Fixed frequency discontinuous conduction mode flyback power converters employing zero voltage switching
First Claim
1. A power supply system for supplying power to a load, the power supply system comprising:
- a flyback power converter including an input for receiving an input voltage, an output for supplying an output voltage, a transformer having a plurality of windings coupled between the input and the output, a first power switch coupled to the transformer, and a clamping circuit having a capacitor, a diode, and a second power switch coupled to one of the plurality of windings, the capacitor and the diode of the clamping circuit coupled in parallel between said one of the plurality of windings and the second power switch; and
a control circuit coupled to the flyback power converter, the control circuit configured to operate the flyback power converter in a discontinuous conduction mode and control the first power switch and the second power switch at a fixed frequency to allow an effective capacitance across the first power switch to discharge to said one of the plurality of windings to cause a voltage across the first power switch to decrease to substantially zero to achieve substantially zero voltage switching during turn on of the first power switch.
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Accused Products
Abstract
A power supply system includes a flyback power converter and a control circuit coupled to the flyback power converter. The power converter includes an input, an output, a transformer having a plurality of windings coupled between the input and the output, a first power switch coupled to the transformer and a clamping circuit having a capacitor, a diode, and a second power switch coupled to one of the plurality of windings. The capacitor and the diode are coupled in parallel between the winding and the second power switch. The control circuit is configured to operate the power converter in a discontinuous conduction mode and control the first power switch and the second power switch at a fixed frequency to achieve substantially zero voltage switching during turn on of the first power switch. Various other example power supply systems, power converters, and methods for controlling a power converter are also disclosed.
25 Citations
15 Claims
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1. A power supply system for supplying power to a load, the power supply system comprising:
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a flyback power converter including an input for receiving an input voltage, an output for supplying an output voltage, a transformer having a plurality of windings coupled between the input and the output, a first power switch coupled to the transformer, and a clamping circuit having a capacitor, a diode, and a second power switch coupled to one of the plurality of windings, the capacitor and the diode of the clamping circuit coupled in parallel between said one of the plurality of windings and the second power switch; and a control circuit coupled to the flyback power converter, the control circuit configured to operate the flyback power converter in a discontinuous conduction mode and control the first power switch and the second power switch at a fixed frequency to allow an effective capacitance across the first power switch to discharge to said one of the plurality of windings to cause a voltage across the first power switch to decrease to substantially zero to achieve substantially zero voltage switching during turn on of the first power switch. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for controlling a flyback power converter to operate in a discontinuous conduction mode, the flyback power converter including a transformer having a plurality of windings, a first power switch coupled to the transformer, a capacitor, a diode, and a second power switch coupled to one of the plurality of windings, the capacitor and the diode coupled in parallel between said one of the plurality of windings and the second power switch, the first power switch and the second power switch switched at a fixed frequency to achieve substantially zero voltage switching during turn on of the first power switch, the method comprising:
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discharging at least a portion of a voltage of the capacitor to said one of the plurality of windings; in response to discharging the capacitor, clamping a voltage of said one of the plurality of windings such that current circulates through the diode and the second power switch to prevent the capacitor from being charged; and switching the second power switch off to drain the voltage of said one of the plurality of windings to an input of the flyback power converter thereby causing a voltage across the first power switch to be substantially zero. - View Dependent Claims (12, 13, 14, 15)
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Specification