| 摘要 |
PURPOSE:To suppress power consumption low regardless of the voltage level of an input power source by feeding back a part of a current to the negative input terminal of a differential amplifier. CONSTITUTION:First, a driving transistor 21 is turned on with output Vso by inputting the reference voltage Vref to the positive input terminal (+) of a differential amplifier from a reference electrode. And, a light emitting element 11 is supplied with a driving current 1a by inputting input power Vcc. Thereupon, the light emitting element 11 emits a light, and transmits a light signal to a light receiving element 12. Here, for the driving current 1a from the light emitting element 11, one part (1b) is negatively fed back to the differential terminal 33, and the other greater part of it (1c) falls to GND through a current utilizing resistor R11. And, it imaginaryly, shorts by feeding back a current to the differential amplifier 33, so the fed-back voltage Vk of the differential amplifier 33 becomes approximately equivalent to the fixed reference voltage Vref. From this matter, the voltage applied to the resistor R11 for current limitation can always be fixed to Vk (Vref), regardless of the input voltage of the input voltage Vcc. |
