LOW VOLTAGE POWER SUPPLY SYSTEM FOR AN ELECTRIC BLANKET OR THE LIKE
A power supply system for outputting low voltage electrical power from a high voltage power source includes an isolation-type power conversion device, such as a transformer having a primary high voltage side and an isolated secondary low voltage side. The low voltage side is interconnected with a power output arrangement, which is adapted to supply low voltage power to a load, which may be in the form of an electric blanket or the like. A switching arrangement is interconnected with the high voltage primary side of the power conversion device, for providing intermittent operation of the power conversion device. The period of intermittent operation of the power conversion device is controlled via a control arrangement, to vary the power output from the low voltage secondary side of the transformer and thereby to the electrical load. The control arrangement is preferably in the form of a pulse width modulation (PWM) control, which receives inputs from a controller that is powered from the isolated secondary low power output of the power conversion device via isolated primary and secondary circuits, to vary the duty cycle of the switching power conversion device. The power supply includes a burst logic circuit that provides high frequency intermittent operation of the power conversion device through the switching arrangement when the controller is off, to supply low voltage power to the controller which enables initial operation of the controller and thereby operation of the power conversion device. The low voltage output is interconnected with a load detection arrangement which disables the controller in the event the load is disconnected from the low voltage output. An over-voltage switch is also interconnected with the low voltage output, to shutdown the power supply in the event the voltage of power supplied to the low voltage output exceeds a predetermined low voltage threshold.