Browse Prior Art Database

Width Regulator for Cathode Ray Tube Display

IP.com Disclosure Number: IPCOM000042936D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Ainscow, F: AUTHOR [+2]

Abstract

Width regulation is needed in a cathode ray tube (CRT) display to bring the picture to a specified size, to correct East-West pincushion distortion by dynamically varying the line scan amplitude, and, in high-function displays, to allow variable picture format by maintaining constant picture width with variable line rate. In all raster-scan circuits, width is determined by the power supply voltage applied to the horizontal deflection coil. Since line scan is a high-power function, control of the width involves regulating the supply voltage at a high power level. Any form of DC series circuit must dissipate considerable power, and if a wide range of control is needed, the regulator may dissipate more power than the scan circuit itself.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 3

Width Regulator for Cathode Ray Tube Display

Width regulation is needed in a cathode ray tube (CRT) display to bring the picture to a specified size, to correct East-West pincushion distortion by dynamically varying the line scan amplitude, and, in high-function displays, to allow variable picture format by maintaining constant picture width with variable line rate. In all raster-scan circuits, width is determined by the power supply voltage applied to the horizontal deflection coil. Since line scan is a high-power function, control of the width involves regulating the supply voltage at a high power level. Any form of DC series circuit must dissipate considerable power, and if a wide range of control is needed, the regulator may dissipate more power than the scan circuit itself. In the circuit to be described, high-efficiency regulation of picture width in a color CRT display is achieved by the use of a switching regulator in which switch-off is made to occur when the current in the switch is zero, thus minimizing commutation loss. The use of switching regulators to reduce power dissipation is well known. The dominant power-loss mechanism in such regulators is commutation loss in the power switching device. This occurs because no semiconductor can be made to switch off instantaneously, and during the switching process, large voltages are developed across the switch while current is still flowing. This effect is aggravated by an inductive load. In contrast, commutation loss at switch-on is largely eliminated if the load is inductive. The load current drawn by a line scan circuit becomes negative - that is, energy is returned to the power supply - during a part of each line period. In the circuit to be described, the reverse current passes through a diode in antiparallel with the switch device, so that the current in the switch is zero for a period of time. The switch-off time is controlled in such a way that it always occurs during the zero current period. By this means, switch-off commutation loss is eliminated. In the conventional way, regulation is achieved by controlling the switch-on time. This results in some commutation loss, but substantially less than would normally be incurred at switch-off. Fig. 1 is a simplified circuit diagram of the regulator. The line flyback pulse is applied to ramp g...