Video signal control circuit including automatic brightness and contrast control responsive to excess crt beam current

Claim 2

A video signal control circuit, comprising: Video amplifier means for amplifying a video signal supplied to an input terminal thereof; a signal transmission channel connected to said video amplifier means at a junction for transmitting a video signal applied thereto by said video amplifier means to a cathode ray tube; gain control means coupled to said video amplifier means for controlling the gain of said video amplifier means in accordance with a gain determining voltage; first voltage supply means coupled to said video amplifier means and said signal transmission channel for supplying a voltage thereto; second voltage supply means coupled to said gain control means for supplying a voltage thereto; brightness control means coupled to said first voltage supply means for varying the voltage supplied by said first voltage supply means to thereby vary the DC potential applied to said signal transmission channel, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is varied; contrast control means coupled to said second voltage supply means for varying the voltage supplied by said second voltage supply means to thereby vary the gain of said video amplifier means determined by said gain control means, whereby the contrast of an image displayed by said cathode ray tube is varied; and level control means coupled to said signal transmission channel and responsive to said voltage supplied by said second voltage supply means for varying the DC potential on said signal transmission channel.

Claim 3

A video signal control circuit in accordance with claim 1 wherein said level control means comprises a level control transistor having collector and emitter electrodes coupled in shunt relationship to said signal transmission channel and a base electrode coupled to said second voltage supply means.

Claim 4

A video signal control circuit in accordance with claim 1 wherein said video amplifier means comprises a video amplifier transistor and said gain control means comprises a gain control transistor, said video amplifier transistor having collector and emiiter electrodes coupled in series to said first voltage supply means and a base electrode coupled to said input terminal, said gain control transistor having collector and emitter electrodes connected in shunt relationship with said base and emitter electrodes of said video amplifier transistor and a base electrode coupled to said second voltage supply means.

Claim 5

A video signal control circuit in accordance with claim 3 further comprising an input resistor to couple said input terminal to said video amplifier transistor base electrode; and a diode interconnected between said input terminal and said video amplifier transistor emitter electrode.

Claim 6

A video signal control circuit, comprising: video amplifier means for amplifying a video signal supplied to an input terminal thereof; a signal transmission channel coupled to said video amplifier means for transmitting a video signal applied thereto by said video amplifier means to a cathode ray tube; gain control means coupled to said video amplifier means for controlling the gain of said video amplifier means in accordance with a gain determining voltage; first voltage supply means coupled to both said video amplifier means and said signal transmission channel for supplying a DC voltage thereto; second voltage supply means coupled to said gain control means for supplying DC voltage thereto; beam current detecting means coupled to said cathode ray tube for detecting when said beam current exceeds a predetermined value; brightness control means coupled to said first voltage supply means for varying the DC voltage supplied to said signal transmission channel by said first voltage supply means, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is varied; contrast control means coupled to said second voltage supply means for varying the DC voltage supplied to said gain control means by said second voltage supply means to thereby vary the gain of said video amplifier means determined by said gain control means, whereby the contrast of an image displayed by said cathode ray tube is varied; and brightness limiting means coupled to said first and second voltage supply means and responsive to said detected cathode ray tube beam current in excess of said predetermined value for simultaneously varying the DC voltage supplied to said signal transmission channel by said first voltage supply means and the DC voltage supplied to said gain control means by said second voltage supply means, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is limited and the contrast of said image is reduced.

Claim 7

A video signal control circuit, comprising: video amplifier means for amplifying a video signal supplied to an input terminal thereof; a signal transmission channel coupled to said video amplifier means for transmitting a video signal applied thereto by said video amplifier means to a cathode ray tube; gain control means coupled to said video amplifier means for controlling the gain of said video amplifier means in accordance with a gain determining voltage; first voltage supply means coupled to both said video amplifier means and said signal transmission channel for supplying a DC voltage thereto; second voltage supply means coupled to said gain control means for supplying DC voltage thereto; beam current detecting means coupled to said cathode ray tube for detecting when said beam current exceeds a predetermined value; brightness control means coupled to said first voltage supply means for varying the DC voltage supplied to said signal transmission channel by said first voltage supply means, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is varied; contrast control means coupled to said second voltage supply means for varying the DC voltage supplied to said gain control means by said second voltage supply means to thereby vary the gain of said video amplifier means determined by said gain control means, whereby the contrast of an image displayed by said cathode ray tube is varied; and brightness limiting means coupled to said first and second voltage supply means and responsive to said detected cathode ray tube beam current in excess of said predetermined value for simultaneously varying the DC voltage supplied to said signal transmission channel by said first voltage supply means and the DC voltage supplied to said gain control means by said second voltage supply means, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is limited and the contrast of said image is reduced.

