| 摘要 |
PURPOSE:To keep the luminance of an LED element constant even under the variation in output voltage of a power source and in ambient temperature by a method wherein the constant voltage output from a constant voltage generation circuit is impressed between the gate and the source of an output transistor which controls drive current as a bias voltage in response to control signals. CONSTITUTION:The LED drive circuit 10 is equipped with an MOS structural logic circuit 11 provided in an IC chip 12 and with an analog switch 14 acting in response to the output signal S from said logic circuit 11. The constant voltage output Ec from the constant voltage circuit 13 has been impressed on the analog switch 14, and the switch 14 opens in response to the coming of the output signal s into ''H'' level; then, the output Ec is impressed between the gate and the source of the MOS output transistor 17. The transistor 17 is connected to the power source 20 in its source, and the LED element 19 is connected to its drain circuit. Therefore, when the output Ec is impressed between the gate and the source of the transistor 17, it turns ON and a drive current flows to the LED element 19. |
