| 摘要 |
PURPOSE:To shorten the falling time without loss of the rising time of an LED by connecting an impedance circuit between the collector and the emitter of a drive transistor and between the emitter and the ground terminals. CONSTITUTION:An impedance circuit 101 connected between the collector and the emitter of a drive transistor 1 is a series circuit of a resistor 11 and a capacity 12, and an impedance circuit 102 connected between the emitter and the ground terminal is formed of a resistor 13. When an input pulse signal is transferred from H to L levels, the emitter potential of the transistor 1 is dropped simultaneously in response to the base potential since the emitter potential of the transistor 1 is substantially constant at the voltage between the base and the emitter. On the other hand, the collector potential abruptly rises since the collector current does not flow to an LD2, and a voltage across the circuit 101 abruptly increases. Accordingly, charge is quickly charged in the capacity 12. This charging current is supplied by the discharge of the charge stored in the parasitic capacity of the LED2, the falling time of the LED2 is largely improved. |
