Automatic exposure control for camera - achieves constant response by operational or differential amplifier

摘要

An automatic exposure control for a camera has a differential or operational amplifier with one input from the film speed sensor and the other from the photocell. The output is fed back to a transistorised control with switching circuits for the exposure settings. The system uses switching circuits with constant threshold voltages so that a constant response is obtained over a wide range of conditions. The exposure settings are also independent of the supply voltage for the switching circuits. An adjustable control (2) and a series connection of a photo-resistor (3) and transistor (4) are switched in parallel to the power source (1). The tap of the control (2) is connected to the inverted input of a differential amplifier (5). The latter's output is fed back to the transistor's (4) base.