The invention provides a self-adaptive threshold calibration zero-crossing detection circuit. The self-adaptive threshold calibration zero-crossing detection circuit comprises a zero-crossing
comparator, a phase
inverter, a trigger, a dynamic
comparator, a counter and a decoder, the input end of the zero-crossing
comparator is connected with GND, switch node
voltage, an inversion
signal of a lower power tube grid
control signal and the output end of the decoder, and the output end of the zero-crossing comparator is connected with the input end of the phase
inverter; the input end of the phase
inverter is connected with the output end of the zero-crossing comparator, and the output end is connected with the input end of the trigger; the input end of the trigger is connected with the output end of the phase inverter and an inversion
signal of an upper power tube grid
control signal, and the output end of the trigger is connected with the input end of the dynamic comparator; the input end of the dynamic comparator is connected with GND, switch node
voltage and the output end of the trigger, and the output end is connected with the input end of the counter; the input end of the counter is connected with the output end of the dynamic comparator, and the output end is connected with the input end of the decoder; the input end of the decoder is connected with the output end of the counter, and the output end is connected with the input end of the zero-crossing comparator. The flip threshold of the zero-cross detection circuit is changed, and when the inductive current zero-cross phenomenon occurs in a DCM type, the reverse inductive current when the lower power tube is turned off is reduced.