Patent ID: 6483723
Filing Date: 2002-11-19
Classification: H02M,Y02B

Abstract:
A switching power supply comprising:a DC-DC converter (A) including: (a) four switching sections of a first high-side switching section, a second high-side switching section, a first low-side switching section, and a second low-side switching section, each having (1) a switching device that is turned ON/OFF according to a switching signal from the outside, (2) a diode connected in parallel with said switching device, and (3) a capacitance connected in parallel with said switching device; (b) a transformer having (1) a primary winding, and (2) a first secondary winding and a second secondary winding connected in series whose junction point is a common terminal; (c) a first rectifying section and a second rectifying section, each having (1) a rectifying device and (2) a snubber connected in parallel with said rectifying device, said snubber having a snubber capacitor; and (d) a smoothing section having a first input terminal and a second input terminal, for smoothing an input supplied via said input terminals, and for outputting said smoothed input; in said DC-DC converter, (B) the cathode of said first high-side switching section is connected with the higher potential terminal of a substantially steady direct voltage source, the anode of said first high-side switching section is connected with the cathode of said first low-side switching section, and the anode of said first low-side switching section is connected with the lower potential terminal of said substantially steady direct voltage source; (C) the cathode of said second high-side switching section is connected with said higher potential terminal of said substantially steady direct voltage source, the anode of said second high-side switching section is connected with the cathode of said second low-side switching section, and the anode of said second low-side switching section is connected with said lower potential terminal of said substantially steady direct voltage source; (D) one terminal of said primary winding of said transformer is connected with the junction point between said first high-side switching section and said first low-side switching section, and the other terminal of said primary winding is connected with the junction point between said second high-side switching section and said second low-side switching section; (E) a terminal other than said common terminal of said first secondary winding of said transformer is connected with the anode of said first rectifying section, a terminal other than said common terminal of said second secondary winding is connected with the anode of said second rectifying section, and said common terminal is connected with said first input terminal of said smoothing section; and (F) the cathode of each of said first rectifying section and the second rectifying sections are connected with said second input terminal of said smoothing section; and a switching control section for (A) determining a delay time based on a resonance cycle depending on the equivalent capacitance of said snubber in each of said first rectifying section and said second rectifying section, and the leak inductance on the secondary side of said transformer with said primary winding short-circuited; and (B) outputting said switching signal with a predetermined switching frequency and a predetermined phase to each of said four switching sections, thereby (a) achieving a first period and a second period sequentially with predetermined time lengths and predetermined cycle periods, (1) during said first period, said first high-side switching section and said second low-side switching section are ON and said second high-side switching section and said first low-side switching section are OFF, and (2) during said second period, said first high-side switching section and said second low-side switching section are OFF and said second high-side switching section and said first low-side switching section are ON; (b) at the end of said first period, turning OFF one of said first high-side switching section and said second low-side switching section said delay time later than the turning-OFF of the other switching section; and (c) at the end of said second period, turning OFF one of said second high-side switching section and said first low-side switching section said delay time later than the turning-OFF of the other switching section.