This invention relates to cathode ray tube displays having saddle-type deflecting coils, more specifically, cathode ray tube displays improved to reduce temperature rise of their deflection yokes.

Recently, the amount of information displayed on monitors is increasing as the demands of operating systems such as Windows (the operating system by Microsoft) increase. As a result, higher display resolutions are required. For example, resolution of 1024× 768 dots has been generalized for personal computers, and resolution of 1600×1028 dots has become more popular for work station usages. Displays having a white background are frequently used in Windows. As a result, the average luminance of the screen increases and flickers often become noticiable. Therefore, the vertical deflection frequency is generally predetermined to be at least 70Hz while the conventional frequency is 60Hz.

As the resolution becomes higher and the vertical deflection frequency increases, the horizontal deflection frequency inevitably rises. As a result, the increased temperature of the deflection yoke attached to a cathode ray tube display becomes problematic.

Several methods to reduce such a temperature rise have been disclosed in various references including Published Unexamined Japanese Patent Application No. Sho 59-186239. For example, reducing the diameter of the bare wire which forms the saddle-type coils of the deflection yoke is to no more than 0.15mm reduces the temperature rise due to skin effect. Also, temperature rise due to eddy current loss can be reduced by using litz wires.

However, several drawbacks are found in the above-mentioned methods of forming saddle-type coils. For instance, the wires are easily broken in the winding process, or the cost of the wire material is prohibitive.

EP-A-0 424 946 A2 refers to a color cathode ray tube apparatus having reflection means in form of saddle-type horizontal and saddle-type vertical coils. The ray tube apparatus has an extended cylindrical neck accomodating an electron gun for outputting three in-line electron beams. The deflection means are arranged to extend on outer surfaces of said neck and the funnel. The length of the saddle-type horizontal deflection coil in a direction to the tube axis should not be less than 90 mm to improve the heat radiation characteristics.

Patent abstracts of JP, Vol. 10, no. 11 (E-374) & JP-A-60175345 discloses a deflection yoke which has a saddle-type horizontal deflection coil. To increase the coil surface area for improving the radiation efficiency it is proposed to arrange the conductive part of the frontal end or the rear end of the horizontal deflection coil as saddle shape on the core while bending the same in the centre direction of the deflection yoke outside the core.

This invention aims to provide cathode ray tube displays which reduce the temperature rise of the deflection yokes without using either extra-fine wires or litz wires. For this purpose, the radiation of heat from the saddle-type coils is increased.

In order to achieve this goal, the cathode ray tube display of this invention according to claim 1 comprises a cathode ray tube main body and a deflection yoke located at the rear periphery of the main body. The deflection yoke comprises a saddle-type horizontal coil, an insulating frame located outside the saddle-type horizontal coil, a vertical coil and a ferrite core located outside the insulating frame. The saddle -type horizontal coil is partially exposed from the screen-side end face of the ferrite core toward the screen. The first structural characteristic of this invention is that the surface area of the exposed portion of the saddle-type horizontal coil is predetermined to be from 100 cm² to 298 cm².

The vertical coil can be a saddle-type vertical coil or a toroidal coil.

The saddle-type vertical coil is also partially exposed from the screen-side end face of the ferrite core toward the screen. The second structural characteristic of this invention according to claim 3 is that the surface area of the exposed portion of the saddle-type or toroidal vertical coil is predetermined to be from 55 cm² to 185 cm².

According to the first or second structure, the exposed portion of either the saddle-type horizontal coil or the saddle-type vertical coil is increased so that the heat radiation effect is improved. Therefore, the temperature rise of the deflection yoke can be reduced without using either extra-fine wires or litz wires. The details are as follows.

When a deflection yoke operates, its energy loss changes into heat, thus the temperature rises. The temperature begins to rise as the operation starts, and reaches equilibrium after a predetermined amount of time. The energy loss of the saddle-type coils is very high, and is the main factor in the temperature rise of the deflection yoke. As the horizontal deflection frequency becomes high, the ohmic loss due to the skin effect of the wires forming the saddle-type coils and eddy current loss on the saddle-type coils increase. As a result, the temperature rise of the deflection yoke becomes remarkable. In order to reduce such a temperature rise, several methods have been proposed. For example, the heating-up is reduced by decreasing the ohmic loss and the eddy current loss of the saddle-type coils. Another method is to promote the heat radiation from the deflection yoke (saddle-type coils). This invention focuses on the latter method.

