A circuit breaker capable of microcontroller-based fault detection having a backup circuit for causing the circuit to trip in response to a microcontroller fault or a failure of a regulated power supply powering the microcontroller. The circuit breaker includes an RC circuit connected to an SCR. The resistor of the RC circuit is connected between the anode and gate of the SCR, and the capacitor is connected between the gate and cathode of the SCR. The microcontroller has a first pin coupled to the RC circuit, which is initially in a high input impedance state. In the event of a microcontroller fault or power supply failure, the capacitor will charge to a voltage sufficient to activate the SCR and trip the breaker. If the microcontroller startup routine is successful, the pin is configured as an output and is pulled low, shorting out the capacitor.