Power regulator to battery powered servo project

Using Arduino Project Guidance
1

I'm building a battery powered bare ATmega320 project. I want this to run for about a year without changing batteries. I want to keep the size of this thing rather small.

The AVR is in power_down mode and gets woken up twice a day by an RTC (which has a battery of its own). When the AVR wakes up, it will operate a micro-servo (about 650 mA, perhaps a bit more) for about 2 seconds, then go back to sleep. The servos will be switched off via a P-channel MOSFET when not used.

My question is: how should I power the AVR? I've been looking at various LDOs and switched regulators, but the problem is finding one that can deliver the current for the servos while still having a small enough quiescent current for the main battery (perhaps 2 to 4 AA cells?) last a year.

Any ideas or suggestions?

2

Why not power everything from 3xAA alkaline cells (4.5v) or 4 x AA NiMh cells (4.8v) or (if your servo will work at 3.7v) a 1S LiPo cell. That way you don't need any wasteful voltage regulation.

If your servo will work at 3v you could use 2 x AA alkaline cells.

Have you seen Nick Gammon's power saving tutorial?

...R

3

The servo (SG90) is rated 4.8 to 6 V. Getting rid of voltage regulation would be an interesting approach, but not so easy in this case perhaps.

Maybe the voltage regulator I'm looking for does not exist: too high output current together with too low quiescent current in my requirements...

Yes, I've read the excellent power saving tutorial by Gammon. In his experiments I believe that he did not use a power regulator.

4

If You would use 4 AA cells You have 6 volts to the servo If You tap 4.5 volts, grond to 3 cells, and feed the proceesor from that, would that work? Doing some math the servo only consumes some 260 mAh. A mostly sleeping processor..... It looks doable.

5

Use a regulator which has a shutdown pin. Many of the Pololu ones do. Control that from the Arduino.

Use a separate regulator or no regulator for the Arduino.

6

If I can build on what @MorganS has said, use two separate batteries - one for the servo and one for the Arduino.

...R

7

I'm now considering a variant with 4 AA cells (6V), and where the full voltage is connected through a MOSFET to the servo, and then a LDO or possibly a switched regulator to generate 5V to the AVR.

8

Don't forget about boost regulators. Modern ones are so efficient that it is usually worthwhile to run the Arduino on an unregulated 3.7V LiPo and boost that up to 6V for the periods that the servo must operate.

9

That is an option, but then I need to find a boost regulator capable of outputting at least 600mA when boosting from 3.7V to about 4.8-6V which is what the servo wants. Maybe the regulator should be able to output even more in case the servo draws more current at startup or something.