As shown in the figure, 555 and R1, R2, C1 form an astable multivibrator, with an oscillation frequency of about 10kHz and a duty cycle of nearly 50%. VT2 and VT3 are used as switch tubes to expand the current. When the oscillation square wave is at a high level, VT2 and VT3 are turned on and discharge to LC; when it is at a low level, the energy stored in L supplies power to the load through the freewheeling diode circuit. When overvoltage occurs, DW breaks down, VT1 is saturated and turned on, and the c pole is at a low level (<0.7V), which resets 555 and stops oscillating, playing a role in voltage stabilization and dynamic balance.