C2/R 1 of the circuit is connected in parallel to form a step-down or current-limiting circuit, four diodes form a rectifier circuit, C 1 is a filter circuit, and R2 is a current-limiting circuit.

When the top of the alternating current is positive and the bottom is negative, the current is reduced through R 1/C2, flows from 2 of the rectifier to 1, then flows through the series circuit of R2 and D2, reaches the ground, and then flows from the ground to 4 of the rectifier and then to 3 to return to the negative terminal of the power supply.

When the bottom of alternating current is positive and the top is negative, it flows from the rectifier 3 to 1, then flows through the series circuit of R2 and D2, reaches the ground, then flows from the ground to the rectifier 2, then flows to the step-down circuit composed of R 1/C2, and finally returns to the negative terminal of the power supply.