| 摘要 |
An amplification factor selection circuit for an automatic light emission control circuit which enables selection of an amplification factor in accordance with an F-value, comprises a flash bulb for emitting a flash light to an object, a photo-sensor for sensing a light reflected from the object, an amplifier for amplifying the photo-current of the photosensor, a capacitor for starting charging upon emission of the flash light, a semiconductor device for controlling a charging current of the capacitor in accordance with an output of the amplifier, a light emission suppress circuit for suppressing the light emission when the capacitor is charged up to a predetermined level. A first reference voltage applied to the input terminal of the amplifier and a second reference voltage applied to the output of the transistor are relatively controlled. Two constant current sources are connected to opposite ends of a resistor and a point on the resistor is clamped to a predetermined potential. One of the voltages developed at the opposite ends of the resistor is used as the first reference voltage and the other is used as the second reference voltage to control the point on the resistor clamped to the predetermined potential. |
