JPH0555668U - CRT display device shield structure - Google Patents

Abstract

(57) [Summary] [Purpose] Lightweight CR with good serviceability.
An object is to realize a shield structure for a T display device. [Structure] A strip-shaped conductive sheet (3) and a metal plate (5) are arranged around a deflection yoke (2). The conductive sheet (3) and the metal plate (5) are attached to the chassis frame (6),
(7) electrically connected to the ground lead wire (9)
Leakage electric field is reduced by grounding to the ground via.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a shield structure for a CRT (cathode ray tube) display device, and more particularly to a shield structure for reducing a leakage electric field from the CRT display device.

[0002]

[Prior Art]

 FIG. 6 is an explanatory diagram for explaining a state in which an electric field is generated. (61) is a P (v) power source, and (62) and (63) are plate-shaped conductors connected to both electrodes of the power source (61). In this case, the electric field E generated between the conductors (62) and (63) is calculated from the potential difference P (V) between the conductors (62) and (63) and the distance d (m) ( Electric field E (v / m) = P / d (Equation 1)).

Here, when the power source (61) fluctuates with time, the electric field E also changes with time. The electric field at this time is called an alternating electric field. The process of generating an alternating electric field in a CRT display device can be classified into the following three cases.

[0004] When caused by the power circuit and power cable of the CRT display device. The frequency of the alternating electric field in this case is 50/60 Hz. If a switching power supply is used in the power supply circuit, the above frequencies include 20 to 100 KHz.

[0005] When caused by a circuit that vertically deflects the electron beam in a CRT. In this case, an alternating electric field of 50 to 120 Hz is generated.

[0006] Caused by a horizontal deflection circuit or a circuit that generates the voltage required to perform the scan. The alternating electric field frequency at this time is 2 KHz to 400 KHz.

Recently, attention has been focused on the influence of the alternating electric field (which is a so-called leakage electromagnetic field) on the bodies of people who work in connection with VDT (visual display terminal). Immediately, when the electric conductors (62) and (63) are replaced with the electric field source and the human body, the electric field E (v / m) due to the distance d (m) between the electric field source and the human body and the voltage P (v) is The human body will be affected. In Sweden, a standard for leakage electromagnetic fields (MPR-II) was established in 1990, and this movement has spread to the whole world.

This standard is roughly classified into two types, that is, BANDI (5 KHz to 2 KHz) and BAND II (2 KHz to 400 KHz) depending on the frequency band. Here, the electric field in the frequency band corresponding to BANDII is generated mainly due to the switching power supply, the horizontal deflection circuit and the high voltage generation circuit as described above. Since these circuits generate a high voltage in terms of circuit operation, the voltage p (V) has a relatively large value with respect to the distance d (m) from the human body, and even when VDT and the human body are relatively distant from each other. The effect of the electric field E (v / m) on the human body cannot be ignored.

Conventionally, a method as shown in FIG. 7 has been adopted in order to reduce such a leakage electric field. FIG. 7 is an external view showing a shield structure of a conventional CRT display device. (71), (72), (73), and (74) are conductive metal plates and are the ground (GND) and deflection of the CRT. It is connected to the earth via the ground of the circuit and the high-voltage generating circuit, and also to the ground via the power cord of the AC mains power source, and shields the electric field leaked from the left, right, back and top surfaces of the CRT display device. The metal plate (71) is usually provided with punched small holes in order to consider the heat dissipation inside the device.

In this way, when the whole rear part of the device is shielded by the metal plate connected to the earth, the electric field outside the device is not affected by the voltage generated by the horizontal deflection circuit and the high voltage generation circuit but by the metal plate (71 ), (72), (73), and (74), but the potential of the metal plate (71) and so on is grounded to earth, so that it eventually goes to the outside of the device. The leakage electric field can be greatly reduced.

[0011]

[Problems to be solved by the device]

 The method of shielding the entire rear part of the device with the metal plate as described above is effective against the leakage electric field, but has a drawback that the weight of the device is significantly increased by the metal plate. There was also a problem in serviceability because the set could not be repaired without removing the metal plate.

The present invention has been made in view of such circumstances, and it is an object of the present invention to realize a shield structure for a CRT display device that is lightweight and has good serviceability.

[0013]

[Means for Solving the Problems]

 The present invention is a shield structure of a CRT display device for reducing a leakage electric field radiated from the CRT display device, which is a conductive strip having a strip shape around a part or the entire circumference of a voltage generating circuit for generating a voltage. And the conductive strip is grounded to the ground via the chassis frame of the CRT display device or the ground foil of the circuit board.

[0014]

[Action]

 Since the voltage generating circuit is locally shielded by the belt-shaped conductive belt, the CRT display device can be shielded with a light weight and the serviceability can be improved.

[0015]

【Example】

 FIG. 1 is an external view showing an embodiment of a shield structure of a CRT display device of the present invention. In the figure, (1) is a CRT, (2) is a DY (deflection yoke), (3) is a belt-shaped conductive sheet for preventing a leakage electric field, and (5) is a belt for preventing a leakage electric field. The widths of (3) and (5) are about the same as the width (L) of DY (2) as shown in the left side view of FIG. (6), (7) and (8) are chassis frames, and (9) is an earth lead wire included in the power cord. The earth lead wire (9) is electrically connected to the chassis frame (8). There is. Further, since the chassis frames (6) and (7) are electrically connected to the chassis frame (8), the chassis frames (6) and (7) are also grounded via the ground lead wire (9). There is. Although not shown, the secondary side ground foil of the printed circuit board (circuit board) is electrically connected to the chassis frames (6), (7), (8), and the secondary side ground foil is Grounded to ground via ground lead (9).