The temperature of the saddle-type coils of the deflection yoke changes corresponding to time. In the following equation, "Q" indicates the heat which the saddle-type coils generate in a unit time. "W" indicates the mass of the saddle-type coils. "A" indicates the surface area of the saddle-type coils. "a" indicates the heat radiation coefficient. "c" indicates the specific heat of the saddle-type coils, and "θ" indicates the temperature rise. The heat generated during the time dt is Qdt. This heat partially raises the temperature of the saddle-type coils by dθ , and the rest of the heat is radiated from the surface of the saddle-type coils during the time dt. Therefore, the heat equilibrium can be represented by equation (1).$$\text{Q • dt = c • W • dθ + a • A • θ • dt}$$

The following equation (2) is obtained by solving the equation (1) where the initial condition of the temperature rise θ is zero.$${\text{θ = θ}}_{\text{f}}{\text{• (1 - e}}^{\text{-t/T}}\text{)}$$

Here, θ_f indicates the final temperature of the saddle-type coils and T indicates time constant, both of which are obtained from the following equation (3) or (4).$${\text{θ}}_{\text{f}}\text{= Q / (a • A)}$$$$\text{T = c • W / (a • A)}$$

When the radiation coefficient "a" is fixed, Q should be decreased or A should be increased compared to equation (3) in order to reduce the temperature rise of the saddle-type coils. Decreasing Q means to reduce the ohmic loss or eddy current loss of the saddle-type coils, or it means to decrease the consumption current by improving the deflection sensitivity of the saddle-type coils. Increasing "A" means to enlarge the surface area of the saddle-type coils.

Heat convection phenomenon should also be taken into consideration in improving the heat radiation effect of the saddle-type coils. As shown in FIG. 3, when an object of t°C is in air of t_o °C (t > t_o), the air near the surface of the object receives the object's heat by contact and radiation, and becomes lighter as its temperature rises. Thus, convections are generated so that the air takes away the heat. "a_c" indicates the heat which is taken away from a unit of surface area in a unit time due to this heat convection. The value of a_c becomes bigger as the difference (t - t_o) between the temperatures of the object and that of the air is greater (cf. equation (5)).$${\text{a}}_{\text{c}}{\text{= C • H}}^{\text{-1/4}}{\text{(t - t}}_{\text{o}}{\text{)}}^{\text{5/4}}{\text{\hspace{1em}\hspace{1em}\hspace{1em}[W / (m}}^{\text{2}}\text{• °C)]}$$

In this equation, C indicates the constant and H indicates the height of the object. Therefore, the air contacting with the object should be as cool as possible so that the temperature rise of the saddle-type coils can be reduced.

Based on such reasons, the saddle-type coils of the cathode ray tube display of this invention improves the heat radiation effect. For this purpose, the surface area of the deflection yoke which is not surrounded with the ferrite core is enlarged so that the heat radiating surface area is increased and the heat convection is promoted.

FIG. 1 is a plan view of a cathode ray tube display of the first embodiment of this invention.

FIG. 2 is a side view of a cathode ray tube display of the second embodiment of this invention.

FIG. 3 is a schematic view describing heat radiation due to heat convection.

FIG. 4 is a graph showing the relation between the exposed surface area of the saddle-type horizontal coil and the temperature rise of the same coil. The saddle-type horizontal coil is partially exposed from the screen-side end face of the ferrite core of the deflection yoke toward the screen.

FIG. 5 is a graph showing the relation between the exposed surface area of the saddle-type vertical coil and the temperature rise of the same coil. The saddle-type vertical coil is partially exposed from the screen-side end face of the ferrite core of the deflection yoke toward the screen.

The embodiments of this invention are explained below by referring to the drawings.

FIG. 1 is a plan view of a 41cm(17") • 90° cathode ray tube display according to the first embodiment of this invention. A cathode ray tube main body 1 comprises a glass panel 2 and a glass funnel 3 connected to the rear of the glass panel 2. An electron gun (not shown) is attached to the rear of the glass funnel 3. A deflection yoke 8 is attached to the rear periphery of the glass funnel 3. The deflection yoke 8 comprises a saddle-type horizontal coil 4, an insulating frame 5 located outside the saddle-type horizontal coil 4, a saddle-type vertical coil 6 located outside the insulating frame 5, and a ferrite core 7 located outside the saddle-type vertical coil 6. The saddle-type coils (4, 6) are formed by winding a bundle of normal wires (not litz wires) of 0.25mm diameter. Numeral 9 indicates the screen-side end face of the ferrite core 7. The saddle-type horizontal coil is partially exposed from the end face 9 toward the screen, and the surface area of the exposed part is set to be 185cm².

