Re: [uCsimm] Inductors' Issue of Switching Power Supply

From: Tom Walsh (
Date: Fri Mar 31 2000 - 01:18:11 EST

Xinhua Rong wrote:

> Hi all,
> I am quite new to switching power supply design. I found in the recommended application diagram of MAX series there is one 100uH inductor. I wonder there is any requirement about this component. My current consideration is: big enough current,

    Several amps.

> low loss (high efficiency),

    As long as you use the largest wire that will wind the number of turns (single layer) to cover the core.

> high frequency (how high? several MHz?).

    More like 1 mhz should be fine.

> If I have to homebrew it, what should I do? Such as, how many turns on Amidon FT-50-47 toroid? Thank you for your help!

Use 38 turns of 24 gauge wire and that should put you at about 100 uH. There is a formula for determining the number of turns for a given permeability core. Unfortunately, you need a data sheet from Amidon that specifies the AL (inductance in mH / 1000 turns of wire), from this AL value you can calculate the
turns to reach your inductance:

Number of turns = 1000 X ---------------------
                                             / desired inductance in mH
                                            / -------------------
                                           / AL value (mh/1000 turns)

the formula is "1000 time the square root of (desired in mH divided by AL)"

I got my winding sheet from them many years ago when I purchased a couple of experimenters kits.


Tom Walsh - WN3L - Embedded Systems Consultant
'', ''
"Windows? No thanks, I have work to do..."

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