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Turning off uC / Sleeping during inactivity? Battery-circuit

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swbluto

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Hello, I'm trying to design a circuit that sends a signal whenever it detects too low of a voltage or too high of a voltage on any of the battery's cells. I've already breadboarded the circuit and programmed the uC and it works great, however, it only really needs to be used when battery is being used, and the 34 mA current doesn't help much during long rest periods. I've learned that you can tell the microcontroller to "go to sleep", but apparently the voltage regulator still draws 9 mA of idle current. Are there voltage regulators with extremely low idle current? I haven't found any and it seems I need to "turn off the voltage regulator" -

So.... how to do that? I was thinking about using a current shunt which is fed into an amplifier(like some kind of op-amp) that sends it to a comparator(to detect if current is being used) that drives a mosfet that effectively halts current to the voltage regulator. The two op-amps used in the amplifier and comparator would be power-supplied by cells. Is that a sound design to minimize current usage during idle periods? Any other possible or possibly common solutions to this problems? My googling skills seem to be failing me with this problem, suggesting it might specialized, but there are a ton of battery-powered devices that experience periods of inactivity and automatically "sleep" to minimize current usage, right? I think I just may be using a not-so-common search query.

I've also been thinking about periodically waking up once in a great while(Like once a day), just in case the battery might be self-discharging, but I don't think I should have too many problems designing that. Any help or insights would definitely be appreciated, though!
 
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swbluto

New Member
Sweet! A voltage regulator with power-down mode would be awesome!

Anyways, it's an atmega168. I don't think I should have too many problems finding the appropriate lullaby sequence (I think it can be directly programmed), and the wake-up seems like it should be as simple as a voltage signal to one of the pins, which seems like it could be implemented using the current-shunt->amplifier->comparator (dual op-amp possibility?) design, although anything else would certainly be worth knowing.

I think the uC can take either 3.3V or 5v. Also, they're lithium cells, which could range from 2v to 4.2v a cell in their normal operating mode - they could theoretically go down to 0v per cell, but I'm hoping my circuit should help prevent that!

Since I'm trying to make this as low-power as possible, maybe the 3.3V operation would be better? But would it be more practical than 5V?

This circuit is being designed to protect batteries with at least 4 cells in series, so a lower voltage range of 2V (by tapping one cell) to an upper available voltage range of 16.8V is possible.
 
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