POWER SUPPLY CIRCUIT WITH FUNCTION OF PREVENTING REVERSE FLOW NOISE

摘要

A power supply circuit for preventing a counter-electromotive force, induced in a load unit incorporating a motor through inertial rotation of the motor when the main swith of an electric apparatus having output terminals connected to the load unit is turned off, from flowing reversibly into the power supply circuit. The circuit comprises a switching element have a diode function of preventing reverse flow of the counter-electromotive force to the power supply circuit side connected to the power supply line leading to the output terminal of the power supply circuit to be connected to a load unit. The switching element is turned on when the power supply of the apparatus is turned on and turned off when the power supply of the apparatus is turned off. Since the ON-state resistance of the switching element is low, voltage drop at each output terminal is low when the switching element is turned on and the adverse effect of the counter-electromotive force is prevented while sustaining the voltage supply accuracy of the power supply circuit. A silicon P channel MOSFET may be employed as the switching element.