JP2009152154A - Discharge lamp lighting device, and backlighting device for liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve moving image display quality when a liquid crystal display device is used, improve a service life of an illumination device, and prevent reduction in reliability. <P>SOLUTION: A discharge lamp lighting device includes a lighting circuit HB1 for lighting a hot-cathode lamp FL with a high frequency, and a preheating circuit HC1 to give power to a filament of the hot-cathode lamp FL. The lighting circuit HB1 has the main lighting period during which the number of bright spots generated in the filament of the hot-cathode lamp FL becomes 2, and at least one light control waiting period during which the lamp luminous flux output is small compared with the main lighting period and the number of the bright spots becomes ≤1, and the main lighting period and the light control waiting period are periodically repeated. During the light control waiting period, there is provided with at least one of a state having no bright spot in the filament of the hot cathode lamp FL or a turnoff period in an arc-extinguishing state, and during the main lighting period, the output power to a discharge tube of the hot-cathode lamp FL is made substantially constant. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting device and a liquid crystal display backlight device for lighting a hot cathode fluorescent lamp.

  In transmissive liquid crystal display devices that are currently in practical use, a direct backlight device (see FIG. 19) is generally used in order to improve display uniformity. Regarding the display quality of this liquid crystal display device, it is known that display blur such as outline blur occurs in a hold type display system such as liquid crystal. As one of the techniques for improving the display blur, an impulse-type light emitting display system such as a CRT is provided by providing a lighting period and a dimming lighting period (or a non-lighting period) of a lighting device within one frame period. There is a method of realizing.

For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-72988) proposes a technique for blinking and lighting a CCFL (cold cathode fluorescent lamp) that is a backlight light source of a liquid crystal display device. Further, as a technique in which an HCFL (hot cathode fluorescent lamp) widely used as a light source for general illumination is applied to a display device, there is JP-A-60-72198. This prior art is an example in which a hot cathode fluorescent lamp is turned on and off. Further, in Patent Document 3 (Japanese Patent Laid-Open No. 63-69195), a hot cathode lamp is used as a backlight light source of a liquid crystal display device, and the luminous output of the hot cathode lamp is increased by using a plurality of bright spots on the lamp filament. Technology is disclosed.
JP 2002-72988 A Japanese Unexamined Patent Publication No. 60-72198 JP-A-63-69195

  Impulse lighting is difficult with the technique of Patent Document 1. For one thing, the light output of a CCFL (cold cathode fluorescent lamp) cannot be increased. That is, since the cold cathode lamp uses glow discharge, the lamp current cannot be increased, and the lamp output is reduced during impulse lighting. Even if the lamp current is forcibly increased and the lamp output is increased to realize the impulse lighting control with a large output, a problem occurs in the lamp life and the reliability of the product is lowered.

  For example, when the electrode life of the CCFL is 60,000 hours with a constant lamp current of 8 mA (rms), the ratio of the lighting time to the lighting time is 1: 1 (50% lighting), and the lamp current during the lighting period is doubled to 16 mA. When lit at (rms), the lamp electrode is destroyed in only a few thousand hours. This is because electrode consumption due to ion collision in the discharge tube of the cold cathode lamp increases exponentially with respect to the current.

  Furthermore, the CCFL also has a problem that uneven brightness tends to occur when blinking is lit. In CCFL, it is well known that the lamp voltage is high and the difference in luminance from the low potential side is likely to occur due to the leakage current on the high potential side. Light emission occurs, and the luminance difference increases. For this reason, in order to perform impulse lighting using CCFL, the number of lamps, circuit breakdown voltage, and the number of circuit elements are very large.

  From the above, it can be seen that it is difficult to realize impulse lighting with uniform screen brightness using CCFL in a large liquid crystal display device.

  The technique of Patent Document 2 is a technique for performing impulse lighting in a hot cathode fluorescent lamp. Although this conventional technique can perform impulse lighting with an increased lamp output, there is a problem in the life of the lamp electrode. That is, the peak current of the lamp current immediately after starting becomes extremely large, and the filament electrode is damaged.

  This is a phenomenon that occurs because the vapor pressure of mercury enclosed in the lamp is low immediately after starting. In other words, the mercury vapor density in the lamp decreases while the lamp is extinguished, and the mercury vapor pressure immediately increases immediately after the lamp is turned on, but the mercury atom density is low until the vapor pressure stabilizes. Therefore, there are few electron collisions of the discharge tube, and as a result, a state where the tube voltage is low occurs instantaneously. Such a phenomenon is not observed when the blinking frequency is several kHz or more, but the above phenomenon occurs in the impulse lighting in the vicinity of several hundred Hz. This phenomenon differs slightly depending on the lamp gas. Particularly noticeable is the case where krypton (Kr) is mixed and enclosed in the lamp. Since the lamp current increases in the state where the tube voltage is reduced immediately after starting, the current is concentrated on a part of the filament electrode, and the electron radioactive material (emitter) applied to the filament electrode is scattered. is there.

