Low-cost power factor correction circuit and method for electronic ballasts

Claim 1

A power factor corrected circuit comprising: rectifier means for rectifying voltage from an AC source; power converter means actuated by a control pulse signal for converting the rectified voltage into current pulses, the magnitude of the current pulses being dependent upon the duty cycle of the pulse signal; capacitive bulk energy storage means for storing the output of the power converter means as a bulk DC voltage; feedback signal means for developing a feedback signal related to the level of the bulk DC voltage; oscillating inverter means for converting the bulk DC voltage into an AC signal for driving a load at a frequency that is substantially greater than the frequency of the AC source; means for providing a reference waveform signal that is derived from the oscillations of the inverter; pulse-width modulation means for providing as an output the control pulse signal, the pulse width modulation means including comparator means for comparing a combination of the reference waveform signal and the feedback signal with a threshold voltage, the pulse width modulation means further including an output terminal that is actuated when the combination of the reference waveform signal and the feedback signal exceeds the threshold voltage, such that a change in the level of the feedback signal causes an adjustment of the duty cycle of the control pulse signal so as to regulate the level of the bulk DC voltage.

Claim 9

A method for controlling the power factor of a ballast circuit, comprising the following steps: (a) rectifying an AC supply voltage; (b) converting the rectified AC supply voltage to current pulses using a switching power converter that is controlled by a pulse signal of variable duty cycle, the magnitude of the current pulses being dependent upon the duty cycle of the pulse signal; (c) storing the output energy of the power converter as a bulk DC voltage across a capacitive energy storage means; (d) converting the bulk DC voltage into an AC signal with an oscillating inverter that drives a load at a frequency substantially greater than the frequency of the AC supply voltage; (e) deriving a reference waveform signal from the oscillations of the inverter; (f) deriving a feedback signal that is related to the level of the bulk DC voltage; (g) creating a composite control signal by combining the reference waveform signal with the feedback signal; (h) generating the pulse signal used to control the power converter by comparing the composite control signal with a fixed reference voltage.

Claim 10

A method for controlling the power factor of a ballast circuit, comprising the following steps: (a) rectifying an AC supply voltage; (b) converting the rectified AC supply voltage to current pulses using a switching power converter that is controlled by a pulse signal of variable duty cycle, the magnitude of the current pulses being dependent upon the duty cycle of the pulse signal; (c) storing the output energy of the power converter as a bulk DC voltage across a capacitive energy storage means; (d) converting the bulk DC voltage into an AC signal with an oscillating inverter that drives a load at a frequency substantially greater than the frequency of the AC supply voltage; (e) deriving a reference waveform signal from the oscillations of the inverter; (f) deriving a feedback signal that is related to the level of the bulk DC voltage; (g) creating a composite control signal by combining the reference waveform signal with the feedback signal; (h) generating the pulse signal used to control the power converter by comparing the composite control signal with a fixed reference voltage.