| 摘要 |
PROBLEM TO BE SOLVED: To provide an LED drive circuit capable of executing light control smoothly to the low quantity of light by solving the problem that lightness looks varied step by step in an area with the extremely low quantity of light or a light-emitting diode (LED) is suddenly lighted off when changing the lightness of the LED under PWM control.SOLUTION: The LED drive circuit is formed by connecting a circuit in which a resistor RH and a power transistor TRH are connected in series and a resistor RL and a power transistor TRL are connected in series, respectively, in parallel with the light-emitting diode LED. PWM signal generation circuits H and L output PWM signals of a predetermined pulse width, respectively, and drive the transistors TRH and TRL, respectively. When the power transistors TRH and TRL are turned on, respectively, a current flows to the LED via current limit resistors RH and RL, respectively, and when both the power transistors are simultaneously turned on, currents flowing through RH and RL are summed, thereby controlling a smooth lightness change to a low-illuminance area. |
