Step-up switch recommendations please

[dt]

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.

 

[jasen]

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).

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

 

[[email protected]]

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:
http://datasheets.maxim-ic.com/en/ds/MAX1870A.pdf
but it doesn't have pins. It does however have an eval board that you
can buy.

 

[Don Foreman]

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.

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.

 

[[email protected]]

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.

You might want to poke around at http://www.linear.com , 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

 

[dt]

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