High efficiency low-power power supply circuit

A power supply circuit (20) includes a rectifier (25) , a charging circuit 26), and a storage capacitor (22). An AC signal (VAC) is rectified by the rectifier (25) thereby generating a rectified signal (VR) between a first node (43) and a ground node (GND). The capacitor (22) is coupled between an output node (+) and the grond node (GND). If the rectified signal (VR) is greater than a first predetermined voltage then the output node is decoupled from the first node. If the rectified signal (VR) is below the first predetermined voltage then the charging circuit supplies a substantially constant charging current from the firs node, through the charging circuit (26), to the output node, and to the capacitor (22), provided that the voltage (Vo) on the capacitor is below a second predetermined voltage (Vomax) and provided that the rectfied signal is adequately high with respect to the capacitor voltage (Vo). Due to the charging current, the voltage on the storage capacitor is restored to the desired second predetermined voltage.