SparkFun Forums

[ManicMaurice]

Ok totally disclosure, I am a 100% complete electronics novice. But I am at the beginning of fulfilling a long time curiosity and am starting to build a few small electronics projects.

My first question involves 3.7v lithium ion batteries. As I understand it the rating of 3.7v is only because the batteries run at 3.7v for the majority of their operating time before needing to be recharged. When freshly charged they output up to 4.2v and after extended use they drop down as low as 3.1v.

What would I need to go about regulating this to a constant 3.7v until it begins to drop and then allowing the battery to drop no lower than say 3.5v before cutting all power transmission?

I'm not looking for a circuit design or schematics. Just friendly advice on the components necessary to achieve my task. However if someone wants to go wild and fill my simple mind with possible circuits and schematics I won't turn them down.

[nukez]

I'm very new to electronic too ! but i've readed alot on tutorial here and maybe i'm wrong but i would say 3.3V Zener diodes ( COnnected in reverse)

Some one else can say if i'm wrong or not ?

[emf]

It can be done, of course, but why do you want to regulate to 3.7V? That's a strange voltage dictated by the battery chemistry, not because it is particularly useful on its own.

Most people are actually looking for a regulated voltage of 3.3V or 5V to run a microcontroller. There are plenty of nice, easy-to-use switching regulators which will give you a nice, regulated 3.3 or 5V over the 4.2 - 3.1V range the lithium battery supplies, boosting the voltage if it's too low, "buck"ing it if it's too high. On this site, there's this one, but there are literally hundreds of others out there.

Or perhaps you're looking to power some LEDs and want to maintain the same brightness over the battery's output range. In that case, a constant current LED driver running off the unregulated battery voltage might be what you're looking for.

How much current do you plan on drawing? Is efficiency or long battery life important? Does your lithium battery have a built-in low voltage protection circuit?

[skimask]

Also keep in mind that a LOT of pieces/parts/chips/etc that run a on a nominal 3.3v are completely capable of running at 4.1v and 3.0v and so on.....therefore, this almost completely eliminates the need for regulators in a lot of cases. Just depends on what you want to do and what the datasheets say for the parts you want to use.

[ManicMaurice]

Thanks for the quick replies guys.

I'm looking to use the battery to power a very small heating coil. I don't expect to be pulling more than 1.5 or 2 amps at most. More than that and I have found that I risk blowing up the heating coil. I landed on the 3.7v because my rudimentary math concerning the voltage of the battery and resistance of the heating coil (approximately 3 ohms). It places the numbers right around 1.23 amps of power, which leaves me plenty of leeway in anticipation of the manufacturing variance (+/- 0.2 ohms) in the heating coils I'm using.

[ManicMaurice]

I did a little more digging on Sparkfun and I came up with this item. by looking at the specsheet it appears that they make a 3.8v version that would fit my needs nicely.

Thanks everyone