JPH0745387A - Discharge tube lighting circuit - Google Patents

Abstract

PURPOSE:To express the light and darkness of an optical image faithfully and without flickering by providing a gate logic circuit which mixes picture signals and harmonic pulses to light a discharge tube and controls the synchronization, on the primary side of a step-up transformer. CONSTITUTION:A signal control circuit 7 mixes input image signal pulses 1 in a circle and higher harmonic pulses 2 in a circle, taking the logical product of both signals. This mixed low-voltage drive pulses 3 in a circle are inputted into a step-up transformer 3 through a buffer transistor circuit, and they are converted into high-voltage drive pulses 4 in a circle required for a discharge tube. The pulses 4 in a circle are supplied to a discharge tube 5 through a high-voltage capacitor 4 for current control so as to emit a light. That is, the pulses 3 in a circle inputted into the transformer 3 are ones being made by increasing or decreasing the number of pulses 2 in a circle with the width of pulses 1 in a circle whose width is modulated according to the light and darkness of an optical image. Accordingly, the number of pulses 4 in a circle on the secondary side of a transformer 3 is controlled, and the increase and decrease of the brightness of the emission of a discharge tube corresponding to the light and darkness of an optical image can be gotten, and a desired optical image can be materialized faithfully on a display picture element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION In recent years, a large-sized display device has been attracting attention as a means for transmitting information to the masses in a wide area. The large-scale display device is required to have a function of displaying a television image, and is required to have a high-luminance, uniform light emitting surface and an inexpensive color light emitting image element. A heat ray lamp, a hot cathode discharge tube, a cold cathode discharge tube, an LED or the like is used as a light emitting source of a light emitting element, but the present invention is a hot cathode discharge tube or a cold cathode discharge tube (hereinafter, both are collectively referred to as a discharge). The abbreviated as “tube” is used to provide a luminescent image element for a large-sized display device.

[0002]

2. Description of the Related Art FIG. 1 shows an example of the basic structure of a conventional discharge tube lighting circuit used in a large-sized display device using a discharge tube as an image element. We have already applied for a discharge tube lighting circuit that connects a switching element to one end of the discharge tube and uses a video signal as an input to the switching element to turn on / off the current to the discharge tube according to the video signal to control the emission brightness. Is.

The discharge tube lighting circuit comprises a high frequency pulse generation circuit 2, a step-up transformer 3, a current limiting high voltage capacitor 4, and a signal control circuit 6, and a discharge tube 5 serving as a load uses a cold cathode discharge tube. A triac is used for the switching element of No. 6. The operating principle is 1 for input terminal 1
A DC voltage of 0 and several V is input and converted into a high frequency pulse having a frequency of several tens KHz by the high frequency pulse generation circuit 2, and this is converted into a high frequency pulse by the step-up transformer 3 which is necessary for discharging the discharge tube 5, that is, for lighting.
It is converted into a sine wave AC voltage of about 00V. The output side of the step-up transformer 3 is connected to a high-voltage capacitor 4 for controlling discharge current for stabilizing lighting, and the discharge tube 5 is supplied with power via the high-voltage capacitor 4 for current limiting and lights up. The signal control circuit 6 is connected to one terminal of the discharge tube 5 and controls ON / OFF of the current flowing through the discharge tube 5 in response to the video signal 6 to control the emission brightness of the discharge tube.

[0004]

In order to faithfully reproduce an optical image on a large-sized display device, it is necessary to increase / decrease the emission brightness of the discharge tube in response to minute changes in light and darkness of the optical image. . In the conventional discharge tube lighting circuit shown in FIG. 1, the signal control circuit 6 directly controls the current to the discharge tube 5, and when the signal control circuit 6 is OFF, the high voltage circuit side of the step-up transformer 3 is completely open. . Therefore, when the signal control circuit 6 is OFF, energy remains stored in the coil inductance of the step-up transformer 3, the current control high-voltage capacitor 4 and the tube capacitance of the discharge tube 5, and the OFF operation is left to the natural discharge. Becomes Further, since the high frequency and high voltage driving is performed, the energy accumulated in the internal capacitance of the switching element is large, and the switching element does not rapidly turn to the OFF state at the time of OFF, and the ON state remains. Therefore, the step-up transformer 3 when the signal control circuit 6 is OFF
It was difficult to control the minute emission luminance faithfully corresponding to the brightness of the optical image, such as the discharge light emission could not be completely turned off due to the residual accumulated energy on the high voltage circuit side and an afterimage was generated.

