Method and apparatus for determining zero-crossing of an AC input voltage to a power supply

摘要

A controller (146) for a switched mode power supply (100) includes a drive signal (140) generator (138) and a zero-crossing detector. The drive signal generator (138) is to be coupled to control switching of a switch (114) included in the power supply (10) to regulate an output (Vo, Io) of the power supply. The zero-crossing detector is coupled to the drive signal generator (138) and coupled to receive a current sense signal (142) representative of a switch current (144) flowing through the switch (114). The zero-crossing detector generates a zero-crossing signal in response to comparing the current sense signal (142) with a reference signal representative of a zero-crossing current threshold. The zero-crossing signal indicates when a zero-crossing condition of an AC line input voltage (102) of the power supply exists.