TI DC-DC Interference Problem Fixed!

Post by **marshallh** » Thu Mar 30, 2006 7:55 pm

I'm using a 7.4v lithuim ion DVD player battery @ 4200mah. It works great until about 7.1v where the psone screen starts cutting out. The voltage only gets this low when your battery is almost dead, though.

Anybody know how accurate a PIC microctronller ADC is? I've heard they're spotty but I might try making a battery meter with one of my spare PICs. Possibly even use a thermistor and turn on a fan automatically when the heatsinks get hot?

codeman · Post by **codeman** » Thu Mar 30, 2006 8:35 pm

if you go to microchip.com and look at the table it says what the resolution of the A/D is. It's common to have either an 8 or 10 bit resolution on the ones that are equipped with an A/D.

Also, keeping the inductor happy by allowing a current path is really important. I took a power electronics class where we did simulations of inductor based systems, and circuits with small currents had an inductor spike of over 1kV!!

timmeh87 · Post by **timmeh87** » Thu Mar 30, 2006 9:06 pm

i hooked up my new converter (pth08000), and guess what... no lines! i dont even need an inductor

. im making a more detailed post about it.

Post by **Skyone** » Thu Mar 30, 2006 9:29 pm

Tim, I have a pth08000, can you post your schematics?

G-force · Post by **G-force** » Mon Apr 10, 2006 9:32 pm

Thank you marsh-man!

Now all I need is a heftier battery than my AA's and I can finish this long-overdue project.

timmeh87 · Post by **timmeh87** » Mon Apr 10, 2006 9:46 pm

oh, btw marshall... did you see the post in 42 a while back about that IC that can be set up as a battery meter in the exact same way you were planning to do? worth taking a look at

joevennix · Post by **joevennix** » Mon Apr 10, 2006 10:09 pm

It's the LM3914, made by National... don't even try to get a free sample, they charge $8 shipping for one...

I've also found some "Battery Fuel Gauges" on TI (search) that seemed like, with the correct circuit, would work fine. These chips can directly drive LED's with their outputs, or you can set them into serial output mode. They're worth taking a look (and not to mention coughfreecough). I ordered one to play around with.

EDIT: Here's the TI product, the BQ2010.

Here's the datasheet. Warning: PDF file.

And here's a tutorial on using the IC. Warning: PDF file.

timmeh87 · Post by **timmeh87** » Mon Apr 10, 2006 10:56 pm

i actually tried to make a circuit with the BQ2012, thats the one that i never finished. it wasnt as easy as it seemed at first...

i still have 5 left, but i think i might try using the LM3914 for my portable instead. you can just buy them at digikey for probably a dollar or two.

joevennix · Post by **joevennix** » Mon Apr 10, 2006 10:59 pm

Yeah, good idea. They're like a buck at Jameco, not sure about the shipping though...