I am looking for any resources on how to construct a relatively high power (25A, 13.8V) voltage stabilizer (or voltage booster if you like) for my 13.8V powered ham radio.

The problem I try to resolve is powering the radio from both only batteries, and from car battery. So I would like to be protected against both voltage drop especially in first scenario and voltage spikes in the second one.

There is still a plenty of charge in a AGM 12 battery when the voltage is around 12,.4 volts but the radio PSU cuts off when the voltage drops that low.

I know that there are ready to buy solutions, but they are not very accessible in my part of the world, and I would like to at least know the principle they operate on :)

Many thanks in advance!


What about LM2587 in flyback regulation mode in parallel? Is it possible? I have only found a description of boost converter mode parallel application.


Great application note from National about SEPIC design: http://www.national.com/an/AN/AN-1484.pdf

  • \$\begingroup\$ are these deep-cycle AGM batteries? Even if they are deep cycle, do not drain then below 50%, because you will decrease their life too much (it would be more economical in the long term to buy two batteries, instead of depleting one below 50%). The 50% mark will be somewhere 12.00 and 12.25 V depending on the battery, load, temperature, battery age. Anyway never run below 12.00V. If it is not deep-cycle, but a starter-battery, then you should not even run them below 80%, and that will be just about 12.4V (+-0.1V), so to be safe do not discharge below 12.5V. \$\endgroup\$ – miernik Apr 9 '11 at 19:58

Setting up parallel switching regulators is hard. They might not run in sync and start supplying each other. Also, you're saying you want 25A. You would need a ton of those regulators to make it work, if it would work at all.

My suggestion is to get some big coils and FETs that can handle currents like 30 - 40A and a buck-boost converter. Alternatively, you could begin with a buck converter and regulate to a like 10V, and then boost up to 13.8V again. Don't expect to find these regulators in a package that will supply, you'll have to add external components. Don't forget that a buck converter needs to handle 25*13.8/10 = 34.5A+ (not accounting effiency) , because the voltage is lower.


You can parallel flybacks, if you wanted to, but synchronizing the phases can be messy. Designing flybacks necessitates designing transformers - for an application which doesn't require isolation, there's no need for that level of complexity.

You could try and design a SEPIC since it works well for inputs both higher and lower than the desired target.

The car battery itself shouldn't have an issue with spikes - the alternator feeding the battery, well, that's another matter. : ) You can put TVS clamps on the input-side to clip any nastiness coming through.

  • \$\begingroup\$ SEPIC design looks promising, seems to fit the my use case very well. Thanks! \$\endgroup\$ – Kamil Zadora Mar 25 '11 at 7:31

protected by Dave Tweed Aug 11 '14 at 10:36

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