Power supply with near valley switching in near valley window time period
AssigneeFairchild Semiconductor Corporation
InventorsZhibo Tao, Jung-Sheng Chen, Li Lin, Kai-Fang Wei, Chih-Hsien Hsieh, Hangseok Choi, Yue-Hong Tang
Life of this patent
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Abstract
A switched-mode power supply with near valley switching includes a quasi-resonant converter. The converter includes a switch element that is turned on not only at the valley, but also in a window range of ΔtNVW close to the valley, where the voltage across the switch element is at its minimum. This advantageously reduces switching loss and maintains a balance between efficiency and frequency variation.
Claims21
A controller for controlling a converter, the controller comprising:
- a zero-cross detection circuit configured to generate a zero-cross indicative signal indicating a zero-crossing of a drain-source resonance voltage of a transistor relative to an input voltage, the zero-cross indicative signal being asserted when the drain-source resonance voltage is less than the input voltage;
- a first pulse generating circuit configured to generate a near valley window (NVW) signal by asserting the NVW signal in response to the assertion of the zero-cross indicative signal and de-asserting the NVW signal a near valley window time period later;
- a second pulse generating circuit configured to generate a blanking signal by asserting the blanking signal in response to the transistor being turned on and de-asserting the blanking signal a blanking period later;
- and
- a gate control circuit configured to turn on the transistor in response to the blanking signal being de-asserted while the NVW signal is asserted.
A method for controlling a converter, the method comprising:
- generating a zero-cross indicative signal indicating a zero-crossing of a drain-source resonance voltage of a switch relative to an input voltage of the converter, the zero-cross indicative signal being asserted when the drain-source resonance voltage is less than the input voltage;
- determining a near valley window time period beginning at a time corresponding to the assertion of the zero-cross indicative signal;
- determining a blanking period beginning at a time corresponding to a turning on of the switch, and
- turning on the switch in response to the blanking period ending within the near valley window time period.
A switched mode power supply comprising:
- a primary winding;
- a metal oxide semiconductor (MOS) transistor that is coupled to the primary winding;
- and
- a controller that is configured to control a switching operation of the MOS transistor to couple and decouple the primary winding to an input voltage,
- wherein the controller comprises:
- a zero-cross detection circuit configured to generate a zero-cross indicative signal indicating a drain-source resonance voltage of the MOS transistor relative to the input voltage at resonance, the zero-cross indicative signal being asserted when the drain-source resonance voltage is less than the input voltage;
- a first pulse generating circuit configured to generate a near valley window (NVW) signal by asserting the NVW signal in response to the assertion of the zero-cross indicative signal and de-asserting the NVW signal a near valley window time period later;
- a second pulse generating circuit configured to generate a blanking signal by asserting the blanking signal in response to the transistor being turned on and de-asserting the blanking signal a blanking period later;
- and
- a gate control circuit configured to turn on the MOS transistor in response to the blanking signal being de-asserted while the NVW signal is asserted.
Dependencies are inferred from the claim text.