Battery charger using ATtiny24A

[queen245]

Hi,

Iam a newbie to this forum and to ATtiny.

Iam looking for reference circuit for a battery charger using ATtiny24A.
Atmel website gives a reference using ATtiny15.

Appreciate any inputs in this regard.

Thanks in advance.

[adafruit_support_mike]

Exactly what kind of circuit are you trying to build, and what kind of batteries do you want to charge?

There are lots of options.. you can make a charger that plugs into the wall and charges a dozen batteries at the same time, or you can make a battery charging circuit that lives in a device that gets plugged into a wall wart from time to time. You can make a trickle charger that keeps batteries fresh for a long time, or you can make a high-speed charger that gets flat batteries up and pushing electrons as fast as possible. You can charge a cell phone or iPod battery, or you can charge a car battery.

On top of that, you have to charge different kinds of batteries in different ways.. if you use a nickel/metal hydride battery charger in lithium polymer batteries, you'll probably get a fire, if not an explosion.

If you're looking to charge, say, a lithium polymer cell phone battery, there are dedicated chips that will do the job really well and cost less than half what even a cheap microcontroller will.

[queen245]

Thanks for your response.

Well... iam looking out to design a Solar to 3.7v, 13.8AH Lithium-polymer battery charger.

I would like to use a picopower microcontroller ATtiny24A and I am looking for reference designs around.

Appreciate any light in this area.

Thanks aton!

[philba]

Is your professor requiring the ATTiny 24A? Like mstone says, there are really good charger chips out there.

I'll give you a hint - most Tinys are very similar, differing mostly by flash size.

[adafruit_support_mike]

Okay.. solar to LiPo is nice and specific, and I gather you're running the ATTiny from the battery, not using it to control how the battery charges.

13.8 amp-hours though? Dang..

Someone will need to check me on this, but I'm pretty sure people have adapted the Adafruit LiPo charger:

http://www.adafruit.com/products/259

to work with a solar panel supply. You can probably find links to reference projects in the Adafruit blog.

If I understand you correctly though -- you're using the LiPo to power the ATTiny, not using the ATTiny to regulate charging of the LiPo -- you pretty much have two separate circuits: a battery charger, and a battery-powered microcontroller.

LiPo charging is fussy enough that it's probably best to use a dedicated chip. I happen to use Microchip MCP73811Ts, which cost about 50c each, but other people have different preferences. They're all cheap, small, and are optimized to do all the measuring-deciding-and-controlling as efficiently as possible though.

Running a microcontroller from a battery is really a separate subject from battery charging. You'll want to look at the brownout and low-power shutdown modes the chip offers, and design accordingly. Given the Brick-o-Power you're charging though, I doubt you'll need to sweat over the micropower design principles.

If you're specifically trying to build a charger controlled by the microcontroller, look at the datasheets for dedicated charging chips to get an idea of how the LiPo charging process works. Your battery pack may also have a datasheet that tells you how that specific unit wants to be charged. Once you understand the trickle current/constant current/constant voltage dance, you'll be able to program the ATTiny to do the same thing.