Device for controlling a gas-discharge lamp for use in a motor vehicle

Claim 1

A device for controlling a gas-discharge lamp (L) for use in a motor vehicle, including: a supply device (1) for the lamp (L), having an input for connection to the battery (2) of the vehicle and an output for connection to the lamp (L) and including an inverter (1b) with a control input (1a) for receiving a control signal which can modify the electrical power supplied to the lamp (L), and regulating circuitry (5) connected to the lamp (L) and to the control input (1a) of the supply circuit (1) for detecting the voltage across the lamp (L) and the current flowing through the lamp (L) and for applying to the control input (1a) of the supply device (1) a control signal for causing a high electrical power to be supplied during the switching-on and warming-up of the lamp (L) and a subsequent reduction of the power to a predetermined operating level, characterised in that the regulating circuitry comprises: means (15) for generating signals indicative of a reference current which is variable in steps and, during successive time intervals defined by a clock-signal generator (41), decreases according to respective predetermined functions as the voltage detected across the lamp (L) increases, the functions corresponding substantially to respective predefined constant values of the power supplied to the lamp (L), and comparator means (10) for comparing the reference-current values generated with the current detected in the lamp (L) and, in dependence on the difference between them, generating an error signal usable for generating the control signal for the supply device (1).