  By the way, the lifetime of a hot cathode lamp is roughly divided into filament disconnection and emitter depletion. Filament breakage may be due to mechanical damage, but it is generally considered that discharge current concentration on the filament is the main cause. The emitter depletion is caused by the filament temperature being too high. That is, when the preheating current increases and the filament temperature rises, the emitter evaporates and peels from the electrode.

  In the technique of Patent Document 2, an attempt is made to reduce the preheating current. However, this has the effect of reducing the filament temperature rise due to the combined current of the lamp current and the preheating current and suppressing the emitter evaporation, but the electrode damage due to the concentration of the discharge current due to the peak current cannot be avoided as described above. .

  In the technique of Patent Document 3, a plurality of bright spots are formed on an electrode in a hot cathode fluorescent lamp to increase the output of the lamp. However, since it is not impulse lighting, display blur cannot be improved.

  The present invention has been made to solve such problems of the prior art, and when used in a liquid crystal display device, the moving image display quality is improved, the lifetime of the lighting device is improved, and the reliability is lowered. It is an object of the present invention to provide a discharge lamp lighting device that can prevent the above-described problem.

  In order to solve the above-described problem, the invention of claim 1 is a lighting circuit HB1 for lighting a hot cathode lamp FL at a high frequency and a preheating circuit for supplying power to the filament of the hot cathode lamp FL as shown in FIG. As shown in FIG. 2, the lighting circuit HB1 includes a main lighting period t1 to t2 in which the number of bright spots generated in the filament of the hot cathode lamp FL is two, and a lamp compared with the main lighting period. It has at least one dimming standby period t2 to t3 in which the luminous flux output is small and the number of bright spots is 1 or less, and the main lighting period and the dimming standby period are periodically repeated. .

  According to a second aspect of the present invention, in the first aspect of the present invention, the dimming standby period has at least one extinguishing period in which the filament of the hot cathode lamp FL has no bright spot or is extinguished. And

  The invention of claim 3 is characterized in that, in the invention of claim 2, output power to the discharge tube of the hot cathode lamp FL is substantially constant during the main lighting period (FIGS. 5 and 6).

  According to a fourth aspect of the present invention, in the second or third aspect of the invention, as shown in FIGS. 11 to 13, the dimming lighting in which the filament of the hot cathode lamp FL has one bright spot during the dimming standby period as shown in FIGS. A continuous lighting switching means having a period, wherein the time ratio of the main lighting period is zero and the time ratio of the extinguishing period in the dimming standby period is zero in response to a switching signal SEL for continuous lighting. And

  The invention of claim 5 is characterized in that, in the invention of claim 3, the voltage Vf applied between the filaments of the hot cathode lamp FL by the preheating circuit is a substantially square wave (FIGS. 8 and 9).

  According to a sixth aspect of the present invention, in the third to fifth aspects of the present invention, the AC voltage applied to the filament is lower than the AC frequency of lamp operation or DC, and the plurality of metal pins that support the filament are in the axial direction of the lamp discharge path. In the hot cathode lamp (FIG. 10) having two lamp electrodes arranged in the same manner, one lamp electrode FE2 creates a bright spot E21 in the center direction of the lamp discharge tube, and the other lamp electrode FE1 is opposite to the center direction of the lamp discharge tube. A bright spot E11 is formed in the direction of, and a plurality of bright spots are generated in the filaments FE1 and FE2 by alternately generating the bright spots.

  According to a seventh aspect of the present invention, in the first to sixth aspects of the invention, when the discharge tube wall temperature of the hot cathode lamp changes from a low state to a high state, the main lighting period and the dimming standby periods The period is long and the time ratio of the main lighting period is increased (FIG. 14).

  The invention of claim 8 is a backlight device for liquid crystal display comprising the discharge lamp lighting device according to any one of claims 1 to 7 (FIG. 19).

  According to a ninth aspect of the present invention, in the backlight device for a liquid crystal display including the discharge lamp lighting device according to the fourth aspect, the continuous lighting switching means operates in accordance with a video signal input to the liquid crystal display device. And

  According to the first aspect of the present invention, in the lighting control that repeats the lighting state and the dimming state, the damage of the electrode is reduced by dividing the bright spot (arc discharge spot) generated in the filament of the hot cathode lamp immediately after lighting. it can. Therefore, instantaneous high output lighting is possible without increasing the number of lamps. Further, luminance unevenness near the lamp filament is improved. Therefore, there is no unevenness in the luminance distribution, which is useful for a discharge lamp lighting device that performs impulse lighting.

  According to the invention of claim 2, even in the lighting control that repeats the light-off state and the light-on state, damage to the electrode can be reduced by dividing the bright spot generated in the filament of the hot cathode lamp immediately after lighting. Therefore, instantaneous high output lighting is possible without increasing the number of lamps. Also, by making the extinguishing period, the luminous flux peak ratio can be increased, and ideal impulse lighting is achieved. Therefore, it is useful for a discharge lamp lighting device that performs impulse lighting.

