Switching power supply

• US 20020001210A1
• Filed: 05/29/2001
• Published: 01/03/2002
• Est. Priority Date: 06/01/2000
• Status: Active Grant

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yoshida, Koji, Kuranuki, Masaaki
• Granted Patent: US 6,452,816 B2
• Time in Patent Office: Days
• US Class Current: 363/98
• 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 1/38 Means for preventing simultaneous conduction of switches
• CPC Class Codes: H02M 3/3376 with automatic control of output voltage or current
• 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 an isolation type DC-DC converter for performing full-wave rectification in the secondary of a transformer, two switching sections 11 and 13 alternately switch ON and OFF, thereby reversing the current I3 flowing through a primary winding 3a of the transformer 3. A switching control circuit 7 outputs switching signals G1 and G3 to the switching sections 11 and 13, respectively, thereby controlling the switching of the switching sections. A load current sensing section 9 senses the amount of load current, then compares it with a predetermined threshold value. When the amount of load current sensed is smaller than the threshold value, a delay circuit 8 delays the switching signals G1 and G3 to the switching sections 11 and 13 for a predetermined delay time. The delay time is set to be substantially equal to ¼ of the resonance period determined by the self-inductance of the primary winding 3a of the transformer 3.

Claims

1. A switching power supply comprising:

A) a DC-DC converter comprising;

a) four switching sections consisting of a first switching section, a second switching section, a third switching section, and a fourth switching section, each comprising

     1) a switching device turned ON and OFF by switching signals from the outside, and

     2) a diode and a capacitor each connected to said switching device in parallel;

b) a transformer comprising a primary winding and at least one secondary winding;

c) a rectifying circuit for performing full-wave rectification on the output of said transformer; and

d) a smoothing circuit for smoothing the output of said rectifying circuit;

wherein

a) the end (cathode) of said first switching section on the cathode side of said diode and the cathode of said third switching section are connected to a high potential terminal of a substantially constant DC voltage source;

b) the cathode of said second switching section is connected to the end (anode) of said first switching section on the anode side of said diode, while the anode of said second switching section is connected to a low potential terminal of said substantially constant DC voltage source;

c) the cathode of said fourth switching section is connected to the anode of said third switching section, while the anode of said fourth switching section is connected to said low potential terminal of said substantially constant DC voltage source; and

d) one end of said primary winding of said transformer is connected to the junction point between said first switching section and said second switching section, while the other end of said primary winding is connected to the junction point between said third switching section and said fourth switching section;

B) a switching control section for outputting said switching signals to said switching devices at a predetermined switching frequency;

C) a load current sensing section for sensing the amount of load current output from said DC-DC converter; and

D) a delay section for delaying said switching signals of said switching control section for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

2. A switching power supply of claim 1, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

3. A switching power supply of claim 1, wherein said delay time is substantially ¼

of the resonance period determined by the self-inductance of said primary winding of said transformer.

4. A switching power supply of claim 3, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

5. A switching power supply of claim 4, wherein said load current sensing section senses said amount of load current from a current flowing through at least one of said switching sections.

6. A switching power supply of claim 4, wherein said load current sensing section senses said amount of load current from a current flowing through said primary winding.

7. A switching power supply of claim 4, wherein said load current sensing section senses said amount of load current from the input current of said DC-DC converter.

8. A switching power supply of claim 4, wherein said load current sensing section senses said amount of load current from the output current of said DC-DC converter.

