JP2006196417A - Method of driving cold cathode fluorescent lamp and its driving power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable phosphor to emit light with high luminance and have long life. <P>SOLUTION: The cold cathode fluorescent lamp comprises a transformer TS of which secondary coil L2 has a middle point NP grounded; a first rectifier diode D1 of which anode is connected to one end of the secondary coil of the transformer TS; a second rectifier diode D2 of which cathode is connected to the other end of the secondary coil, wherein a pulse voltage is applied to the primary coil L1 of the transformer TS, positive differential pulse-like voltage induced on one end side of the secondary coil is applied to the anode 13 of the cold cathode fluorescent lamp 10 through the first rectifier diode D1 and negative differential pulse-like voltage induced on the other end side of the secondary coil is applied to the cathode 14 of the cold cathode fluorescent lamp 10 through the second rectifier diode D2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, an anode with a phosphor and a field emission type linear cathode are arranged to face each other, and electric field energy necessary for light emission of the phosphor is given to the facing space between the anode and the cathode. The present invention relates to a driving method of a field emission type cold cathode fluorescent lamp to which an anode-cathode voltage Vak) is applied, and a driving power source thereof.

In this type of cold cathode fluorescent lamp, a flat anode with a phosphor and a cathode that emits electrons across the entire anode surface of the anode are arranged opposite to each other, and a voltage Vak is applied between the anode and cathode to apply electrons. There is a type in which the phosphor is excited to collide with the phosphor to cause the phosphor to excite and emit light (see Patent Document 1). In such a field emission type cold cathode fluorescent lamp, it is necessary to apply a voltage Vak between the anode and the cathode to form an electric field for emitting electrons from the cathode in the opposite space in order to emit light from the phosphor. There is. There is a voltage-current characteristic shown in FIG. 3 between the anode-cathode voltage Vak and the emission current Ie (amount of electron emission from the cathode). In FIG. 3, the horizontal axis represents the anode-cathode voltage Vak (kV / mm), and the vertical axis represents the emission current Ie (mA / cm ² ). In the anode-cathode voltage Vak, Vth is an operation start voltage necessary for the phosphor to start emitting light, for example, about 1.1 kV, and V1-V2 is an operating voltage range necessary for the phosphor to emit light. For example, about 2.0-2.5 kV (emission current Ie is about several mA, for example), V0 is a rated voltage, for example, about 3.0 kV (emission current Ie is about 8-10 mA, for example).

In the conventional field emission type cold cathode fluorescent lamp, the anode-cathode voltage Vak having the above relationship with respect to the emission current Ie is applied in the form of a DC voltage between the anode and the cathode, and the phosphor itself emits light. The service life was extremely short and the practicality was low.
Japanese Patent Laid-Open No. 05-251021

  The problem to be solved by the present invention is to provide a method of driving a cold cathode fluorescent lamp so that the phosphor emits light with a required luminance and the light emission lifetime can be extended, and a driving power source thereof.

  In the conventional field emission type cold cathode fluorescent lamp, the inventor has applied the anode-cathode voltage Vak in the form of a direct current voltage between the anode and the cathode, so that the emission life of the phosphor is short. In view of this, a cold cathode fluorescent lamp has been developed that extends its light emission lifetime and can be put to practical use. As a result, we have succeeded in developing a technology that can improve the light emission lifetime of a phosphor by applying a pulse voltage between the anode and cathode. However, since this pulse voltage requires the cathode to be grounded and a high voltage of about 6 kV, for example, must be applied to the anode, even if the light emission life of the phosphor itself is improved, A pulse power source to be generated is required, and new problems such as an increase in weight and cost of the pulse power source have occurred. As a result of further earnest research, the present invention has been completed. That is,

 (1) The cold cathode fluorescent lamp driving method according to the present invention is a cold cathode fluorescent lamp driving method in which an electric field is formed in the space between the anode and the cathode and electrons are emitted from the cathode. Two positive and negative differential pulse voltages that are equal to or higher than the operating voltage required for light emission of the body are generated in synchronization with the rising edges, and a positive differential pulse voltage is applied to the anode and a negative differential pulse voltage is applied to the cathode. It is characterized by doing.

  According to the present invention, first, the phosphor is not continuously irradiated with electrons, a differential pulse voltage is periodically applied between the anode and the cathode to emit electrons from the cathode, and the emitted electrons are emitted from the phosphor. Since the irradiation time of the electrons to the phosphor is extremely short, in other words, the excitation light emission operation of the phosphor can be completed in a short time, the emission lifetime characteristics of the phosphor are greatly improved. In this case, when the phosphor emits light, it has an afterglow characteristic (time from the stop of irradiation of the excitation light until the light emission disappears), so that the display characteristic of the cold cathode fluorescent lamp is not impaired. That is, in the present invention, the cold cathode fluorescent lamp is not continuously driven at a direct current voltage to excite the phosphor to emit light, but the phosphor is intermittently excited to emit light, so that the lifetime of the phosphor is greatly improved.

