Auto Power Off: Save Batteries





Introduction: Auto Power Off: Save Batteries

This little circuit allows your microcontroller to cut the power off.

To turn the circuit on press the button.

To turn it off drive the "to microcontroller" signal high using whichever condition you like. For battery applications you might want to have a voltage reading on another pin (a voltage divider will do the job) and drive the pin high when a certain threshold has been reached.

INPUT is the voltage source (battery).

OUTPUT is the voltage applied to the circuit you want to switch off.

Can't be easier.

Parts Used [part number of this example]:

Qty Device
1 P-Channel Mosfet [IRF9Z24]

2 NPN Transistor [2N2222]

1 Push Button momentary switch

3 100k resistor

1 6k8 resistor

Step 1: Result

Short video of the circuit in action.



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    I don't know much about electronics, but will the mosfet be able to handle 5V 1A?


    Can you plz explain how it works?

    This is really interesting, but I am looking for this same circuit smaller, because my project needs to fit in a small case.

    Is there a way to replace the mosfet with any tipe of transistor?, like the 2N3904?

    Hi, it doesn´t work until i place a 10uF between B and E of T2

    Interesting project... Any idea how could we use time? For example: I would like to turn on the microcontroller every hour, collect information from sensors and transfer data to central, then shut it down until next hour. Thanks.

    2 replies

    You cannot shutdown the microcontroller if you want to wake it up automatically afterwards. What you can do is put all your sensors on the power output of this circuit (not the microcontroller) if they don't have a power saving mode. Then you should find out how to put your microcontroller to sleep (low power mode) and use a watchdog timer to wake it up. You should then connect the button pin that goes to the transistor to a microcontroller pin and set it high when you want to wake up the sensors.

    T1 base ---^√^√^√^√^-------microcontroller pin


    Of course you could also use the same pin of the mocrocontroller that sets the circuit off and set it to LOW to turn the circuit ON again. I will let you figure this part out :) (play with more transistors, watch out for shorts though)

    This is a great idea, I barely know anything about IC's, But I find it hard to believe tha these isn't a specific IC meant exactly for that (without a breadboard and everything)

    1 reply

    There are probably battery protection ICs ,but anyway, all ICs are built with transistors resistors in the end some simple functions can be achieved with few discrete parts .

    nice tutorial. You should mention that this schema is useful to disconnect all devices in cirquit, otherwaise you can use sleep mode with power off on microcontroller. google arduino sleep modes.

    1 reply

    Thanks. Yes, the circuit cuts all the flow from Input to Output, although it does not have to be the same power rail as the micro's. This kind of circuit might come handy when powering things from a lipo for example.