  According to the invention of claim 3, the brightness of the hot cathode lamp can be controlled to be constant immediately after lighting. Since the light output of the lamp is proportional to the electric power of the arc tube, stable impulse lighting without light fluctuation is possible. Therefore, it is useful for a discharge lamp lighting device that does not flicker in impulse lighting.

  According to invention of Claim 4, it can change from impulse lighting to continuous lighting according to a condition. That is, the efficiency can be improved by changing to the continuous lighting according to the situation with respect to the decrease in the lamp luminous efficiency due to the impulse lighting. Therefore, it is useful for a discharge lamp lighting device for impulse lighting for the purpose of power saving.

  According to the invention of claim 5, the bright spot generated in the filament can be stably generated at both ends of the filament. As a result, since the filament temperature can be controlled appropriately, the evaporation of the lamp emitter can be reduced, and the life of the lamp can be improved. Therefore, the present invention is useful for a discharge lamp lighting device that performs impulse lighting of a hot cathode lamp over a long period of time.

  According to the invention of claim 6, in the lamp in which the filament is arranged in parallel to the lamp discharge path, the length of the discharge path becomes constant, and the flicker near the lamp electrode can be reduced. Further, since the discharge spreads to the end of the lamp, light can be emitted from the entire lamp. Therefore, the present invention is useful for a discharge lamp lighting device that illuminates uniformly over a wide range in impulse lighting.

  According to the invention of claim 7, when the lamp tube wall temperature is lit from a low state, a large electric power can be applied to the lamp, and the lamp temperature can be stabilized quickly. As a result, the time required for lamp light flux stabilization can be shortened. Therefore, it is useful for a discharge lamp lighting device that instantaneously stabilizes lamp light output.

  According to invention of Claim 8, the backlight apparatus for liquid crystal displays which has the effect of Claims 1-7 can be provided.

  According to the ninth aspect of the present invention, since the impulse lighting and the continuous lighting can be adjusted according to the image without any sense of incongruity, it is possible to provide a backlight device for liquid crystal display that achieves both display blur and power saving without making the user aware of it. .

(Embodiment 1)
FIG. 1 is a circuit diagram showing a configuration of Embodiment 1 of the present invention. Hereinafter, the circuit configuration will be described. The AC input terminal of the full-wave rectifier DB is connected to the commercial AC power source Vin. A power factor correction circuit PFC1 is connected to the DC output terminal of the full-wave rectifier DB. The power factor correction circuit PFC1 includes a step-up chopper circuit, and the smoothing capacitor on the output side is charged with the DC voltage Vdc boosted from the peak voltage of the pulsating voltage that is full-wave rectified by the full-wave rectifier DB. . The oscillator OSC5 improves the input power factor by controlling the switching element of the step-up chopper circuit at a high frequency so that the average value of the input current from the commercial AC power supply Vin is similar to the input voltage. ing.

  An inverter circuit HB1 is connected to the smoothing capacitor on the output side of the power factor correction circuit PFC1. The inverter circuit HB1 forms a half-fridge circuit by a series circuit of a pair of switching elements Q1 and Q2 that are alternately turned on and off, and a coupling capacitor Cd1 between the connection point of the switching elements Q1 and Q2 and the ground. A series circuit of a resonance inductor Lr1 and a resonance capacitor Cr1 is connected via The oscillator OSC1 controls on and off of the switching elements Q1 and Q2 of the inverter circuit HB1 alternately at a high frequency, thereby controlling each operation of starting, lighting, and dimming the discharge lamp FL. A series circuit of a discharge lamp FL and a current detector CS1 is connected to both ends of the resonance capacitor Cr1. The current detector CS1 detects the discharge tube current of the discharge lamp FL and outputs the signal to the preheating circuit HC1.

  The two filament electrodes of the discharge lamp FL1 are connected to the two output transformers Tr1 and Tr2 of the preheating circuit HC1, respectively. That is, the secondary side of the preheating transformer Tr2 is connected to the filament on the low voltage side (current detector CS1 connection point) of the lamp, and the filament on the lamp high voltage side (connection point of the resonance capacitor Cr1 and the resonance inductor Lr1). Is connected to the secondary side of the preheating transformer Tr1. The preheating circuit HC1 is an inverter circuit including a switching element Q3. In the switching element Q3, the switch ON time is controlled by the oscillator PWM1. The oscillation frequency of the oscillator PWM1 is set to a half frequency of the oscillator OSC1.

  The dimming signal generator DIM1 periodically generates a PWM signal for lighting the lamp. When this PWM signal becomes High, the oscillator OSC1 oscillates at a frequency close to the resonance frequency of the resonance capacitor Cr1 and the resonance inductor Lr1, thereby instantly starting the lamp and lighting the lamp. Thereafter, when the PWM signal becomes low, the switching output is reduced and the lamp is turned off. In order to reduce the switching output, for example, the oscillation frequency may be increased so that the resonance effect is weakened.

