Browse Prior Art Database

Board Level Detection of CRT Source in a Display

IP.com Disclosure Number: IPCOM000121564D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Eagle, DJ: AUTHOR [+2]

Abstract

This article describes a simple circuit that allows a display to electronically detect which source of CRT has been fitted and to provide a signal that may be used by other circuitry to adjust control ranges or other parameters, as required. It allows multiple supply sourcing without manually changing wire links or connections.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Board Level Detection of CRT Source in a Display

      This article describes a simple circuit that allows a
display to electronically detect which source of CRT has been fitted
and to provide a signal that may be used by other circuitry to adjust
control ranges or other parameters, as required.  It allows multiple
supply sourcing without manually changing wire links or connections.

      It is desirable that all components in a display product should
have multiple sources in order to ensure continuity of supply and
competitive pricing, especially the CRT.  No CRT vendors seem capable
of providing a product with identical characteristics.  Differences
usually exist in heater current requirements, yoke impedances, drive
sensitivities, linearity and phosphur or cutoff performance. What is
therefore required is a method for detecting which CRT type has been
fitted, and, automatically adjusting the parameters of needed from
the display's circuit card in accordance with the detected CRT type.

      The circuit described in this article offers the CRT-detection
facility whilst also offering improved heater voltage control
compared with a standard arrangement, which usually involves feeding
the heater through a resistor from either an unregulated low voltage
rail or from a tapped winding on the line output transformer.  This
improved regulation will lead to increased CRT life.  An additional
benefit is that of compatibility.  If the product has already been
shipped with a single type of CRT, there is no provision for
discriminating jumpers in the CRT connectors. If an additional CRT
source is brought on stream, the CRT connectors themselves cannot be
changed or there would be a field-compatibility problem.  The circuit
described allows a new circuit card to be compatible with both
sources of CRT.

      The basic idea is to use the difference in heater
characteristics betwe...