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US 10,256,735 B2Granted
Power supply with near valley switching
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
Estimating the term…
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.
Claims14
An electrical circuit comprising:
- a controller that is configured to detect a zero-crossing of a drain-source resonance voltage of a metal oxide field effect transistor (MOSFET) that is coupled to a primary winding of a transformer relative to an input voltage, to generate a signal indicating occurrence of a near valley window time period in response to detecting the zero-crossing of the drain-source resonance voltage of the MOSFET, and to turn on the MOSFET before or after a minimum value of the drain-source resonance voltage of the MOSFET within a range of time during the near valley window time period when a blanking period during which the MOSFET is prohibited from being turned on ends within the near valley window time period,
- wherein the controller comprises:
- a clamping circuit that is configured to clamp a sensed drain-source voltage of the MOSFET to generate a clamped voltage;
- a replica circuit that generates a replica of the clamped voltage within the controller;
- and
- a zero-crossing detection circuit that detects the zero-crossing of the drain-source resonance voltage of the MOSFET from the replica of the clamped voltage.
3 more elements
A method comprising:
- sensing a drain-source resonance voltage of a primary switch at resonance, the primary switch being at resonance when an inductance of a primary winding of a transformer to which the primary switch is coupled resonates with a capacitance when the primary switch is turned off;
- allowing the primary switch to be turned on within a range of time during a near valley window time period that occurs during a negative half cycle of the drain-source resonance voltage of the primary switch relative to an input voltage;
- and
- turning on the primary switch before or after a minimum value of the drain-source resonance voltage of the primary switch during the near valley window time period,
- wherein sensing the drain-source resonance voltage of the primary switch at resonance comprises:
- detecting an auxiliary voltage at an auxiliary winding of the transformer;
- clamping the auxiliary voltage to generate a clamped voltage;
- and
- detecting a zero-crossing of the drain-source resonance voltage of the primary switch from the clamped voltage.
6 more elements
A switched mode power supply comprising:
- a transformer having a primary winding and a secondary 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 primary switch to couple and decouple the primary winding to an input voltage, to detect a drain-source resonance voltage of the MOS transistor at resonance, to start a near valley window time period in response to zero-crossing of the drain-source resonance voltage, and to allow the MOS transistor to be turned on before or after a minimum value of the drain-source resonance voltage of the MOS transistor within a range of time during the near valley window time period,
- wherein the controller is an integrated circuit (IC) and comprises:
- a clamping circuit that is configured to clamp a sensed drain-source resonance voltage of the MOSFET to generate a clamped voltage;
- a replica circuit that generates a replica of the clamped voltage inside the controller;
- and
- a zero-crossing detection circuit that detects the zero-crossing of the drain-source resonance voltage of the MOS transistor from the replica of the clamped voltage.
6 more elements
Dependencies are inferred from the claim text.