POWER CIRCUIT PROTECTION APPARATUS FOR PREVENTING OPERATION OF TRANSFORMER IF SECONDARY WINDING IS ABNORMAL DUE TO OPEN OR SHORT CIRCUIT

摘要

PURPOSE: A power circuit protection apparatus is provided to prevent operation of a transformer in case where the secondary winding of the transformer is abnormal due to open or short circuit. CONSTITUTION: A power circuit protection apparatus comprises a transformer(202), output units(207,208), a PWM control unit(204), a voltage sensing unit(209), a blocking unit(210), and a comparing unit(211). The transformer has a primary coil and a secondary coil. A rectified DC voltage is applied to the primary coil, and one or more voltages different from each other are induced to the secondary coil having a winding ratio different from that of the primary coil. The output unit receives voltages output through the secondary coil of the transformer, rectifies and smooths the received voltages, and outputs voltages different from each other. The PWM control unit feeds back the voltages output from the output unit, and outputs a PWM signal having adjusted duty cycle. The voltage sensing unit senses voltages induced at the secondary coil of the transformer. The blocking unit blocks interferences between voltages sensed by the voltage sensing unit and a first reference voltage. The comparing unit compares fluctuation of the first reference voltage and a second reference voltage, and outputs a signal for determining whether to operate the PWM control unit.