The control circuit for maintaining constant power in power factor
corrected electronic ballasts and power supplies maintains constant power
in a variable load. This constant power control circuit provides a closed
loop constant power management process for gas discharge lamps by adding
a scaled lamp voltage to a scaled voltage that is equivalent to the
measured lamp current. This sum is then fed to a comparator for
comparison with a fixed reference voltage. If there is a difference
between the sum and the reference voltage, the comparator sends this
information to an error amplifier of the gas discharger lamp power
control circuit for corrective measures and closed loop control of gas
discharge lamp power. Since the sum always must attain the same value as
determined by reference voltage, when the lamp voltage increases from its
nominal or initial value, the lamp current is decreased by a
corresponding ratio to maintain a constant power in the gas discharge
lamp.