Cathode current limiting circuit for projection television display systems
AssigneeKoninklijke Philips Electronics N.V.
InventorWilliam G. Miller
Life of this patent
Estimating the term…
Abstract
A cathode current limiting circuit and method, for use with projection color television display systems to prevent overheating and possible cracking of the blue cathode ray tube (CRT) when a continuous blue background is presented, monitors differences between the respective low level red, green, blue (RGB) signals sent from the video signal processor to the CRT drive which produces the respective RGB cathode or beam currents. When the low level blue signal exceeds both of the red and the green signals by a predetermined differential, the circuit sends a feedback signal to the video signal processor to limit the blue signal and, thus, the cathode current from the CRT drive.
Claims19
A cathode current limiting circuit for use with a projection color television display having a video processor for processing received television signals and for producing low level red (R), green (G) and blue (B) signals, a cathode ray tube (CRT) drive for receiving the low level RGB signals and for producing high level RGB signals, and respective cathode ray tubes for receiving the high level RGB signals, said cathode current limiting circuit including a first sensing device comprising:
- inputs for receiving said low level RGB signals;
- a monitoring circuit for monitoring differences between voltages of the low level RGB signals;
- and
- an output for producing an output signal when the voltage of one of the low level RGB signals exceeds the voltage of all of the other low level RGB signals, the output signal being applied as a feedback signal to the video processor for adjusting the low level RGB signals to limit a cathode beam current of the CRT to which the high level RGB signal, corresponding to the low level RGB signal having the highest voltage, is applied.
A method of limiting the cathode current of a projection color television display system having a video processor for processing received television signals and for producing low level red (R), green (G) and blue (B) signals, a cathode ray tube (CRT) drive for receiving the low level RGB signals and for producing high level RGB signals, and respective cathode ray tubes for receiving the high level RGB signals, said method comprising the steps of:
- receiving the low level RGB signals;
- monitoring differences between the low level RGB signals
- producing an output signal when one of the low level RGB signals exceeds each of the other low level RGB signals;
- and
- feeding back the output signal to the video processor to adjust the low level RGB signals to limit the cathode beam current of the CRT to which the high level RGB signal, corresponding to the low level RGB signal having the highest voltage, is applied.
Dependencies are inferred from the claim text.