Automatic exposure control devices using bi-directional transistors

An automatic exposure control circuit for a photographic camera including a light measuring circuit for generating an output signal representative of scene brightness, a storage capacitor for storing the output signal, and an electric timing circuit for controlling exposure time through exposure terminating means in accordance with the stored output signal, comprising:

• at least one mechanical switch operated in association with the camera shutter releasing operation;
• a bi-directional bi-polar transistor including a collector and emitter connected between said light measuring circuit and said storage capacitor, said bi-directional transistor further including a base and having the capability of conducting current from the collector to the emitter thereof and vice versa when bias potential is applied to said base;
• a biasing circuit for generating said bias potential and connected to said at least one mechanical switch and said base, whereby the application of said bias potential is controlled by said at least one mechanical switch;
• and
• an electric power source and at least one power bus for connecting one terminal of said power source to said light measuring circuit, said storage capacitor, said electric timing circuit and exposure terminating means, and wherein said biasing circuit includes a bias resistor connected between said base and said power bus, said at least one mechanical switch being connected between said one terminal of said power source and a junction point at which said bias resistor is connected with said power bus.

An automatic exposure control circuit for a photographic camera including a light measuring circuit for generating an output signal representative of scene brightness, a storage capacitor for storing the output signal, and an electric timing circuit for controlling exposure time through exposure terminating means in accordance with the stored output signal, comprising:

• at least one mechanical switch operated in association with the camera shutter releasing operation;
• a bi-directional bi-polar transistor including a collector and emitter connected between said light measuring circuit and said storage capacitor, said bi-directional transistor further including a base and having the capability of conducting current from the collector to the emitter thereof and vice versa when bias potential is applied to said base;
• a biasing circuit for generating said bias potential and connected to said at least one mechanical switch and said base, whereby the application of said base potential is controlled by said at least one mechanical switch, said biasing circuit includes semiconductor switching means for controlling the application of bias potential to the base of said bi-directional transistor, said semiconductor switching means being controlled by said at least one mechanical switch;
• and
• an automatic diaphragm control circuit for controlling the diaphragm aperture in accordance with said output signal and a power source, and wherein said at least one mechanical switch is connected between one terminal of said power source and said automatic diaphragm control circuit, and said biasing circuit is connected between the base of said semiconductor means and the junction of said at least one mechanical switch and said automatic diaphragm control circuit.

An automatic exposure control circuit for a photographic camera including a light measuring circuit for generating an output signal representative of scene brightness, a storage capacitor for storing the output signal, and an electric timing circuit for controlling exposure time through exposure terminating means in accordance with the stored output signal, comprising:

• at least one mechanical switch operated in association with the camera shutter releasing operation;
• a bi-directional bi-polar transistor including a collector and emitter connected between said light measuring circuit and said storage capacitor, said bi-directional transistor further including a base and having the capability of conducting current from the collector to the emitter thereof and vice versa when bias potential is applied to said base;
• and
• an impedance conversion circuit connected between said storage capacitor and said electric timing circuit for generating electric current commensurate with the scene brightness at its output, and wherein said light measuring circuit includes an operational amplifier and a photodiode connected between a pair of input terminals of said operational amplifier, the output of said impedance conversion circuit being connectable to one of said pair of input terminals to feedback the output of said impedance conversion circuit to said light measuring circuit, and means for selectively connecting the output of said impedance conversion circuit to either said operational amplifier or said electric timing circuit.