JP3716500B2 - Driving method of discharge device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a discharge device that emits visible light, ultraviolet light, and the like, and more particularly to a driving method of a discharge device used for a light source for indoor / outdoor lighting, display, or liquid crystal display backlight.
[0002]
[Prior art]
There are various methods for driving a light source using discharge, for example, a fluorescent lamp for illumination or display, a flat discharge device, or the like. A conventional inverter driving method for lighting a liquid crystal backlight is configured to light a fluorescent lamp using a sine wave of several tens of kHz as disclosed in, for example, Japanese Patent Application Laid-Open No. 63-110962. . For the discharge tube, a cold cathode or a hot cathode fluorescent lamp having a tube diameter of about 3 to 6 mm is used. For example, mercury and argon are enclosed inside the discharge tube, and ultraviolet rays generated by the discharge excite the phosphor. Light is emitted and the LCD panel is illuminated to display characters and images.
[0003]
In general, a general lighting lamp is lit using a commercial frequency of 50 or 60 Hz, but there is a lamp that is lit at several tens of kHz.
[0004]
[Problems to be solved by the invention]
However, the discharge device using the above driving method has a problem that the light emission efficiency is lowered and the power consumption is increased particularly when the tube diameter of the discharge tube is reduced. For example, the luminous efficiency of fluorescent lamps with a diameter of 2 to 3 mm used as backlights for liquid crystal display devices is only about half that of fluorescent lamps with a diameter of about 25 mm, reducing the power consumption of liquid crystal display devices. It was the biggest cause that could not be. In particular, in a battery-driven liquid crystal display device such as a notebook personal computer, low power consumption of the backlight has been a very big problem.
[0005]
An object of the present invention is to provide a driving method for improving the light emission efficiency of such a discharge device and at the same time reducing the power consumption.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the driving method of the discharge device according to the present invention uses a voltage having a driving waveform different from the conventional one. That is, in order to discharge the discharge device, a first voltage having a first frequency is applied to the electrodes. Furthermore, a second voltage having a second frequency higher than the first frequency, in particular, a high frequency of 2.4 MHz to 20 MHz is superimposed on the first voltage. As the second high-frequency voltage generation circuit, a simple circuit configuration can be obtained by using an inductance, for example, a coil. Further, the voltage waveform having the second frequency may be an attenuation waveform synchronized with the first frequency.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing an embodiment of a driving method of an external electrode type discharge tube according to the present invention. In the figure, 20 is a discharge tube, 21 and 22 are electrodes provided on the outer surface of the discharge tube, 23 and 24 are drive voltage generation circuits having a first frequency, and 25 and 26 are the drive voltage generation circuits 23 and 24, respectively. In this embodiment, the coils 25 and 26 are used in the second drive voltage generation circuit having the second frequency connected to the second drive voltage generation circuit. As the driving voltage having the second frequency, a voltage generated by ringing between the coils 25 and 26 and the circuit system stray capacitance is used.
[0008]
V1 and V2 are voltages applied to the electrodes 21 and 22, and in addition to the first voltage having the first frequency, the second voltage having a second frequency higher than the first frequency is added to the first voltage. A so-called electrodeless discharge of the field discharge type is performed in superposition with the voltage of 1.
[0009]
2 and 3 are voltage waveform diagrams showing an embodiment of the drive waveform. From the drive voltage generation circuit having the first frequency, the rectangular wave voltages V1 and 11 shown in FIG. 12 rectangular wave voltages V2 having a half-cycle phase shift are generated. Further, as shown in FIG. 3, a driving voltage generating circuit having a second frequency in these waveforms, in this case, ringing by adding an inductance (coil) Are superimposed on 11 and 12 respectively. The voltage waveforms 13 and 14 are discharge voltage waveforms, and by applying this voltage to the discharge tube, high efficiency can be achieved.
[0010]
The result of driving the discharge tube using the drive waveform according to the present invention and measuring the discharge emission characteristics will be described. As shown in FIG. 1, the discharge tube 20 used in the experiment is made of soda glass having an inner diameter of 3 mm, for example, and the pair of electrodes 21 and 22 are both 10 mm long and 5 mm wide, and the outer surface of the discharge tube. It is provided above. The electrode may be wound around the entire outer surface of the discharge tube. The distance between both electrodes is 60 mm, and a three-wavelength white phosphor is applied to the inner wall of the discharge tube. For example, mercury, neon 7 kPa, and argon 748 Pa are sealed inside the discharge tube.
[0011]
The basic shape of the drive voltage waveform is the same as that shown in FIG. 3, and coils 25 and 26 are used as the second driving wave voltage generation circuit. The drive voltage having this second frequency is the coils 25 and 26. And a voltage generated by ringing between the circuit and the stray capacitance. In this embodiment, a coil with a simple configuration is used as the second drive voltage generation circuit, but any inductance component may be used.
