Method and apparatus for AC-to-DC power conversion

摘要

In one aspect, the present invention reduces electromagnetic interference (EMI) caused by a capacitive dropper power supply by synchronizing the openings and closings of a shunt switched used for regulation control of the DC output voltage generated by the power supply, to zero crossings of AC current from the current-limiting resistor disposed in series at the AC input of the power supply. In one or more other embodiments, the capacitive dropper power supply includes disconnect circuitry that senses a loss of the input AC voltage source and in response wholly or partly disconnects internal regulation control circuitry from the supply's output filter capacitor to reduce the current drawn from the filter capacitor, thereby reducing the decay rate of the DC output voltage from the filter capacitor. The contemplated power supply may also be implemented in a Bipolar, BiCMOS or CMOS process, for realization in a compact integrated circuit device.

主权项

1. A capacitive dropper power supply configured to operate as an AC-to-DC power converter and comprising:
an input circuit configured for connection to an AC voltage source, said input circuit including a bridge rectifier that is coupled in series to the AC voltage source through a current-limiting capacitor and provides a current signal at a bridge output that is derived from the AC voltage source; an output circuit that includes an output filter capacitor that is coupled to the bridge output through a reverse blocking element; a shunt switch coupled across the bridge output so that the current signal flows into the output circuit when the shunt switch is open and is shunted back to the AC voltage source when the shunt switch is closed, wherein a DC voltage signal is developed at a supply output of the output circuit by the current signal being permitted to flow into the output circuit and thereby charge the output filter capacitor; a regulation control circuit configured to regulate the DC voltage signal by opening and closing the shunt switch responsive to sensing the DC output voltage of the capacitive dropper power supply relative to a target voltage and further configured to synchronize the openings and closings of the shunt switch to detected zero crossings of AC current from the current-limiting capacitor.