9. A switching power supply comprising:

A) a DC-DC converter comprising;

a) four switching sections consisting of a first switching section, a second switching section, a third switching section, and a fourth switching section, each comprising

     1) a switching device turned ON and OFF by switching signals from the outside, and

     2) a diode and a capacitor each connected to said switching device in parallel;

b) a first voltage dividing capacitor and a second voltage dividing capacitor interconnected in series;

c) a transformer comprising a primary winding and at least one secondary winding;

d) a rectifying circuit for performing full-wave rectification on the output of said transformer; and

e) a smoothing circuit for smoothing the output of said rectifying circuit;

wherein

a) the opposite end of said first voltage dividing capacitor to the end thereof connected to said second voltage dividing capacitor is connected to a high potential terminal of a substantially constant DC voltage source;

b) the opposite end of said second voltage dividing capacitor to the end thereof connected to said first voltage dividing capacitor is connected to a low potential terminal of said substantially constant DC voltage source;

c) the cathode of said first switching section is connected to said high potential terminal of said substantially constant DC voltage source;

d) the cathode of said second switching section is connected to the anode of said first switching section, while the anode of said second switching section is connected to said low potential terminal of said substantially constant DC voltage source;

e) either the anodes or the cathodes of said third switching section and said fourth switching section are interconnected, while the opposite ends of said third switching section and said fourth switching section to the junction point thereof are connected to the respective ends of said primary winding of said transformer; and

f) one end of said primary winding is connected to the junction point between said first switching section and said second switching section, while the other end of said primary winding is connected to the junction point between said first voltage dividing capacitor and said second voltage dividing capacitor;

B) a switching control section for outputting said switching signals to said switching devices at a predetermined switching frequency;

C) a load current sensing section for sensing the amount of load current output from said DC-DC converter; and

D) a delay section for delaying said switching signals of said switching control section for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

10. A switching power supply of claim 9, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

11. A switching power supply of claim 9, wherein said delay time is substantially ¼

of the resonance period determined by the self-inductance of said primary winding of said transformer.

12. A switching power supply of claim 11, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

13. A switching power supply comprising:

A) a DC-DC converter comprising;

a) four switching sections consisting of a first switching section, a second switching section, a third switching section, and a fourth switching section, each comprising

     1) a switching device turned ON and OFF by switching signals from the outside, and

     2) a diode and a capacitor each connected to said switching device in parallel;

b) a first voltage dividing capacitor and a second voltage dividing capacitor interconnected in series;

c) a transformer comprising a primary winding, at least one secondary winding, and an auxiliary winding;

d) a rectifying circuit for performing full-wave rectification on the output of said transformer; and

e) a smoothing circuit for smoothing the output of said rectifying circuit;

wherein

a) the opposite end of said first voltage dividing capacitor to the end thereof connected to said second voltage dividing capacitor is connected to a high potential terminal of a substantially constant DC voltage source;

b) the opposite end of said second voltage dividing capacitor to the end thereof connected to said first voltage dividing capacitor is connected to a low potential terminal of said substantially constant DC voltage source;

c) the cathode of said first switching section is connected to said high potential terminal of said substantially constant DC voltage source;

d) the cathode of said second switching section is connected to the anode of said first switching section, while the anode of said second switching section is connected to said low potential terminal of said substantially constant DC voltage source;

e) either the anodes or the cathodes of said third switching section and said fourth switching section are interconnected, the junction point thereof is connected to said low potential terminal of said substantially constant DC voltage source, and the opposite ends of said third switching section and said fourth switching section to said junction point thereof are connected to the respective ends of said auxiliary winding; and

f) one end of said primary winding is connected to the junction point between said first switching section and said second switching section, while the other end of said primary winding is connected to the junction point between said first voltage dividing capacitor and said second voltage dividing capacitor;

B) a switching control section for outputting said switching signals to said switching devices at a predetermined switching frequency;

C) a load current sensing section for sensing the amount of load current output from said DC-DC converter; and

D) a delay section for delaying said switching signals of said switching control section for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

14. A switching power supply of claim 13, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

15. A switching power supply of claim 13, wherein said delay time is substantially ¼

of the resonance period determined by the self-inductance of said primary winding of said transformer.

