## Choice of inductor for buck converter

## Choice of inductor for buck converter

(OP)

I am implementing a MPPT solar battery charger (buck converter). The type of converter design have been discussed in my previous post http://www.eng-tips.com/viewthread.cfm?qid=350101

I have finally decided to implement a Interleaved buck converter with 4 leg. With separate driver and mosfet pairs.

12V - 500 Watt Charger (That gives a max current of 41.67A)

Current per converter - 41.67A/4 = 10.42A(per converter)

Vin

Vin

Vout - 11V

Iout - 15A/leg (4 leg in parallel therefore 60A in total, well above the max current produced from panel to be safe)

Freq - 500KHz

I

Substitute the values here http://schmidt-walter.eit.h-da.de/smps_e/abw_smps_... for inductance calculation

Inductance - 8.759x10

I have chosen the inductor http://in.mouser.com/ProductDetail/Coilcraft/SER29...

I have finally decided to implement a Interleaved buck converter with 4 leg. With separate driver and mosfet pairs.

**My Design Specs:**12V - 500 Watt Charger (That gives a max current of 41.67A)

Current per converter - 41.67A/4 = 10.42A(per converter)

Vin

_{max}- 18V

Vin

_{min}- 15V

Vout - 11V

Iout - 15A/leg (4 leg in parallel therefore 60A in total, well above the max current produced from panel to be safe)

Freq - 500KHz

I

_{ripple}- 1A

Substitute the values here http://schmidt-walter.eit.h-da.de/smps_e/abw_smps_... for inductance calculation

Inductance - 8.759x10

^{-6}HI have chosen the inductor http://in.mouser.com/ProductDetail/Coilcraft/SER29...

**Questions:**- Is my choice of inductor good?
- Do i only have to worry about the max current in the inductor (I
_{sat}) or do i have to worry about the voltage across an inductor too?

Thanks

Regards

Gokkul

## RE: Choice of inductor for buck converter

You may meet saturation, but that seems unlikely with your 18 V max in and 11 V out specification. You are running at 500 kHz, so your maximum voltsecond surface will be 14 microvoltseconds (at near 100% conduction). I don't find any data for absorbed voltseconds in the data sheet. But, since your operation is in "the lower left corner" in most of the diagrams, I wouldn't worry. If you see saturation, you can easily increase the switching frequency.

Gunnar Englund

www.gke.org

--------------------------------------

Half full - Half empty? I don't mind. It's what in it that counts.

## RE: Choice of inductor for buck converter

Frequency response and Isat are the critical factors for this inductor, rather than voltage drop (since the first two determine the latter). With the caveat about Isat tolerance, the inductor looks like a good choice for the application.

## RE: Choice of inductor for buck converter

Will keep that in mind :).

Thanks

Regards

Gokkul

## RE: Choice of inductor for buck converter

"Power Capacity @ 100 KHz"mentioned.Does this mean each inductor can operate only at a specified power level?

If so how do i know if the inductor i have chosen can operate at my required power level.

PDF attached.

Thanks

Regards

Gokkul

## RE: Choice of inductor for buck converter

You know yours is okay because you've done the calculation yourself, and satisfied the Isat limits and frequency response.

## RE: Choice of inductor for buck converter

That is reassuring.

Thanks for the response.

Thanks

Regards

Gokkul