Step-up switch recommendations please

Hi, I'm new to the group and wonder if anyone can recommend a switch that will give me 12.6v output from 10-14v (12v lead acid battery). I would like 5A output and even up to 10A if possible, but may also accept only 3A for a simple solution. In going through some of the options on National, Microchip, etc, my greatest challenge seems to be finding a solution that makes current easy to vary (eg: with a pot or discrete resisters).

My application is a 3 cell lithium charger. The primary requirement is constant voltage while not exceeding current appropriate to the cells on charge (I have a variety of sizes to charge). I have a fairly solid understanding of lithium charging requirements and the risks associated with these cells. Although I can get help with SMT chips they must at least have leads! and I would prefer bigger stuff.

I have a successful LM2577 based design which takes the voltage up to about 16v and then I use an L200 to bring it down to 12.6v. The L200 also gives me control over output current with a resister array. This works well at lower currents but I now want higher currents and would prefer to avoid the step-up then -down design. I don't have the knowledge to design my own high output stages so am hoping that you folk can offer some advice. Thank you, David.

Reply to
dt
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non-inverting buck/boost DC-DC converters are hard to find, but that's apparently what you require.

If you can work with -12.6V (instad of +12.6V) an inverting converter may be the easiest solution.

Bye. Jasen

Reply to
jasen

If you need the step-up and step-down functions, putting a step-up to

16V in front of a step-down is not a bad way to go. If you want less heat, look for more efficient converters, but I don't think you'll find a better overall architecture than what you have.

There is this part:

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but it doesn't have pins. It does however have an eval board that you can buy.

Reply to
lens

I think Maxim has an app note on SEPIC converters. These can deliver regulated output to a load with voltage either higher or lower than the source.

Reply to
Don Foreman

You might want to poke around at

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, too.

And maybe download their LT-Spice (aka SwCADIII). It has a menu option, FIle-->Switch Selector Guide, that might be of some use. It takes rough switcher specs and creates example switching PSU circuits, for which you can then immediately run simulations. You can also alter the circuits and run them. LT-Spice is very good for general-purpose circuit simulation, too.

- Tom Gootee

Reply to
tomg

Thanks, guys. You've helped me narrow down the search. David.

Reply to
dt

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