I have a supply rail which depending on battery condition and whether the system is on charge can range from approximately 9V (at low-battery cutoff) to 15V (with charger connected). From this I am currently powering a LM2586S-ADJ based boost converter which is currently set for an output voltage of 24V.

The 24V rail doesn't actually need to be as high as 24V. I have not yet figured out exactly what voltage it needs to be but I would guess around 14V or so.

I am considering reducing the set-point to improve system power efficiency. Possibly to a value below the maximum input voltage. It is not a problem for my circuit if the output voltage rises above the set-point when the input voltage is above the set point.

Are there likely to be any problems with operating a boost converter (specifically the LM2586S-ADJ but I'm also interested in more general answers) with an input voltage that may sometimes be above the set-point voltage?

  • \$\begingroup\$ Does Webench allow that configuration? Datasheet suggests that in flyback configuration, it is possible for the input voltage to be above or below the output voltage. \$\endgroup\$
    – Justme
    Commented Sep 14, 2020 at 20:38
  • \$\begingroup\$ I don't think webbench allows you to specify a range of acceptable output voltages, but it's a while since I used it. \$\endgroup\$ Commented Sep 14, 2020 at 20:39

1 Answer 1


It depends upon the converter.

For a common non-synchronous boost converter it is usually no problem.

When the input is above the set point the duty cycle will go to zero, regulation will be lost and the output current will be supplied through the pass diode.

I've used that approach with an LT1949 device that was fed from a battery to avoid brown-outs.

It looks like the LM2586S-ADJ would support that mode of operation.


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