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[DPRG] Power supply and charger help

Subject: [DPRG] Power supply and charger help
From: Jon Hylands jon at huv.com
Date: Wed Jan 6 15:50:56 CST 2010

On Wed, 06 Jan 2010 16:40:03 -0500, "joe.whitmore"
<joe.whitmore at botworkplace.com> wrote:

>I'm looking for something that can power a load from an AC source 
>converted to a regulated DC output (consumer wall ward) and will charge 
>a 7-12V battery source. And when unplugged the battery will power the 
>load. Essentially a UPS for a DC load.
>
>I've looked at UPS circuits but they were limited to diodes and required 
>the wall voltage source to be higher than the battery voltage. And the 
>charging was limited to trickle charging lead-acids.
>
>I want to be able to use NiMh or NiCds (LiPo would be cool too). And 
>have it function similar to how an iPod or cell phone works. You get a 
>low battery, plug it in and keep using it while it's recharging.
>
>My problem is that I don't know what the technical terms are for what 
>I'm describing. Please point me to the correct terms or to circuits that 
>do what I'm looking for.

Joe,

I'm working on exactly that right now (except I'm not including the
battery charger). I'm using a Linear LTC4412 chip:

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1142,C1079,P2220

If you look at the data sheet, Figure 4 (on page 10) is how I'm trying
to set it up, minus the microcontroller.

I'll be getting a prototype PCB tomorrow, and I'll let you know how it
works out. If I get it working, I will be offering a board on my store
(probably about 1.25" x 2") that will have MOSFETs, a fuse, a wall
power plug, a battery in terminal block, and a power out terminal
block. The MOSFETs I'm using are rated for 100 watts, so they should
be able to handle 12 volts at about 8 amps.

If you're set on on-board charging, Maxim has some nice chips for
doing NiMh batteries, and one of those could certainly be incorporated
into this circuit.

Later,
Jon


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