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A switching power supply circuit that obtains a predetermined DC voltage output from an input AC power supply includes a full-wave rectifier and a boost circuit connected to the rectifier. The boost circuit generates a DC output having a predetermined voltage value from the rectifier output. A power

A switching power supply circuit that obtains a predetermined DC voltage output from an input AC power supply includes a full-wave rectifier and a boost circuit connected to the rectifier. The boost circuit generates a DC output having a predetermined voltage value from the rectifier output. A power factor improving circuit controls an ON-period of an output transistor of the boost circuit, based on feedback of the DC voltage output, and a dynamic over-voltage-protection circuit controls the ON-period of the output transistor as it performs a switching operation. The switching power supply circuit facilitates an over-voltage-protection function that prevents inductor buzzing with an integrated circuit having a small number of pins.

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1. A switching power supply circuit configured to produce a DC voltage output from an input AC power supply, the switching power supply circuit comprising: a full-wave rectifier configured to full-wave rectify the input AC power supply;a boost circuit configured to generate the DC voltage output wit

1. A switching power supply circuit configured to produce a DC voltage output from an input AC power supply, the switching power supply circuit comprising: a full-wave rectifier configured to full-wave rectify the input AC power supply;a boost circuit configured to generate the DC voltage output with a predetermined voltage value from an output terminal voltage of the rectifier, the boost circuit including a boost inductance element having a first end connected to an output terminal of the rectifier,a switching device connected between a second end of the inductance element and a reference potential,a rectifying device, anda capacitor connected to the second end of the inductance element via the rectifying device; anda power factor controller configured to control an ON-period of the switching device based on an error signal obtained by amplifying a difference between feedback of the DC voltage output and a reference voltage;the power factor controller configured to compare the DC voltage output feedback with a first protection voltage as the reference voltage, for shortening the ON-period of the switching device by an amount of time corresponding to a difference between the DC voltage output feedback and the first protection voltage. 2. The switching power supply circuit according to claim 1, wherein the power factor controller includes: a zero-cross detection circuit configured to detect a zero-cross time of an inductor current of the inductance element, for generating a signal that turns the switching device ON;an oscillator circuit configured to output an oscillation signal that increases monotonically at a time at which the switching device is turned ON;a comparator circuit configured to generate a signal that turns the switching device OFF if a value of the oscillation signal reaches a value of the error signal; anda dynamic over-voltage-protection circuit configured to monitor the DC voltage output feedback and cause the oscillator circuit to increase a gradient at which the oscillation signal increases monotonically, the increase corresponding to the difference between the first protection voltage and the DC voltage output feedback. 3. The switching power supply circuit according to claim 2, wherein the power factor controller further includes a static over-voltage-protection circuit configured to use a second protection voltage higher than the first protection voltage as the reference voltage. 4. The switching power supply circuit according to claim 2, wherein: the oscillator circuit includes an integration circuit configured to charge a capacitor with a constant current and to use a charging voltage of the capacitor for the oscillation signal; andthe dynamic over-voltage-protection circuit is configured to generate an additional charging current having a magnitude corresponding to the difference between the DC voltage output feedback and the first protection voltage, for charging the capacitor. 5. The switching power supply circuit according to claim 4, wherein the power factor controller further includes a static over-voltage-protection circuit configured to use a second protection voltage higher than the first protection voltage for the reference voltage. 6. A power supply circuit to generate a DC voltage output, comprising: a power factor controller configured to control an ON-period of a switching device of the power supply circuit, based on a difference between the DC voltage output and a reference voltage;wherein, to control the ON-period, the power factor controller is configured to compare a feedback of the DC voltage output with a first protection voltage as the reference voltage, and to shorten the ON-period of the switching device by an amount of time corresponding to a difference between the DC voltage output feedback and the first protection voltage. 7. The power supply circuit according to claim 6, wherein the power factor controller further includes a static over-voltage-protection circuit configured to use a second protection voltage higher than the first protection voltage as the reference voltage. 8. A method comprising: comparing a DC voltage output of a power supply circuit with a reference voltage; andcontrolling an ON-period of a switching device of the power supply circuit, based on a difference between the DC voltage output and a reference voltage. 9. The method of claim 8, the controlling comprising shortening the ON-period of the switching device by an amount of time corresponding to the difference.