| 摘要 |
PURPOSE: A device for controlling brightness for display is provided to invert voltage applied to the display by current flowing in a diode in accordance with external brightness without control under a microcomputer. CONSTITUTION: A current of photo diode(40) varies according to external brightness. An amplifying part(50) compares outputs of the photo diode(40) with the first reference voltage for amplification. An inverting part(60) compares outputs of the amplifying part(50) with the second reference voltage for inversion and control. A switching part(20) controls voltage applied to a display(10) according to output values of the amplifying part(50). The photo diode(40) is connected to an inverting input terminal(-) of the first OP amplifier(OP1) of the amplifying part(50) via the first resistance(R1). A non-inverting input terminal(+) of the first OP amplifier(OP1) is connected to the first reference voltage set by distributing a power terminal(VCC) by the second and third resistances(R2,R3). An output terminal of the first OP amplifier(OP1) is connected for feedback to the inverting input terminal(-) and the fourth resistance(R4). The output terminal of the first OP amplifier(OP1) is connected to a non-inverting input terminal(+) of the second OP amplifier(OP2) in the inverting part(60) via the fifth resistance(R5). An inverting input terminal(-) of the second OP amplifier(OP2) is connected to the second reference voltage set by distributing a power terminal(VCC) by the sixth and seventh resistance(R6,R7). An output terminal of the second OP amplifier(OP2) is connected to a transistor(TR) base terminal of the switching part(60) via the ninth resistance(R9).
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