FIG. 4 indicates the relation between the exposed surface area S_H of the saddle-type horizontal coil 4 and the temperature rise Δt_H of the same coil. The shapes and positions of the insulating frame 5, the saddle-type vertical coil 6 and the ferrite core 7 are illustrated in FIG. 1. The deflection yoke 8 is operated such that the horizontal deflecting frequency is 82kHz, the vertical deflection frequency is 71Hz, anode voltage is 25kV, and the raster size is 309 × 232mm. The temperature rise Δt_H of the saddle-type horizontal coil 4 is defined by the difference between the highest temperature of the saddle-type horizontal coil 4 and the average ambient temperature around the deflection yoke 8. The surface area S_H is varied by fixing the wire winding angle and extending the coil to the screen side.

According to FIG. 4, the Δt_H reducing effect appears when S_H is 100cm² or more. The value of Δt_H is the smallest when S_H is 185cm², and later the value of Δt_H increases. These results occur when the coil length of the saddle-type horizontal coil 4 is extended to the screen side in order to increase S_H. As a result, the deflection center is shifted to the screen side and the deflection sensitivity is deteriorated, thus the Δt_H reducing effect is decreased. When S_H exceeds 298cm², the Δt_H reducing effect is lost, Therefore, the surface area S_H is predetermined to be 185cm² in this embodiment. However, the temperature rise Δt_H of the saddle-type horizontal coil 4 can be reduced if S_H ranges from 100 to 298cm².

FIG. 2 is a side view of a 41cm(17") • 90° cathode ray tube display according to the second embodiment of this invention. Similar to the first embodiment, a cathode ray tube main body 10 comprises a glass panel 11 and a glass funnel 12 connected to the rear of the glass panel 11. An electron gun (not shown) is attached to the rear of the glass funnel 12. A deflection yoke 17 is attached to the rear periphery of the glass funnel 12. The deflection yoke 17 comprises a saddle-type horizontal coil 13, an insulating frame 14 located outside the saddle-type horizontal coil 13, a saddle-type vertical coil 15 located outside the insulating frame 14, and a ferrite core 16 located outside the saddle-type vertical coil 15. The saddle-type coils (13, 15) are formed by winding a bundle of normal wires (not litz wires) of 0.25mm diameter. Numeral 18 indicates the screen-side end face of the ferrite core 16. The saddle-type vertical coil is partially exposed from the end face 18 toward the screen, and the surface area of the exposed part is predetermined to be 115cm².

FIG. 5 indicates the relationship between the exposed surface area S_v of the saddle-type vertical coil 15 and the temperature rise Δt_v of the same coil. The shapes and positions of the insulating frame 14, the saddle-type horizontal coil 13 and the ferrite core 16 are shown in FIG. 2. The deflection yoke 17 is operated such that the horizontal deflecting frequency is 82kHz, the vertical deflection frequency is 71Hz, anode voltage is 25kV, and the raster size is 309×232mm. The temperature rise Δt_v of the saddle-type vertical coil 15 is defined by the difference between the highest temperature of the saddle-type vertical coil 15 and the average ambient temperature around the deflection yoke 17. The surface area S_v is varied by fixing the wire winding angle and extending the coil to the screen side.

According to FIG. 5, the Δt_v reducing effect appears when S_v is 55cm² or more. The value of Δt_v is lowest when S_v is 115cm². Between an S_v of 115cm² and 185cm² the value of Δt_v continues to increase until, at 185cm², Δt_v again decreases. This result occurs because eddy current loss due to the increase of interlinkage between the horizontal deflection magnetic field and the saddle-type vertical coil 15 as S_v becomes bigger. The interlinkage and the eddy current loss are saturated if the value of S_v exceeds 185cm². When the value of S_v exceeds 185cm², the saddle-type vertical coil 15 becomes too large, and the direct current resistance is increased. Such equipment cannot be practically used.

Therefore, the surface area S_v is set to be 115cm² in this embodiment. However, the temperature rise Δt_v of the saddle-type vertical coil 15 can be reduced if S_v ranges from 55 to 185cm².

The deflection yoke of each embodiment explained above comprises a saddle-type vertical coil. However, the vertical coil can be replaced by a troidal type coil. A troidal type vertical coil can be wound on the ferrite core.

As mentioned above, the cathode ray tube display of this invention can improve its heat radiation effect and reduce temperature rise. For this purpose, the surface area of the saddle-type coil part which is exposed from the screen-side end face of the ferrite core of the deflection yoke toward the screen is enlarged in order to create the effect of expanding radiation surface area and convection of the heat. Therefore, neither expensive extra-fine wires nor litz wires are necessary for these saddle-type coils. In addition, the breakage of wires can be reduced during the coil winding process.