I'd like to integrate a PoL DC/DC converter such as this one from Mornsun : KUB4812QB-10A

It will convert from a battery (48V) to an auxilary 12V bus on which will be connected a 12V Lead-Acid or Lithium-ion battery.

I've had trouble in the past with isolated DC/DC PoL modules where they couldn't run without a diode at the output lest it fries after a couple of ON/OFF cycles (current from the battery feeding back to the output and frying part of the output stage)

I've yet to have a definitive answer as to why this pre-biased operation is not allowed on these modules but the magic smoke escape was very repeatable.

Should I expect the same kind of behaviour from a non-isolated DC/DC such as the one from Mornsun? This point is not exactly explained in details in the datasheet...


simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ I don't see why to expect the behaviour to be different. Instead of "PoL converter" you could search for "battery charger" \$\endgroup\$ Feb 16, 2023 at 17:42

1 Answer 1


Judging from its efficiency, the DC-DC you're planning to use is a synchronous buck. These can both source and sink current.

If output voltage exceeds the setpoint, the controller will turn on the bottom MOSFET more to bring output voltage back to the setpoint. This is expected behavior: the synchronous buck works as a boost converter in reverse and pumps energy out of the output caps back into the input caps to solve the overvoltage condition. It's a useful feature.

In your case if the DC-DC is set to output 12V and the battery is above that, it will try to discharge the battery by transferring all its energy into the input. Will it survive? For this it would need current limiting on the bottom MOSFET, but implemented in the other direction from what's usual (sinking instead or sourcing) so that would require a special circuit in the chip which is only used in this case. So it's probably going to smoke.

Just get something designed to charge a battery.


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