| 摘要 |
PURPOSE:To accelerate discharge of the charge accumulated in an LED and facilitate high speed modulation of the LED by a method wherein a reverse current source transistor and a reverse voltage protective diode are added to a differential type LED driving circuit. CONSTITUTION:A reverse current source transistor 7 and a reverse voltage protective diode 8 are added to a differential type LED driving circuit. When a differential transistor (Tr) 2 is on, a differential current between a current Io determined by a maximum current control circuit and a current Ic supplied by a reverse current source is applied to an LED 4 and the LED 4 is turned into a light emitting state. When the Tr 2 is turned off, the current Io becomes zero and the current Ic is applied to the LED 4 and the charge accumulated in the LED 4 is discharged instantly. After the discharge, the reverse voltage of the LED 4 is limited by the forward voltage of a diode 8. With this constitution, the discharge of the charge accumulated in the LED 4 is accelerated so that high speed modulation of the LED can be realized. |
