AC voltage sensor with low power consumption

A power converter, comprising:

• an energy transfer element coupled between an input of the power converter and an output of the power converter;
• a power switch coupled to the input of the power converter and the energy transfer element;
• and
• a power converter controller coupled to generate a drive signal coupled to control switching of the power switch to control a transfer of energy from the input of the power converter to the output of the power converter in response to a feedback signal representative of the output of the power converter, wherein the power converter includes:
• an input sense circuit to receive an input sense signal representative of an input of a power converter;
• a zero-crossing detector coupled to the input sense circuit to be responsive to the input sense signal falling below a first zero-crossing threshold and rising above a second zero-crossing threshold to determine zero-crossing intervals of the input of the power converter;
• a timer circuit coupled to the zero-crossing detector to determine peak intervals of the input of the power converter in response to the zero-crossing intervals, the timer circuit coupled to generate an enable signal in response to the zero-crossing detector, wherein the enable signal is coupled to be received by the input sense circuit, to synchronize sensing of the input of the power converter to occur during the peak intervals of the input of the power converter;
• and
• a comparator circuit coupled to the input sense circuit and the timer circuit, wherein the comparator is coupled to detect if the input of the power converter is greater or less than one or more thresholds during the peak intervals of the input of the power converter.

A method for sensing an input of a power converter, comprising:

• receiving an input sense signal representative of the input of the power converter;
• detecting zero-crossing intervals of an ac input voltage in response to the input sense signal falling below a first zero-crossing threshold and rising above a second zero-crossing threshold;
• synchronizing a timer to the ac input voltage in response to the detected zero-crossing intervals;
• closing a line sense switch in response to the timer to enable sensing of the input sense signal during peak intervals of the ac input line voltage;
• and
• opening the line sense switch in response to the timer to disable sensing of the input sense signal during intervals other than the peak intervals of the ac input line voltage.