| 摘要 |
PROBLEM TO BE SOLVED: To enable electronic equipment, such as a wrist watch, provided with a solar battery to sufficiently utilize the capacity of a battery by always maintaining the optimum charging current in such a way that the charging current is reduced when the voltage of the battery rises in order to prevent the overcharging of the battery and, when the voltage drops, the control for increasing the current is performed by not simply turning on/off the current, but by increasing/reducing the current in accordance with the charged state of the battery. SOLUTION: A light shutter having a variable light shielding area is positioned on the top side of a solar battery 1 and a voltage detector 4 which monitors the voltage of a battery 2 and a driving circuit 12 which changes the light shielding area of the light shutter are provided so that the battery 2 may be charged continuously with an appropriate current by increasing/reducing the light receiving area of the solar battery 1 by adjusting the light shielding area of the light shutter in accordance with the voltage of the battery 2. The light shutter is composed of a liquid crystal shutter 11, a mechanical movable light shielding plate, etc., and when the shutter is composed of the liquid crystal shutter 11, its shutter section and displaying section can be synthesized in a single liquid crystal cell. The sense of beauty of the display of the displaying section can be improved when a reflection type polarizing plate is put on the liquid crystal cell or a high polymer liquid crystal cell is used.
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