Control circuit and method for maintaining high efficiency over broad current ranges in a switching regulator circuit
DC CAFCFirst Claim
1. A circuit for controlling a switching voltage regulator, the regulator having (1) a switch circuit coupled to receive an input voltage and including a pair of synchronously switched switching transistors and (2) an output circuit including an output terminal and an output capacitor coupled thereto for supplying current at a regulated voltage to a load, the control circuit comprising:
- a first circuit for monitoring a signal from the output terminal to generate a first feedback signal;
a second circuit for generating a first control signal during a first state of circuit operation, the first control signal being responsive to the first feedback signal to vary the duty cycle of the switching transistors to maintain the output terminal at the regulated voltage; and
a third circuit for generating a second control signal during a second state of circuit operation to cause both switching transistors to be simultaneously OFF for a period of time if a sensed condition of the regulator indicates that the current supplied to the load falls below a threshold fraction of maximum rated output current for the regulator, whereby operating efficiency of the regulator at low output current levels is improved.
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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.
529 Citations
57 Claims
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1. A circuit for controlling a switching voltage regulator, the regulator having (1) a switch circuit coupled to receive an input voltage and including a pair of synchronously switched switching transistors and (2) an output circuit including an output terminal and an output capacitor coupled thereto for supplying current at a regulated voltage to a load, the control circuit comprising:
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a first circuit for monitoring a signal from the output terminal to generate a first feedback signal; a second circuit for generating a first control signal during a first state of circuit operation, the first control signal being responsive to the first feedback signal to vary the duty cycle of the switching transistors to maintain the output terminal at the regulated voltage; and a third circuit for generating a second control signal during a second state of circuit operation to cause both switching transistors to be simultaneously OFF for a period of time if a sensed condition of the regulator indicates that the current supplied to the load falls below a threshold fraction of maximum rated output current for the regulator, whereby operating efficiency of the regulator at low output current levels is improved. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 43)
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34. A circuit for controlling a switching voltage regulator, the regulator having (1) a switch circuit coupled to receive an input voltage and including a pair of synchronously switched switching transistors and (2) an output circuit including an output terminal and an output capacitor coupled thereto for supplying current at a regulated voltage to a load, the control circuit comprising:
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a first means for generating a voltage feedback signal indicative of the voltage at the output; a second means for generating a first control signal during a first state of circuit operation, the first control signal being responsive to the voltage feedback signal to vary the duty cycle of the switching transistors to maintain the output terminal at the regulated voltage; and a third means for generating a second control signal during a second state of circuit operation to cause both switching transistors to be simultaneously OFF for a period of time if a sensed condition of the regulator indicates that the current supplied to the load falls below a threshold fraction of maximum rated output current for the regulator, the period of time having a duration which is a function of the current supplied to the load by the regulator. - View Dependent Claims (35, 36, 37, 38, 39, 40)
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41. A method for controlling a switching voltage regulator, the regulator having (1) a switch circuit coupled to receive an input voltage and including a pair of synchronously switched switching transistors and (2) an output circuit including an output terminal and an output capacitor coupled thereto for supplying current at a regulated voltage to a load, the method comprising the steps of:
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(a) monitoring a signal from the output terminal to generate a first feedback signal; (b) varying the duty cycle of the switching transistors in response to the first feedback signal to maintain the output terminal at the regulated voltage during a first state of circuit operation; (c) turning both switching transistors simultaneously OFF for a period of time during a second state of circuit operation following the first state of circuit operation, so as to allow the output capacitor to maintain the output substantially at the regulated voltage by discharging during the second state of circuit operation, the period of time beginning when the current supplied to the load falls below a threshold fraction of maximum rated output current for the regulator, and having a duration which is a function of the current supplied to the load by the regulator; and (d) turning at least one of said switching transistors ON to recharge the output capacitor following the second state of circuit operation. - View Dependent Claims (42)
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44. A circuit for controlling a switching voltage regulator, the regulator having (1) a switch circuit coupled to receive an input voltage and including a pair of synchronously switched switching transistors and (2) an output circuit including an output terminal and an output inductor coupled thereto for supplying current at a regulated voltage to a load, the circuit comprising:
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a first circuit for monitoring a signal from the output terminal to generate a first feedback signal; a second circuit for generating a first control signal during a first state of circuit operation, the first control signal being responsive to the first feedback signal to vary the duty cycle of the switching transistors to maintain the output terminal at the regulated voltage; and a third circuit for monitoring the current to the output terminal to generate a second control signal during a second state of circuit operation when the monitored current compares in a predetermined manner to a threshold indicative of a polarity reversal condition in the output inductor, said second state causing one of said switching transistors to be maintained OFF, such that the switch circuit is prevented from coupling the output circuit to ground. - View Dependent Claims (45, 46, 47, 48, 49, 50)
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51. A method for controlling a switching voltage regulator, the regulator having (1) a switch circuit coupled to receive an input voltage and including a pair of synchronously switched switching transistors and (2) an output circuit including an output terminal and an output inductor coupled thereto for supplying current at a regulated voltage to a load, the method comprising the steps of:
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(a) monitoring a signal from the output terminal to generate a first feedback signal; (b) varying the duty cycle of the switching transistors in response to the first feedback signal to maintain the output terminal at the regulated voltage during a first state of circuit operation, wherein the current to the load has a polarity; and (c) maintaining one of said switching transistors OFF for a period of time following the first state of circuit operation to de-couple the output circuit from ground during the period of time so as to prevent the current to the load from reversing polarity. - View Dependent Claims (52, 53, 54)
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55. A circuit for controlling a switching voltage regulator, the regulator having (1) a switch circuit coupled to receive an input voltage and including a pair of synchronously switched switching transistors and (2) an output circuit including an output terminal and an output capacitor coupled thereto for supplying current at a regulated voltage to a load, the control circuit comprising:
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drive circuitry for the pair of synchronously switched switching transistor; feedback circuitry, coupled to the drive circuitry to control the duty cycle of the pair of synchronously switched switching transistors, the feedback circuitry forming a feedback path in the regulator between the output circuit and the drive circuitry by which feedback information indicative of the current supplied to the load by the regulator conditions the duty cycle of the pair of synchronously switched switching transistors; and logic circuitry, coupled to the feedback circuitry and the drive circuitry, which prevents the drive circuitry from turning on either of the pair of synchronously switched switching transistors if the feedback information indicates that the current supplied to the load by the regulator falls below selected sleep mode current level, wherein the synchronously switched switching transistors are prevented from being turned on for a period of time that is a function of the current supplied to the load by the regulator. - View Dependent Claims (56)
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57. An improved circuit for controlling a switching voltage regulator, the regulator having (1) a switch circuit coupled to receive an input voltage and including a pair of synchronously switched switching transistors and (2) an output circuit including an output terminal and an output capacitor coupled thereto for supplying current at a regulated voltage to a load, and wherein the control circuit varies the duty cycle of the switching transistors to maintain the output terminal at the regulated voltage, the improvement comprising:
circuitry incorporated in the control circuit for detecting a condition in the output circuit indicative of the current supplied to the load falling below a threshold fraction of maximum rated output current for the regulator and for turning off both switching transistors simultaneously for a period of time if the supplied current falls below the threshold, the period of time having a duration which is a function of the current supplied to the load by the regulator.
Specification