提出了一种用于反激式开关电源中对AC输入电压进行过零检测的方法及实现电路,通过在固定时间之内检测初级电感电流来判断AC电压是否过零。针对内部集成了功率MOS管的单片反激式开关电源IC,可以通过复用芯片功率管漏端引脚来实现检测目的,减少了芯片引脚数量。基于0.5μm BCD工艺,采用Hspice对电路进行仿真,仿真结果表明,提出的AC电压过零检测技术在不增加芯片引脚数量的同时也能够准确实现AC电压的过零检测。 A method and implementation circuit for zero-crossing detection of AC input voltage in flyback switching power supply are proposed. The AC voltage is zero-crossing by detecting the primary inductor current within a fixed time. For the internal integrated power MOS tube monolithic flyback switching power supply IC, you can reuse through the chip power transistor drain pin to achieve the purpose of detection, reducing the number of chip pins. Based on the 0.5μm BCD process, Hspice is used to simulate the circuit. The simulation results show that the AC voltage zero-crossing detection technique can accurately detect the AC voltage zero crossing without increasing the pin count of the chip.