  The preheating circuit HC1 also controls the power supplied to the lamp filament in accordance with the PWM signal of the dimming signal generator DIM1. That is, when the PWM signal becomes High, the inverter circuit HB1 turns on the lamp. During this period, the detection signal from the lamp current detector CS1 is received and the preheating power is controlled to be small. Further, when the lamp is turned off, the PWM signal becomes Low, so that the preheating power is increased.

  FIG. 2 shows a current voltage waveform during the operation of the present embodiment. The figure shows how the voltage Vla of the lamp FL, the tube current ila, the two filament currents if1 and if2 on the high voltage side, the filament voltage Vf1 on the high voltage side, and the waveform of the switch current iQ3 of the switching element Q3 are changed. ing.

  When the PWM signal output from the dimming signal generator DIM1 becomes High at time t0, the oscillator OSC1 switches from a state where the oscillation frequency is high to a frequency close to the resonance frequency of the resonance inductor Lr1 and the resonance capacitor Cr1. Reduce. Then, a high resonance voltage is generated at both ends of the resonance capacitor Cr1, and the lamp is immediately started.

  At time t1, the lamp starts and current ila flows through the lamp. From the time when the lamp is lit, the lamp voltage Vla rapidly decreases and the lamp is in an arc discharge state. When the lamp is lit, the current detector CS1 sends a detection signal to the preheating circuit HC1, and the preheating circuit HC1 receives it, shortens the switch ON time of the switching element Q3, and performs the operation of reducing the preheating power. Yes.

  When the PWM signal output from the dimming signal generator DIM1 becomes Low at time t2, the oscillator OSC1 increases the switching frequency and increases the impedance of the inductor Lr1. As a result, the lamp current ila decreases and the lamp is turned off.

  At this time, the preheating circuit HC1 performs an operation of extending the switch ON time of the switching element Q3 to increase the preheating power and maintaining the filament electrode in a temperature state necessary for restarting.

  At time t3, the state is the same as at time t0. As described above, the discharge lamp lighting circuit repeatedly turns on and off the lamp.

  Next, the operation of the double spot (bright spot division) of the hot cathode lamp will be described. Since the hot cathode lamp is lit in the arc discharge region, current concentration (spot) occurs in the filament electrode portion. It is a double spot that generates two spots. The mechanism of generation utilizes the fact that the generation of electrons in the discharge tube and the inflow location change due to the potential difference of the filament electrode.

The following is simply considered.
1) Electrons in the discharge tube are generated from the lowest potential and flow to the highest potential.
2) It is necessary to flow a current (preheating current) for emitting thermoelectrons to the filament in advance.
3) A potential difference occurs between both ends of the filament due to the preheating current of the filament.
4) The position of electron emission and electron inflow changes depending on the potential difference of the filament electrode.

  Various methods for generating a double spot have been proposed. When the fluorescent lamp is lit at a high frequency, a double spot is generated by the following method.

A. A DC voltage is applied to the filament.
B. A phase difference is provided between the lamp current and the preheating current (particularly 90 °).
C. Different lamp current frequency and preheating current frequency.
D. Shunt with an impedance element.

  Although any method can be used to realize a double spot, in this embodiment C.I. The method will be described.

  FIG. 3 shows a current waveform at the time of starting the lamp. In the figure, the lamp current ila and the filament currents if1 and if2 are shown. It is the figure which expanded the waveform of the time t1 (just after a start) in FIG. 2 to the time-axis direction.

  The operating frequency of the preheating circuit HC1 is operating at half the operating frequency of the inverter circuit HB1. Prior to time t1, since there is no lamp current ila, only a preheating current flows through the filament. That is, the current flowing in from the if1 side terminal flows out of the if2 side terminal. At this time, if1 is positive means that if1> if2 in terms of potential.

  At time t1, the lamp starts to discharge and an electron current is generated. In this figure, when ila is positive (+), it means that electrons are generated from the filament on the ground side and flow toward the filament on the high voltage side.

  At time t11, the lamp current ila is positive and the filament current if1 is positive. At this time, the electrons flow into the position having the highest potential in the discharge tube, that is, the terminal on the if1 side.

  At time t12, the lamp current ila is negative and the filament current if1 is positive. Since the lamp current ila is negative, electrons are now emitted from the filament. At this time, electrons are emitted from a position having the lowest potential in the discharge tube, that is, from a terminal on the if2 side.

  At time t13, the lamp current ila is positive and the filament current if1 is negative. At this time, the electrons flow into the position having the highest potential in the discharge tube, that is, the terminal on the if2 side.

  At time t14, the lamp current ila is negative and the filament current if1 is negative. At this time, electrons are emitted from the discharge tube at the lowest potential, that is, from the terminal on the if1 side.

