JPH0812796B2 - DC discharge lamp lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention illuminates a DC discharge lamp, which is a display element of a large image display device used in a stadium, a baseball field, etc. It relates to the device.

[Prior Art] A display device using a direct-current discharge lamp has been developed as a display element that obtains high contrast in the sunlight outdoors. For outdoor use, high contrast ratio can be obtained by increasing the maximum brightness under strong external light. However, when used in the evening or at night, it is necessary to reduce the maximum brightness from 1/2 to 1/3 in the daytime due to glare.At this time, the contrast is not the maximum brightness but the minimum brightness level (black level). It becomes important.

In the conventional image display, as a method of controlling the brightness gradation, so-called time width control is adopted, which controls the time width of a lamp current (main discharge current) of a substantially constant DC level effective for the brightness control. Further, in order to improve the display responsiveness, after the power is turned on, all the display lamps are always lit by a slight discharge current from a bypass circuit different from the main discharge current. FIG. 6 shows such a conventional lighting device.

In FIG. 6, the filament 2 of the DC discharge lamp 1
DC power source Ea is connected to one end of
To form a micro-discharge circuit, and the filament 2
A DC power supply Eb, a current limiting resistor 5, a switching element 6 and a series circuit of a diode 9 are connected to the other end and the anode 3 to form a main discharge circuit. The DC power source Eb is composed of a first DC power source Eb ₁ , a switch element 7, a second DC power source Eb ₂ and a bypass diode 8. The filament 2 is heated by the DC power source Ef.

In this circuit, the DC power source Ea always allows a minute discharge current to flow in the lamp 1, and while the switch elements 6 and 7 are on, the lamp 5 is added via the resistor 5 in addition to the above minute discharge current. The main discharge current flows in the first channel. The switch element 7 is set shorter than the ON time of the switch element 6, and Eb ₂ is added to the DC power source Eb ₁ to obtain the main discharge start voltage.

In the lighting device of FIG. 6, since the main discharge current of the lamp is controlled in time width, lamp dimming (luminance gradation control) is performed.
At this time, a lamp current pause time is generated. Therefore, when the lamp is started (discharge breakdown) every time the lamp is image-scanned, a start delay time is generated and the display responsiveness is not deteriorated. Has been done. As a result, it is not necessary to start the lamp with a high voltage for each scan, and more display responsiveness can be obtained. Further, since there is no start-up delay, the linearity of gradation control at low brightness is maintained, and as a result, excellent displayability can be obtained.

However, there is a drawback in that the minimum luminance is relatively high when a slight discharge current is passed through the lamp 1 so that the lamp 1 is constantly turned on. For this reason, when the surroundings are dark and the maximum brightness is lowered at night, in the evening, etc., the contrast is deteriorated. or,
Since it becomes impossible to use it in a dark room such as an indoor event, it is difficult to expect a show-up effect.

As described above, the display device having the conventional lighting device has a drawback that the installation place is limited.

As a method of solving this, it is sufficient if the minute discharge current constantly flowing can be further reduced, but it was experimentally found that this is limited due to the following reasons.

That is, when controlling the main discharge current of the lamp over the time width, it was found that a pulsed voltage higher than the power supply voltage of the main discharge current was generated in the minute discharge lamp voltage immediately after the main discharge current of the lamp was turned off. This pulsed voltage is
As shown in the figure, it occurs every time the time width of the lamp current is controlled. This pulsed voltage has a temperature characteristic that it becomes high especially at low temperatures and becomes high below 0 ° C.

The above-mentioned lamp temperature, main discharge current, and minute discharge current are the secondary factors for the height of this pulsed voltage. The primary factor is the characteristics of the DC discharge lamp, which is the display element we used this time. It is determined by the shape of the discharge lamp, the type of internal gas, the pressure, etc., but in any case, the cause of this pulsed voltage is considered to be the vibration of the discharge phenomenon of the lamp anode.

If this pulse voltage reaches the power supply voltage of the minute discharge current or more, the lighting state in the minute discharge cannot be maintained,
The lamp goes out, and thereafter, unless the power is turned on again and the starting voltage for starting the discharge is applied, not only the brightness control but also the slight discharge lighting cannot be performed.

Therefore, the power source for the minute discharge which causes the minute discharge current cannot control the brightness unless the main discharge current is applied with a voltage higher than the pulse voltage immediately after the main discharge current is turned off. By the way, since the pulsed voltage has the above-described change factor, the minute discharge current is reduced under the condition of the factor that maximizes this change, and therefore the minute discharge power supply voltage cannot be reduced. On the contrary, there is a way to increase the power supply voltage, but this is impossible because the loss in the current limiting resistor becomes large.

