Protect circuit from Overcharged Battery

[milesguidon]

I have a device with ICs in it that are rated to 3.6V or 3.7V for normal use, and I am powering it with a 3.7V (nominal voltage) Li-Ion battery.


The battery fully charges to ~4.2V. Powering a circuit with this fully charged Li-Ion battery means I will have overvoltage conditions after charging, until the battery is drained lower than ~3.7V.

What is the simplest way to limit the battery voltage to 3.7V or below? Zener diode (how?) ?

Thanks!

 

[Artlav]

What about an LDO voltage regulator?
Something like LP2985IM5-3.6.
That would keep the voltage at 3.6V from as little as 3.8V.

 

[milesguidon]

What about an LDO voltage regulator?
Something like LP2985IM5-3.6.
That would keep the voltage at 3.6V from as little as 3.8V.

Thanks for the reply!

Wouldn't this have odd behavior at input voltages *lower* than the specified output voltage? For example, the circuit works just fine when Vcc = 3.0V. How would a 3.6V LDO fare when Vin = 3.0V? I'm concerned about using LDOs because I need to use the battery all throughout its discharge from "fully charged" to ~2.8V

 

[FoxyRick]

The LDO is fair idea, but it will waste a lot of battery capacity. That said, do the IC's stop functioning properly when the cell voltage goes below 3.6V? If so, that itself is wasting a lot of the cell's capacity. It still has a lot of energy left to give at that point.

Perhaps a low power buck/boost switching regulator would be a better idea? That might get you more run time as well as regulating the voltage to 3.6V.

Edit: I was typing this before you posted your reply (I was multitasking - I don't type that slowly). Looks like you answered my question.

- - - Updated - - -

In that case, a simple switching regulator might work. I think some will just stop switching when the input voltage drops below the set output and pass the input straight through. In fact, you could just regulate to 3.0V anyway.