JP3108916U - Liquid crystal display - Google Patents

Abstract

Even when a step-up transformer with a simplified configuration is used, a cold cathode tube is reliably lit even when the temperature is low, without complicating the electrical configuration.
An inverter circuit 1 that generates a lighting drive output for lighting a cold cathode tube 2 that is a light source of a backlight of a liquid crystal panel, and a power supply unit that generates a DC output 21 that is an operating power supply and supplies the output to the inverter circuit 1 3, when the cold cathode tube 2 starts lighting, the voltage of the DC output 21 supplied from the power supply unit 3 to the inverter circuit 1 is set to an initial voltage higher than the normal voltage, and the cold cathode tube is set. When the initial voltage application period, which is a predetermined period, has elapsed after the start of lighting of No. 2, lighting control means 15 is provided for reducing the voltage of the DC output 21 to the normal voltage.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device including an inverter circuit that generates a lighting drive output for lighting a cold cathode tube serving as a light source of a backlight of a liquid crystal panel. More specifically, the present invention relates to a DC output having a voltage higher than a normal voltage. The present invention relates to a liquid crystal display device that drops the voltage of the operating power supplied to the inverter circuit to a normal voltage when a predetermined period has elapsed after the LED is supplied to the inverter circuit and lighting of the cold cathode tube is started.

  In many cases, a cold cathode tube is used as a light source of a backlight used in a liquid crystal display device. In order to start lighting the cold cathode tube, it is necessary to apply a pulse having a voltage higher than the operating voltage for maintaining the lighting. For this reason, for example, as shown in FIG. 8A, an inverter circuit is used that generates a normal lighting pulse P92 after generating a high-voltage pulse P91 when supply of operating power is started. . However, since the cold cathode tube has a low gas pressure when the temperature is low and it is difficult to start lighting, the cold cathode tube has a property that the applied voltage must be increased when the temperature is low as shown in FIG. . For this reason, at a low temperature, lighting may not be started only by applying the high-pressure pulse P91 only once.

  FIG. 7 shows a technique proposed for solving such a problem (referred to as a first conventional technique). That is, when the supply of the operating power supply is started, after one high-voltage pulse P91 is generated, the operation from the constant voltage DC power supply 91 is performed via the transistor Q9 to the inverter circuit 92 that generates the normal lighting pulse P92. Leading power. A comparator 94 is provided in which the output of the oscillation circuit 95 for generating a triangular wave is led to the plus input, and the output of the integrating circuit composed of the resistor R9 and the capacitor C9 is led to the minus input. The output of the comparator 94 is used to control the on / off state of the transistor Q9.

  For this reason, when the constant voltage DC power supply 91 starts output of the operating power supply, the transistor Q9 is switched on and off at a period equal to the oscillation frequency of the oscillation circuit 95 in a period determined by the time constant of the integration circuit. Further, as the time elapses from the time when the constant voltage DC power supply 91 starts outputting the operation power supply, the ratio of the ON period gradually increases, and finally the ON state is maintained. Therefore, as shown in FIG. 8B, the inverter circuit 92 outputs a high voltage pulse P91 a plurality of times. In addition, the period during which the normal lighting pulse P92 is output gradually increases, and finally it is continuously output. For this reason, even if the cold cathode tube 93 is a case where temperature is low, it will start lighting reliably (for example, refer patent document 1).

  Further, a technique shown in FIG. 9 has been proposed (referred to as a second conventional technique). That is, in this technique, a transformer in which the primary coil L11 and the secondary coil L12 are wound so that the degree of coupling between the primary coil L11 and the secondary coil L12 is reduced to the step-up transformer T11 that generates high voltage. Used. For this reason, when the current flowing through the primary coil L11 is switched, a lighting drive output as shown at 41 in FIG. 3 is sent from the secondary coil L12.