[0005]

In the present invention, the signal control function in the discharge tube lighting circuit shown in FIG.
Provided on the next side, that is, the input side. That is, by controlling the low voltage circuit side of the primary side of the step-up transformer, the open state on the high voltage circuit side is prevented and the control element circuit is simplified because it is on the low voltage side. A gate circuit is provided on the primary side of the step-up transformer, and the video signal pulse-width modulated corresponding to the brightness of the optical image and the high frequency pulse are mixed in the gate circuit. The number of low-voltage driving pulses obtained by this is controlled by the video signal pulse width, and by inputting this to the input of the step-up transformer, the number of high-voltage driving pulses obtained at the secondary side of the step-up transformer, that is, the output is increased or decreased, and the light emission of the discharge tube is increased. The brightness is faithfully expressed on the display pixel in correspondence with the brightness of the optical image.

[0006]

By introducing the discharge tube lighting circuit according to the present invention, a display device capable of faithfully expressing the brightness of an optical image without causing an afterimage can be obtained.

[0007]

Embodiment 1 The present invention will be specifically described below with reference to the drawings. FIG. 2 shows the configuration of a discharge tube lighting circuit according to an embodiment of the present invention. FIG. 3 shows the output waveform of each part.

The basic circuit configuration of the present invention will be described. As a signal indicating the light and darkness of an optical image, a pulse width modulated video signal 6 whose pulse width is increased or decreased corresponding to the lightness and darkness is given and connected to one end of an input of a signal control circuit 7. The high frequency pulse generation circuit 2 is separated from the input part of the step-up transformer 3 and is independent, and is connected to the other input end of the signal control circuit 7. The signal control circuit 7 is composed of a NAND gate and a buffer transistor circuit for inputting to the step-up transformer 3. By taking a logical product of the input video signal pulse and the high frequency pulse, the video signal pulse and the high frequency pulse are obtained. Is mixed with. The mixed low-voltage drive pulse is input to the step-up transformer 3 through the buffer transistor circuit and converted into a high-voltage drive pulse necessary for lighting the discharge tube. The principle that the high-voltage drive pulse is supplied to the discharge tube 5 through the current-limiting high-voltage capacitor 4 and emits light is the same as that already described.

That is, the low-voltage drive pulse as the input of the step-up transformer 3 is such that the number of high-frequency pulses is controlled and increased or decreased according to the width of the video signal pulse whose pulse width is modulated according to the brightness of the optical image. Therefore, the number of high-voltage drive pulses appearing on the secondary side of the step-up transformer 3 is controlled, so that it is possible to increase or decrease the discharge tube light emission brightness corresponding to the brightness of the optical image, and to faithfully display the desired optical image on the display pixel. It can be realized.

[0010]

Example 2

In the first embodiment of the present invention, the video signal pulse and the high frequency pulse are independent of each other. Here, depending on the timing of the video signal pulse and the high frequency pulse, a short pulse may occur in the low voltage drive pulse mixed by the signal control circuit 7. In this case, the high-voltage drive pulse obtained through the step-up transformer 3 lacks the energy required to excite the step-up transformer 3, and thus does not have the voltage wave height required for light emission, and does not substantially contribute to the discharge light emission of the discharge tube. That is, there is a problem that so-called flickering of the display occurs, such that light is not emitted depending on the mutual timing of the video signal pulse and the high frequency pulse. The output pulse waveform of the discharge tube lighting circuit of FIG. 2 will be specifically described with reference to FIG.

FIG. 4 is an output pulse waveform of each part showing timing. The video signal 1 and the high frequency pulse generation circuit 2 are independent of each other, and their timings are random. Therefore, the high-frequency pulse side may have already risen at the rising and falling edges of the video signal pulse, and the low-voltage drive pulse, which is the logical product of the video signal pulse and the high-frequency pulse, is normally transformed at the rising and falling edges of the video signal pulse. Short pulses can occur that are less than the pulse width required for excitation.

When this low-voltage driving pulse is input to the step-up transformer 3, the pulse width is not a desired pulse width.
At the end, a pulse having a low output voltage wave such as a high voltage pulse is generated at a portion corresponding to a short pulse of the low voltage drive pulse. In the case of a high-voltage driving pulse such as this high-voltage pulse, it does not contribute to the discharge tube light emission, and it becomes uncertain whether the light is emitted depending on the timing, that is, the light emission flickers.

