Parasitic power supply system for supplying operating power to a control device

摘要

A system and method to parasitically take electrical power from a source of ac load power to provide a voltage source to directly power an associated control device is described. The system utilizes a controllable transconductance device to both selectively provide power to a controlled load and to develop a predetermined voltage to directly power the control device in a system where the ac load power is applied at one terminal and is passed through the transconductance device to be returned through the load. The system includes a means for establishing the predetermined voltage level to power the control device and for continuously monitoring that voltage level to maintain it as required, whether power is applied to the load or not. Alternative voltage regulators to provide isolated or non-isolated power to the control device irrespective of whether or not power is applied to the load are also described.