Moreover, if the current is simply reduced while leaving the slight discharge power supply voltage as it is, the lamp voltage at the time of slight discharge lighting increases, and it becomes impossible to maintain lighting after all, so the power supply voltage increases. Therefore, the minute discharge current cannot be reduced.

As described above, in the method in which the minute discharge current is always passed through the bypass of the main discharge current, the minute discharge is lit, and the time width of the main discharge current is controlled for each scanning, the power source voltage for the minute discharge is determined by the surrounding environment. Therefore, it is impossible to reduce the brightness when the slight discharge is turned on.

[Problems to be Solved by the Invention] The present invention has been provided in view of the above points,
Every time the lamp is scanned with an image, a discharge start pulse is applied to replace the mode of constant discharge, and at this time, the display responsiveness associated with the occurrence of the discharge start delay time of the lamp, which has been a concern in the past, is not degraded. The purpose is to significantly reduce the minimum luminance (black luminance) of the display and improve the display contrast ratio while maintaining good displayability.

[Means for Solving the Problems] FIGS. 1 and 2 are diagrams showing the principle of operation of the present invention. Second
The figure is an operation chart of FIG.

When the image control signal Vc is output from the display control circuit 10 at 60 Hz, the brightness control of the lamp 1 is started at this timing. The brightness control is a scanning signal from the display control circuit 10.
The luminance data output at the same time as Vc is input, and the output is performed by the PWM circuit 11 that controls the time width. With the output of the PWM circuit 11,
The time width of the main discharge current of the DC discharge lamp 1 is controlled by the switch element 6. The display control circuit 10 and the PWM circuit 1
1, the switch element 6 and the like constitute the brightness control means.

When the scanning signal Vc is output as shown in FIG. 2 (a), the delay time T ₁ is created by the timer 20 as shown in FIG. 2 (b), and immediately after this delay time T ₁ is shown in FIG. 2 (c). As shown in, the timer 21 produces the delay time T ₂ . During this delay time T ₂ , the switch element 22a of the high-voltage switch circuit 22 is turned on, and the lamp 1 slightly discharges via the resistor 4. still,
The timers 20 and 21, the high-voltage switch circuit 22 and the like constitute the minute discharge control means.

By the way, the delay time T ₁ is regulated in relation to the cycle 16.7 msec (in the case of 60 Hz) until the next scanning signal Vc comes in, and the lamp 1 is connected to the DC power supply during (16.7 msec−T ₁ msec).
At Ea, it needs to be long enough to start lighting and slightly discharge. This state is determined from the experimental data shown in FIG. FIG. 3 shows the relationship between the value of the power source Ea and the starting time of the lamp 1. If the voltage value of the power source Ea is 500 V, it means that the lamp 1 starts when applied for 0.5 msec.

Further, the scanning signal Vc is always output after the power of the large-scale image device is turned on and the system is started. This is because the present invention activates the lamp of each display element by this scanning signal Vc, which is a reference signal for that purpose, and has an appropriate time width shown in FIG. 3 for the cycle of the scanning signal Vc having a frequency of 60 Hz. T ₂ pulse with phase (timer 21
Output), the lamp 1 is periodically and slightly discharged, and then the time width of the main discharge current is controlled by the low-voltage DC power supply V ₁ much lower than the voltage value of the power supply Ea. Because it is. There is a problem if the scanning signal Vc disappears each time the brightness becomes zero in relation to the brightness data from the display control circuit 10. This is because the output pulse T ₂ of the timer 21 is not output for 16.7 msec from the first pulsed scanning signal Vc to the next scanning signal Vc, so that a delay of one cycle occurs in image generation. If this phenomenon occurs frequently, the image becomes grainy.

From the above operation, the brightness control of the lamp 1 is 60Hz periodically.
Each time the control is performed, the lamp 1 is set in a slightly discharged state before the control is started. By doing this, like the conventional example,
Immediately after turning off the main discharge current with the switch element 6, the main discharge power supply
There is no disadvantage that a pulsed voltage higher than V ₁ or the voltage of the power source Ea for slight discharge is generated and the slight discharge lighting cannot be maintained.

