Fluorescent display tube with pulse voltage driving to the cathodes at different times

Abstract

This fluorescent display tube includes an anode and a plurality of filament-shaped cathodes both provided in an envelope, a support as one of a pair of support bodies which support the cathodes is electrically divided for each of the cathodes and at the time of driving, and a cathode driving IC gives pulse voltages to the cathodes at different timing. Since the voltages are applied to the arranged cathodes sequentially, current flowing through the cathode driving IC can be small as compared with a case where voltages are simultaneously applied to a plurality of cathodes. Heat generation of the cathode driving IC is suppressed, and costs required for the cathode driving IC are reduced.

Claims

1. A fluorescent display tube comprising: an envelope allowing an interior thereof to be held in a high-vacuum state; an anode in which a phosphor layer is adhered onto an anode conductor provided on an inner surface of the envelope; a plurality of filament-shaped cathodes placed above the anode in the envelope by a pair of support bodies supporting both ends of each of the cathodes; an anode driving unit for driving the anode; and a cathode driving unit for driving the cathodes, wherein by driving the anode and the cathodes by the anode driving unit and the cathode driving unit, respectively, electrons discharged from the cathodes are made to collide against the anode so as to allow the phosphor layer to emit light, and wherein at least one of the pair of support bodies is electrically divided for each of the cathodes, and the cathode driving unit gives pulse voltages to each of the cathodes at different timing.

2. The fluorescent display tube according to claim 1, wherein the cathode driving unit can arbitrarily change a pulse width of the pulse voltage.

3. The fluorescent display tube according to claim 1, wherein the cathode driving unit gives the pulse voltage only to the cathode corresponding to the anode which is to emit light.

4. The fluorescent display tube according to claim 1, wherein the cathode driving unit and the anode driving unit are respectively formed from separate driving elements.

5. The fluorescent display tube according to claim 1, wherein the cathode driving unit and the anode driving unit commonly use one power source.

6. The fluorescent display tube according to claim 1, wherein the cathode driving unit and the anode driving unit commonly use one driving element.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic block diagram of a fluorescent display tube according to a first embodiment;

(2) FIG. 2 is a diagram showing the fluorescent display tube when an entire surface lights to light an entire display pattern and showing pulse voltage given to cathodes in the first embodiment;

(3) FIG. 3 is a diagram showing, in a vertically contrasting manner, pulse voltage given to the cathodes at the time of normally lighting and at the time of dimming lighting in the first embodiment;

(4) FIG. 4 shows the fluorescent display tube at the time of standby electricity lighting when a portion of the display pattern is lighted, and pulse voltage given to the cathodes in the first embodiment;

(5) FIG. 5 is a schematic block diagram of a fluorescent display tube according to a second embodiment;

(6) FIG. 6 is a schematic block diagram of a fluorescent display tube according to a third embodiment; and

(7) FIG. 7 is a diagram showing a power source configuration in a conventional fluorescent display device.

DETAILED DESCRIPTION

(8) A first embodiment of the present invention will be described with reference to FIGS. 1 to 4.

(9) FIG. 1 is a schematic block diagram of a fluorescent display tube 1 according to the first embodiment. This fluorescent display tube 1 includes an envelope 2, and an interior of the envelope 2 is held in a high-vacuum state. The envelope 2 is formed by assembling insulative material, e.g., plate material made of glass for example into a box shape using sealing glass. Although details are not illustrated, an inner surface of a substrate configuring a portion of the envelope 2 is provided with an anode conductor connected to an anode wire 3, a phosphor layer is adhered onto the anode conductor, and an anode 4 of a predetermined light-emitting pattern is configured. Inside the envelope 2, a control electrode 6 (also called grid) connected to a control electrode wire 5 is placed above an anode 4. Inside the envelope 2, a plurality of filament-shaped cathodes 7 are stretched above the control electrode 6. Both ends of each of the cathodes 7 are connected to pairs of support bodies 8a and 8b. Ones (right side in FIG. 1) of the pairs of support bodies 8a and 8b are a plurality of supports 8a which are electrically divided for each of the cathodes 7 and which respectively fix one ends of the cathodes 7. The other ones (left side in FIG. 1) are electrically and structurally integral, but are a plurality of anchors 8b having arm structures which function as leaf string for giving tensions to the other ends of the cathodes 7.

(10) In this embodiment, although the supports 8a are electrically divided for each of the cathodes 7 to individually and sequentially driving the plurality of filament-shaped cathodes 7 by pulse voltages as will be described later, the anchors 8b may electrically be divided instead of the supports 8a, or both of them may electrically be divided.

