After the mechanical switch S1 is closed, the voltage at two ends of the load R quickly charge the capacitor C to working power supply voltage through the current limitation of charging unit C-SW. During the breaking of mechanical switch S1, the mechanical switch S1 must have partial voltage and the voltage at two ends of the load R drops. When the potential difference between the capacitor C and the load R is greater than the turn-on voltage of the voltage detection switch V-SW, the capacitor C discharges the load R by using voltage detection switch V-SW, which makes the voltage at two ends of the load R rises rapidly and the potential difference at two ends of the mechanical switch S1 drops quickly, thus achieving the purpose of quickly extinguishing the arc of mechanical switch S1.