| 摘要 |
PURPOSE:To obtain an arbitrary fine constant current from the output of a current mirror circuit by connecting a photo diode to the input terminal of the current mirror circuit by making it to a reverse bias. CONSTITUTION:In order to control the current of an LED2, one edge of the LED2 is grounded through a variable resistance R16 to a terminal 7 connected to an LED driving power source V1 and other edge is grounded. A resistance value R1 is made variable and the light emitting output of the LED2 is controlled. As the result, the output current of a photo diode 3 connected to the collector of a transistor TR4 and a bias power source terminal 8 is changed. The current comes to be the collector current of a TR5 and is transferred by the current mirror circuit composed of the TR4 and 5. Consequently, by the control of the resistance value R1, an arbitrary fine constant current can be obtained.
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