Switching power supply with delay circuit for light-load period

• US 6,452,816 B2
• Filed: 05/29/2001
• Issued: 09/17/2002
• Est. Priority Date: 06/01/2000
• Status: Expired due to Term

• 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
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US09/867,038
• Publication Number:
  US 20020001210A1
• Time in Patent Office: 476 Days
• Field of Search: 363/17, 363/25, 363/26, 363/97, 363/98
• US Class Current: 363/17
• 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) a full bridge inverter including first and second series pairs of switching sections, each switching section having

     1) a switching device turned ON and OFF by switching signals, 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, said primary winding connected between the junction point of said first series pair of switching sections and the junction point of said second series pair of switching sections;

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;

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 for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

2. The 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. The switching power supply of claim 1, wherein said predetermined delay time is substantially ¼

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

4. The 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. The 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. The 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 of said transformer.

7. The 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. The 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) a half bridge inverter including first and second series pairs of switching sections and a series of two voltage dividing capacitors, each switching section having

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

     2) a diode and a capacitor each connected to said switching device in parallel, said second series pair of switching sections connected between the junction point of said first series pair of switching sections and the junction point of said series of voltage dividing capacitors;

b) a transformer comprising a primary winding and at least one secondary winding, said primary winding connected between the junction point of said first series pair of switching sections and the junction point of said series of voltage dividing capacitors;

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;

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 for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

10. The 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. The switching power supply of claim 9, wherein said predetermined delay time is substantially ¼

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

12. The 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) first and second series pairs of switching sections, each switching section having

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

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

b) two voltage dividing capacitors 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

said first series pair of switching sections and said voltage dividing capacitors constitute a half bridge inverter,

said primary winding of said transformer is connected between the junction point of said first series pair of switching sections and the junction point of said voltage dividing capacitors, and

said second series pair of the switching sections are connected in parallel to said auxiliary winding of said transformer;

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 for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

14. The 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. The switching power supply of claim 13, wherein said predetermined delay time is substantially ¼

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

16. The 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) a push-pull inverter including first, second, third, and fourth switching sections, each switching section having

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

     2) a diode and a capacitor each connected to said switching device in parallel, wherein said third and fourth switching sections are interconnected in series, and the series of said third and fourth switching sections is connected between the same polarity terminals of said first and second switching sections;

b) a transformer comprising two primary windings interconnected in series, and at least one secondary winding, the series of said primary windings connected in parallel to said series of the third and fourth switching sections;

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;

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 for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

18. The 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. The switching power supply of claim 17, wherein said predetermined delay time is substantially ¼

of the resonance period determined by the self-inductances of said primary windings.

20. The 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) first, second, third, and fourth switching sections, each switching section having

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

     2) a diode and a capacitor each connected to said switching device in parallel, said first and second switching sections constituting a push-pull inverter, said third and fourth switching sections being interconnected in series;

b) a transformer comprising two primary windings interconnected in series, at least one secondary winding, and an auxiliary winding, wherein the series of said primary windings is connected between the same polarity terminals of said first and second switching sections, and said auxiliary winding is connected in parallel to said series of the third and fourth switching sections;

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;

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 for a predetermined delay time depending on said amount of load current sensed by said load current sensing section.

22. The 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. The switching power supply of claim 21, wherein said predetermined delay time is substantially ¼

of the resonance period determined by the self-inductances of said two primary windings.

24. The 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.