Control circuit and method for maintaining high efficiency over broad current ranges in a switching regulator circuit

• US 5,994,885 A
• Filed: 11/25/1997
• Issued: 11/30/1999
• Est. Priority Date: 03/23/1993
• Status: Expired due to Term

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Flatness, Randy G., Wilcox, Milton E.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Patel, Rajnikant B.
• Application Number:
  US08/978,167
• Time in Patent Office: 735 Days
• Field of Search: 323/285, 323/283, 323/224, 323/290, 323/287, 323/284, 323/268, 323/275
• US Class Current: 323/285
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• 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 circuit and method for controlling a switching voltage regulator having (1) a switch including one or more switching transistors and (2) an output adapted to supply current at a regulated voltage to a load including an output capacitor. The circuit and method generates a control signal to turn said one or more switching transistors OFF under operating conditions when the voltage at the output is capable of being maintained substantially at the regulated voltage by the charge on the output capacitor. Such a circuit and method increases the efficiency of the regulator circuit particularly at low average current levels.

Claims

1. A circuit for controlling a switching voltage regulator having a switch and an output adapted to supply current at a regulated voltage to a load including an output capacitor, the switch coupled between an input voltage and an output voltage and including one or more switching transistors, the circuit comprising:

a first circuit for monitoring an output to generate a first feedback signal;

a second circuit for generating a first control signal during a first state of circuit operation, the second circuit including a one-shot circuit that generates the first control signal to switch the one or more switching transistors "on" or "off" over a first period of time to maintain the output at the regulated voltage, the one-shot circuit being triggered responsive to the first feedback signal, the first period of time being responsive to at least one of the input voltage and the output voltage.

2. The circuit of claim 1, wherein the first period of time is responsive to the input voltage.

3. The circuit of claim 2, wherein:

the switch is coupled to an inductor;

the first period of time is decreased in response to a decrease in the input voltage; and

an oscillation frequency of the ripple current through the inductor is increased from an audible frequency to one that does not generate substantial user audible noise.

4. The circuit of claim 1, wherein the first period of time is responsive to the output voltage.

5. The circuit of claim 4, wherein:

the switch is coupled to an inductor;

the first period of time is increased in response to a decrease in the output voltage; and

the total decrease in current through the inductor is increased while the first control signal is generated.

6. The circuit of claim 1, wherein the circuit includes a capacitor coupled to the one-shot circuit and a variable current source for controlling the discharging rate of the capacitor, the discharging rate being responsive to at least one of the input voltage and the output voltage to control the first period of time.

7. The circuit of claim 6, wherein the first period of time is responsive to the input voltage.

8. The circuit of claim 7, wherein:

the switch is coupled to an inductor;

the first period of time is decreased in response to a decrease in the input voltage; and

an oscillation frequency of the ripple current through the inductor is increased from an audible frequency to one that does not generate substantial user audible noise.

9. The circuit of claim 6, wherein the first period of time is responsive to the output voltage.

10. The circuit of claim 9, wherein:

the switch is coupled to an inductor;

the first period of time is increased in response to a decrease in the output voltage; and

the total decrease in current through the inductor is increased while the first control signal is generated.

11. A switching voltage regulator that generates an output at an output node from an input at an input node, the output node coupled to an output capacitor, the regulator comprising:

a switching transistor having a first terminal coupled to the input node, a second terminal, and a third terminal;

a driver circuit having a first terminal, and a second terminal coupled to the second terminal of the switching transistor;

an inductor having a first terminal coupled to the third terminal of the switching transistor, and a second terminal coupled to the output node;

a feedback circuit having a first terminal coupled to the output node, and a second terminal, the feedback circuit producing a feedback signal at the second terminal of the feedback circuit;

a feedback control circuit having a first terminal coupled to the second terminal of the feedback circuit, and a second terminal, the feedback control circuit producing a trigger signal at the second terminal of the feedback control circuit, said trigger signal being produced responsive to the feedback signal;

an off-time control circuit having a first terminal and a second terminal, the off-time control circuit producing an off-time control signal at the first terminal of the off-time control circuit, the second terminal of the off-time control circuit being coupled to one of the input node or the output node;

a one-shot generator having a first terminal coupled to the second terminal of the feedback control circuit, a second terminal coupled to the first terminal of the off-time control circuit, and a third terminal coupled to the first terminal of the driver circuit, the one-shot generator generating a switch signal on the third terminal to cause the driver to place the switching transistor in an off state starting upon receipt of the trigger signal, and continuing for a first period of time determined by the off-time control signal.

12. The regulator of claim 11, wherein the feedback circuit produces a voltage feedback signal at the second terminal of the feedback circuit.

13. The regulator of claim 11, wherein the feedback circuit produces a current feedback signal at the second terminal of the feedback circuit.

14. The regulator of claim 13, wherein the regulator further comprises a voltage feedback circuit having a first terminal coupled to the output node, and a second terminal, the voltage feedback circuit producing a voltage feedback signal at the second terminal of the voltage feedback circuit, and wherein the feedback control circuit has a third terminal coupled to the second terminal of the voltage feedback circuit, and the trigger signal is produced responsive to the current feedback signal and the voltage feedback signal.

15. The regulator of claim 11, wherein the second terminal of the off-time control circuit is coupled to the input node, and the off-time control signal is generated responsive to a voltage at the input node to vary the first period of time.

16. The regulator of claim 15, wherein the off-time control circuit produces an off-time control signal that decreases the first period of time in response to a decrease in the voltage at the input node, whereby an oscillation frequency of the ripple current through the inductor is increased from an audible frequency to a substantially inaudible frequency.