Claim 8

A video signal control circuit in accordance with claim 5 wherein said brightness limiting means comprises transistor switch means connected in common relationship to said first and second voltage supply means and adapted to be activated by said beam current detecting means.

Claim 9

A video signal control circuit in accordance with claim 6, wherein said transistor switch means comprises a transistor having collector and emitter electrodes interconnected between said first and second voltage supply means and said beam current detecting means and adapted to exhibit a conducting state when said beam current detecting means detects that said beam current exceeds said predetermined value.

Claim 10

A video signal control circuit, comprising: video amplifier means for amplifying a video signal supplied to an input terminal thereof; a signal transmission channel coupled to said video amplifier means for transmitting a video signal applied thereto by said video amplifier means to a cathode ray tube; gain control means coupled to said video amplifier means for controlling the gain of said video amplifier means in accordance with a gain determining voltage; first voltage supply means coupled to said video amplifier means and said signal transmission channel for supplying a voltage thereto; second voltage supply means coupled to said gain control means for supplying a voltage thereto; each of said first and second voltage supply means comprising a current source connected to a voltage source, said voltage source selectively providing an output voltage determined by a control voltage applied thereto and an output current provided by said current source, and said current source providing an output current determined by a regultaing voltage applied thereto; beam current detecting means coupled to said cathode ray tube for detecting when said beam current exceeds a predetermined value; brightness control means coupled to said first voltage supply means for varying the voltage supplied by said first voltage supply means to thereby vary the DC potential applied to said signal transmission channel, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is varied; contrast control means coupled to the voltage source of said second voltage supply means for varying the output voltage supplied by said voltage source of said second voltage supply means to thereby vary the gain of said video amplifier means determined by said gain control means, whereby the contrast of an image displayed by said cathode ray tube is varied; and brightness limiting means coupled to the respective current sources of said first and second voltage supply means and responsive to said detected cathode ray tube beam current in excess of a predetermined value for varying the output currents provided by said respective current sources to thereby simultaneously vary the DC potential applied to said signal transmission channel and the gain of said video amplifier means determined by said gain control means, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is limited and the contrast of said image is reduced.

Claim 11

A video signal control circuit, comprising: video amplifier means for amplifying a video signal supplied to an input terminal thereof; a signal transmission channel coupled to said video amplifier means for transmitting a video signal applied thereto by said video amplifier means to a cathode ray tube; gain control means coupled to said video amplifier means for controlling the gain of said video amplifier means in accordance with a gain determining voltage; first voltage supply means coupled to said video amplifier means and said signal transmission channel for supplying a voltage thereto; second voltage supply means coupled to said gain control means for supplying a voltage thereto; each of said first and second voltage supply means comprising a current source connected to a voltage source, said voltage source selectively providing an output voltage determined by a control voltage applied thereto and an output current provided by said current source, and said current source providing an output current determined by a regultaing voltage applied thereto; beam current detecting means coupled to said cathode ray tube for detecting when said beam current exceeds a predetermined value; brightness control means coupled to said first voltage supply means for varying the voltage supplied by said first voltage supply means to thereby vary the DC potential applied to said signal transmission channel, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is varied; contrast control means coupled to the voltage source of said second voltage supply means for varying the output voltage supplied by said voltage source of said second voltage supply means to thereby vary the gain of said video amplifier means determined by said gain control means, whereby the contrast of an image displayed by said cathode ray tube is varied; and brightness limiting means coupled to the respective current sources of said first and second voltage supply means and responsive to said detected cathode ray tube beam current in excess of a predetermined value for varying the output currents provided by said respective current sources to thereby simultaneously vary the DC potential applied to said signal transmission channel and the gain of said video amplifier means determined by said gain control means, whereby the brightness of an image displayed by said cathode ray tube in response to said video signal is limited and the contrast of said image is reduced.

Claim 12

A video control circuit in accordance with claim 8 wherein said current source comprises a first transistor having a current output electrode and a control electrode, said control electrode being connected to said brightness limiting means for receiving a regulating voltage therefrom, and said voltage source comprises a second transistor having a control electrode connected to said current output electrode and a voltage output electrode; said voltage output electrode included in said first voltage supply means being coupled to said video amplifier means and said signal transmission channel, and said voltage output electrode included in said second voltage supply means being coupled to said gain control means.

