Auto Power Off Circuit for Microcontrollers

An auto power-off circuit for microcontrollers is designed to reduce power consumption by cutting off power after the microcontroller finishes its task. This is especially useful in battery-powered devices, IoT applications, and energy-efficient designs.

Below is an explanation of a simple auto power-off circuit using a P-Channel MOSFET and a push-button switch.

🛠️ Components Required:

1. P-Channel MOSFET (e.g., IRF9540, AO3401, or similar)
2. NPN Transistor (e.g., 2N2222 or BC547)
3. Push-button switch
4. Resistors (10kΩ, 1kΩ)
5. Microcontroller (e.g., Arduino, ESP8266)
6. Capacitor (Optional, for debounce)

⚡ Circuit Description:

1. Power Control (P-Channel MOSFET):

   • The P-Channel MOSFET acts as a power switch, controlling the supply to the microcontroller.
   • Its Source (S) is connected to the positive power supply (e.g., Vcc or battery).
   • Its Drain (D) is connected to the microcontroller's Vcc pin.

2. Push-Button:

   • A momentary push-button switch is connected between the Gate (G) of the MOSFET and ground, allowing initial power-on.

3. Microcontroller Pin (AUTO_OFF Pin):

   • One of the microcontroller's GPIO pins is used to hold the MOSFET gate low to keep the system powered after the button is released.

4. NPN Transistor (Optional, for Isolation):

   • The NPN transistor ensures the GPIO pin can reliably pull the gate of the MOSFET low.

🔄 Operation:

1. Power-On Phase:

   • Pressing the push-button pulls the Gate of the MOSFET to Ground, turning it ON.
   • The microcontroller starts running.

2. Sustain Phase:

   • The microcontroller immediately sets its AUTO_OFF GPIO pin to LOW, keeping the MOSFET ON even after the button is released.

3. Power-Off Phase:

   • When the microcontroller completes its task, it sets the AUTO_OFF GPIO pin to HIGH (or floating).
   • The MOSFET gate voltage rises, turning it OFF and cutting power to the microcontroller.

📊 Schematic Diagram:

Here’s a basic textual representation:

• Source → Vcc
• Drain → Microcontroller Vcc
• Gate → Pull-up Resistor + Connected to NPN transistor & GPIO

📝 Example Code (Arduino):

✅ Advantages:

• Very low power consumption in the OFF state.
• Simple and reliable design.
• Suitable for battery-powered systems.