3.7V Rechargable battery as arduino power supply

Question

I have an arduino and a telit GM862 module which requires 3.4V-4.2V power supply. So far I have constructed a 12V limiter to plug it into a car power supply and a step-down converter which converts 12V to 3.8V so the custom board which consists of arduino and telit is plugged into a car power supply and arduino is powered with 12V and telit with 3.8V.

Now I would like to modify the project such that the board could be powered by 3.7V Li-ion or Li-Po battery or 12V. To do that I would still need a step down converter which converts 12V to 3.7 (or little higher) when plugged into 12V charger and 3.7V to the voltage required to power arduino as the battery so the battery would power both, telit module and arduino.

Has anyone constructed a similar project that could serve as a reference for the project I would like to build? I would be very thankful if anyone could suggest any helpful resource or name any ICs which are useful to construct such step-up and/or step-down voltage converters.

Thank you!

Answer 1

You don't need a separate step-down converter, if you already have a charging IC for the battery. A lot of charger ICs take input voltages of 12V and allow the load circuit to be connected in parallel to the battery. I personally would go for an IC with an 12V input and an option to charge the battery over USB. However, I don't have build such a circuit and have no experience with a specific device. A list of manufacturers had to include maxim and microchip.

Answer 2

For Li-Po or Li-Ion you'll need an appropriate charge circuit / battery controller. These can be quite complex. The battery must not go flat or it's dead for good. The BQ2000T from Texas Instruments is a good (and popular) starting point for such a circuit.

The AVR on the Arduino can run happily at 3.7V. If you have any level translation between the AVR and your board you would be able to ditch that as it would be no longer needed.

You'd normlly run at 3.3V not 3.7 or 3.8 as it's more of a standard voltage. Are you sure that 3.8 is right for your board, and that's not the absolute maximum?