  As described above, it can be seen that the lamp current is distributed to two locations of the filament every half cycle. As a result, since the peak current of the lamp can be distributed to the two filaments, the effective average current of the arc spot portion is reduced.

  In addition, since the current of the preheating circuit that applies a potential to the filament is reduced as the lamp current is generated, the preheating power of the filament can be reduced. As a result, an increase in the temperature of the arc spot portion generated in the filament can be suppressed.

  In this example, the filament current is controlled to decrease when the lamp is lit, but the filament temperature changes relatively slowly, so the temperature may be controlled throughout the extinguishing period and the lighting period.

  By the way, a similar arc spot division is possible even if the relationship between the lamp frequency and the preheating frequency is set to be twice the operating frequency of the preheating circuit HC1 = the operating frequency of the inverter circuit HB1.

  FIG. 4 shows the current waveform at that time. FIG. 4 shows the lamp current ila and the filament currents if1 and if2 as in FIG. The operation differs from FIG. 3 in that the current is divided into the filament currents if1 and if2 during the half cycle of the lamp current. Therefore, it differs from FIG. 3 in that the peak current is divided.

  In this example, the stress on the electrode can be reduced by reducing the effective average current of the lamp current. This is because by dividing the arc spot into two, local heat generation due to the occurrence of arc discharge on the filament electrode is reduced, and the evaporation of the emitter can be reduced. The energy of local heat generation is considered to be the product of the cathode fall voltage of the discharge lamp and the discharge current. Therefore, if the discharge current of the lamp is halved, the local heat generation is also halved.

  In addition, there is an effect that emission of filament thermoelectrons is stabilized. A state where the electrode temperature of the spot portion is optimal in a state where one arc spot is lit, and a state where the electrode temperature of each spot portion is optimal in a state where two arc spots are lit. In the latter case, the latter can supply more thermoelectrons. This is because the surface area of the emitter at the optimum temperature is increased.

  In a hot cathode lamp, the temperature of the emitter greatly affects the lifetime. If the temperature is too high, it will evaporate, and if it is too low, thermionic electrons cannot be supplied sufficiently. For this reason, it is a general design method for a discharge lamp lighting device of a hot cathode lamp to adjust the preheating current applied to the filament during lighting so that the temperature is optimal at the time of lighting.

  The importance of this filament temperature design is further increased when the lamp is lit for a long period of tens of thousands of hours. Therefore, it is designed at a temperature lower than that of a normal discharge lamp lighting device in order to suppress emitter evaporation. That is, the emitter surface temperature is lowered so that the minimum required amount of thermoelectrons is generated.

  When the lamp is lit continuously, the required amount of thermoelectrons is constant, so there is no problem with this design method. However, if the lamp is flashed and the lamp current peak is nearly double that of continuous lighting, instantaneous supply of thermoelectrons becomes difficult.

  If the present invention is used, the number of thermionic electrons emitted from the emitter increases even at the lamp current peak generated at each start-up, so that the lamp life can be extended.

  According to the present invention, instantaneous high-power lighting is possible without increasing the number of lamps as in the case of using CCFLs (cold cathode fluorescent lamps), and display performance can be improved when used in a liquid crystal display device. .

(Embodiment 2)
FIG. 5 is a circuit diagram showing Embodiment 2 of the present invention. Hereinafter, the configuration will be described. In the figure, in addition to the discharge lamp lighting circuit having the same configuration as that of the first embodiment, the dimming signal of the dimming signal generator DIM1 and the output power detection signal Vs1 of the half-fridge type inverter circuit HB1 are input, and the inverter circuit HB1 An error amplifier EA1 that controls the switching frequency and the switch-on time is connected.

  FIG. 6 is a diagram showing an operation state of the present embodiment. In the figure, the lamp voltage Vla, the lamp current ila, the dimming signal DIM1, and the light output waveform output from the lamp are shown. The operation of repeatedly turning on and off the lamp is the same as in the first embodiment. The second embodiment is greatly different from the first embodiment in that the lamp current is controlled so as to keep the lamp power constant during the lighting period. That is, in the lamp lighting period, the lamp current is increased immediately after the lamp is started, and the light output of the lamp is controlled to be constant.

  As described above, there is a phenomenon in which the lamp voltage decreases immediately after starting the lamp. At this time, if the lamp current is controlled to be constant, the rise of light is delayed. FIG. 7 shows a light rising waveform in the conventional control. The reason why the light output of the lamp becomes low immediately after the start is that the lamp power is reduced. The lamp power is obtained by the product of the lamp voltage and the lamp current. By controlling this instantaneous power, the light output can be quickly started up.

  In the present embodiment, the lamp light output can be instantaneously stabilized, so that fluctuations in the waveform of the light output due to variations in temperature and lamp gas can be suppressed. As a result, an ideal impulse light source can be realized, and display blur can be improved satisfactorily when applied to a liquid crystal display device.

