Switching power supply circuit

• US 7,095,629 B2
• Filed: 08/05/2004
• Issued: 08/22/2006
• Est. Priority Date: 08/06/2003
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Yasumura, Masayuki
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US10/528,543
• Publication Number:
  US 20060114697A1
• Time in Patent Office: 747 Days
• Field of Search: 363/16, 363/127, 363/15, 363/25, 363/24
• US Class Current: 363/16
• CPC Class Codes: H01F 27/325 Coil bobbins formers for coils in general H01F5/02
• CPC Class Codes: H01F 29/02 with tappings on coil or winding; with provision for rearrangement or interconnection of windings
• CPC Class Codes: H01F 3/14 Constrictions; Gaps, e.g. air-gaps in magnetic shunt paths H01F3/12
• CPC Class Codes: H02M 1/0058 by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/33571 Half-bridge at primary side of an isolation transformer
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A switching power supply circuit in which, in order to both provide high power conversion efficiency of a complex resonant converter having a synchronous rectifier circuit and reduce a circuit scale and cost by simplifying the circuit, a synchronous rectifier circuit of a winding voltage detection system is provided on a secondary side of the complex resonant converter, a coupling coefficient is decreased to about 0.8 by setting a gap length in an isolated converter transformer to about 1.5 mm, and numbers of turns of a primary winding and secondary windings are set such that a level of a voltage induced per turn (T) of the secondary windings is 2 V/T. Thus, since magnetic flux density at a core of the isolated converter transformer is decreased to a certain value or lower, a secondary side rectified current can be in a continuous mode even under a condition of heavy load.

Claims

1. A switching power supply circuit comprising:

a switching unit formed with switching devices for performing switching so as to interrupt a direct-current input voltage input to the switching unit;

a driving unit for switching-driving said switching devices;

an isolated converter transformer for transmitting a switching output of said switching unit from a primary side to a secondary side thereof, said isolated converter transformer having wound thereon at least a primary winding and a secondary winding;

a primary side resonant capacitor connected to a predetermined part on the primary side so as to form a primary side resonant circuit for converting an operation of said switching unit into a resonance type operation with at least a leakage inductance component of the primary winding of said isolated converter transformer and a capacitance of the primary side resonant capacitor;

a primary side partial voltage resonant circuit for performing a partial voltage resonant operation during a period that the switching devices forming said switching unit are turned off, said primary side partial voltage resonant circuit being formed by a capacitance of a partial resonant capacitor connected in parallel with at least one of the switching devices forming said switching unit and the leakage inductance component of the primary winding of said isolated converter transformer; and

a synchronous rectifier circuit for providing a secondary side direct-current output voltage as a voltage across a secondary side smoothing capacitor by performing a rectifying operation on an alternating voltage induced in the secondary winding of said isolated converter transformer and charging said secondary side smoothing capacitor with a rectified current;

wherein said synchronous rectifier circuit includes;

a first field-effect transistor inserted between one end of said secondary winding and a negative electrode terminal of said secondary side smoothing capacitor;

a second field-effect transistor inserted between another end of said secondary winding and the negative electrode terminal of said secondary side smoothing capacitor;

a first driving circuit for detecting, by a resistive element, a secondary winding voltage corresponding to a half-wave period in which said first field-effect transistor makes a rectified current flow, and outputting a gate voltage for turning on said first field-effect transistor; and

a second driving circuit for detecting, by a resistive element, a secondary winding voltage corresponding to a half-wave period in which said second field-effect transistor makes a rectified current flow, and outputting a gate voltage for turning on said second field-effect transistor, wherein

a magnetic flux density of said isolated converter transformer is set to a predetermined value so that the secondary side rectified current flowing through the synchronous rectifier circuit as a result of said rectifying operation is in a continuous mode irrespective of a variation in a condition of a load connected to said secondary side direct-current voltage.

2. The switching power supply circuit as claimed in claim 1, wherein,

in order to set the magnetic flux density of said isolated converter transformer to a certain value, a coupling coefficient between the primary side and the secondary side is set to a predetermined value by making a gap length formed in the isolated converter transformer a predetermined value.

3. The switching power supply circuit as claimed in claim 1, wherein,

in order to set the magnetic flux density of said isolated converter transformer to a certain value, numbers of turns of said primary winding and said secondary winding are set such that a voltage level induced per turn of said secondary winding is a predetermined value.

4. The switching power supply circuit as claimed in claim 1, further comprising a constant-voltage control unit for performing constant-voltage control on said secondary side direct-current output voltage by variably controlling a switching frequency of said switching unit according to a level of said secondary side direct-current output voltage.

5. The switching power supply circuit as claimed in claim 1, wherein the secondary winding of the isolated converter transformer comprises

a litz wire band formed by aligning a plurality of litz wires having elemental wires of a wire diameter less than a predetermined value and forming the plurality of litz wires into a band shape.

6. The switching power supply circuit as claimed in claim 1, wherein the secondary winding of the isolated converter transformer comprises

a flat woven wire formed by weaving a plurality of litz wires having elemental wires of a wire diameter less than a predetermined value into a flat shape.

7. The switching power supply circuit as claimed in claim 1, wherein the secondary winding of the isolated converter transformer comprises

a laminated film band formed by laminating a plurality of film-shaped conductors having a cross-sectional area less than a predetermined value, the film-shaped conductors being covered with an insulating film.

8. The switching power supply circuit as claimed in claim 4, claim 5, or claim 6, wherein,

both end parts of said litz wire band, said flat woven wire, or said laminated film band are preliminarily soldered, and then each soldered to a lead wire.