[0012]
FIG. 4 shows the relationship between the ringing period and the luminance when a ringing voltage by adding a coil is used as the second drive voltage. As a basic drive voltage, a pulse having a period of 8 μs, a pulse width of 1.7 μs, and a voltage of 300 V was applied. The luminance with a ringing period of 0 is a value when only the basic rectangular voltage pulse shown in FIG. 2 is applied and discharged. As is apparent from the figure, the luminance increases significantly when the period of the superimposed high-frequency voltage is 50 ns (20 MHz) or more. For example, the luminance is required to be equal to or higher than that of a cold cathode fluorescent lamp that is usually used for use in a liquid crystal backlight, and the luminance of the cold cathode fluorescent lamp having the same shape and similar driving conditions is about 800 cd / mm. m ² is obtained, and in order to obtain luminance higher than this, the ringing period may be selected between 70 ns (about 14 MHz) and 350 ns (about 2.8 MHz). Furthermore, the highest luminance is obtained between 100 ns and 250 ns. From this result, high luminance can be achieved by superimposing a high-frequency voltage of 20 MHz or less as the drive voltage having the second frequency. In particular, it is desirable to superimpose a high frequency voltage of 2.8 MHz to 14 MHz.
[0013]
FIG. 5 shows the relationship between the ringing period and the minimum sustaining voltage. A ringing period of 0 is a sustain voltage when no high frequency is superimposed as in FIG. The discharge voltage is desirably 140 V or less of the sustain voltage of the cold cathode fluorescent lamp described above from the drive circuit, and the condition for this voltage drop is 50 ns (20 MHz) to 420 ns (about 2.4 MHz). The lowest sustain voltage was less than half that when no high frequency was superimposed. This is thought to be due to the fact that the negative glow region decreases and the cathode fall voltage decreases due to the superposition of high frequency.
[0014]
FIG. 6 shows the relationship between the ringing period and the relative light emission efficiency, where the efficiency when no high frequency is superimposed is 1. The light emission efficiency hardly changes until the period is about 40 ns, but becomes higher at 50 ns (20 MHz) or more, and is up to twice or more. As in FIG. 5, the range in which the efficiency increases is between 50 ns (20 MHz) and 420 ns (about 2.4 MHz), and decreases to the same extent as when no high frequency is superimposed when the period is 500 ns or more.
[0015]
FIG. 7 shows the relationship between the inductance of the coil inserted to generate ringing and the relative light emission efficiency. As in FIG. 6, the efficiency when no high frequency is superimposed is shown as 1. FIG. From the experimental results, the ringing period T (ns) Inductance L (.mu.H) is holds the relationship of L = T ^2/1156. There is an error in the efficiency measurement when discharging with a voltage having ringing, and the value that reveals the superiority of efficiency compared to the case where high frequency is not superimposed is about 1.2 times that without the above-described case The range of inductance that is required and provides high efficiency was between 2 μH and 150 μH.
[0016]
FIG. 8 shows an example of a driving voltage waveform in the case where an inductance (coil) of 10 μH is inserted as one of the conditions for obtaining high-efficiency light emission. A high-frequency attenuation voltage pulse of about 9.3 MHz generated by ringing is superimposed.
[0017]
FIG. 9 shows an example of a driving voltage waveform when an inductance (coil) of 330 μH is inserted. The frequency in this case is about 1.9 MHz, the period is long with respect to the basic voltage pulse, and since the whole is in the form of a high-frequency pulse, the effect of high-frequency superposition is small and the efficiency is not improved much.
[0018]
According to the present invention, a first voltage having a first frequency is applied to the discharge device, and a discharge is formed by this voltage. Next, when a second voltage having the second frequency is superimposed, electrons, ions, or plasma existing in the already formed discharge vibrates with changes in the electric field due to the voltage superposition. If the second frequency is selected between 2.4 MHz and 20 MHz, the resonance phenomenon of electrons, ions, plasma, and the like also occur. This raises the temperature of these particles. As a result, the electron temperature approaches a value preferable for emitting visible light or ultraviolet light, and as a result, the luminous efficiency is improved.
[0019]
In a conventional discharge tube, such as a fluorescent lamp, most of the space charge necessary for maintaining the discharge is generated in the negative glow. In order to form this negative glow, a relatively large electric power is required. However, according to this driving method, since the electron density and ion density in the discharge space, particularly in the positive column portion, increase, the negative glow may be small. Therefore, less power is injected into the discharge tube, resulting in improved luminous efficiency. Furthermore, the discharge sustaining voltage also decreases, and at the same time, a significant reduction in power consumption is possible.
[0020]
FIG. 10 shows an example in which the present invention is applied to a flat plate type discharge device, where 23 and 24 are drive voltage generation circuits having a first frequency, and 27 and 28 are the drive voltage generation circuits described above. A second drive voltage generation circuit having a second frequency connected to each of circuits 23 and 24. 31 and 32 are discharge electrodes formed on a substrate 36 made of soda glass, for example, and the entire surface thereof is covered with a dielectric 33. A soda glass face plate 35 is coated with a phosphor 34 on the inner surface. Xenon, argon, neon, krypton, and other rare gases and mercury are enclosed inside or in a mixture. The operation of the flat plate type discharge device is exactly the same as that of the above-described discharge tube, and the effect thereof is also the same.
