| 摘要 |
PURPOSE:To adjust the brightness of many display elements at the same time over a wide range by connecting a variable voltage type three-terminal regulator to the output terminal of a DC power source and varying the output voltage of the three-terminal regulator. CONSTITUTION:This circuit is constituted of a DC power source 1, the variable voltage type three-terminal regulator 2, the display elements, e.g. LEDs 3, an LED control part 4 which controls the illumination and extinction of the LEDs 3, etc. Then resistors R1 and R2 set the variation range of the output voltage VOUT of the three-terminal regulator 2 and a variable resistor VR adjusts the output voltage VOUT. Further, resistors r1-rn connected to the respective LEDs 3 in series are resistors for determining the ranges of currents flowing to the LEDs 3; and a capacitor C1 is a high-frequency by-pass capacitor and a capacitor C2 is a capacitor which stabilizes the output voltage VOUT of the three- terminal regulator 2. Consequently, overcurrent flow is eliminated and the life of the display elements 3 can be prolonged, and a single power source is used in common to circuits other than a display part.
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