  According to the present embodiment, instantaneous high-power lighting can be performed without increasing the number of lamps as in the case of using CCFL, and display performance can be improved when used in a liquid crystal display device.

(Embodiment 3)
FIG. 8 is a circuit diagram showing Embodiment 3 of the present invention. Hereinafter, the configuration will be described. In the present embodiment, the voltage waveform of the preheating circuit HC2 is different.

  FIG. 8 shows a discharge lamp lighting circuit similar to that of the first embodiment, but the voltage waveform applied to the lamp filament of the preheating circuit HC2 is different. That is, the preheating circuit HC2 is a half-bridge inverter, and a rectangular wave voltage is applied to the lamp filament.

  FIG. 9 shows waveforms during the operation of the present embodiment. In the figure, lamp current ila and filament currents if1 and if2 are shown. The waveform of if1 shows a combined waveform of a rectangular wave and a divided sine wave. The frequency of the rectangular wave current flowing through the filament is the same as the lamp current frequency. However, the phase of the rectangular wave current and the phase of the lamp current are shifted by 90 degrees.

  In the period A, the lamp current ila is negative, and a current appears at the terminal on the if1 side having a low potential. In the period B, the lamp current ila is negative, and at this time, a current appears at the terminal on the if2 side having a low potential. In the period C, the lamp current ila is positive, and at this time, a current appears at a terminal on the if1 side having a high potential. In the period D, the lamp current ila is positive, and a current appears at the terminal on the if2 side having a high potential at this time.

  The present embodiment is different from the first embodiment in the operation at the moment of transition from the period A to the period B and from the period C to the period D. That is, in this embodiment, the time for the lamp current to move from if1 to if2 is short by using a rectangular wave. When a sine wave is used, current movement of if1 and if2 occurs slowly, but in this case, it has been found that arc spot generation becomes unstable.

  When a rectangular wave is used as in this embodiment, the position of the arc spot is stabilized, and flickering near the filament electrode can be reduced.

  This embodiment is particularly effective when the voltage frequency for filament preheating is higher than the frequency of the lamp current.

(Embodiment 4)
FIG. 10 is an explanatory diagram of the fourth embodiment. This embodiment relates to the position of spot generation. As a lamp used for a liquid crystal backlight or the like, a hot cathode lamp (seamless lamp) having a structure as shown in FIG. 10 has been proposed. Since this type of lamp emits light up to the lamp end, it is suitable for a backlight of a liquid crystal display device.

  The figure shows an example in which double spot lighting is performed in a lamp having lamp filaments FE1 and FE2. In the figure, A discharge is performed between E11 of filament FE1 and E21 of filament FE2, B discharge is performed between E12 of filament FE1 and E22 of filament FE2, and arc spots are generated at two locations. It is shown.

  In this embodiment, since the change in the length of the discharge path of the A discharge and the B discharge can be reduced, the lamp voltage is stable and flickering does not occur.

(Embodiment 5)
FIG. 11 shows the configuration of the fifth embodiment. This example relates to dimming control. FIG. 11 shows a discharge lamp lighting circuit similar to that of the first embodiment, except that the dimming signal generator DIM1 is controlled by the mode switch SEL.

  The mode switch SEL will be described. The mode switch SEL gives a mode switching signal for switching between blinking lighting and continuous lighting to the dimming signal generator DIM1. When switching to continuous lighting by the mode switching signal, the dimming signal generator DIM1 sets the lamp power for continuous lighting to be small according to the ratio between the lighting time and the light-off time at the time of blinking lighting. At this time, control is performed such that the operating frequency of the preheating circuit HC1 for preheating the filament is changed, the preheating power is reduced, and spot generation is changed to one place.

  FIG. 12 is a diagram illustrating an operation state of the present embodiment. In the figure, lamp voltage Vla, lamp current ila, dimming signal generator DIM1 output, switching signal of mode switch SEL, and light output are shown.

  Before the time t2, the mode switch SEL outputs a Low signal, and after the time t2, outputs a High signal. Before time t2, the lamp is in a state of periodically flashing. A starting voltage is applied to the lamp at time t5, the lamp starts at time t6, and the lamp is continuously lit thereafter. During the period from t2 to t5, the lamp extinguishing time before t2 is set.

  FIG. 13 shows an optical output waveform at the time of mode switching. In the figure, the average value of the lamp power, the switching signal of the mode switch SEL, and the light output is shown. At time t2, the lamp lighting is changed from blinking lighting to continuous lighting. That is, the lamp power is given to the lamp in an impulse manner before t2, but after t2, it is given as a continuous power. The average value of the optical output waveform is controlled so that there is no change between before t2 and after t2. That is, control is performed so that the average discharge tube power of the lamp is the same.

