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I am trying to use a non-synchronous buck converter with closed-loop voltage control for battery charging applications.

It needs to work in a wide operating range:

  • Input voltage from 12V to 25V
  • Output voltage from 3V to 8.5V
  • Output current from 0 to 2.5A

Usually buck converters are calculated for a single operating point. How could I calculate the inductor and the input and output capacitors to optimize the efficiency of the converter in this wide range?

Maybe should I define a maximum value for the inductor ripple current? I think it is useless to use a high value inductor, anyway for low output currents is not possible avoid working in discontinuous mode.

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    \$\begingroup\$ Look under "Related" to the right, I believe it answers all your questions. \$\endgroup\$
    – Harry Svensson
    Nov 9, 2017 at 5:21
  • \$\begingroup\$ Sure thing. It's called forced continuous mode. It is however not possible with a asynchronous converter. I do however sense an XY-problem. \$\endgroup\$
    – winny
    Nov 9, 2017 at 6:52

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Normally you design for a current ripple ratio of 0.4, at the combination of input and output voltage, where the peak inductor current is at its maximum. For the buck, this is at maximum input voltage and minimum output voltage (or smallest duty cycle), assuming your load demands the same power regardless of output voltage.

I can recommend the book Switching Power Supplies A-Z, S. Maniktala, on this matter.

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