[0021]
Summarizing the above results, the frequency of the second voltage superimposed on the first voltage having the first frequency is preferably 2.4 MHz to 20 MHz, and the inductance value is between 2 μH and 150 μH. do it.
[0022]
When the driving method according to the present invention is used in a liquid crystal display device such as a notebook personal computer, the power of the backlight can be reduced, and a display device with high luminance and low power consumption can be realized.
[0023]
In the above-described embodiment, the example of the first voltage having a period of 8 μs and a pulse width of 1.7 μs is described. However, if the frequency of the first voltage is set to 30 kHz or more and the width of the rectangular wave pulse is 10 μs or less, the above-described example is used. The same effect can be obtained. Further, when the peak-to-peak value of the voltage having the second frequency is smaller than the peak-to-peak value of the voltage having the first frequency, the effect of improving the light emission efficiency is great.
[0024]
Moreover, although the external electrode type discharge tube has been described in the above embodiment, it is needless to say that the electrode may be provided inside the discharge tube like a fluorescent lamp.
[0025]
【The invention's effect】
As described above, according to the driving method of the present invention, in addition to the first voltage having the first frequency as the voltage applied to the electrode, the second frequency higher than the first frequency, in particular, With a simple driving method of superimposing a second voltage having a high frequency of 2.4 MHz to 20 MHz, which has not been conventionally used, on the first voltage, the luminance and luminous efficiency of the discharge device can be increased. Further, the discharge sustaining voltage can be lowered. As a result, since the power consumption of the discharge device can be greatly reduced, there is an effect that a low power consumption liquid crystal display device and the like suitable for battery driving can be obtained. Further, the second high frequency voltage generation circuit has an advantage that a simple and inexpensive circuit configuration can be obtained by using an inductance, for example, a coil.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment of a driving method of a discharge device according to the present invention.
FIG. 2 is a voltage waveform diagram of an embodiment according to the driving method of the present invention.
FIG. 3 is a voltage waveform diagram of an embodiment according to the driving method of the present invention.
FIG. 4 is a characteristic diagram showing a relationship between a ringing period and luminance.
FIG. 5 is a characteristic diagram showing a relationship between a ringing period and a minimum discharge sustaining voltage.
FIG. 6 is a characteristic diagram showing a relationship between a ringing period and relative luminous efficiency.
FIG. 7 is a characteristic diagram showing the relationship between inductance and relative luminous efficiency.
FIG. 8 is a drive voltage waveform diagram;
FIG. 9 is a drive voltage waveform diagram.
FIG. 10 is a schematic view showing an example in which the present invention is applied to a flat plate type discharge device.
[Explanation of symbols]
11, 12,... Drive voltage waveform 13, 14 having the first frequency,... Discharge tube drive waveform 15, 16 according to the present invention, drive voltage waveform 20 having the second frequency,. ………… Discharge tubes 21, 22 ………… Electrodes 23, 24 ………… Drive voltage generating circuits 25, 26 having a first frequency …… Coils 27, 28 ………… Second frequency Drive voltage generation circuits 31 and 32 having electrodes 33... Electrode 33..... Dielectric 34. …substrate.

Claims (9)

A first voltage having at least one pair of electrodes, a first voltage having a first frequency applied to at least one of the electrodes, and a second voltage having a second frequency higher than the first frequency being applied to the first voltage A method for driving a discharge device, wherein the frequency of the second voltage to be superimposed is selected between 2.4 MHz and 20 MHz. A first voltage having a first frequency is applied to at least one of the electrodes of an electrodeless discharge device in which at least one pair of electrodes is provided outside the discharge space, and is higher than the first frequency. A method of driving a discharge device in which a second voltage having a second frequency is superimposed on the first voltage, wherein the frequency of the second voltage to be superimposed is selected between 2.4 MHz and 20 MHz. A method for driving the discharge device. 3. The driving method according to claim 1, wherein a voltage having an amplitude that is periodically attenuated or increased is used as the voltage having the second frequency, and the period of the attenuation or increase is synchronized with the period of the first frequency. A method for driving a discharge device. 4. The driving method according to claim 1, wherein the amplitude of the voltage having the second frequency is made smaller than the amplitude of the voltage having the first frequency. 5. The driving method according to claim 1, wherein a voltage having a second frequency is generated by an inductance component inserted in series with the first voltage, and the inductance component is selected between 2 μH and 150 μH. A method of driving a discharge device, characterized in that 6. The driving method according to claim 1, wherein an inductance component is generated by a coil. 7. The driving method according to claim 1, wherein a first voltage having a first frequency is applied to all the discharge electrodes, and a second frequency having a second frequency higher than the first frequency is applied. A method for driving a discharge device, wherein a voltage is superimposed on the first voltage. A backlight configured to illuminate an object to be illuminated using the discharge device lit by the driving method according to claim 1. 9. A liquid crystal display device comprising the backlight according to claim 8 disposed adjacent to a liquid crystal panel.

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