| 摘要 |
PROBLEM TO BE SOLVED: To provide an LED lighting circuit capable of controlling dimming deeper than a PWM dimming lower limit. SOLUTION: There are provided a step-down chopper circuit 1 configured to supply an LED current I1 to an LED light source section 2 when the oscillation of a switching element Q1 is controlled and a dimming control section 3 configured to control the LED current I1 by controlling the oscillation of the switching element Q1. The dimming control section 3 comprises an oscillation frequency control section 32 configured to control an oscillation frequency f1, a PWM control section 31 configured to control PWM on-duty Du2, and a drive section 33 configured to turn on/off the switching element Q1 based on the oscillation frequency f1 and the PWM on-duty Du2 and when the dimming degree is in the range of the PWM dimming lower limit or more, the PWM control section 31 controls dimming by varying the PWM on-duty Du2, and when the dimming degree is in the range of less than the PWM dimming lower limit, the PWM control section 31 does not vary the PWM on-duty Du2 and sets the oscillation frequency f1 higher than that when the dimming degree is in the PWM dimming lower limit. COPYRIGHT: (C)2011,JPO&INPIT |
