| 摘要 |
PURPOSE:To make emitted light intensity uniform in accordance with an electric current to each LED by providing an LED array obtained by series connecting of LEDs, switching elements respectively connected in parallel to the LEDs and a constant current device supplying an electric power to the LED array. CONSTITUTION:Phototransistors T1, T2,...Tn are turned ON if they make a pair with light emitting diodes E1, E2, ... En connected to output terminals of an LED driver 1 turned to L level. On the contrary, phototransistors T1, T2, ... Tn remain in OFF states if they make a pair with light emitting diodes E1, E2, ... En connected to H-level output terminals of the driver 1. In the phototransistor turned ON, an area between an emitter and a collector is clamped by a saturation voltage. However, because a forward voltage of the LED connected to the ON phototransistor in a parallel system is higher than the saturated voltage, all the currect flows to the phototransistor and does not flow to the LED. On the other hand, the current flows to the LED connected to the OFF phototransistor in a parallel system. An electric current passing through LEDs L1, L2,...Ln or the transistors T1, T2,...Tn in this manner is a constant current (is) supplied from a constant current device 2. |
