Patent ID: 7439687

Claim:
A discharge lamp lighting circuit for supplying electric power to light a discharge lamp, the discharge lamp lighting circuit comprising: control circuitry to generate a control signal for controlling a magnitude of the electric power based on a voltage between electrodes of the discharge lamp, and electric power supply circuitry to supply the electric power to the discharge lamp based on the control signal from the control circuitry, wherein the control circuitry comprises: differential computation circuitry to differentiate a signal according to the voltage between the electrodes with respect to time, and to generate a first differential signal, and first integral computation circuitry to integrate a second differential signal which monotonously increases and decreases as the first differential signal increases and decreases with respect to time, and to generate a first integral signal, wherein the control circuitry is operable to generate the control signal so that the electric power decreases with an increase in the first integral signal.