If the level of the ringing pulse in this lighting drive output is indicated by V41 and the output voltage determined by the winding ratio between the primary coil L11 and the secondary coil L12 is indicated by V42, the coupling between the primary coil L11 and the secondary coil L12 Since the degree is small, ringing (overshoot) becomes large. Therefore, the ratio (V41 / V42) becomes large. That is, the PP value of the lighting drive output is a large value. Accordingly, since the lighting drive output having a large PP value is applied to the cold cathode tube 2, the cold cathode tube 2 easily starts glow discharge. Then, after glow discharge is started, current flows through the cold cathode tube 2 and the load of the secondary coil L12 shifts from a state equivalent to no load to a normal load state. As a result, the output voltage of the secondary coil L12 becomes a voltage V42 determined by the ratio of the number of turns of the primary coil L11 and the secondary coil L12, and the lighting is subsequently maintained by this voltage.
JP-A-5-326165

  However, when the first prior art is used, the following problems occur. That is, when the transistor Q9 is turned on and the supply of operating power to the inverter circuit 92 is started, an inrush current flows to the ground level through the primary coil of the step-up transformer, and the counter electromotive force due to the inrush current causes the secondary coil to enter the secondary coil. It is said that a high voltage pulse P91 is generated. However, as a property of the coil, the inrush current is difficult to flow (in the case of a capacitor, it is good that the inrush current flows at the start of supply of the operating power supply. Are known). For this reason, in order to generate a pulse P91 having a voltage high enough to start the lighting of the cold cathode tube 93 by the inrush current in the secondary coil, it is necessary to use a transformer having a special configuration as the step-up transformer. Has become expensive. Further, it is necessary to control the transistor Q9 so that the ON state continues after gradually increasing the time ratio of turning on. Therefore, even when the on / off state of the transistor Q9 is controlled by a microcomputer, the control method becomes complicated, and it takes time to create software.

  When the second prior art is used, the following problems have occurred. That is, in order to manufacture a transformer with a small degree of coupling between the primary coil L11 and the secondary coil L12, the primary coil and the secondary coil cannot be wound coaxially, and must be wound individually. . In addition, it is necessary to form a gap for leaking magnetic flux in the core that becomes a magnetic circuit for coupling the primary coil L11 and the secondary coil L12. For this reason, the structure of the transformer is complicated, and the transformer is expensive.

  Further, as a general property of a cold cathode tube, even when lighting is started, when the temperature of the cold cathode tube is low, the luminance is insufficient in the period until the temperature of the cold cathode tube becomes high. This often occurs. However, this phenomenon remains as a problem that cannot be solved even when the first conventional technique or the second conventional technique is used.

  The present invention was devised to solve the above-described problems, and the purpose of the present invention is to reduce the temperature without complicating the electrical configuration even when a step-up transformer with a simplified configuration is used. The cold cathode tube can be surely lit even when it is low, and when the start of lighting of the cold cathode tube is ensured, the cold cathode tube is caused by the high voltage of the lighting drive output The deterioration of the cold-cathode tube due to the length of the high period of the voltage of the lighting drive output can also be suppressed when it is possible to suppress the deterioration of the brightness and to prevent the lack of luminance after the start of the cold-cathode tube lighting. It is an object of the present invention to provide a liquid crystal display device that can suppress the change in brightness of the displayed image and make the change in brightness of the displayed image inconspicuous.

  In addition, the purpose of the present invention is to make the voltage of the DC output supplied to the inverter circuit higher than the normal voltage when starting the lighting of the cold cathode tube, and after starting the lighting of the cold cathode tube, a predetermined period of time is required. When the time has elapsed, the voltage of the DC output supplied to the inverter circuit is lowered to the normal voltage, so that the temperature can be increased without complicating the electrical configuration even when using a step-up transformer with a simplified configuration. An object of the present invention is to provide a liquid crystal display device capable of reliably lighting a cold cathode tube even when the temperature is low.

  Further, in addition to the above purpose, by changing the voltage of the DC output supplied to the inverter circuit at the start of lighting, in the direction of decreasing when the temperature of the cold cathode tube increases, and in the direction of increasing when the temperature decreases, An object of the present invention is to provide a liquid crystal display device capable of suppressing deterioration of a cold cathode tube caused by a high voltage of a lighting drive output even when the start of lighting of the cold cathode tube is ensured.