  In the above features, it is necessary to apply a high voltage (driving voltage) between the anode and the cathode for light emission of the phosphor, but the cathode is grounded and the driving voltage is applied to the anode with a differential pulse voltage at a high voltage. Instead, the drive voltage is shared between the voltage applied to the anode side and the cathode side, so the drive voltage of the cold cathode fluorescent lamp can be reduced to half, and the drive voltage for the cold cathode fluorescent lamp is a low voltage The specification is sufficient, and the size and weight can be reduced and the cost can be reduced. In addition, the drive power source can be easily handled.

  In particular, according to the present invention, the cold cathode fluorescent lamp can be driven at a low voltage, such as a backlight of a liquid crystal display device. This is a great advantage. This is because liquid crystal electronic devices incorporating backlights have become smaller and thinner, and along with this, cold cathode fluorescent lamps incorporated as backlights in electronic devices have become smaller, smaller, etc. This is because it is required.

  In the driving method of the cold cathode fluorescent lamp of the present invention, as a specific configuration, a transformer in which the middle point of the secondary side coil is grounded on the driving side, and an anode is connected to one end side of the secondary side coil of the transformer. 1 and a second rectifier diode having a cathode connected to the other end of the secondary coil, a pulse voltage is applied to the primary coil of the transformer, and the anode of the cold cathode fluorescent lamp has two A positive differential pulse voltage induced on one end of the secondary coil is applied via the first rectifier diode, and a negative differential pulse voltage induced on the other end of the secondary coil is applied to the cathode of the cold cathode fluorescent lamp. Can be applied via a second rectifier diode. In this configuration, a high voltage required between the anode and the cathode can be applied easily and reliably.

  In the driving method of the cold cathode fluorescent lamp of the present invention, the anode is formed into a planar shape, the cathode extends in a line substantially parallel to the anode surface, and the opposing conductive wire is formed on the surface of the conductive wire. The carbon thin film with a large number of fine protrusions can be formed, and unevenness for assisting electric field concentration can be formed on the surface of the conducting wire. In this configuration, the electric field concentration performance of the fine protrusions can be further effectively improved, the amount of electron emission can be increased, and the phosphor can emit light with high brightness. Therefore, the voltage applied between the anode and the cathode can be further reduced. can do.

 (2) A cold cathode fluorescent lamp driving power source according to the present invention is a cold cathode fluorescent lamp driving power source in which an electric field is formed in a space facing the anode and cathode to emit electrons from the cathode toward the anode. Voltage generating means for generating two differential pulsed voltages whose positive and negative voltages are equal to or higher than the operating voltage necessary for light emission of the phosphor in synchronism with each other, and positive of both differential pulsed voltages Voltage application means for applying a differential pulse voltage to the anode of the cold cathode fluorescent lamp and a negative differential pulse voltage to the cathode of the cold cathode fluorescent lamp are provided.

  According to the driving power source for the cold cathode fluorescent lamp of the present invention, a differential pulse voltage is applied between the anode and the cathode, so that electrons are emitted from the cathode of the cold cathode fluorescent lamp in response to the differential pulse voltage and The electron irradiation time is extremely short, in other words, the excitation light emission operation of the phosphor can be completed in a short time, and the cold cathode fluorescent lamp can be driven so that the emission life of the phosphor is improved. In this case, when the phosphor emits light, it has an afterglow characteristic (time from the stop of irradiation of the excitation light until the light emission disappears), so that the display characteristic of the cold cathode fluorescent lamp is not impaired.

  In particular, according to the cold cathode fluorescent lamp driving power source of the present invention, the cold cathode fluorescent lamp can be driven at a low voltage, and therefore, its usefulness as a low voltage driving specification as a backlight for a liquid crystal display device is extremely high. . In other words, in addition to the recent demands for low-voltage drive specifications in addition to the reduction in thickness and size of liquid crystal display devices and the reduction in power consumption, the backlight also requires low-voltage drive in addition to lower power consumption. Of course, this is a great advantage. This is because liquid crystal electronic devices incorporating backlights have become smaller and thinner, and along with this, cold cathode fluorescent lamps incorporated as backlights in electronic devices have become smaller, smaller, etc. This is because it is required.

