Method for controlling a motor vehicle lighting device that uses LEDs

A motor-vehicle lighting device, comprising:

• a first set (3-A) of LEDs (5) that form a first branch (7-A) of a circuit provided with at least one first electronic switch (11-A) that can be activated by being closed to power the LEDs of the first branch (7-A);
• a second set of LEDs (3-B) that form a second branch (7-B) of a circuit provided with at least one second electronic switch (11-B) that can be activated by being closed to power the LEDs of the second branch (7-B);
• a third set of LEDs (3-C) that form a third branch (7-C) of a circuit provided with at least one third electronic switch (11-C) that can be activated by being closed to power the LEDs of the third branch (7-C);
• and
• a driving device (13) designed to supply to each first, second, and third electronic switch a respective first, second, and third driving signal having a rectangular waveform, a constant frequency, and a duration that can be adjusted according to a PWM control in order to control the current supplied to each set of LEDs and the brightness of the LEDs themselves,
• the second driving signal being spaced apart from the first driving signal by a time phase t1, and the third driving signal being spaced apart from the second driving signal by a time phase t2,
• said device being characterized in that the driving device (13) is configured for generating the phases t1 and t2 different from one another obtained according to the following operations:
• defining limits in frequency of an interval of interest in which a radiated or conducted electromagnetic disturbance produced by said lighting device must not exceed a maximum threshold value θmax;
• supplying to each first, second, and third electronic switch a respective first, second, and third driving signal having a rectangular waveform, a constant frequency, and a duration that can be adjusted according to a PWM control in order to control the current supplied to each set of LEDs and the brightness of the LEDs themselves, the second driving signal being spaced apart from the first driving signal by the time phase t1, and the third driving signal being spaced apart from the second driving signal by the time phase t2;
• comparing the measured or simulated waveform of the electromagnetic disturbance deriving from the phases t1 and t2 with the maximum threshold value within the interval of interest defined;
• and
• in the case where the waveform of the disturbance exceeds the threshold, recalculating two phases t1 and t2 once again different from one another;
• otherwise, selecting the last phases t1 and t2 calculated and using them in the PWM control.