Lighting circuit of automotive lamp
A lighting circuit turns on a plurality of semiconductor light sources. Multiple current sources are each coupled to a corresponding semiconductor light source. A switching converter supplies a driving voltage V OUT across each of multiple series connection circuits each formed of the semiconductor light source and the current source. A converter controller employing a ripple control method turns on a switching transistor of the switching converter in response to a voltage across any one of the multiple current sources decreasing to a bottom limit voltage.
1. A current driver circuit structured to drive a plurality of semiconductor light sources, the current driver circuit comprising:
a plurality of current sources each structured to allow an on/off state thereof to be controlled independently according to a PWM signal, and to each be coupled to a corresponding semiconductor light source in series;
an interface circuit structured to receive, from an external processor at a first time interval T 1 , a plurality of control data that indicates an on/off duty cycle for the plurality of current sources; and
a dimming pulse generator structured to generate a plurality of PWM signals for the plurality of current sources, and to gradually change, at a second time interval T 2 that is shorter than the first time interval T 1 , a duty cycle of each of the plurality of PWM signals from a value indicated by the corresponding control data before updating to a value indicated by the corresponding control data after updating,
wherein, the dimming pulse generator is switchable between a first mode and a second mode according to setting data,
and wherein, with T 1 /T 2 =a, and with the difference in the value between the control data after updating and the control data before updating as ΔX, (i) in the first mode, the dimming pulse generator changes the duty cycle at the second time interval T 2 in a stepwise manner in steps of ΔY=ΔX/a, and (ii) in the second mode, the dimming pulse generator immediately changes the duty cycle from a value indicated by the corresponding control data before updating to a value indicated by the corresponding control data after updating.
2. The current driver circuit according to claim 1 , wherein each of the plurality of current sources comprises:
a series transistor and a sensing resistor arranged in series with a corresponding semiconductor light source;
an error amplifier structured to adjust a voltage of a control electrode of the series transistor based on a voltage drop that occurs across the sensing resistor; and
a PWM switch arranged between a gate and a source of the series transistor.
3. The current driver circuit according to claim 1 , wherein the first mode and the second mode are switchable for each of the plurality of current sources independently.
4. The current driver circuit according to claim 1 , wherein the setting data is appended to the control data.