JPH01120540A - Image display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a backlight lighting circuit for an image display device.

[Conventional technology]

Image display devices that use an image display plate such as a transparent layer liquid crystal panel for image display generally use a backlight device such as a fluorescent discharge tube as a light source. Fluorescent discharge tubes are generally inexpensive, have high color temperature, high brightness, and high efficiency, so they are often used in N-image display devices. There was a decline.

FIG. 2 shows a characteristic diagram showing the temperature-luminance characteristics of a puff light device using a cold cathode fluorescent discharge tube used in a conventional image display device.

What can be seen from the figure is that the brightness at low temperatures is extremely low, and at around 20a' Celsius, it is about 1/4 of the brightness at room temperature.

Among image display devices, devices such as television receivers that are used indoors are rarely used in low temperatures, especially when the ambient temperature is below freezing. There was no need to take any special measures against the discharge tubes.

[Problem that the invention seeks to solve]

However, among image display devices, electronic viewfinders and the like built into video cameras are required to operate under exactly the same environment as the video camera. Also, it is a video monitor for playing back immediately after recording with a video camera.
It is also required to operate under the same environment.

The environment in which the video camera is used cannot be indoors or outdoors. Furthermore, it is not unusual for it to be used at low temperatures, such as below freezing.

Therefore, in conventional video monitor devices that use image display boards such as transmissive liquid crystal panels, which are not designed to be used at temperatures below freezing, the brightness of the screen will drop significantly at low temperatures. In some cases, it was unable to function as a video monitor device.

Therefore, the present invention aims to solve the problems of the image display device using the conventional transmission shadow image display board, and its purpose is to reduce the tube current of the fluorescent discharge tube used as a backlight. The objective is to compensate for the brightness of the fluorescent discharge tube at low temperatures by using the temperature characteristics of the capacitor used for limiting.

[Means for solving problems]

The image display device of the present invention uses a transmission-type image display board, and reduces the amount of transmitted light from a backlight device using fluorescent discharge tubes. In an image display device that displays an image by control, a capacitor is connected in series with the fluorescent discharge tube to limit the tube current of the fluorescent discharge tube, and the temperature coefficient of the capacitance value of the capacitor is at least below room temperature to minus Celsius. It is characterized by a negative hot water temperature coefficient between 20 degrees.

〔Example〕

FIG. 1 shows an overall block diagram of an image display device including essential parts of the present invention. The same figure is ti! Image display image display 2 also uses a color liquid crystal electronic view 7 that uses a color liquid crystal panel in the electronic viewfinder used in the video camera.
This is an example of Ai/Da.

A video composite signal is input to input 1, and part of it is input to Y-C separation circuit 2, which separates the luminance signal and color signal, and passes through color demodulation circuit 3, producing three primary color signals of R+G and H. . The primary color signals are then sent to the RGI 30, which performs rotation of the three primary colors in accordance with the arrangement of color filters on the liquid crystal panel 5.
/f * Manually powered by Le5. Further, a part of the video composite signal input to the human input 1 passes through a sync separation circuit 6 and a sync circuit 7 to produce a sync signal. The signal is then inputted to the liquid crystal panel 6 via a clock generation circuit 8 and a level shift circuit 8 in order to create a lock necessary for driving the liquid crystal panel 5. Here, the liquid crystal panel 5 used is an active matrix type having a built-in shift register and driver.

Further, power is supplied to the input 10 from the video camera body. The supplied power is used by the switching power supply circuit 11 to generate necessary voltages for each part. Further, the input 10 is also directly connected to a backlight lighting circuit 12 that includes the main parts of the present invention, and supplies power to the backlight lighting circuit 12 to light the cold cathode fluorescent discharge tube 13. As mentioned in the prior art, the color liquid crystal electronic viewfinder is required to have a very wide operating range, so it is necessary to ensure a sufficient range even at low temperatures.

FIG. 3 shows a backlight lighting circuit diagram for explaining the present invention in detail. In the figure, a cold cathode fluorescent discharge tube 25 is used for the backlight, and the circuit type is a self-excited bush-pull circuit. The circuit operation will be explained below.

A description will be given starting from a state in which the power supply 14 is turned on to the circuit via the choke mile 15. First, when the power is turned on, transistor 2
Assume that 1 is energized. A current flows through the flefter winding 17, and at the same time, a voltage is induced in the base winding 18, and the transistor 21 is further driven in the current-carrying direction. Then, the transistor 21 rapidly becomes saturated due to the positive feedback action of the base winding, and the voltage from the power supply 14 increases to the collector winding 17.
Since it is applied to both ends of the core, the core magnetic flux increases linearly, and the core becomes saturated. As the transformer 16 neutralizes, the current increases rapidly and reaches a value limited by the drive voltage provided by the base winding 1118, after which the collector winding 11
The voltage across 17 drops and transistor 21 begins to switch off. Therefore, an induced voltage in the opposite direction is generated in the transformer 16, and a voltage is similarly induced in the collector winding 17 of the transistor 20 connected to the transformer 16.
As a result, the transistor 20 starts to conduct Ti.

