Lighting circuit for discharge lamp

Abstract

A discharge lamp lighting circuit 1 includes an electric power supply part and a control part. The control part generates a control signal (Sc) for controlling the magnitude of electric power based on a lamp voltage (VL) of a discharge lamp. The electric power supply part supplies the electric power based on the control signal (Sc) from the control part to the discharge lamp. The control part hasa differential computation part for differentiating a lamp voltage corresponding signal (VS) with respect to time and generating a first differential signal Sd1 (=dVS / dt), and an integral computationpart for integrating a second differential signal (Sd2) which monotonously increases and decreases as the first differential signal (Sd1) increases and decreases with respect to time and generating afirst integral signal (Si1), and generates the control signal (Sc) so that the electric power decreases with an increase in the first integral signal (Si1).

Description

technical field [0001] The present invention relates to a lighting circuit for a discharge lamp. Background technique [0002] Discharge lamps such as metal halide lamps used in vehicle headlights and the like are generally turned on as follows. That is, a high-voltage pulse (several tens of kV) is first applied to promote dielectric breakdown between the electrodes, thereby generating a discharge arc between the electrodes, and conducting between the electrodes. Next, a large power is supplied in order to increase the luminous intensity as soon as possible. Then, the inter-electrode voltage (lamp voltage) of the discharge lamp increases as the luminous efficiency increases due to evaporation of the metal enclosed in the tube, and the supplied power is gradually reduced in accordance with the increase in the lamp voltage. In this way, overshooting is prevented while the luminous intensity of the discharge lamp converges to a prescribed intensity as quickly as possible. ...

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