  According to this embodiment, the electrode loss of the lamp can be reduced and the luminous efficiency of the lamp can be improved. When the hot cathode lamp is turned on by impulse, the luminous efficiency of the lamp decreases. This is because the electrode loss of the lamp increases. The lamp electrode loss is considered to be divided into two elements, that is, electric power for heating the filament and heat generation by the cathode fall voltage part of the lamp. In particular, it can be seen that the electric power for heating the filament increases because the lamp extinction period exists.

  For example, consider a case where the lamp lighting time ratio is 50%. In this case, preheating power is required to keep the filament temperature optimal during the lamp extinction period. This is electric power necessary for sufficient supply of thermoelectrons during restart. In general, in order to maintain the temperature in a state where the filament can be started at any time, it is necessary to continuously apply a power of about 1 to 2 W per electrode in the absence of a lamp current. That is, when the lamp lighting time ratio is 50%, an average of 0.5 W to 1 W of electric power that does not contribute to lamp emission is generated per filament. When a hot cathode lamp is used in a liquid crystal display device, at least about 4 lamps are required for 32 inches, and this loss is generated at about 4 to 8 W. Therefore, there is a drawback that the energy efficiency of the entire liquid crystal display device is greatly reduced. There is no such loss in continuous lighting.

  In the present embodiment, the light output is kept constant, and the switching signal from the mode switch SEL is switched from the blinking lighting of the double spot to the continuous lighting of the single spot, so that, for example, the video signal with little display blur is changed to the continuous lighting. In addition, the energy consumption of the liquid crystal display device can be reduced.

  Note that the switching signal of the mode switch SEL may be generated by determining from the video signal content or the program content. In this case, the power consumption can be reduced even if the user does not perform any operation, which is preferable.

(Embodiment 6)
FIG. 14 shows the operation of the sixth embodiment. This example improves the light output characteristics immediately after starting the lamp and accelerates the rise of the light output. In the figure, average values of lamp power and light output are shown.

  At time t0, the power of the liquid crystal display device is turned on and the lamp is started. The lamp is continuously lit at time t0 to t10. During this time, the arc spot is divided into two and the lamp current is lit at the maximum current. The maximum current is the maximum value of the lamp current when the arc spot temperature does not exceed the design upper limit when the preheating current applied to the filament is minimized. Then, when the predetermined time t10 is reached, the control shifts to a normal lighting state.

  About time t10, although an optimal value is calculated | required from the gas composition etc. of a lamp | ramp, it is about 1-2 minutes. When a mode switching signal is generated at time t20, the lamp shifts to a continuous lighting state.

  With the above control, the rising of the luminous flux can be improved in the lamp low temperature state immediately after the lamp is started.

  FIG. 15 shows a light rising waveform in the conventional control for comparison.

  In CCFL (Cold Cathode Fluorescent Lamp) and the like, there is a technique for temporarily increasing the lamp current in order to quickly increase the lamp brightness. However, with CCFL, if the current is increased, the life may be deteriorated, so that the current increase lighting for a long time is impossible. On the other hand, in the HCFL (hot cathode fluorescent lamp), high output is possible without impairing the life by keeping the filament temperature optimal.

  If this embodiment is used, the light output of the lamp can be stabilized quickly while satisfying the lamp life.

  In addition, control of Embodiments 1-6 is applicable also to a 2 lamp lighting circuit as shown in FIG. In the two-lamp lighting circuit of FIG. 16, in the embodiment of FIG. 5, two lamps FL1A and FL1B are connected in series, and each filament is preheated by the secondary side outputs of the preheating transformers Tr1, Tr2 and Tr3. The primary sides of the preheating transformers Tr1, Tr2, Tr3 are connected in series, and the voltage across the capacitor Cr2 is applied. Other configurations are the same as those of the embodiment of FIG.

(Embodiment 7)
FIG. 17 shows a circuit diagram of the seventh embodiment. In this example, a plurality of lamps are impulse-lighted in a liquid crystal display device to improve display blur. In the figure, a discharge lamp lighting circuit similar to that of the first embodiment is provided, and four inverter circuits INV1 to INV4 including a preheating circuit are connected in parallel to the output of the power factor correction circuit PFC1. The dimming signals d1 to d4 are input from the dimming signal generator Dim to the oscillation control circuits OSC1 to OSC4 of INV1 to INV4, respectively.

  In an actual liquid crystal display device, as shown in FIG. 19, four lamps FL1 to FL4 are arranged in parallel.

  FIG. 18 is a diagram showing the operation timing of each part. In the figure, lamp currents of the lamps FL1 to FL4 and dimming signals d1 to d4 are shown. The dimming signals d1 to d4 are output in synchronization with the update cycle of the image display signal. Each lamp FL1-FL4 blinks corresponding to the dimming signals d1-d4. For example, the inverter INV1 performs a turn-on / off operation according to the dimming signal d1. Then, the display blur of the liquid crystal display device can be improved by sequentially turning on the lamps as shown in the figure.

  By using this embodiment, it is possible to easily improve display blur, which is a drawback of the liquid crystal display device, and in particular, it is possible to improve moving image display performance.