  In the driving power source for a cold cathode fluorescent lamp according to the present invention, preferably, the voltage generating means includes a transformer with the middle point of the secondary coil grounded, and the voltage applying means has one end of the secondary coil of the transformer. A first rectifier diode having an anode connected to the side, and a second rectifier diode having a cathode connected to the other end of the secondary coil.

  Of course, the cold cathode fluorescent lamp of the present invention is not limited to a backlight for a liquid crystal display device, and can be applied to other uses such as an illumination lamp.

  According to the present invention, it is possible to achieve high-luminance emission and long life of the phosphor.

  Hereinafter, a driving method of a field emission cold cathode fluorescent lamp according to an embodiment of the present invention and a driving power source thereof will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing a cold cathode fluorescent lamp and its driving power source according to Embodiment 1, and FIG. 2 is a diagram showing voltage waveforms of respective parts of the driving power source and voltage waveforms between the anode and cathode of the cold cathode fluorescent lamp, FIG. 3 is a diagram showing the relationship between the anode-cathode voltage Vak and the emission current Ie, and FIG. 4 is a cross-sectional view showing the structure of the cold cathode fluorescent lamp.

  Referring to FIG. 1, 10 is a cold cathode fluorescent lamp, and 20 is a drive power source. The cold cathode fluorescent lamp 10 is configured by disposing an anode 13 with a phosphor 12 and a linear cathode 14 facing each other in a vacuum vessel 11.

  The drive power supply 20 includes a voltage generation unit 20a and a voltage application unit 20b. The voltage generating means 20a includes a transformer TS in which the middle point NP of the secondary coil L2 is grounded. The voltage generation means 20a includes means for applying a pulse voltage between both ends of the primary coil L1 of the transformer TS, but is not particularly shown. The voltage applying means 26 includes a first rectifier diode D1 having an anode connected to one end of the secondary coil L2 of the transformer TS, and a second rectifier diode D2 having a cathode connected to the other end of the secondary coil L2. With. The cathode of the first rectifier diode D1 is connected to the anode 13 of the cold cathode fluorescent lamp 10, and the anode of the second rectifier diode D2 is connected to the cathode 14 of the cold cathode fluorescent lamp 10.

  Referring to FIG. 2, a pulse voltage Vp shown in FIG. 2A is applied between both ends of the primary coil L1 of the transformer TS. A positive differential pulse voltage Va shown in FIG. 2B is induced and generated at one end L2a of the secondary coil L2 of the transformer TS, and the generated differential pulse voltage Va is the anode of the cold cathode fluorescent lamp 10. 13 is applied. A negative differential pulse voltage Vk shown in FIG. 2C is induced and generated at the other end L2b of the secondary coil L2, and the generated differential pulse voltage Vk is applied to the cathode 14 of the cold cathode fluorescent lamp 10. Applied. In this case, the rising edges of both differential pulse voltages Va and Vk are synchronized. The voltage between the peak values of the differential pulse voltages Va and Vk is a voltage at which electrons can be emitted from the cathode 14 toward the anode 13 and the emitted electrons can collide with the phosphor 12 to emit light. . As described above, the voltage Vak shown in FIG. 2D is applied between the anode and the cathodes 13 and 14 of the cold cathode fluorescent lamp 10, and electrons are emitted from the cathode 14 toward the anode 13. It collides with the phosphor 12 and emits light.

Here, the relationship between the anode-cathode voltage Vak and the emission current Ie (electron emission amount) of the cold cathode fluorescent lamp 10 will be described with reference to FIG. 3. The horizontal axis represents the anode-cathode voltage Vak (kV / mm). ), The vertical axis represents the emission current Ie (mA / cm ² ). In the anode-cathode voltage Vak, Vth is an operation start voltage, for example, 1.1 kV, and V1-V2 is an operation voltage range in which the phosphor emits light, for example, 2.0-2.5 kV. The range of the operating voltage can be determined as appropriate. V0 is a rated voltage, for example, 3.0 kV. Therefore, the anode-cathode voltage Vak shown in FIG. 2D can be set within this operating voltage range.

  The structure of the cold cathode fluorescent lamp 10 will be described in detail with reference to FIG. 4. Reference numeral 10 denotes the entire cold cathode fluorescent lamp. 11 is a vacuum vessel, 12 is a phosphor, 13 is an anode, and 14 is a cathode. The shape of the vacuum vessel 11 can take various forms depending on the use of the light source including the backlight. The front surface 11a of the vacuum vessel 11 is made of a glass substrate, quartz, sapphire, or the like. On the inner surface of the front surface portion 11a, an anode 13 is formed in a thin film by sputtering, EB vapor deposition or the like of a metal such as ITO (indium oxide / tin) or aluminum. The phosphor 12 is applied to the anode 13 by a slurry application method, a screen printing method, an electric perturbation method, a sedimentation method, or the like. The cathode 14 is arranged to extend linearly in one direction at a distance from the anode 13. The cathode 14 is a field emission type cathode that emits electrons toward the anode 13 by an electric field generated between the anode 13 and the anode 13 by applying an anode-cathode voltage Vak. The cathode 14 is formed by a conductive wire 14a and a carbon thin film 14b having a number of nanotubes, nanowalls, and other fine protrusions formed on the surface of the conductive wire 14a.

