Automatic brightness control and warning circuit for image intensifier tube

Claim 1

An automatic brightness control and warning circuit for an image intensifier tube which includes a photocathode, a microchannel plate having input and output electrodes and a phosphor screen, comprising: (a) a screen current rectifying circuit which rectifies a current of the phosphor screen and obtains a signal corresponding to the brightness of the phosphor screen; (b) a differential amplifier which compares the signal obtained in the screen current rectifying circuit with a reference signal and generates a signal which increases proportionally to the phosphor screen current; (c) a gas discharge tube; (d) a transistor connected in series with the gas discharge tube with respect to a power source of the gas discharge tube and connected at its control input terminal with the signal of the differential amplifier; thereby an internal resistance of the transistor being controlled; (e) a direct current power source applying a bias voltage to the microchannel plate; (f) a photoconductor connected with the direct current power source in series with respect to the microchannel plate and photoelectrically coupled to the gas discharge tube; and (g) a delaying element provided in a path for the signal from an output terminal of the phosphor screen current rectifying circuit and a control input terminal of the transistor; whereby enabling automatic brightness control so as to slightly increase the phosphor screen current in the automatic brightness control region of the brightness of the phosphor screen, and when an incident light into the photocathode is excessive, blinking the phosphor screen by a relaxation oscillation determined by the delaying element and the characteristic of the gas discharge tube.