The strip-shaped conductive sheet (3) has a structure as shown in FIG. In the figure, (31) is an electrically insulating sheet of polycarbonate or the like, which is for preventing a metal foil (32) described later and a part of DY (2) from electrically contacting each other. .. (32) is a metal foil, and the metal foil (32) is preferably an aluminum foil (AL) in order to reduce the magnetic influence on DY (2). Reference numeral (33) is a hole for attaching the conductive sheet (3) with a screw or the like, and when attached, the metal foil (32) and the screw are configured to be electrically conductive by contact.

Then, the conductive sheet (3) is attached as shown in FIGS. 5 (A) and 5 (B). That is, the conductive sheet (3) is sandwiched between the chassis frame (6) and the metal plate (5), and the conductive sheets (3) are attached so as to be electrically connected to each other. Further, as shown in the left side view of FIG. 4, the conductive sheet (3) is attached at a position covering the main body of DY (2) as seen from the side, and the metal plate (5) is perpendicular to DY (2). Install the DY (2) at a position that covers the body of the DY (2) directly below.

The conductive sheet (3) and the metal plate (5), which are grounded to the ground as described above, are arranged so as to surround the outer periphery of DY (2), so that the electric field leaking from DY (2) is prevented. It is possible to reduce it to a very small level. However, it is not necessary to attach the conductive sheet (3) and the metal plate (5) at the same time, and the purpose can be achieved by only one of them depending on the level of the leakage electric field.

FIG. 2 is an external view showing another embodiment of the shield structure of the CRT display device of the present invention. In the figure, (4) is a strip-shaped metal plate that also serves as a chassis for preventing a leakage electric field, and its width is substantially the same as the width of DY (2), and it is the same as the conductive sheet (3). The leakage electric field can be mitigated by mounting at the same position.

Also, it is possible to reduce the leakage electric field by using a flat cable instead of the conductive sheet (3) and the metal plate (4). According to the flat cable, it is possible to have a structure in which it is mounted on the printed circuit board with a connector or the like, and it is possible to more easily reduce the leakage electric field. In this case, the connector may be connected to the ground foil.

Further, if necessary, a conductive sheet (3) is provided around the flyback transformer (FBT), so that the leakage electric field can be shielded at a higher level.

By adding a capacitor of about 3000 (PF) between the anode terminal of the CRT and the ground, it is possible to reduce the leakage electric field especially on the CRT tube surface side. By doing so, it is possible to further reduce the leakage electric field.

[0023]

[Table 1]

Table 1 shows data of the leakage electric field of the 14-inch CRT display device. In the table, 0 ° is the CRT tube surface side (front direction), 90 ° is the flyback transformer side (left side surface direction), 180 ° shows the measured data on the CRT neck side (backward direction) and 270 ° shows the measured data on the power source side (right side direction). Thus, by implementing the shield structure of the CRT display device of the present invention, the level of the leakage electric field can be kept within the MPR-II standard (2.5 (v / m)).

In the present embodiment, the shield structure has been described by taking DY as an example of the leakage electric field generation source, but other leakage electric field generation sources such as a switching power supply and a flyback transformer (FBT) are used. ), Etc. can be shielded in the same way.

Since the present invention is configured as described above, the leakage electric field can be reduced, and in particular, the shield such as DY which is the source of the leakage electric field in the frequency band of MPR-II standard BANDII is effectively used. can do.

Further, since the structure is such that the shield is locally provided, the air permeability is good, the temperature rise in the device can be suppressed, and the reliability of the circuit parts can be improved.

[0028]

[Effect of the device]

 According to the shield structure of the CRT display device of the present invention, it is possible to realize the shield structure of the CRT display device which is lightweight and has good serviceability.

[Brief description of drawings]

FIG. 1 is an external view showing an embodiment of a shield structure of a CRT display device of the present invention.

FIG. 2 is an external view showing another embodiment of the shield structure of the CRT display device of the present invention.

FIG. 3 is an overall configuration diagram of a conductive sheet (3).

FIG. 4 is a left side view of the shield structure of the CRT display device of the present invention.

FIG. 5 is an explanatory view of a mounting structure of a conductive sheet (3).

FIG. 6 is an explanatory diagram for explaining generation of an electric field E.

FIG. 7 is an external view of a shield structure of a conventional CRT display device.

[Explanation of symbols]

 1 CRT 2 DY 3 Conductive Sheet 4 Metal Plate 5 Metal Plate 6 Chassis Frame 7 Chassis Frame 8 Chassis Frame 9 Ground Lead Wire 10 Conductive Screw 31 Electrical Insulation Sheet 32 Metal Foil 33 Mounting Hole 61 Power Supply 62 Conductor 63 Conductive body

Claims (2)

[Scope of utility model registration request] 1. A shield structure for a CRT display device for reducing a leakage electric field radiated from the CRT display device, comprising a strip-shaped conductive material around a part or the entire circumference of a voltage generating circuit for generating a voltage. A shield structure for a CRT display device, characterized in that a band is arranged and the conductive band is grounded to ground via a chassis frame of the CRT display device or a grounding foil of a circuit board. 2. The shield structure for a CRT display device according to claim 1, wherein the voltage generating circuit is a deflection yoke or a flyback transformer.