| 摘要 |
<p>PURPOSE:To obtain a circuit where a light sensor can be commonly shared over a wide working illuminance range by providing a switch unit with a reference voltage generating unit connected to an amplifying feedback resistor in parallel to form a closed circuit. CONSTITUTION:When a light sensor 2 is subjected to light application, it generates short-circuit current of photocurrent Ish. Without a reference voltage generating unit 4 and an ideal diode 5, an inverted terminal of an operational amplifier 1 is equivalently 0 V so that its output voltage will be Vout = Ish x (Rf1 + Rf2). If the generating unit 4 and the diode 5 are added to both ends of an amplifying feedback resistor 3-1, the generating unit 4 functions as a differential amplifier circuit so that V0 = Vout - Vreff appears at its output V0. When input voltages at a non-inverted terminal and at an inverted terminal of the opperational amplifier 15 are assumed to be V+,V-, resistances 14,17,18 are all equal to one another, so that V+ = 1/2Vout and V- = (Vreff + V0)/2 wherein V+ = V- is satisfied according to conditions of virtual short-circuit and V0 can be easily obtained.</p> |