(11) An anode driving IC 10 as a driving element which is an anode driving unit for driving the anode 4 is provided in the envelope 2. This anode driving IC 10 also functions as a control electrode driving IC which is a control electrode driving unit for driving the control electrode 6. Therefore, this anode driving IC 10 is connected to an anode grid power source VH, and an input-side terminal of the anode driving IC 10 is located outside the envelope 2. A portion of an output-side terminal of the anode driving IC 10 is connected to anode wire 3, and the other portion of the output-side terminal is connected to the control electrode wire 5.

(12) A cathode driving IC 11 as a driving element which is a cathode driving unit for driving the cathodes 7 is provided in the envelope 2. The input-side terminal of the cathode driving IC 11 is connected to a cathode power source VHF which is located outside the envelope 2. The output-side terminal of the cathode driving IC 11 is electrically divided into the same number of terminals as those of the cathodes 7 so that the plurality of cathodes 7 can individually be driven. The divided output-side terminals are guided to the outside of the envelope 2, and are connected to amplifier circuits 12 composed of transistors Tr located outside the envelope 2.

(13) FIG. 2 is a diagram showing the fluorescent display tube 1 at the time of an entire surface lighting when the entire display pattern of the anode 4 is lighted and showing driving timing of the plurality of cathodes 7 in the first embodiment. When the entire surface of the display pattern lights, the cathode driving IC 11 sequentially gives pulse voltages to the electrically independent plurality of cathodes 7 while deviating timing one by one in the arranged order. The anode driving IC 10 gives predetermined voltages to the anode 4 and the control electrode 6. According to this, electrons are discharged from the cathodes 7, the electrodes are accelerated and controlled by the control electrode 6, and the electrons collide against the anode 4, and the phosphor layer emits light. Light emission of the phosphor layer of the anode 4, i.e., light emission of the display pattern is observed through the translucent envelope 2. In the illustrated example, as display patterns, thick (black finished) literatures, i.e., DVD and MP3 in an upper stage, AM 18:00 in a middle stage, and other symbols in a lower stage express that they are displayed in a luminescent manner.

(14) According to the fluorescent display tube 1 of this embodiment, the supports 8a of the pairs of support bodies 8a and 8b which support the filament-shaped cathodes 7 are electrically divided for each of the cathodes 7, and when the cathodes 7 are driven, pulse voltages are given to the cathodes 7 at different timing. That is, voltages are applied to the plurality of filament-shaped cathodes 7 which are arranged side by side while deviating the cathodes 7 one by one. Therefore, as compared with a case where the voltages are simultaneously applied to the plurality of filament-shaped cathodes 7, current flowing through the cathode driving unit (cathode driving IC 11 in this embodiment) may be small. For example, when it is necessary to flow current of 30 mA through one cathode 7, the cathodes 7 are driven one by one and two or more cathodes 7 are not driven simultaneously in this embodiment. Therefore, only current of 30 mA which is for one cathode 7 flows as instantaneous current. However, in the conventional fluorescent display tube described in the column of Related Art, since currents flows through all of the plurality of cathodes collectively, current of 30 mAthe number of cathodes flows. If there are ten cathodes, current of 300 mA flows but in this embodiment, only 30 mA is enough, and a current amount is reduced to 1/10. Generally, to flow more current through the IC, it is necessary to make a wire width in the IC thicker, an outer shape of the IC becomes large and costs thereof increase. According to this embodiment, since the amount of current flowing through the IC is small, heat generation of the cathode driving IC 11 is suppressed, and it is unnecessary to make the wire width in the IC thick. Therefore, costs required for the cathode driving IC 11 can also be reduced.

(15) FIG. 3 is a diagram showing pulse voltage Ef given to the cathodes 7, an upper diagram shows normal lighting, and a lower diagram shows dimming lighting. Here, the dimming lighting means adjustment of light emitting brightness of a display pattern in accordance with peripheral brightness, more specifically, the dimming lighting means adjustment carried out when peripheral brightness becomes dark to lower the light emitting brightness of the display pattern which is set in accordance with a state where periphery is bright.

(16) A case where the fluorescent display tube 1 of this embodiment is applied to an in-car display device such as display devices of various kinds of meters and a car navigation system for example will be described. In the case of the in-car display device, since periphery is generally bright during the day, a display pattern emits light at brightness of a predetermined value or higher to secure display visibility. However, at evening to night, since the display which is set during daytime is too bright, dimming lighting for lowering the light emitting brightness of the display pattern is carried out by shortening the lighting time. However, peripheral darkness and temperature of the cathodes 7 become high, there is a problem that red heat of the cathodes 7 becomes outstanding if no countermeasure is taken, and display quality is deteriorated.

