Estimating inductance coil when charging supercap

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I want to charge a supercap (400F/2.7V) with a step-down (buck) topology and PWM (AVR), but how to estimate the inductance value of the coil when f_PWM is e.g. 1 kHz? (ESR at 1 kHz noted in datasheet) And what type of coil is best suited for this job? (peak current is 10A)

http://www.maxim-ic.com/images/a...

RES

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At 10 amps, you probably want to go much higher frequency than 1 KHz as the inductor size is inversely related to frequency. It would also be easier to use a chip specifically for the purpose rather than involving the AVR to do the control loop. The datasheets for the buck converters will give you guidance regarding how to calc the required inductor.

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There are many books/docs etc that give the formulas for sizing components for a switchmode supply. Here's one: http://www.ti.com/lit/an/slva477...

A big caveat: designing switchmode supplies is a rather tricky task. I'm with Kartman here - you should use an off-the-shelf chip, and use its reference design.

- S

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Adding to the above, charging a super-cap is a very different ball-game compared to a standard (more or less resistive) load. Among other things, you have to cope with L*C resonant frequencies that are quite uncommon for standard switchers.

I suggest that you take a look at the energy harvesting chips made by Linear Tech. They all have switchers designed to charge batteries or super-caps. Take a look at the spec sheet. Actually, as I look at their web site, they have a whole page oriented toward devices for charging super-caps.

http://www.linear.com/products/s...

Take a look at the Design Notes listed in the column on the right side of the page. Lots of good information, there. Also, their "LT Journal" articles. Top notch stuff.

Jim

 

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