| 摘要 |
PROBLEM TO BE SOLVED: To provide a lighting circuit capable of attaining characteristics similar to an incandescent lamp at a comparatively simple structure in dimming control of a light-emitting diode, and a light source device having the lighting circuit. SOLUTION: The lighting circuit 1 has a smoothing circuit 14 for detecting a size of a dimming control value as an on-duty dimming control signal, a PWM signal generation circuit 15 for outputting a PWM signal corresponding to the on-duty dimming control value by comparing output of the smoothing circuit 14 with a triangular wave signal, and an AND circuit AND which takes a logical product of the dimming control signal and the PWM signal. The output of the AND circuit is input into a drive circuit 16 of a switching element SW1 for switching supply current to the light-emitting diode 2, and performs ON-OFF control of the switching element SW1. Thus, an amount of current supplied to the light-emitting diode 2 per unit time becomes square times of the dimming control value in comparison with the time of rated lighting, and dimming characteristics similar to the incandescent lamp can be attained. COPYRIGHT: (C)2011,JPO&INPIT |