Transistor 20 is then quickly switched on and transistor 21 is switched off. Thereafter, the operation is similar to that when the transistor 20 is switched on, and this cycle is repeated, resulting in continuous oscillation. The voltage generated by the continuous oscillation is generated in the load winding 19, which is a secondary winding, according to the winding ratio with respect to the collector winding 17, and is passed through the cold cathode through the current limiting capacitor 24 that limits the tube current. The fluorescent discharge tube 25 is turned on. The relationship between the brightness of the cold cathode fluorescent discharge tube 25 and g current is proportional, and as the tube current increases, r4If also increases. Therefore, it can be seen that in order to increase the brightness, it is sufficient to increase the capacitance of the current limiting capacitor 24 that limits the 9F current and lower the impedance. In the present invention, the current limiting capacitor 24 has a low temperature capacitance value of several 1 with respect to room temperature.
A capacitor that is larger than 0% was used. Note that normal temperature is defined here as plus 25 degrees.

FIG. 4 shows the capacitance change characteristics with respect to temperature of the capacitor used in the present invention. The capacitor is a ceramic capacitor mainly made of strontium titanate, and the Curie point of the capacitance is set to around minus several tens of tts. The capacitance change at low temperatures, especially around minus 20 ff, is more than 30% thicker than the normal temperature of plus 25 ff. The one is YN type or Y58!J,
, YST type, and D type. FIG. 6 shows the results of improving brightness by increasing the tube current at low temperatures using the capacitor described above. The solid line graph shows the conventional characteristics shown in FIG. 2 for comparison.

According to FIG. 5, the brightness at low temperatures, especially near minus 20 If, is about twice that of the conventional system, and even near zero degrees Celsius, the brightness is significantly improved by about 30%.

Therefore, according to the present invention, the brightness at low temperatures can be significantly compensated for.

In order to achieve the effects of the present invention, the temperature coefficient of the tube current limiting capacitor is sufficient to compensate for the brightness of the cold cathode fluorescent discharge tube, and the temperature characteristics of the cold cathode fluorescent discharge tube must be adjusted under all A degree conditions. Ideally, they should be the same.

6 and 7 show an example in which the method of connecting the g-current limiting capacitor has been slightly improved in the backlight lighting circuit shown in FIG. 3 for explaining the present invention. In the figure, only the secondary side of the oscillation transformer 30 is shown, and the primary side circuit is omitted.

In FIG. 6, a ceramic capacitor 27 such as a YN type, which has a large capacitance change rate at low temperatures, and an SL type, which has a small capacitance change rate with temperature changes, are used as tube current limiting capacitors. This is an example in which ceramic capacitors 28 such as the following are connected in series. The effect shown in the figure is that by limiting the upper limit of the change in the capacitance value of the combined capacitor 27.28, which is a tube current limiting capacitor, at low temperatures, the tube current can be unlimited at extremely low temperatures. The purpose is to prevent the flow to 29.

In Fig. 7, a ceramic capacitor 27 such as YN type 1 and a ceramic capacitor 2 such as 5LIJ1 are shown, contrary to Fig. 6.
This is an example in which 8 are connected in parallel. The effect of this figure is to limit the lower limit of the change in the capacitance value of the six-component capacitor at high temperatures, and to limit the lower limit of the tube current flowing through the cold cathode fluorescent discharge tube 29 at high temperatures.

In the present invention, a self-excited bush-pull circuit is shown as the backlight lighting circuit, but the same thing can be achieved even if it is a separately excited type or a single circuit. Further, although a cold cathode fluorescent discharge tube is shown as an example of the fluorescent discharge tube, the same effect can be obtained even if a hot cathode fluorescent discharge tube is used.

Furthermore, the scope of application of the present invention also includes liquid crystal television equipment and projectors such as the reflective liquid crystal display device W1.

Further, within the scope of the claims of the present invention, the temperature coefficient of the capacitor used for limiting the tube current is below normal temperature (here defined as 25 degrees Celsius) or below -20 degrees Celsius, and has a negative temperature coefficient. However, there is no problem even if the temperature is below minus 20 degrees Celsius or above 25 degrees Celsius.

〔Effect of the invention〕

As described above, the image display II of the present invention solves the conventional problem that the brightness of the backlight light source decreases at low temperatures, making it extremely difficult to see at low temperatures, and depending on the temperature, it can be almost impossible to see. We were able to solve this problem using a very simple and reliable method of brightness compensation based on the temperature characteristics of . The best part of the present invention is that it does not require the addition of any negative parts, and it does not require any additional parts.
The brightness compensation was performed without the need for adjustment. Furthermore, since the amount of compensation can be changed by simply changing to a capacitor with a different temperature characteristic, it is possible to use a variety of fluorescent tubes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color liquid crystal electronic viewfinder for explaining one embodiment of the present invention. FIG. 2 is a temperature-luminance characteristic diagram of a backlight device used in a conventional image display 8H. FIG. 3 is a backlight lighting circuit diagram for explaining the present invention. FIG. 4 is a temperature-capacitance change characteristic diagram of the capacitor used in the present invention. FIG. 5 is a temperature-luminance characteristic diagram of the backlight device used in the image display device of the present invention. FIG. 6 is a backlight lighting circuit diagram showing a part of another embodiment of the present invention. FIG. 7 is a backlight lighting circuit diagram showing a part of another embodiment of the present invention. 2G...Capacitor 22.23...Resistance or more Applicant: Seiko Epson Corporation Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 7

Claims (1)

[Claims] In an image display device that uses a transmission type image display board and displays an image by irradiating an amount of transmitted light from a backlight device using fluorescent discharge tubes, the fluorescent discharge tubes are used to limit the tube current of the fluorescent discharge tubes. A capacitor is connected in series with the capacitor, and the temperature coefficient of the capacitance value of the capacitor exhibits a negative temperature coefficient at least between a temperature below room temperature and minus 20 degrees Celsius.