High-efficiency, low-power power supply circuit

摘要

A power supply circuit includes a rectifier, a charging circuit, and a storage capacitor. An AC signal is rectified by the rectifier thereby generating a rectified signal VR between a VR node and a GND node. The capacitor is coupled between an output voltage VO node and the GND node. If VR is greater than a first predetermined voltage VP then the VO node is decoupled from the VR node. If VR is below VP then the charging circuit supplies a substantially constant charging current from the VR node, through the charging circuit, to the VO node, and to the capacitor, provided that VO on the capacitor is below a second predetermined voltage VO(MAX) and provided that VR is adequately high with respect to VO. Due to the charging current, the voltage VO on the storage capacitor is restored to the desired second predetermined voltage.

主权项

1. A circuit for charging a capacitor, wherein the capacitor has a first lead coupled to an output voltage VO node, and wherein the capacitor has a second lead coupled to a GND node, the circuit comprising:
a full wave bridge rectifier that supplies a rectified voltage signal (VR) onto a VR node, and that supplies a ground potential GND onto the GND node; and a charging circuit that: 1) decouples the VO node from the VR node when VR is greater than a first predetermined voltage VP and, 2) supplies a charging current (ICHARGE) from the VR node and onto the VO node when VR is less than VP provided that VO is less than a second predetermined voltage VO(MAX) and provided that VR is greater than VO, wherein the second predetermined voltage VO(MAX) is determined by a Zener voltage of a Zener diode and a source-to-gate voltage of a depletion mode field effect transistor (dep-FET).