Dual-mode PFM boost converter
First Claim
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1. A dual-mode pulse frequency modulation boost converter comprising:
- a power conversion circuit that receives an input voltage at a first level and that generates an output voltage at a second level, wherein the power conversion circuit includes a switching transistor to generate the output voltage;
a pulse frequency modulator configured to control the switching transistor;
an inner control loop configured to sense a switching current flowing through the switching transistor and to generate a first feedback signal to the pulse frequency modulator to turn the switching transistor off for a predefined duration when the switching current reaches a predetermined level, wherein the predetermined level is substantially constant in a first mode and is controlled by an output voltage feedback signal in a second mode; and
an outer control loop configured to sense a load current, wherein the output control loop turns the pulse frequency modulator off when the load current is greater than a reference level during the first mode and forces the pulse frequency modulator to stay on during the second mode.
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Abstract
A dual-mode pulse frequency modulation boost converter operates in a hysteretic mode during light load currents to regulate an output voltage using a substantially fixed peak switching current and operates in a continuous mode during heavy load currents to regulate the output voltage using a variable peak switching current. The boost converter senses load power to automatically switch between the hysteretic mode and the continuous mode.
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Citations
24 Claims
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1. A dual-mode pulse frequency modulation boost converter comprising:
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a power conversion circuit that receives an input voltage at a first level and that generates an output voltage at a second level, wherein the power conversion circuit includes a switching transistor to generate the output voltage; a pulse frequency modulator configured to control the switching transistor; an inner control loop configured to sense a switching current flowing through the switching transistor and to generate a first feedback signal to the pulse frequency modulator to turn the switching transistor off for a predefined duration when the switching current reaches a predetermined level, wherein the predetermined level is substantially constant in a first mode and is controlled by an output voltage feedback signal in a second mode; and an outer control loop configured to sense a load current, wherein the output control loop turns the pulse frequency modulator off when the load current is greater than a reference level during the first mode and forces the pulse frequency modulator to stay on during the second mode.
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2. A dual-mode switching regulator comprising:
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a switch; a pulse frequency modulator that controls switching cycles of the switch; and a first feedback loop that detects when the switch conducts a current above a selected threshold during each switching cycle and outputs a peak-current detection signal to the pulse frequency modulator in response to turn off the switch for a predefined duration, wherein the selected threshold is a substantially fixed threshold in a first mode and a variable threshold in a second mode. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A switching converter comprising:
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a semiconductor switch; a pulse frequency modulation controller configured to turn the semiconductor switch on and off; a peak current detector configured to sense current flowing through the semiconductor switch and to output a peak current pulse to the pulse frequency modulation controller when the sensed current is above a reference peak level, wherein the pulse frequency modulation controller turns off the semiconductor switch for a predetermined duration in response to the peak current pulse; a feedback voltage detector configured to sense an output voltage of the switching converter and to output a control signal to the pulse frequency modulation controller, wherein the control signal is in an active phase and turns on the pulse frequency modulation controller when the sensed output voltage is less than a first predefined voltage, and wherein the control signal is in an inactive phase and turns off the pulse frequency modulation controller when the sensed output voltage is greater than a second predefined voltage; and a load sensor configured to detect load current and to output a override control signal to force the pulse frequency modulation controller to remain on when the load current is greater than a predetermined level, wherein the reference peak level of the peak current detector is a variable peak level that varies with the sensed output voltage when the override control signal is active. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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19. A method for improving efficiency of a switching regulator that uses pulse frequency modulation to control a switch, the method comprising the steps of:
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turning on a pulse frequency modulator for a burst period when an output of the switching regulator is less than a first level, wherein one or more switching cycles for the switch occur in the burst period; turning on the switch in each switching cycle until the switch conducts a peak current followed by a switch off-time of a predetermined duration; operating the switching regulator in a hysteretic mode for a first range of load currents, wherein the peak current for the switch is substantially fixed and the pulse frequency modulator turns off when the output of the switching regulator is greater than a second level; and operating the switching regulator in a continuous mode for a second range of load currents, wherein the peak current for the switch varies according to a feedback signal indicative of an output of the switching regulator and the pulse frequency modulator is forced on to extend the burst period until the variable peak current is less than a predefined level. - View Dependent Claims (20, 21, 22)
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23. A switching regulator using a dual-mode pulse frequency modulation technique comprising:
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means for operating in a hysteretic mode, wherein regulation of an output of the switching regulator is performed using a pulse frequency modulator to operate a switch with a substantially fixed peak switching current; and means for operating in a continuous mode, wherein regulation of the output of the switching regulator is performed using the pulse frequency modulator to operate the switch with a variable peak switching current. - View Dependent Claims (24)
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Specification