  The cathode 14 is positively set to have a surface roughness that makes it easier for the surface of the conducting wire 14a to generate electric field concentration. The surface roughness unevenness 14c is further formed on the fine protrusions formed only by the carbon thin film 14b. 14d is formed and acts as an electric field concentration assisting part that promotes electric field concentration at the fine protrusions. This surface roughness is microscopic but may be visible irregularities. For example, the unevenness | corrugation which twists several conducting wires and the unevenness | corrugation which carries out the threading process of the conducting wire surface may be sufficient.

  In the cold cathode fluorescent lamp 10 having the above configuration, the phosphor 12 emits light only during a very short period in which the anode-cathode voltage Vak composed of the differential pulse voltages Va and Vb is applied. The light emission life of the phosphor 12 can be extended. Further, since the anode-cathode voltage Vak is pulsed, the peak-to-peak voltage can be increased, and the increased voltage causes electrons to be emitted from the cathode 14 at a high speed and collide with the phosphor 12. Therefore, with respect to the phosphor 12 made of a laminate of several phosphor particles, electrons can be easily penetrated into the interior of the phosphor particles instead of the surface layer to emit light, and the luminous efficiency is increased. can do.

  The present invention is not limited to the above-described embodiment, and includes various changes or modifications within the scope described in the claims.

It is a figure which shows the field emission type cold cathode fluorescent lamp and its drive power source concerning embodiment of this invention. 2 is a timing chart for explaining the operation of the drive circuit of FIG. 1. It is a figure which shows the voltage-current characteristic of the cold cathode fluorescent lamp of FIG. It is sectional drawing which shows the structure of a cold cathode fluorescent lamp.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cold cathode fluorescent lamp 20 Drive power supply 20a Voltage generation means 20b Voltage application means

Claims (5)

  In the driving method of a cold cathode fluorescent lamp in which an electric field is formed in the opposing space between the anode and the cathode and electrons are emitted from the cathode, the differential between the positive and negative differentials in which the voltage between the peak values is equal to or higher than the operating voltage required for the phosphor emission A driving method of a cold cathode fluorescent lamp, characterized in that a pulsed voltage is generated in synchronization with rising, and a positive differential pulsed voltage is applied to an anode and a negative differential pulsed voltage is applied to a cathode.   A transformer with the middle point of the secondary coil grounded on the drive side, a first rectifier diode with an anode connected to one end of the secondary coil of the transformer, and a cathode connected to the other end of the secondary coil A pulse voltage is applied to the primary coil of the transformer, and a positive differential pulse voltage induced at one end of the secondary coil is applied to the anode of the cold cathode fluorescent lamp as the first rectifier diode. The negative differential pulse voltage induced on the other end side of the secondary coil is applied to the cathode of the cold cathode fluorescent lamp via the second rectifier diode. The driving method of the cold cathode fluorescent lamp according to claim 1.   The anode has a planar shape, and the cathode includes a conductive wire extending in a line substantially parallel to the anode surface and facing, and a carbon thin film with a large number of fine protrusions for electric field concentration formed on the surface of the conductive wire, 3. The driving method for a cold cathode fluorescent lamp according to claim 1, wherein the conductive wire has an unevenness for assisting electric field concentration formed on a surface thereof.   In a cold cathode fluorescent lamp drive power supply that forms an electric field in the space between the anode and cathode and emits electrons from the cathode toward the anode, the voltage between the peak values of the anode and the cathode is required for the phosphor to emit light. Voltage generating means for generating two differential pulsed voltages having positive and negative values that are equal to or higher than the normal operating voltage in synchronization with rising edges, and a positive differential pulsed voltage of both differential pulsed voltages is applied to the anode of the cold cathode fluorescent lamp, A drive power supply for a cold cathode fluorescent lamp, comprising voltage applying means for applying a differential pulse voltage to each cathode of the cold cathode fluorescent lamp. The voltage generating means includes a transformer in which the middle point of the secondary coil is grounded,
The voltage application means includes a first rectifier diode having an anode connected to one end of the secondary coil of the transformer, and a second rectifier diode having a cathode connected to the other end of the secondary coil. The drive power supply for a cold cathode fluorescent lamp according to claim 4.

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