Automatic brightness compensation circuit

Claim 2

In a television receiver including a transistorized video amplifier system direct current coupled to a cathode-ray tube for translating a video signal thereto, said video amplifier system including transistors subject to changes in conduction in response to conditions or of receiver operation in addition to video signal changes thereby varying the brightness of the cathode-ray tube image, a said receiver also including a brightness limiting circuit coupled with the high voltage system of the television receiver for producing a control voltage indicative of the total average beam current, the control voltage being coupled with the video amplifier system for controlling the operation thereof to maintain the total average beam current in the cathode-ray tube constant at a predetermined brightness level, and said receiver further including a power supply to provide a direct current potential subject to undesired variation, an automatic compensation system including in combination: a semiconductor amplifier device; bias circuit means coupled to said amplifieR device and energized by said power supply and responsive to charges in voltage of the power supply to develop an output signal from a said amplifier device; and means direct current coupling said semiconductor amplifier device to said transistorized video amplifier system through at least in part a portion of said brightness limiting circuit for applying said output signal to said transistorized video amplifier system with a polarity and amplitude to compensate the change conduction of said video amplifier system and maintain said predetermined brightness level in the cathode-ray tube.

Claim 3

The compensation system of claim 1 in which said semiconductor amplifier device is positioned to be subjected to substantially in the same temperature variations as the video amplifier system in the television receiver, and said semiconductor device has a temperature response characteristic to produce a change in the output signal thereof to compensate changed conduction in said amplifier system due to temperature variation.

Claim 4

The television receiver of claim 1 in which said video amplifier system includes a transistor having an emitter electrode and the brightness limiting circuit includes a further transistor coupled between said emitter electrode and the receiver power supply, said further transistor having a base electrode with a brightness control potentiometer connected thereto, and said further transistor forming at least part of the means direct current coupling said semiconductor amplifier device to said video amplifier system.

Claim 5

In a television receiver including a transistorized video amplifier system direct current coupled to input electrode means by a cathode-ray tube, said cathode-ray tube having a final anode and high voltage supply means for energizing the same, said video amplifier system including a transistor subject to changed conduction in response to power supply voltage variation in said receiver, an automatic beam control system for regulating brightness of the image in said cathode-ray tube, including in combination: limiter circuit means comprising a first transistor amplifier device direct current coupled between said high voltage supply means and said video amplifier system for controlling the voltage applied to said video amplifier system and including a video signal filter means, responsive only to average changes in said high voltage supply resulting in image brightness changes, coupled to said first transistor amplifier device to control the conductivity thereof to adjust the voltage in said video amplifier system applied to said cathode-ray tube for maintaining image brightness below a given level, said brightness limiting circuit including an adjustable control for selecting said brightness control level; and second transistor amplifier device direct current coupled to said brightness control circuit and energized by the receiver power supply circuit to be responsive to voltage changes thereof, said second transistor amplifier device having gain and polarity to develop a signal in said brightness limiting circuit for applying a voltage to said video amplifier system to compensate for conduction changes therein due to variations in the voltage from the receiver power supply.

Claim 6

In a television receiver including a transistorized video amplifier system direct current coupled to input electrode means by a cathode-ray tube, said cathode-ray tube having a final anode and high voltage supply means for energizing the same, said video amplifier system including a transistor subject to changed conduction in response to power supply voltage variation in said receiver, an automatic beam control system for regulating brightness of the image in said cathode-ray tube, including in combination: limiter circuit means comprising a first transistor amplifier device direct current coupled between said high voltage supply means and said video amplifier system for controlling the voltage applied to said video amplifier system and including a video signal filter means, responsive only to average changes in said high voltage supply resulting in image brightness changes, coupled to said first transistor amplifier device to control the conductivity thereof to adjust the voltage in said video amplifier system applied to said cathode-ray tube for maintaining image brightness below a given level, said brightness limiting circuit including an adjustable control for selecting said brightness control level; and second transistor amplifier device direct current coupled to said brightness control circuit and energized by the receiver power supply circuit to be responsive to voltage changes thereof, said second transistor amplifier device having gain and polarity to develop a signal in said brightness limiting circuit for applying a voltage to said video amplifier system to compensate for conduction changes therein due to variations in the voltage from the receiver power supply.