Power loss of switching power supply circuit for supplying constant voltage

• US 20020044469A1
• Filed: 08/09/2001
• Published: 04/18/2002
• Est. Priority Date: 08/16/2000
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Yasumura, Masayuki
• Granted Patent: US 6,456,509 B1
• Time in Patent Office: Days
• US Class Current: 363/125
• CPC Class Codes: H02M 1/009 having two or more independently controlled outputs for DC-DC converter with intermediate AC H02M3/33561
• CPC Class Codes: H02M 3/33576 having at least one active switching element 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

In making constant a direct-current output voltage obtained by rectifying an alternating voltage generated in a secondary winding of an isolating converter transformer PIT, an active clamp circuit formed with an auxiliary switching device, a clamp capacitor, and a clamp diode is connected in parallel with a parallel resonant capacitor to be supplied with the alternating voltage, instead of using a three-terminal regulator and a chopper regulator, which step down and make constant the direct-current output voltage. A control circuit effects PWM control of the auxiliary switching device of the active clamp circuit and thereby equivalently changes capacitance of the parallel resonant capacitor. Thus, the direct-current output voltage is made constant, and power loss caused in making the direct-current output voltage constant is reduced.

Claims

1. A switching power supply circuit comprising:

a switching means including a switching device for intermittently outputting a direct-current input voltage inputted thereto;

an isolating converter transformer including a primary winding and at least first and second secondary windings, said isolating converter transformer being adapted to transmit an output, obtained in said primary winding, of said switching means to said secondary windings and to have a desired degree of coupling to loosely couple said primary winding and said secondary windings to each other;

a primary-side parallel resonant circuit formed by said primary winding and a primary-side parallel resonant capacitor, said resonant circuit being provided for converting operation of said switching means into voltage resonance type operation;

a secondary-side resonant circuit formed by connecting a secondary-side resonant capacitor to said first secondary winding;

a first direct-current output voltage generating means formed by including said secondary-side parallel resonant circuit and adapted to supply a first direct-current output voltage by performing rectifying operation on an alternating voltage obtained from said first secondary winding;

a second direct-current output voltage generating means provided with a rectifier circuit for performing rectifying operation on an alternating voltage obtained from said second secondary winding and adapted to supply a second direct-current output voltage; and

a constant-voltage control means including a capacitor disposed between a secondary-side reference ground and an anode of a rectifier diode forming the rectifier circuit provided for supplying said second direct-current output voltage; and

an active clamp circuit formed by connecting at least a clamp capacitor and an auxiliary switching device in series and disposed in parallel with said capacitor, said constant-voltage control means being adapted to effect constant-voltage control on said second direct-current output voltage by controlling a conduction angle of said auxiliary switching device according to a level of said second direct-current output voltage.

3. A switching power supply circuit as claimed in claim 1 or 2, wherein said first secondary winding is formed by winding a wire of said second secondary winding.

4. A switching power supply circuit as claimed in claim 1 or 2, further including a second constant-voltage control means for effecting control for constant voltage by driving said switching device for switching operation in such a manner that switching frequency of said switching device is variably controlled according to level of said first direct-current output voltage, while an off period of said switching device within a switching cycle is fixed and an on period of said switching device is changed.

5. A switching power supply circuit as claimed in claim 4, wherein said second constant-voltage control means includes a control transformer, said control transformer having a detecting winding connected in series with said primary winding of said isolating converter transformer for detecting a resonance current;

a driving winding for driving said switching means; and

a control winding wound in an orthogonal direction or an oblique direction with respect to the two windings for changing inductance of said driving winding by being changed in control current according to level of said secondary-side direct-current output voltage, whereby said second constant-voltage control means variably controls the switching frequency of said switching device.

6. A switching power supply circuit as claimed in claim 1 or 2, wherein said auxiliary switching device is driven by a self-oscillation driving circuit formed by connecting a driving winding formed by providing a tap to said secondary winding and a capacitor at least in series with each other.

2. A switching power supply circuit comprising:

a switching means including a switching device for intermittently outputting a direct-current input voltage inputted thereto;

an isolating converter transformer including a primary winding and at least first and second secondary windings, said isolating converter transformer being adapted to transmit an output, obtained in said primary winding, of said switching means to said first and second secondary windings and to have a desired degree of coupling to loosely couple said primary winding and said first and second secondary windings to each other;

a primary-side parallel resonant circuit formed by said primary winding and a primary-side parallel resonant capacitor, said resonant circuit being provided for converting operation of said switching means into voltage resonance type operation;

a secondary-side resonant circuit formed by connecting a secondary-side resonant capacitor to said first secondary winding;

a first direct-current output voltage generating means formed by including said secondary-side parallel resonant circuit and adapted to supply a first direct-current output voltage by performing rectifying operation on an alternating voltage obtained from said first secondary winding;

a second direct-current output voltage generating means provided with a rectifier circuit for performing rectifying operation on an alternating voltage obtained from said second secondary winding and adapted to supply a second direct-current output voltage;

a third direct-current output voltage generating means provided with a rectifier circuit for branching and rectifying an alternating voltage obtained from said second secondary winding and adapted to supply at least a third direct-current output voltage; and

a constant-voltage control means including a capacitor disposed between a secondary-side reference ground and an anode of a rectifier diode forming the rectifier circuit provided for supplying said third direct-current output voltage; and

an active clamp circuit formed by connecting at least a clamp capacitor and an auxiliary switching device in series and disposed in parallel with said capacitor, said constant-voltage control means being adapted to effect constant-voltage control on said third direct-current output voltage by controlling a conduction angle of said auxiliary switching device according to a level of said third direct-current output voltage.