| 摘要 |
PURPOSE:To perform high-precision exposure time control over a wide brightness range on a small scale and at low cost by increasing the current level for charging a charging means when field brightness is small, and increasing the number of times of charging of the charging means according to the increase rate. CONSTITUTION:A silicon photodiode 1 corresponds to a light measuring means, a capacitor 9 to the charging means, a comparator 12 to a brightness-time converting means, a comparator 13, a constant current source 14, and a logarithmic compressing diode 15 to a brightness level decision means, NPN transistors (TR) 4 and 5, analog switches 7 and 8, an AND gate 24, and an RS flip-flop 25 to a current level selecting means, a monostable multivibrator 19, a NOR gate 23, and a PNP TR 6 to a recharging control means, a ripple counter 30 to a counting means, and AND gates 27 and 28 and an OR gate 31 to an exposure and control means respectively. Consequently, the high-precision exposure time control over a wide brightness range is performed on the small scale and at low cost.
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