(17) Hence, in this embodiment, dimming lighting is carried out by shortening a pulse width as shown in the lower stage in FIG. 3 as compared with a pulse width at the time of normal lighting shown in the upper stage in FIG. 3, thereby shortening time during which voltage is applied to the cathodes. According to this, since the temperature of the cathodes 7 is optimized when periphery is dark, an inconvenient phenomenon that the cathodes 7 glow does not occur, and display quality is maintained at the same level as the daytime normal lighting. This dimming lighting can be carried out only at a specific portion corresponding to a specific cathode 7 in a display area.

(18) FIG. 4 shows the fluorescent display tube 1 at the time of standby electricity lighting when a portion of the display pattern of the anode 4 lights, and pulse voltage given to the cathodes 7 at the time of the standby electricity lighting in this embodiment. Here, in the display pattern, thick (black finished) literatures show that AM 18:00 in a middle state is displayed in a luminescence manner, and hollow literatures show that DVD and MP3 in an upper stage and other symbols in a lower stage are displayed in a non-luminescence manner.

(19) When such standby electricity lighting is carried out, the cathode driving IC 11 gives pulse voltage only to cathodes 7 (central two cathodes of six cathodes 7 in the illustrated example) which correspond to the display pattern AM 18:00 of the anode 4 which is to emit light as shown in FIG. 4. According to this driving method, since pulse voltage can be given only to necessary cathodes 7 in accordance with the display pattern of the anode 4, power consumption can be saved or reduced. Electricity is applied to the six cathodes 7 when the entire surface lights shown in FIG. 2, but electricity is applied to two cathodes 7 at the time of standby electricity lighting shown as one example in FIG. 4. Therefore, only cathode current is enough at the time of standby electricity lighting as compared when the entire surface lights.

(20) A second embodiment of the present invention will be described with reference to FIG. 5.

(21) A cathode driving IC 11a of a fluorescent display tube 1a is provided therein with a function of the amplifier circuits 12 in the first embodiment (FIG. 1). Therefore, an amplifier device is not provided outside an envelope 2 of the fluorescent display tube 1a. An output-side terminal of the cathode driving IC 11a is electrically divided into the same number of terminals as a plurality of cathodes 7 so that the cathodes 7 can individually be driven. The divided output-side terminals are not guided to the outside of the envelope 2, and are directly connected to a plurality of supports 8a which are ones of pairs of support bodies 8a and 8b. Other configurations are the same as those of the first embodiment. According to the second embodiment, the outside amplifier circuits 12 do not exist, and output of the cathode driving IC 11a can be output directly to each of the cathodes 7. Therefore, a configuration as an entire device can further be simplified.

(22) Although the cathode driving ICs 11, 11a and the anode driving IC 10 utilize separate power sources in the above-described embodiments, if the cathode driving IC 11a and the anode driving IC 10 commonly use one power source VHF as in a third embodiment shown in FIG. 6, since the number of power sources can be reduced, production costs including circuit costs can be reduced.

(23) The cathode driving ICs 11, 11a and the anode driving IC 10 are composed of separate driving elements in the above-described embodiments. Alternatively, if one driving element is commonly used, a function to drive cathodes and a function to drive the anode and the control electrode are incorporated in one element on a software base, it is possible to reduce the circuit costs and production costs as compared with the embodiments.

(24) As described above, according to the fluorescent display tubes 1 and 1a of the embodiments, currents does not flow simultaneously through the plurality of filament-shaped cathodes 7, and a dynamic driving method for sequentially applying pulse voltages to the electrically divided cathodes 7 is employed. Therefore, power consumption can be reduced, and it is possible to drive only one or some of cathodes 7 which correspond to an area to be displayed. Hence, a power consumption cutting-off effect at the time of standby electricity lighting is high. Further, when cathode voltage is low and cathode current is large as in the conventional technique, a range selection of parts is narrow and it is difficult to configure a power source. However, since power consumption of the fluorescent display tubes 1, 1a of the embodiments is small, it is possible to secure flexibility of selection of parts of the driving circuit, and a configuration of the power source can be facilitated as compared with the conventional technique. When control of dimming lighting is performed, since it is possible to adjust voltage by increasing or reducing a width of the pulse voltage, it is possible to solve the inconvenience that red of the cathode 7 becomes outstanding, and sufficient display quality can be achieved.

REFERENCE SIGNS LIST

(25) 1, 1a, 1b fluorescent display tube 2 envelope 4 anode 7 cathode 8 support body 8a support 8b anchor 10 anode driving IC as driving element which is anode driving unit 11 cathode driving IC as driving element which is cathode driving unit 12 amplifier circuit VH anode grid power source VHF cathode power source Tr transistor configuring amplifier circuit