Cathode Ray Tube Module

Abstract

A sealed assembly including a cathode ray tube and high voltage power supply source and terminal elements. The high voltage portions of the power supply and the anode cable and terminal are all enclosed by an implosion safety shroud over the funnel of the tube. The unitary assembly can be replaced as a whole without exposing service personnel to the possibility of high voltage shock.

Description

BACKGROUND OF THE INVENTION

This invention relates to cathode ray tube assemblies and more particularly to an improved cathode ray tube module embodying power supply elements and providing for protection against implosion of the tube and exposure to high voltage shock, particularly when the module is removed from a display unit or other apparatus for servicing.

DESCRIPTION OF THE PRIOR ART

Cathode ray tube units have long been known to require protection against danger to users and particularly to service personnel because of the possibility of implosion of the evacuated tube and attendant danger from flying glass and other parts, and also because of the presence of very high voltages in supply for the anode circuits of the tube.

The implosion hazard has been dealt with variously by requiring service personnel to use protective face masks, gloves and aprons while handling the tube for replacement or by applying one or more of several devices to the tube to make it more implosion resistant or to contain flying particles upon implosion. Some of the means applied to the tube itself have included a compression band around the face plate, tough coatings on the funnel of the tube, and/or conformal shrouds over the funnel wall.

The usual approach to protection against high voltage shock has been to provide interlocks which are intended to insure that primary power has been cut off before access to the tube is possible, coupled with bleeder circuits which are designed to discharge the high voltage supply quickly, before the unit can be open and access to the high voltage wiring or terminals attained. One practical disadvantage to this arrangement is that such interlocks are usually easily circumvented and are often intentionally disabled to facilitate testing procedures during servicing of the unit. Another is that, to assure speedy discharge of capacitors in the high voltage supply once the interlock is open, relatively high current drain paths are connected continuously across the high voltage output. While such a drain path may be provided by what is commonly called a "bleeder trickel" resistor it often constitutes the majority load on the high voltage supply, so that the supply must be much larger than it otherwise would have to be.

SUMMARY OF THE INVENTION

The present invention addresses the aforestated problems by providing a module which comprises a cathode ray tube, high voltage power supply elements, and implosion protection means in a unitary module. An anti-implosion shroud or covering on the funnel of the tube and the faceplate of the tube itself combine to form a permanent enclosure containing the high voltage power supply elements, encapsulating them against exposure and thus danger to service personnel. Such a module can be and preferably is a field replaceable unit which is either discarded or returned for factory repair when elements of either the power supply or the tube fail in service. The added cost of replacing both elements when either fails is offset, at least in large degree, by the fact that the power supply, no longer requiring a large discharge current path, may be of much smaller capacity than heretofore. Accordingly, what is for all practical purposes complete protection against high voltage shock is attained without prohibitive extra cost.

Accordingly, it is a primary object of the present invention to provide an improved cathode ray tube module.

Another object of the invention is to provide a module as aforesaid which provides protection against electrical shock from high voltage power supply elements of and for the cathode ray tube.

Another object of the invention is to provide a cathode ray tube module wherein high voltage power supply protection means is combined with protection against injury from implosion of the cathode ray tube.

Still another object of the invention is to provide a unitary module as aforesaid characterized by such economy of design and construction as to be economically field replaceable as a unit so that at no time are field personnel exposed to danger from implosion scattered particles or high voltage shock.

Other objects, features and advantages of the invention will be apparent from the detailed description set forth hereinbelow and from the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a fragmentary side elevational view of a cathode ray tube module in accordance with the invention, partly broken away to show certain features of internal construction.

FIG. 2 is a schematic diagram showing the relationship of portions of the cathode ray tube, implosion resistant shroud and high voltage power supply circuit elements of the module of FIG. 1.

