Patent ID: 6344982
Filing Date: 2002-02-05
Classification: H02M,H04N

Abstract:
A power supply circuit comprising:a transformer having a primary coil and a secondary coil; a driving power supply connected to a first terminal of said primary coil of said transformer; a first switching element, a capacitor, and a first diode, all connected to a second terminal of said primary coil; and a control circuit for generating a pulse wave to control said first switching element, wherein: said first switching element is comprised of a first MOS type field-effect transistor; a drain of said first MOS type field-effect transistor is connected to the second terminal of said primary coil, a source is connected to a circuit return path, and a gate is connected to said control circuit; a first end of said capacitor is connected to the second terminal of said primary coil, and a second end is connected to the circuit return path; and a cathode of said first diode is connected to the second terminal of said primary coil, and an anode is connected to the circuit return path, and a noise suppression means connected between said transformer and said control circuit for suppressing generation of noise said noise suppression means having, an auxiliary coil in mutually inductive relation with said primary coil, a second diode and a second switching element connected to said auxiliary coil; said second switching element having a second MOS type field-effect transistor; a drain of said second MOS type field-effect transistor is connected to a cathode side of said second diode, a source is connected to the circuit return path, and a gate is connected to said control circuit; a first terminal of said auxiliary coil is connected to the circuit return path, and a second terminal is connected to an anode side of said second diode; and said control circuit generates a pulse signal to control said first switching element and said second switching element in a manner to switch said second switching element into a conducting state while said first switching element is in a non-conducting state and when voltage of said primary coil is greater than voltage of said driving power supply after said first diode conducts, and into a non-conducting state while said first switching element is in a conducting state, to thereby serve as means to suppress noise.