17. The regulator of claim 11, wherein the second terminal of the off-time control circuit is coupled to the output node, and the off-time control signal is generated responsive to a voltage at the output node to vary the first period of time.

18. The regulator of claim 17, wherein the off-time control circuit produces an off-time control signal that increases the first period of time in response to a decrease in the voltage at the output.

19. The regulator of claim 11, wherein the second terminal of the off-time control circuit is coupled to the input node and the off-time control circuit further comprises a third terminal coupled to the output node, and the off-time control signal is generated responsive to a voltage at the input node and a voltage at the output node to vary the first period of time.

20. The regulator of claim 11, wherein the one-shot generator includes a control capacitor coupled between the second terminal of the one-shot generator and ground, and the off time control circuit comprises a variable current source that controls the discharging rate of the control capacitor.

21. The regulator of claim 20, wherein the second terminal of the off-time control circuit is coupled to the input node, and the variable current source controls the discharging rate of the control capacitor responsive to a voltage at the input node to vary the first period of time.

22. The regulator of claim 21, wherein the variable current source controls the discharging rate of the control capacitor to decrease the first period of time in response to a decrease in the voltage at the input node, whereby an oscillation frequency of the ripple current through the inductor is increased from an audible frequency to a substantially inaudible frequency.

23. The regulator of claim 20, wherein the second terminal of the off-time control circuit is coupled to the output node, and the variable current source controls the discharging rate of the control capacitor responsive to a voltage at the output node to vary the first period of time.

24. The regulator of claim 23, wherein the variable current source controls the discharging rate of the control capacitor to increase the first period of time in response to a decrease in the voltage at the output node.

25. The regulator of claim 20, wherein the second terminal of the off-time control circuit is coupled to the input node and the off-time control circuit further comprises a third terminal coupled to the output node, and the variable current source controls the discharging rate of the control capacitor responsive to a voltage at the input node and a voltage at the output node to vary the first period of time.

26. The regulator of claim 25, wherein the off-time control circuit comprises a control circuit that produces a control current to control the variable current source responsive to a voltage at the input node and a voltage at the output node to vary the first period of time.

27. The regulator of claim 26, wherein the control circuit comprises:

a first current source, providing a first current;

a second current source, providing a second current;

a current compensation circuit; and

a current mirror output circuit that outputs the control current.

28. The regulator of claim 27, wherein the current mirror output circuit produces a current proportional to the first current, or to the sum of the first current and the second current, depending on the voltage at the input node and the voltage at the output node.

29. The regulator of claim 27, wherein the second current source causes the second current to be zero when a difference between the voltage at the input node and a voltage at the output node is greater than a predetermined value.

30. The regulator of claim 29, wherein the second current increases responsive to a decrease in the voltage at the input node when the difference between the voltage at the input node and the voltage at the output node is less than the predetermined value.

31. The regulator of claim 27, wherein the current compensation circuit adjusts the control current to compensate for changes in temperature.

33. The circuit of claim 31, wherein the means for generating the off-time control signal causes the period of time to decreases in response to a decrease in the input voltage.

34. The circuit of claim 31, wherein the means for generating the off-time control signal causes the period of time to increase in response to a decrease in the output voltage.

32. A circuit for controlling a switching voltage regulator having a switch and an output adapted to supply current at a regulated voltage to a load including an output capacitor, the switch coupled between an input voltage and an output voltage and including one or more switching transistors, the circuit comprising:

means for generating a current feedback signal;

means for generating a voltage feedback signal;

means for generating a trigger signal responsive to the current feedback signal and the voltage feedback signal;

means for generating an off-time control signal responsive to at least one of the input voltage and the output voltage; and

one-shot means for placing the switch into an off state responsive to the trigger signal, the switch remaining-in the off state for a period of time responsive to the off-time control signal.

35. A switching voltage regulator having an output node and an input node, the output node coupled to an output capacitor, the regulator comprising:

a switching transistor having a first terminal coupled to the input node, a second terminal, and a third terminal;

a driver circuit having a first terminal, and a second terminal coupled to the second terminal of the switching transistor;

an inductor having a first terminal coupled to the third terminal of the switching transistor, and a second terminal coupled to the output node;

a feedback circuit having a first terminal coupled to the output node, and a second terminal;

a feedback control circuit having a first terminal coupled to the second terminal of the feedback circuit, and a second terminal;

a one-shot generator having a first terminal coupled to the second terminal of the feedback control circuit, a second terminal, and a third terminal coupled to the first terminal of the driver circuit, the one-shot generator including a control capacitor coupled between the second terminal of the one-shot generator and ground;

an off-time control circuit having a first terminal coupled to the second terminal of the one-shot generator, and a second terminal coupled to one of the input node or the output node, the off-time control circuit including a variable current source that controls the discharging rate of the control capacitor.

36. The regulator of claim 35, wherein the feedback circuit comprises a voltage feedback circuit.

37. The regulator of claim 35, wherein the feedback circuit comprises a current feedback circuit.

38. The regulator of claim 37, wherein the regulator further comprises a voltage feedback circuit having a first terminal coupled to the output node, and a second terminal, and wherein the feedback control circuit has a third terminal coupled to the second terminal of the voltage feedback circuit.

39. The regulator of claim 35, wherein the off-time control circuit further comprises a second terminal coupled to the input node, and the off time control signal is generated responsive to a voltage at the input node to vary the first period of time.

40. The regulator of claim 35, wherein the second terminal of the off-time control circuit is coupled to the input node.

41. The regulator of claim 35, wherein the second terminal of the off-time control circuit is coupled to the output node.

42. The regulator of claim 35, wherein the second terminal of the off-time control circuit is coupled to the input node and the off-time control circuit further comprises a third terminal coupled to the output node.