Also, since the minute discharge lighting is sufficient for a short time of 2 to 3 msec between 16.7 msec, the brightness level during black when the main discharge current does not flow will be reduced to about 1/5 compared to the conventional one. The contrast will be greatly improved.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows the embodiment, and FIG. 5 shows the operating state thereof. The lamp 1 is a composite discharge lamp composed of three primary color fluorescent discharge paths of R, G and B and one filament 2. In this embodiment, the three discharge lamp structure of R, G, B is used, but four discharge paths of R, G, B, G may be used. For the sake of explanation, each discharge path is lit at a duty ratio of 50% for time width control of the main discharge current, that is, every cycle of 8.8 msec. Further, in the present embodiment, control is performed to light all three discharge paths at the same time with a slight discharge. This is because the number of the high voltage switch circuits 22 is not increased, and the configuration of the entire display device can be simplified.

When the power of the display device is turned on, the power sources V ₁ , Ef, and Ea rise, and the filament 2 is preheated. On the other hand, as shown in FIG. 5A, the scanning signal Vc from the display control circuit 10
It occurs at 60Hz. The scanning signal Vc follows the scanning order in the PWM circuit 11 and is sequentially flip-flop or the like as shown in FIGS. 5 (a) to 5 (c), and the scanning signals V _CR , V _CG
V _CB is internally generated, and a time width of 8.8 msec corresponding to luminance data (currently equivalent to 50% duty ratio) is generated in synchronization with each scanning signal Vc, and the constant current circuit 23 _R , 23 _G , 23 _B switch The transistor 6 _R, which is an element, is operated for a fixed time.

On the other hand, the scanning signal Vc is insulated by the isolator 24, and after the scanning signals Vc are generated by the timers 20 and 21, after a time delay of T ₁ , the switch element 22a of the high voltage switch circuit 22 is turned on for a time T _{2 to} discharge each discharge. The paths R, G and B are slightly discharged at the same time. After (16.7−T ₁ ) msec from the start of this slight discharge control, first, the main discharge current flows through the discharge path _R by the constant current circuit 23 _R , and then the discharge paths G and B and the main discharge current flow through the constant current circuit 23 _R. Flows through _G , 23 _B. This state is shown as an example of a lamp voltage waveform in FIGS.

In such control, after the main discharge time 8.8 msec of each discharge path R, G, B, each discharge path R, G, B is completely extinguished, and no pulsed voltage is generated unlike the conventional example. There is no problem such as instability of lighting maintenance. In addition, the main discharge time of all discharge paths is zero, that is, the black brightness of the display screen where the control brightness is zero is a slight discharge brightness of (16.7-T ₁ ) msec, and the black brightness is lower than that of the conventional example. , Can be significantly reduced.

[Advantages of the Invention] As described above, the present invention provides a brightness control means for controlling the brightness by controlling the pulse width of the DC discharge lamp by the periodic brightness control signal, and a sufficient time for starting the DC discharge lamp. Since the main discharge time of each discharge path is provided, the discharge path is completely extinguished after the main discharge time of the discharge path, because the discharge control means controls the slight discharge circuit for a predetermined time before the start of the brightness control. There is no generation of pulsed voltage as in the conventional example, there is no problem of instability of lighting maintenance, and the main discharge time of all discharge paths is zero, that is, the display screen black where the control brightness is zero. The luminance is a minute discharge luminance during a slight discharge time before the luminance control is started, and the black luminance has an effect of being able to be significantly reduced as compared with the conventional example.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a time chart of the above, FIG. 3 is a characteristic diagram of the same, FIG. 4 is a block diagram showing a specific embodiment of the same, and FIG. 6 is a circuit diagram of a conventional example, and FIG. 7 is an operation waveform diagram of the same. 1 is a DC discharge lamp, 2 is a filament, 3 is an anode, 4,
5 is a resistor, Ea is a DC power supply for slight discharge, and V ₁ is a DC power supply for main discharge.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-295399 (JP, A) JP 62-295397 (JP, A) JP 62-115698 (JP, A) JP 63- 149695 (JP, A)

Claims (1)

[Claims] 1. A direct current discharge lamp having one filament, at least one anode and a discharge path for independently emitting light to each anode, and a direct current power source applied to the direct current discharge lamp through a current limiting resistor. It has a main discharge circuit that sends a main discharge current to obtain effective brightness and a fine discharge circuit that flows a main discharge current to the DC discharge lamp in a minute discharge state. Luminance control means for controlling the brightness by controlling the pulse width of the discharge lamp, and fine discharge control for controlling the on-state of the minute discharge circuit for a predetermined time before the start of the brightness control, which is a sufficient time for starting the DC discharge lamp. And a direct current discharge lamp lighting device.