Soft-switching power converter having power saving circuit for light load operations

• US 7,286,376 B2
• Filed: 11/23/2005
• Issued: 10/23/2007
• Est. Priority Date: 11/23/2005
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: System General Corporation (ON Semiconductor Corporation)
• Inventors: Yang, Ta-yung
• Primary Examiner(s): Laxton; Gary L
• Application Number:
  US11/285,964
• Publication Number:
  US 20070115699A1
• Time in Patent Office: 699 Days
• Field of Search: 363/16, 363/20, 363/21.01, 363/21.02, 363/21.03, 363/21.04, 363/21.07, 363/21.1, 363/21.11, 363/21.12, 363/21.15, 363/21.18, 363/97
• US Class Current: 363/97
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence

Abstract

A soft switching power converter includes a first switch for switching a transformer to transfer energy. A second switch is equipped to switch energy in a capacitor to the transformer to achieve soft switching for the next switching cycle. A control circuit is coupled to an output of the power converter for generating a first signal and a second signal in response to a feedback signal for regulating the output of the power converter. A first delay time is generated after the first switch is turned off and before the second signal is on. A second delay time is generated after the second switch is turned off and before the first signal is on. The second delay time is increased corresponding to a decrement of the feedback signal under light load conditions.

Claims

1. A soft switching power converter, comprising:

a transformer;

a capacitor, coupled to said transformer for soft switching operation;

a first switch, coupled for switching said transformer to transfer energy from an input of said power converter to an output of said power converter;

a second switch, coupled for switching energy in said capacitor to said transformer; and

a control circuit, coupled to said output of said power converter for generating a first signal and a second signal in response to a feedback signal for regulating an output of said power converter, wherein said first signal and said second signal are coupled for switching said first switch and said second switch, respectively;

wherein an on-time of said second signal increases in response to a decrement of said on-time of said first signal in a first range of said feedback signal, a first delay time is generated after said first switch is turned off and before said second signal is enabled, a second delay time is generated after said second switch is turned off and before said first signal is enabled, wherein said second delay time is constant corresponding to said first range of said feedback signal, said second delay time is varied with respect to a second range of said feedback signal, and said second delay time is increased proportionally to a decrement of said feedback signal.

2. The soft switching power convener as claimed in claim 1, wherein said control circuit further comprises an input terminal for programming said second delay time in said first range of said feedback signal.

3. The soft switching power converter as claimed in claim 2, wherein a resistor is connected from said input terminal of said control circuit to a ground reference for programming said second delay time.

4. The soft switching power converter as claimed in claim 1, wherein said control circuit further comprises a threshold to define said first range of said feedback signal or said second range of said feedback signal.

5. The soft switching power converter as claimed in claim 4, wherein said control circuit further comprises a programming terminal for programming said threshold.

6. The soft switching power converter as claimed in claim 5, wherein a resistor is connected from said programming terminal of said control circuit to a ground reference for programming said threshold.

7. A soft switching power supply, comprising:

a transformer;

a capacitor, coupled to said transformer for soft switching operation;

a first switch, coupled for switching said transformer to transfer energy from an input of said power supply to an output of said power supply;

a second switch, coupled to switch energy of said capacitor to said transformer; and

a controller, coupled to said output of said power supply to generate a first signal and a second signal in response to a feedback signal for regulating said output of said power supply, wherein said first signal and said second signal switch said first switch and said second switch, respectively;

wherein a first delay time is generated after said first switch is turned off and before said second signal is enabled, a second delay time is generated after said second switch is turned off and before said first signal is enabled, wherein said controller further comprises an input terminal for programing said second delay time in a first range of said feedback signal, wherein a resistor is connected from said input terminal of said controller to a around reference for programming said second delay time, said second delay time being varied corresponding to a second range of the feedback signal, wherein said second delay time is increased proportionally to a decrement of said feedback signal.

8. The soft switching power supply as claimed in claim 7, wherein said controller further comprises a threshold for defining said first range of said feedback signal or said second range of said feedback signal.

9. The soft switching power converter as claimed in claim 8, wherein said controller further comprises a programming terminal for programming said threshold.

10. A soft switching regulator, comprising:

a magnetic device;

a capacitor, coupled to said magnetic device for soft switching operation;

a first switch, coupled for switching said magnetic device to transfer energy from an input of said regulator to an output of said regulator;

a second switch, coupled to switch energy of said capacitor to said magnetic device; and

a circuit, coupled to said output of said regulator for generating a first signal and a second signal for switching said first switch and said second switch, respectively, wherein said first signal includes a duty cycle for regulating said output of said regulator;

wherein a first delay time is generated after said first switch is turned off and before said second signal is enabled, a second delay time is generated after said second switch is turned off and before said first signal is enabled, wherein said circuit further comprises an input terminal for programming said second delay time in a first range of said duty cycle, said second delay time being varied with respect to a second range of said duty cycle, wherein said second delay time is increased proportionally to the decrement of said duty cycle, wherein said circuit further comprises a threshold for defining said first range of said duty cycle or said second range of said duty cycle, said circuit further comprising a programming terminal for programming said threshold.