| 摘要 |
PURPOSE:To reduce power consumption of a variable resistor and realize a long life and miniature size by a method wherein two transistors are connected to a light emitting device in series and the base bias voltage of one of the transistors is regulated by the variable resistor. CONSTITUTION:The cathode of a light emitting device 2 is connected to the collector of a transistor 3. A source input terminal 1 is connected to the 1st terminal of a variable resistor 4. The 2nd terminal of the variable resistor 4 is grounded. A TTL IC 7404 is used as a drive circuit 7 and two 2SC2954's are used as the transistors 3 and 5. As a light emitting diode of a 0.8mum band is used as the light emitting device 2, 50-100mA of driving current must be applied to the collectors of the transistors 3 and 5. As the DC current amplification factor of the transistor is higher than 30, the base current of the transistor 3 is about 1.7-3.3mA. In such case, the power consumption of the 1kOMEGA variable resistor 4 connected to the base of the transistor 3 is as small as 50mW when a source voltage is 5V. |