DETAILED DESCRIPTION

In FIG. 1 a conventional cathode ray tube 10 has a neck portion 12, shown broken away in the drawing, a bell or funnel portion 14 and a face plate portion 16. Face plate 16 may be of relatively thick, tough glass which is highly resistant to breakage upon damage to the tube or may be of laminar construction, including a glass face plate portion which is part of the evacuated tube itself together with a clear, tough cover plate which may be adherent to or otherwise mounted in association with the face plate itself, all in accordance with well known constructions of the prior art. Moreover, it will be understood that, if desired, a compression band (not shown) may be employed around the periphery of the front part of the tube, adjacent to face plate for rendering the tube more implosion resistant.

In any case, the wall of the funnel portion 14 of the tube, usually relatively thin glass, is a relatively weak part of the tube envelope and subject to fracture with resultant danger to personnel from implosion propelled glass and other tube parts.

To protect against this danger, the illustrated cathode ray tube module includes a shroud 18 which conformally embraces the funnel portion 14 of the tube so as to contain, in cooperation with the faceplate portion 16, the major evacuated volume of the tube. This protects the tube from fracture and contains the parts upon failure of the glass envelope. By way of example, shroud 18 may be vacuum or blow mold formed to its final shape from a suitably flame retardant, electrically insulating thermoplastic prior to assembly onto the cathode ray tube. This pre-shaped part is then firmly and permanently attached to the tube such as by epoxy cement between the undersides of the forward lip portions 20 of shroud 18 adjacent to or, preferably, overlying the sides of face plate 16 as shown. If desired, the entire or, substantially the entire, conformal portion of the inner surface of shroud 18 can be cemented to the outer wall of funnel 14 so as to not only contain the parts if fracture occurs but also tend to reenforce the wall of funnel 14 so as to prevent initial breakage of the tube in this vulnerable region.

In accordance with the invention, the implosion protection shroud 18 includes a power supply chamber 22 which, in the illustrated embodiment, is an integral appendage formed as a unit with the rest of the shroud 18 during the molding thereof, before assembly onto cathode ray tube 10. In accordance with the illustrated construction, chamber 22 is formed with an enlarged upper portion 24 forming a ledge 26 upon which is mounted a power supply circuit card 28.

Circuit card 28 mounts, in turn, a high voltage transformer 30, which, as shown in the circuit diagram of FIG. 2, has a low voltage primary winding 32, a medium voltage secondary winding 34 and a high voltage secondary winding 36 inductively coupled together by a magnetic core structure 38.

Returning to FIG. 1, circuit card 28 also mounts capacitors 40 and 42, medium voltage diode 44, high voltage diodes 46 and 48, and bleeder resistance 50 which are electrically interconnected as shown in FIG. 2 by circuit connections within the structure of card 28. These circuit lines are laminated within the card 28 and are not visible in FIG. 1. Card 28 includes a connection tab portion 50 projecting through a conformal slot in shroud 18 as shown fragmentarily at 52 and having connection lands 54, 56, 58 and 60 for making external connections as shown in FIG. 2. These connections include supply terminals 54 and 56 for transformer winding 32 by which the transformer is energized from any suitable source of power, such as an alternating current source 62 in the order to 30 volts. Terminal 58 provides a connection for the medium voltage output of the supply such as a 300 volt positive DC output for an accelerating grid 64 of tube 10. Such a medium voltage accelerating grid may be, typically, the grid known in the electronics industry as the "G2" grid. The circuit connection from terminal 58 to grid 64 is usually made through a tube base on the end of neck 12 of CRT 10, which is not shown in the broken away view of FIG. 1. However, this connection is indicated by the conductor 66 in FIG. 2.

The high voltage output of the power supply is, in accordance with a primary feature of the invention, entirely enclosed within the shroud or shield structure 18, 22. This high voltage output is supplied from the anode of diode 48 through a circuit line within card 28 to a high voltage cable 68 leading from card 28 to the high voltage connector 70 on the side of the funnel 14 of tube 10. This connection 70 is commonly called the "ultor" connection and supplies high voltage such as 12,000 volts DC to an anode structure 72 within tube 10. Shroud 18 is formed with a channel 74 to accommodate cable 68 and a bubble or dome-like configuration 76 to accommodate ultor connector 70, whereby the entire high voltage line is encapsulated within portions 22, 74, 76 of the shroud structure 18.