[0013]

In the second embodiment of the present invention,
In order to solve the above-mentioned problems, the rising and falling edges of the video signal pulse and the low voltage driving pulse are made coincident with each other, that is, synchronized, to prevent uncertain high voltage driving pulse generation.

[0014]

[Operation] By introducing the discharge tube lighting circuit according to the present invention, it is possible to provide a display light emitting element which can obtain stable light emission without flicker.

The present invention will be specifically described below with reference to the drawings. FIG. 5 shows the configuration of the discharge tube lighting circuit according to the second embodiment of the present invention. Further, FIG. 6 shows the output pulse waveform of each part.

A synchronization control circuit 8 is provided on the input side of the video signal 6 of the discharge tube lighting circuit described in the first embodiment. The synchronization control circuit 8 is composed of a D flip-flop and is composed of a video signal 6
Is one end of the input of the D flip-flop, and the high-frequency pulse generation circuit 2 is used as the clock of this flip-flop.
The output is inverted and used as the input. This D flip-flop output is one end of the input of the signal control circuit 7, and the output of the high frequency pulse generation circuit 2 is applied to the other input end of the signal control circuit 7, which is the same as the first embodiment.

Here, due to the function of the D flip-flop, the state of the input terminal appears at the output terminal at the rising edge of the clock input, and the video signal changes in synchronization with the falling edge of the pulse of the high frequency pulse generating circuit 2 to perform signal control. It becomes the input of the circuit 7. Therefore, the low-voltage drive pulse, which is the logical product of the low-voltage drive pulse and the synchronized video signal pulse, coincides with the trailing edge of the high-frequency pulse, and the pulse width output with insufficient excitation as described above does not occur.

Further, the output of the synchronization control circuit 8 has its pulse width increased or decreased in accordance with the video signal whose pulse width is modulated by the brightness of the optical image. With this pulse width, the number of high-voltage drive pulses for light emission from the discharge tube is increased. Is increased or decreased and the luminance of the discharge tube emission is increased or decreased according to the brightness of the optical image.

[0019]

As described above, according to the present invention, the primary side of the step-up transformer is provided with a simple gate logic circuit for mixing and synchronously controlling the video signal and the high frequency pulse for lighting the discharge tube. As a result, it was possible to provide a discharge tube lighting circuit that can faithfully express the brightness of an optical image without flicker. Further, although the D flip-flop is used as the synchronization control circuit in the present embodiment, the same effect can be obtained by using a so-called phase lock circuit that detects the phase shift between the video signal pulse and the high frequency pulse and performs the synchronization correction. Of course.

[Brief description of drawings]

FIG. 1 is a conventional discharge tube lighting circuit.

FIG. 2 is a discharge tube lighting circuit showing the first embodiment of the present invention.

FIG. 3 is an output waveform of each part of the discharge tube lighting circuit showing the first embodiment of the present invention.

FIG. 4 is an output waveform of each part of the discharge tube lighting circuit according to the first embodiment of the present invention, showing a random timing state.

FIG. 5 is a discharge tube lighting circuit showing a second embodiment of the present invention.

FIG. 6 is an output waveform of each part of the discharge tube lighting circuit showing the second embodiment of the present invention.

[Explanation of symbols]

1 to 6 show the following reference numerals. 1: DC voltage 2: High frequency pulse generation circuit 3: Boost transformer 4: High voltage capacitor for current limitation 5: Discharge tube 6: Video signal 7: Signal control circuit 8: Synchronous control circuit: Video signal pulse: High frequency pulse: Low voltage drive pulse : High-voltage drive pulse: Short pulse: High-voltage pulse: Synchronized video signal pulse

Claims (2)

[Claims] 1. A low-voltage drive pulse is obtained by mixing a high-frequency pulse for lighting a hot cathode discharge tube or a cold cathode discharge tube into a video signal whose pulse width is modulated in accordance with the brightness of an optical image to obtain a low voltage drive pulse. A discharge tube lighting circuit, characterized in that a drive pulse is boosted by a boosting transformer and a high voltage drive pulse obtained at an output is caused to emit light in accordance with the brightness of the optical image. 2. The discharge tube lighting circuit according to claim 1, wherein the video signal and the high frequency pulse are synchronized.