Switching power supply circuit
First Claim
1. A switching power supply circuit, comprising:
- a rectification smoothing section for rectifying and smoothing an ac input voltage to produce a dc input voltage;
a switching section including a plurality of switching elements for switching the dc input voltage to intermittently output the dc input voltage;
a drive section for driving said switching element for switching operation;
an insulating converter transformer including a primary winding provided on a primary side and a secondary winding provided on a secondary side for transmitting the switching output of said switching section from the primary side to the secondary side;
a primary side resonance capacitor connected to a predetermined location of the primary side and having a capacitance for cooperating with a leakage inductance component of said primary winding of said insulating converter transformer to form a primary side resonance circuit for causing said switching section to perform operation of the resonance type;
a secondary side smoothing capacitor;
a synchronous rectification circuit of a winding voltage detection system for rectifying an alternating voltage induced in said secondary winding of said insulating converter transformer and charging said secondary side smoothing capacitor with resulting rectification current to obtain a secondary side dc output voltage as a voltage across said secondary side smoothing capacitor; and
a constant voltage control section for controlling a switching frequency of said switching section so that, when a level of the secondary side dc output voltage is low, the switching frequency is lowered, but when the level of the secondary side dc output voltage is high, the switching frequency is raised to perform constant voltage control of the secondary side dc output voltage;
said insulating converter transformer having a magnetic flux density set lower than a predetermined level so that the secondary side rectification current flowing through said synchronous rectification circuit is maintained in a continuous mode even when the switching frequency drops lower than a predetermined level as a result of the control of said constant voltage control section;
said synchronous rectification circuit including an inductor element having a bead core and inserted in the rectification current path for charging said secondary side smoothing capacitor with the rectification current, said inductor element having a dc superposition characteristic set such that the secondary side rectification current is maintained in the continuous mode where a load to which the secondary side dc output voltage is connected is within a range within which the load decreases to no load.
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Accused Products
Abstract
A switching power supply circuit is disclosed which can achieve a high power conversion efficiency and besides achieve reduction of the circuit scale and the cost by simplification in circuit configuration. The switching power supply circuit includes a synchronous rectification circuit of the winding voltage detection system on the secondary side of a resonance converter. The coupling coefficient of an insulating converter transformer or the induced voltage level per one turn of the secondary winding is set so that the magnetic flux density of the insulating converter transformer may be lower than a fixed level thereby to maintain the secondary side rectification current in a continuous mode even in a heavy load condition. An inductor is inserted in series in a path along which rectification current is to be supplied to a secondary side smoothing capacitor so that reverse current appearing on the rectification current is suppressed by counter electromotive force generated in the inductor to further reduce the reactive power. A dc superposition characteristic of the inductor is set so that abnormal oscillation in a very light load condition (for example, 12.5 W or less) is prevented.
28 Citations
11 Claims
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1. A switching power supply circuit, comprising:
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a rectification smoothing section for rectifying and smoothing an ac input voltage to produce a dc input voltage; a switching section including a plurality of switching elements for switching the dc input voltage to intermittently output the dc input voltage; a drive section for driving said switching element for switching operation; an insulating converter transformer including a primary winding provided on a primary side and a secondary winding provided on a secondary side for transmitting the switching output of said switching section from the primary side to the secondary side; a primary side resonance capacitor connected to a predetermined location of the primary side and having a capacitance for cooperating with a leakage inductance component of said primary winding of said insulating converter transformer to form a primary side resonance circuit for causing said switching section to perform operation of the resonance type; a secondary side smoothing capacitor; a synchronous rectification circuit of a winding voltage detection system for rectifying an alternating voltage induced in said secondary winding of said insulating converter transformer and charging said secondary side smoothing capacitor with resulting rectification current to obtain a secondary side dc output voltage as a voltage across said secondary side smoothing capacitor; and a constant voltage control section for controlling a switching frequency of said switching section so that, when a level of the secondary side dc output voltage is low, the switching frequency is lowered, but when the level of the secondary side dc output voltage is high, the switching frequency is raised to perform constant voltage control of the secondary side dc output voltage; said insulating converter transformer having a magnetic flux density set lower than a predetermined level so that the secondary side rectification current flowing through said synchronous rectification circuit is maintained in a continuous mode even when the switching frequency drops lower than a predetermined level as a result of the control of said constant voltage control section; said synchronous rectification circuit including an inductor element having a bead core and inserted in the rectification current path for charging said secondary side smoothing capacitor with the rectification current, said inductor element having a dc superposition characteristic set such that the secondary side rectification current is maintained in the continuous mode where a load to which the secondary side dc output voltage is connected is within a range within which the load decreases to no load. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification