Continuous conduction mode switching power supply with improved power factor correction

Claim 1

An improved AC-to-DC converter having a rectifier for rectifying an AC input having a sinusoidal waveform, a switching device, and an inductor connected between the rectifier and the switching device, comprising: a first voltage divider connected to the rectifier for dividing down the rectified AC input, to thereby produce a divided-down rectified signal; a first current sensor connected to the switching device for detecting a current charging the inductor when the inductor is in a first position wherein a rectified input current produced by the rectifier charges the inductor, and for generating a first inductor current sense signal indicative of said rectified input current which charges the inductor; a second current sensor including a transformer connected to the inductor and to the switching device for detecting a current discharging from the inductor when the inductor is in a second position wherein said rectified input current which charges the inductor when the inductor is in said first position is discharged from the inductor, and for generating a second inductor current sense signal indicative of said charging rectified input current which is discharged from the inductor, said second current sensor further including an output terminal, a resistor coupled to said output terminal, and a diode coupled between said transformer and said resistor; a second voltage divider connected to an output of the AC-to-DC converter for producing a divided-down output voltage; control means connected to the switching device for alternately placing the inductor in said first position and said second position, said control means including: an error amplifier connected to said second voltage divider for determining a deviation between said divided-down output voltage and a predetermined reference voltage, and for generating an output voltage error signal corresponding to said deviation; a multiplier connected to said error amplifier and said first voltage divider for multiplying said divided-down rectified signal with said output voltage error signal, and for generating a sinusoidal reference signal having a waveform substantially identical to that of said divided-down rectified signal; current control means coupled to said multiplier, said first current sensor, and said second current sensor for determining peak and valley levels of a ripple component of a current running through the inductor, and for producing a control signal to control the switching device in such a manner as to approximate the waveform of said current running through the inductor to the sinusoidal waveform of the rectified AC input, said current control means including; a peak comparator coupled to said first current sensor and said multiplier for comparing said first inductor current sense signal with said sinusoidal reference signal, and for generating a first logic signal when the voltage of said sinusoidal reference signal exceeds that of said first inductor current sense signal; a valley comparator coupled to said second current sensor and said multiplier for comparing said first inductor current sense signal with said sinusoidal reference signal, and for generating a second logic signal when the voltage of said sinusoidal reference signal exceeds that of said second inductor current sense signal; and, latch circuit means coupled to said peak and valley comparators for combining said first and second logic signals, and for generating said control signal.