| 摘要 |
PURPOSE:To prevent the deterioration due to variation in the temperature by varying the diode drive current by the junction temperature detected by the forward voltage of a light emitting diode. CONSTITUTION:A light emitting diode (LED) 4 is driven by a gain variable amplifier 1, and LED drive circuits 2, 3, and jigs junction temperature is detected by a junction temperature detector 5. The detector 5 has a resistor Ri, connected in series with the LED 4, a resistor R, a diode D, and an operational amplifier 6, and the junction temperature is detected by the forward voltage of the LED 4. The detected temperature signal is fed through a voltage control operational amplifier 7 to a gain variable amplifier 1, thereby controlling the drive current of the LED 4. Thus, the nonlinearity between the light emitting power and current of the LED 4 can be improved and the deterioration of the characteristics can be prevented. |
