenuation of HF from skin effect will be small, at least it will be attenuating.

Now, if the ripple amplitude on your output inductor is high enough that serious heating may occur from skin effect, then that heating is the least of your problems as you will never get it through FCC (or whatever regulatory agency standard you test to).