16. A switching power supply of claim 15, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

17. A switching power supply comprising:

A) a DC-DC converter comprising;

a) four switching sections consisting of a first switching section, a second switching section, a third switching section, and a fourth switching section, each comprising

     1) a switching device turned ON and OFF by switching signals from the outside, and

     2) a diode and a capacitor each connected to said switching device in parallel;

b) a transformer comprising a first primary winding and a second primary winding interconnected in series, and at least one secondary winding;

c) a rectifying circuit for performing full-wave rectification on the output of said transformer; and

d) a smoothing circuit for smoothing the output of said rectifying circuit;

wherein

a) the junction point between said first primary winding and said second primary winding is connected to a first potential terminal of a substantially constant DC voltage source;

b) one end of said first switching section is connected to a second potential terminal of said substantially constant DC voltage source, while the other end of said first switching section is connected to the opposite end of said first primary winding to the end thereof connected to said second primary winding;

c) the end of said second switching section on the same side as the connected end of said first switching section to said second potential terminal of said substantially constant DC voltage source is connected to said second potential terminal of said substantially constant DC voltage source, while the other end of said second switching section is connected to the opposite end of said second primary winding to the end thereof connected to said first primary winding; and

d) either the anodes or the cathodes of said third switching section and said fourth switching section are interconnected, and the opposite ends of said third switching section and said fourth switching section to the junction point thereof are connected to the respective ends of said first primary winding and said second primary winding opposite to the junction point thereof;

B) a switching control section for outputting said switching signals to said switching devices at a predetermined switching frequency;

C) a load current sensing section for sensing the amount of load current output from said DC-DC converter; and

D) a delay section for delaying said switching signals of said switching control section for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

18. A switching power supply of claim 17, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

19. A switching power supply of claim 17, wherein said delay time is substantially ¼

of the resonance period determined by the self-inductance of said first primary winding and the self-inductance of said second primary winding.

20. A switching power supply of claim 19, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

21. A switching power supply comprising:

A) a DC-DC converter comprising;

a) four switching sections consisting of a first switching section, a second switching section, a third switching section, and a fourth switching section, each comprising

     1) a switching device turned ON and OFF by switching signals from the outside, and

     2) a diode and a capacitor each connected to said switching device in parallel;

b) a transformer comprising a first primary winding and a second primary winding interconnected in series, at least one secondary winding, and an auxiliary winding;

c) a rectifying circuit for performing full-wave rectification on the output of said transformer; and

d) a smoothing circuit for smoothing the output of said rectifying circuit;

wherein

a) the junction point between said first primary winding and said second primary winding is connected to a first potential terminal of a substantially constant DC voltage source;

b) one end of said first switching section is connected to a second potential terminal of said substantially constant DC voltage source, while the other end of said first switching section is connected to the opposite end of said first primary winding to the end thereof connected to said second primary winding;

c) the end of said second switching section on the same side as the connected end of said first switching section to said second potential terminal of said substantially constant DC voltage source is connected to said second potential terminal of said substantially constant DC voltage source, while the other end of said second switching section is connected to the opposite end of said second primary winding to the end thereof connected to said first primary winding; and

d) either the anodes or the cathodes of said third switching section and said fourth switching section are interconnected, the junction point thereof is connected to said second potential terminal of said substantially constant DC voltage source, and the opposite ends of said third switching section and said fourth switching section to said junction point thereof are connected to the respective ends of said auxiliary winding;

B) a switching control section for outputting said switching signals to said switching devices at a predetermined switching frequency;

C) a load current sensing section for sensing the amount of load current output from said DC-DC converter; and

D) a delay section for delaying said switching signals of said switching control section for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

22. A switching power supply of claim 21, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.

23. A switching power supply of claim 21, wherein said delay time is substantially ¼

of the resonance period determined by the self-inductance of said first primary winding and the self-inductance of said second primary winding.

24. A switching power supply of claim 23, wherein

said delay section delays said switching signals for turning ON said switching devices when said amount of load current sensed by said load current sensing section reduces substantially below a predetermined threshold value.