How to Make Overcurrent Protection Circuit (12V 3A) using 555 Timer IC

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Protecting electronic devices from overcurrent is essential in DIY and professional circuits. In this post, we will build a simple overcurrent protection circuit for a 12V 3A power supply using a 555 Timer IC, a shunt resistor, and a transistor switch. This circuit automatically cuts off the load if the current exceeds 3A.

What You’ll Learn

How to use 555 Timer as a protection controller
Using a shunt resistor to sense current
Simple circuit design with auto cutoff
Optional manual reset feature

Materials for the Project

1X 555 TIMER IC
2X BC547 TRANSISTORS
1X 10 K VARIABLE RESISTORS
2X 1N4007 DIODES
1X 12V RELAY
1X 100uF CAPACITOR
2X 1K RESISTORS
2X 2.2K RESISTORS
3X 10K RESISTORS
1X RED LED
1X GREEN LED
1X MICRO PUSH BUTTON
1X 0.47 OHM 5W RESISTOR
2X 2 PIN TERMINAL
BLOCKS VERO BOARD
JUMPER WIRES

Working Principle

This circuit uses current sensing with a shunt resistor placed in series with the load. When current exceeds 3A, the voltage across the shunt (0.3V) is used to trigger a transistor, which in turn activates the 555 Timer.

The 555 IC is configured in bistable mode, which latches the output and turns OFF the load (through a MOSFET or relay) until a reset button is pressed.

⚡ How Overcurrent is Detected

Using Ohm’s Law:

V = I × R → V = 3A × 0.1Ω = 0.3V

This 0.3V is enough to turn on a transistor (like BC547), which then pulls the 555’s trigger pin LOW.

Circuit Operation

The load draws current from the 12V supply.
If current < 3A → circuit operates normally.
If current > 3A, then voltage across 0.1Ω exceeds 0.3V.
BC547 turns on, triggering the 555 timer.
555 output goes LOW, turning OFF the MOSFET or relay.
The load is disconnected until the RESET button is pressed.

Download Circuit Diagram

Circuit Diagram

✅ Features

Protects your circuit from overload
Simple components and low cost
Optional LED indication and buzzer
Manual reset function for user control

Applications

DIY Power Supplies
Battery Chargers
Motor Control Circuits
Automation Projects
Arduino- and Relay-Based Systems

Conclusion

With this simple 555 timer overcurrent circuit, you can protect your 12V 3A systems safely and affordably. It’s perfect for hobbyists, students, or engineers working with motors, batteries, or Arduino-based automation.