Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

CRT Protection Circuit

IP.com Disclosure Number: IPCOM000092630D
Original Publication Date: 1966-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Bradley, ME: AUTHOR [+3]

Abstract

The circuit is useful in digitally controlled displays operating at extremely high frequencies. The circuit protects the beam control circuits from the adverse effects of arcing currents discharged into the control grid. The circuit also prevents phosphor burn due to failure of the beam control circuits or prolonged beam unblanking caused by improper programming or other external failures.

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 61% of the total text.

Page 1 of 2

CRT Protection Circuit

The circuit is useful in digitally controlled displays operating at extremely high frequencies. The circuit protects the beam control circuits from the adverse effects of arcing currents discharged into the control grid. The circuit also prevents phosphor burn due to failure of the beam control circuits or prolonged beam unblanking caused by improper programming or other external failures.

When arcing occurs, a 1 to 2 microsecond pulse of 2KV attempts to discharge into the CRT control grid and its connected circuits. Due to the bandwidth required. these are of very low impedance and consequently are damaged by the large currents involved. This circuit overcomes this potential source of damage by providing a shunt path through diode D1 and the base- collector path of transistor Q1 to the +36V supply. The 2.4K resistor presents a comparatively high impedance into the beam control circuits. Q1 is selected so that the 1 to 2 microsecond surge produces no damage.

Phosphor burn can result from any one of two possible conditions in the beam control circuits. Certain malfunctions can cause the CRT grid bias to increase to a point at which damage results. This circuit reacts to this condition by increasing the potential of the CRT cathode to the +80V supply potential. As the CRT grid approaches +31V, transistor Q2 conducts and biases transistor Q3 to shutoff. The CRT cathode rises to the +80V supply voltage to cut off the beam within five microsecon...