Mains voltage zero-crossing detector

摘要

A mains voltage zero-crossing detector has a constant voltage forced on an external node by driving transistor devices with appropriate control signals provided by a feedback loop around a highly power efficient class B configuration comprising an operational amplifier having single ended dual outputs and a class B control circuit. Mains power zero crossings may then be detected by monitoring the drive current of devices driven by this amplifier. Wherein Class B control and current mode detection provide accurate detection of the driven signal without depending on any voltage threshold that may depend on temperature, process fabrication and/or supply voltage.

主权项

1. A mains voltage zero-crossing detector, comprising:
a first output driver coupled between an first rail voltage and an external node; a second output driver coupled between a second rail voltage and the external node; an amplifier having first and second differential inputs, and first and second single ended outputs, wherein a first output thereof is coupled to a control input of the first output driver and a second output thereof is coupled to a control input of the second output driver; a feedback network coupled between the external node and the second differential input of the amplifier; a voltage reference coupled to the first differential input of the amplifier; a class B control circuit coupled to the control inputs of the first and second output drivers, wherein the class B control circuit forces one of the first or second output drivers off when the other output driver is conducting, and releases control back to the amplifier as it stops conducting; and a current mode detector circuit coupled to the control inputs of the first and second output drivers, wherein the current mode detector circuit provides mains voltage zero-crossing detection based upon currents applied to the control inputs of the first and second output drivers.