Method and apparatus to switch operating modes in a PFM converter
First Claim
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1. A power converter comprising:
- a switching transistor;
a pulse frequency modulator configured to control the switching transistor, wherein the pulse frequency modulator is enabled during a burst period in which an output of the power converter is less than a predetermined level;
a peak current detector configured to sense current through the switching transistor and to output a peak current pulse to the pulse frequency modulator to turn off the switching transistor when the sensed current exceeds a peak reference level, wherein the peak reference level is substantially constant during a hysteretic mode and is variable during a continuous switching mode; and
a load sensor configured to monitor the output of the peak current detector to change operating modes for the power converter, wherein the power converter changes from the hysteretic mode to the continuous switching mode when the number of peak current pulses in the burst period exceeds a predetermined number.
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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.
105 Citations
10 Claims
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1. A power converter comprising:
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a switching transistor; a pulse frequency modulator configured to control the switching transistor, wherein the pulse frequency modulator is enabled during a burst period in which an output of the power converter is less than a predetermined level; a peak current detector configured to sense current through the switching transistor and to output a peak current pulse to the pulse frequency modulator to turn off the switching transistor when the sensed current exceeds a peak reference level, wherein the peak reference level is substantially constant during a hysteretic mode and is variable during a continuous switching mode; and a load sensor configured to monitor the output of the peak current detector to change operating modes for the power converter, wherein the power converter changes from the hysteretic mode to the continuous switching mode when the number of peak current pulses in the burst period exceeds a predetermined number. - View Dependent Claims (2, 3, 4)
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5. A method to convert operating modes in a switching regulator, 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 a switch occur in the burst period; providing an output from the pulse frequency modulator to turn on the switch in each switching cycle until the switch conducts a peak current followed by a switch off-time of a predetermined duration, wherein the pulse frequency modulator uses a substantially constant threshold to detect the peak current during a hysteretic mode and a variable threshold to detect the peak current during a continuous mode; and converting from the hysteretic mode to the continuous mode when the number of switching cycles in a burst period exceeds a predetermined value. - View Dependent Claims (6, 7, 8)
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9. A switching regulator using a dual-mode pulse frequency modulation technique comprising:
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means for sensing a transition from relatively light load current to relatively heavy load current by monitoring switching cycles of a switch; means for operating the switching regulator in a hysteretic mode during relatively light load current, wherein a pulse frequency modulator uses a first threshold to monitor current conducted by the switch during the hysteretic mode and the switch conducts a substantially fixed peak current during the hysteretic mode; and means for operating the switching regulator in a continuous switching mode during relatively heavy load current, wherein the pulse frequency modulator uses a second threshold to monitor current conducted by the switch during the continuous switching mode and the switch conducts a variable peak current during the continuous switching mode. - View Dependent Claims (10)
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Specification