The circuit of the illustrated power supply is shown to illustrate the principle of embodying the high voltage components of the power supply within the shroud to form a unitary module therewith whereby users and service personnel are protected from high voltage electrical shock as well as from danger of implosion, and also that, when the power supply high voltage elements are thus protected, no bleeder or load resistor is needed between the high voltage output at line 68 and ground. Thus, the high voltage power supply elements 36, 42, 46 and 48, and to the extent that they participate in energization of the same, primary winding 32 and core 38, can be of much smaller energy capacity than would otherwise be required. The medium voltage supply is, in the illustrated embodiment, delivered to the exterior at terminal 58 and therefore a bleeder resistor 50 is required for safety purposes to assure that capacitor 40 has discharged prior to handling by service personnel. However, since this supply yields a voltage only one-fortieth as great as the high voltage supply at cable 68, this load through resistor 50 can be relatively minor.

Except as indicated above, the details of the illustrated circuit are given for example only and form no part, per se, of the present invention. The high voltage power supply utilizes no output capacitor, the distributed capacity 78 between the anode structure 72 and the so-called "DAG" grounded surface 80 on the funnel of the tube 10 serving this purpose. The high voltage supply operates in a conventional voltage doubler manner, diode 46 charging capacitor 42 to approximately the peak of one half cycle of the output of secondary 36 of the transformer, and diode 48 becoming forward biased during the other half cycle operation of the transformer to charge capacitor 78 to nearly double the charge on capacitor 42.

It will be appreciated that many modifications could be made in the manner in which the invention is embodied. For example, where the design of the cathode ray tube employed and the display or other housing in which it is mounted will permit location of the high voltage ultor connection on the tube in registry with the chamber 22, or vice versa, no cable 68 would be necessary, the connector 70 being mounted directly on the circuit board 28. In such a construction, the power supply could be assembled onto the module and the chamber 22 cemented to the remainder of the shroud 18 after the latter had first been slipped onto the funnel 14 of tube 10. In another modification, the shroud 18 and its power supply chamber 22 could be formed in place over the power supply elements and the funnel of the tube after the high voltage power supply elements had been assembled onto the tube by suitable mounting means.

These and other modifications will be apparent to those skilled in the art and therefore are not illustrated.

Accordingly, while the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. A cathode ray tube module comprising

a cathode ray tube,

a power supply adapted to generate high voltage for operation of an anode element of said tube,

a circuit connection between said supply and said anode element,

and a shroud encapsulating said power supply, said circuit connection and portions of said tube adjacent to said connection to form a module operative to prevent exposure of any portion of the high voltage supply and circuit connection.

2. A module in accordance with claim 1 wherein

said cathode ray tube comprises a breakage resistant face plate structure, a tapered funnel portion, and a relatively narrow neck portion, and

said shroud is of breakage resistant material and is attached to said face plate structure and covers substantially the entirety of said funnel portion, from said face plate structure to said neck portion,

whereby said shroud and said face plate in cooperation continue to substantially completely encapsulate said power supply upon damage to said tube.

3. A module as set forth in claim 1 wherein said shroud covers the funnel portion of said cathode ray tube to contain debris in the event of implosion of said cathode ray tube.

4. A module in accordance with claim 3 wherein said shroud is adherent to the outer wall of the funnel of the cathode ray tube throughout a major portion of the outer surface thereof so as to strengthen said wall against implosion.

5. A module in accordance with claim 1 further including an external connector on said power supply projecting through said shroud and providing electrical communication to said power supply.

6. A module in accordance with claim 5 wherein said power supply comprises a transformer and said external connector comprises circuit connectors for energization of said transformer.

7. A module in accordance with claim 6 wherein said transformer has a low voltage primary winding and a high voltage secondary winding, and said power supply comprises a high voltage supply including said secondary winding and a rectifier diode but no load resistor.