Control circuit and method for a flyback converter
First Claim
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1. A control circuit for a flyback converter including a transformer connected with a power switch switched by a control signal for the transformer to convert an input voltage into an output voltage, the control circuit comprising:
- a compensator compensating a feedback signal with a sawtooth wave to generate a compensated feedback signal, the feedback signal being a function of the output voltage; and
a pulse width modulation circuit connected to the compensator to generate the control signal according to the compensated feedback signal and a current sense signal, the current sense signal being a function of a current flowing through the power switch.
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Abstract
A control circuit and method are provided for a flyback converter converting an input voltage to an output voltage, to compensate for an entry point of a burst mode of the flyback converter, so that the entry point is not affected by the input voltage, and audible noise resulted from a higher input voltage is reduced without impacting the light load efficiency of the flyback converter.
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Citations
22 Claims
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1. A control circuit for a flyback converter including a transformer connected with a power switch switched by a control signal for the transformer to convert an input voltage into an output voltage, the control circuit comprising:
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a compensator compensating a feedback signal with a sawtooth wave to generate a compensated feedback signal, the feedback signal being a function of the output voltage; and a pulse width modulation circuit connected to the compensator to generate the control signal according to the compensated feedback signal and a current sense signal, the current sense signal being a function of a current flowing through the power switch. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A control method for a flyback converter including a transformer connected with a power switch switched by a control signal for the transformer to convert an input voltage into an output voltage, the control method comprising:
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detecting the output voltage to generate a feedback signal; detecting a current flowing through the power switch to generate a current sense signal; according to the feedback signal and a preset value, determining whether or not the flyback converter to enter a burst mode; compensating the feedback signal to generate a compensated feedback signal; and generating the control signal according to the compensated feedback signal and the current sense signal; wherein the feedback signal is compensated to prevent an entry point of the burst mode from being affected by the input voltage. - View Dependent Claims (9, 10, 11)
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12. A control circuit for a flyback converter including a transformer connected with a power switch switched by a control signal for the transformer to convert an input voltage into an output voltage, the control circuit comprising:
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a compensator compensating a current sense signal with a sawtooth wave to generate a compensated current sense signal, the current sense signal being a function of a current flowing through the power switch; and a pulse width modulation circuit connected to the compensator to generate the control signal according to a feedback signal and the compensated current sense signal, the feedback signal being a function of the output voltage. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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19. A control method for a flyback converter including a transformer connected with a power switch switched by a control signal for the transformer to convert an input voltage into an output voltage, the control method comprising:
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detecting the output voltage to generate a feedback signal; detecting a current flowing through the power switch to generate a current sense signal; according to the feedback signal and a preset value, determining whether or not the flyback converter to enter a burst mode; compensating the current sense signal to generate a compensated current sense signal; and generating the control signal according to the feedback signal and the compensated current sense signal; wherein the current sense signal is compensated to prevent an entry point of the burst mode from being affected by the input voltage. - View Dependent Claims (20, 21, 22)
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Specification