Abstract: A voltage detecting circuit 21 detects the voltage applied to a load lamp 16, and a current detecting circuit 22 detects the current flowing in a rectifier 14. A controlling section 31 computes the power consumption of the load lamp 16 from the detected voltage and detected current in a half cycle of an alternate current power source voltage using the output of a zero-cross detecting section 15. The controlling section 31 computes the control quantity of PWM control on the basis of computed power consumption. Then, the controlling section 31 fixedly supplies the computed control quantity to a driver circuit 17 in a following half cycle of the alternate current power source voltage. Thereby, the on-duty of a transistor Q1 becomes constant in a half cycle of the alternate current power source voltage, and the current flowing in the rectifier 14 has a sinusoidal waveform. The power factor of the circuit is thus improved, and efficient lamp driving is possible.

Abstract: Disclosed a high pressure discharge lamp driving apparatus for driving a high pressure discharge lamp during a stable operation thereof with an AC lamp current alternating for opposite half-cycle periods, the apparatus comprising an AC lamp current supply for supplying the AC lamp current to the high pressure discharge lamp, a detector for detecting the output AC lamp current to the high pressure discharge lamp, a controller responsive to the detector for controlling the AC supply to output the AC lamp current with a waveform which is characterized by that (i) a mean value in the second half of each half-cycle period is larger than the means value of the first half of each half-cycle period, (ii) no pulse current is contained in the second half of each half-cycle period, (iii) the AC lamp current has a maximum value immediately after polarity change between the positive and negative half-cycle periods, and (iv) the AC lamp current has also a waveform defined by that the ratio (d/a) of the maximum value (d) of

Abstract: Disclosed a high pressure discharge lamp driving apparatus for driving a high pressure discharge lamp during a stable operation thereof with an AC lamp current alternating for opposite half-cycle periods, the apparatus comprising an AC lamp current supply for supplying the AC lamp current to the high pressure discharge lamp, a detector for detecting the output AC lamp current to the high pressure discharge lamp, a controller responsive to the detector for controlling the AC supply to output the AC lamp current with a waveform which is characterized by that (i) a mean value in the second half of each half-cycle period is larger than the means value of the first half of each half-cycle period, (ii) no pulse current is contained in the second half of each half-cycle period, (iii) the AC lamp current has a maximum value immediately after polarity change between the positive and negative half-cycle periods, and (iv) the AC lamp current has also a waveform defined by that the ratio (d/a) of the maximum value (d) of