Abstract: Semiconductor devices are the core part of DC circuit breakers. Compared with the traditional full-control devices (IGBT and MOSFET), a thyristor has gradually become a promising choice for DC circuit breakers due to its low cost and high capacity. However, rapidity and reliability put high demands on the topology of the circuit breakers based on the thyristor. Therefore, this paper proposes a circuit breaker that combines the automatic (fast) and controllable (reliable) shutoff functions. The automatic shutoff function has no fault detection delay, and the thyristor can be turned off immediately by the circuit's response to the fault. The controllable shutoff function can form a reverse current inside the circuit breaker to turn off the thyristor without being affected by external parameters, ensuring that the fault can be isolated reliably. The automatic and controllable shutoff functions use independent energy storage capacitors, so these two functions do not affect each other, which further improves the reliability of the circuit breaker. Finally, the performance of the proposed circuit breaker is verified by the simulation and experiment of 2kW.