(Embodiment 8)
FIG. 19 is an exploded perspective view showing a schematic configuration of a liquid crystal display device using the discharge lamp lighting device of the first to seventh embodiments. A backlight is disposed on the back surface (directly below) of the liquid crystal panel LCP. The backlight includes a housing 22, a reflector 23 and a plurality of hot-cathode fluorescent lamps FL1 to FL4 disposed above the housing 22, It comprises an installed diffusion plate 25 and an optical sheet 26 such as a prism sheet. In addition, an inverter substrate 21 for lighting the hot cathode lamps FL <b> 1 to FL <b> 4 is installed on the back surface of the housing 22. The reflector 23 effectively directs the irradiation light of the hot cathode lamps FL1 to FL4 to the front surface. The diffusion plate 25 has a function of diffusing the light from the hot cathode lamps FL1 to FL4 and the reflection plate 23 and averaging the brightness distribution of the illumination light to the front surface.

It is a circuit diagram which shows the structure of Embodiment 1 of this invention. It is operation | movement explanatory drawing of Embodiment 1 of this invention. It is a wave form diagram which shows the principle of the double spot formation of Embodiment 1 of this invention. It is a wave form diagram which shows the other principle of double spot formation of Embodiment 1 of this invention. It is a circuit diagram which shows the structure of Embodiment 2 of this invention. It is operation | movement explanatory drawing of Embodiment 2 of this invention. It is operation | movement explanatory drawing of the comparative example with respect to Embodiment 2 of this invention. It is a circuit diagram which shows the structure of Embodiment 3 of this invention. It is a wave form diagram which shows the principle of the double spot formation of Embodiment 3 of this invention. It is explanatory drawing which shows the discharge path | route of Embodiment 4 of this invention. It is a circuit diagram which shows the structure of Embodiment 5 of this invention. It is operation | movement explanatory drawing of Embodiment 5 of this invention. It is operation | movement explanatory drawing of the comparative example with respect to Embodiment 5 of this invention. It is operation | movement explanatory drawing of Embodiment 6 of this invention. It is operation | movement explanatory drawing of the comparative example with respect to Embodiment 6 of this invention. It is a circuit diagram for demonstrating the application to the 2 light lighting circuit of Embodiment 1-6 of this invention. It is a circuit diagram which shows the structure of Embodiment 7 of this invention. It is operation | movement explanatory drawing of Embodiment 7 of this invention. It is a disassembled perspective view which shows schematic structure of the liquid crystal display device of Embodiment 8 of this invention.

Explanation of symbols

FL Hot cathode lamp HB1 Inverter circuit HC1 Preheating circuit

Claims (9)

A lighting circuit for lighting a hot cathode lamp at a high frequency;
A preheating circuit for supplying power to the filament of the hot cathode lamp;
The lighting circuit is
A main lighting period in which the number of bright spots generated in the filament of the hot cathode lamp is two;
Having at least one dimming standby period in which the lamp luminous flux output is smaller than the main lighting period and the number of bright spots is one or less,
The discharge lamp lighting device characterized by periodically repeating the main lighting period and the dimming standby period. 2. The discharge lamp lighting device according to claim 1, wherein the dimming standby period has at least one extinguishing period in which the filament of the hot cathode lamp has no bright spot or is extinguished. 3. The discharge lamp lighting device according to claim 2, wherein output power to the discharge tube of the hot cathode lamp is substantially constant during the main lighting period. The dimming standby period has a dimming lighting period in which the hot cathode lamp filament has one bright spot, and the time ratio of the main lighting period is set to zero and the dimming time according to a switching signal to continuous lighting. 4. The discharge lamp lighting device according to claim 2, further comprising continuous lighting switching means for setting a time ratio of a light extinction period in the light standby period to zero. The discharge lamp lighting device according to claim 3, wherein the voltage applied between the filaments of the hot cathode lamp by the preheating circuit is a substantially square wave. The AC voltage applied to the filament is lower than the AC frequency of lamp operation or DC, and in a hot cathode lamp having two lamp electrodes in which a plurality of metal pins supporting the filament are arranged in the axial direction of the lamp discharge path, The lamp electrode creates a bright spot in the center of the lamp discharge tube, and the other lamp electrode creates a bright spot in the direction opposite to the center of the lamp discharge tube. The discharge lamp lighting device according to claim 3, wherein a point is generated. When the discharge tube wall temperature of the hot cathode lamp changes from a low state to a high state, the period of the main lighting period and the plurality of dimming standby periods is lengthened and the time ratio of the main lighting period is increased. The discharge lamp lighting device according to any one of claims 1 to 6. The backlight apparatus for liquid crystal displays provided with the discharge lamp lighting device in any one of Claims 1-7. 5. A liquid crystal display backlight device comprising the discharge lamp lighting device according to claim 4, wherein the continuous lighting switching means operates in accordance with a video signal input to the liquid crystal display device.

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