Patent ID: 8482944

Claim:
An electronic ballast comprising: a diode bridge functional to rectify an AC input voltage from an AC power source; a power factor correction circuit comprising a first capacitor coupled across high and low potential sides of the rectified AC input voltage; a second capacitor effective to store electricity provided from the power factor correction circuit and further coupled across a load, a first resistor coupled along the low potential side of the rectified AC input voltage and between the diode bridge and the power factor correction circuit, a switching element coupled in parallel with the first resistor; an input voltage dividing network comprising second and third resistors, a first node between the second and third resistors further coupled to the gate of the switching element; a third capacitor coupled in parallel with the third resistor to provide a smoothed DC voltage to the gate of the switching element; and a discharging circuit comprising a diode and a fourth resistor coupled in series between the first node and the high potential side of the rectified AC input voltage, the fourth resistor having a resistance value substantially less than a resistance value of the third resistor, wherein a time constant associated with the fourth resistor and the third capacitor is substantially less than a time constant associated with the third resistor and the third capacitor, the discharging circuit arranged to conduct discharging current from the third capacitor to the first capacitor when the voltage across the first capacitor is less than the voltage across the third capacitor, wherein the power factor correction circuit is effective to deliver current from the first capacitor to the second capacitor until the voltage across the third capacitor discharges below a first predetermined voltage when the AC input voltage is removed from the circuit, wherein the discharging circuit is effective to turn off the switching element before the voltage across the second capacitor drops below a second predetermined voltage equal to the peak voltage of the rectified AC input voltage.