Claim 13

A video control circuit in accordance with claim 9 wherein said brightness control means is connected to said second transistor control electrode included in said first voltage supply means and said contrast control means is connected to said second transistor control electrode included in said second voltage supply means; and said brightness limiting means is connected in common relationship to the control electrodes of said first transistors included in said first and second voltage supply means.

Claim 14

A video signal control circuit in accordance with claim 10 wherein said brightness control means and said contrast control means each comprises variable resistance means for producing a variable control voltage in accordance with a manual operation thereof.

Claim 15

A video signal control circuit, comprising: a video amplifying transistor for amplifying a video signal supplied to an input terminal coupled thereto; a signal transmission channel coupled to said video amplifying transistor for transmitting a video signal applied thereto by said video amplifying transistor to a cathode ray tube; a gain control transistor coupled to said video amplifying transistor for controlling the gain of said video amplifying transistor in accordance with a gain determining voltage; first voltage supply means comprised of a first current source transistor having a current output electrode and a control electrode and a first voltage source transistor having a control electrode connected to said current output electrode and a voltage output electrode connected in common relationship to said video amplifying transistor and said signal transmission channel; second voltage supply means comprised of a second current source transistor having a current output electrode and a control electrode and a second voltage source transistor having a control electrode connected to said last-mentioned current output electrode and a voltage output electrode connected to said gain control transistor; brightness control means connected to said first voltage source transistor control electrode for applying a variable control voltage thereto to thereby vary the DC potential supplied by said first voltage source transistor voltage output electrode, whereby the brightness of an image displayed by said cathode ray tube is varied; contrast control means connected to said second voltage source transistor control electrode for applying a variable control voltage thereto to thereby vary the gain determining voltage supplied to said gain control transistor by said second voltage source transistor voltage output electrode, whereby the contrast of an image displayed by said cathode ray tube is varied; a level control transistor coupled to said signal transmiSsion channel and having a control electrode connected to said second voltage source transistor voltage output electrode for compensating variations in the DC potential applied to said signal transmission channel when said contrast control means causes a variation in said gain determining voltage to thereby minimize variations in the brightness of an image displayed by said cathode ray tube when the contrast thereof is varied; beam current detecting means coupled to said cathode ray tube for detecting when the cathode ray tube beam current exceeds a predetermined value; and a brightness limiting transistor coupled to the control electrodes of said first and second current source transistors, respectively, and responsive to a detected excessive beam current for varying the voltage applied to said control electrodes to correspondingly vary the respective output current produced by said first and second current source transistors, whereby the voltages produced at the voltage output electrodes of said first and second voltage source transistors are varied.

Claim 16

A video signal control circuit, comprising: a video amplifying transistor for amplifying a video signal supplied to an input terminal coupled thereto; a signal transmission channel coupled to said video amplifying transistor for transmitting a video signal applied thereto by said video amplifying transistor to a cathode ray tube; a gain control transistor coupled to said video amplifying transistor for controlling the gain of said video amplifying transistor in accordance with a gain determining voltage; first voltage supply means comprised of a first current source transistor having a current output electrode and a control electrode and a first voltage source transistor having a control electrode connected to said current output electrode and a voltage output electrode connected in common relationship to said video amplifying transistor and said signal transmission channel; second voltage supply means comprised of a second current source transistor having a current output electrode and a control electrode and a second voltage source transistor having a control electrode connected to said last-mentioned current output electrode and a voltage output electrode connected to said gain control transistor; brightness control means connected to said first voltage source transistor control electrode for applying a variable control voltage thereto to thereby vary the DC potential supplied by said first voltage source transistor voltage output electrode, whereby the brightness of an image displayed by said cathode ray tube is varied; contrast control means connected to said second voltage source transistor control electrode for applying a variable control voltage thereto to thereby vary the gain determining voltage supplied to said gain control transistor by said second voltage source transistor voltage output electrode, whereby the contrast of an image displayed by said cathode ray tube is varied; a level control transistor coupled to said signal transmiSsion channel and having a control electrode connected to said second voltage source transistor voltage output electrode for compensating variations in the DC potential applied to said signal transmission channel when said contrast control means causes a variation in said gain determining voltage to thereby minimize variations in the brightness of an image displayed by said cathode ray tube when the contrast thereof is varied; beam current detecting means coupled to said cathode ray tube for detecting when the cathode ray tube beam current exceeds a predetermined value; and a brightness limiting transistor coupled to the control electrodes of said first and second current source transistors, respectively, and responsive to a detected excessive beam current for varying the voltage applied to said control electrodes to correspondingly vary the respective output current produced by said first and second current source transistors, whereby the voltages produced at the voltage output electrodes of said first and second voltage source transistors are varied.