  In addition to the above purpose, the period for supplying a DC output with a voltage higher than the normal voltage to the inverter circuit is changed in such a direction that the cold cathode tube becomes shorter when the temperature becomes higher and becomes longer when the temperature becomes lower. Therefore, even when preventing the shortage of luminance after the start of lighting of the cold cathode tube, the liquid crystal display device can suppress the deterioration of the cold cathode tube caused by the longer period during which the voltage of the lighting drive output is high Is to provide.

  In order to solve the above problems, a liquid crystal display device according to the present invention generates an inverter circuit that generates a lighting drive output for lighting a cold cathode tube that is a light source of a backlight of a liquid crystal panel, and a DC output that is an operating power source. Thus, the present invention is applied to a liquid crystal display device including a power supply unit that supplies the inverter circuit. Then, the temperature sensor for detecting the temperature of the cold cathode tube and the DC output voltage supplied to the inverter circuit by the power supply unit are set to an initial voltage higher than the normal voltage to start the cold cathode tube, After starting the lighting of the tube, the voltage of the DC output is lowered stepwise so that when the initial voltage application period, which is a predetermined period, has elapsed since the start of lighting of the cold cathode tube, the power supply unit And a lighting control means that uses a DC output voltage supplied to the circuit as a normal time voltage. The lighting control means decreases in the direction in which the temperature detected by the temperature sensor increases and decreases in temperature. In the direction of increasing, the initial voltage is changed corresponding to the temperature, and in the direction of decreasing when the temperature increases, in the direction of increasing when the temperature decreases, In response to the serial temperature to vary the initial voltage application period.

  That is, the inverter circuit increases the voltage of the lighting drive output when the input DC output voltage is high. Accordingly, at the start of lighting, the voltage of the lighting drive output becomes high. For this reason, since the step-up transformer having a simplified configuration is used, even when the level of the ringing pulse at the start of lighting becomes low, the cold cathode tube can reliably start lighting even at a low temperature. A voltage is applied to obtain a possible glow discharge. Further, the control for switching the voltage of the DC output input to the inverter circuit from the initial voltage to the normal voltage is simple control. In addition, when the temperature of the cold cathode tube is low, the voltage of the lighting drive output is increased to ensure lighting. Further, when the temperature of the cold cathode tube is not low, the voltage of the lighting drive output is lowered, and the voltage applied to the cold cathode tube is suppressed from becoming excessively high. In addition, when the temperature of the cold cathode tube is low, the period during which the voltage of the lighting drive output is high becomes long, and when the voltage of the lighting drive output drops to the normal voltage, the cold cathode tube is sufficiently warmed. . When the temperature of the cold cathode tube is not low, the voltage of the lighting drive output drops to the normal voltage in a short time. Further, when the voltage of the DC output input to the inverter circuit is changed stepwise, the voltage of the lighting drive output changes stepwise, so that the brightness of the cold cathode tube changes with a slight width.

  The liquid crystal display device according to the present invention also generates an inverter circuit that generates a lighting drive output for lighting a cold cathode tube that is a light source of a backlight of a liquid crystal panel, and generates a direct current output that is an operation power supply and supplies the output to the inverter circuit. The present invention is applied to a liquid crystal display device including a power supply unit. Then, when starting the lighting of the cold cathode tube, the voltage of the DC output supplied to the inverter circuit by the power supply unit is set to an initial voltage higher than the normal voltage, and after starting the lighting of the cold cathode tube, a predetermined voltage is set. When the initial voltage application period, which is a period, has elapsed, a lighting control means is provided for reducing the voltage of the DC output supplied to the inverter circuit by the power supply unit to the normal voltage.

  That is, the inverter circuit increases the voltage of the lighting drive output when the input DC output voltage is high. Accordingly, at the start of lighting, the voltage of the lighting drive output becomes high. For this reason, since the step-up transformer having a simplified configuration is used, even when the level of the ringing pulse at the start of lighting becomes low, the cold cathode tube can reliably start lighting even at a low temperature. A voltage is applied to obtain a possible glow discharge. Further, the control for switching the voltage of the DC output input to the inverter circuit from the initial voltage to the normal voltage is simple control.

  Further, in addition to the above configuration, a temperature sensor for detecting the temperature of the cold cathode tube is provided, and the lighting control means is in a direction of decreasing when the temperature detected by the temperature sensor increases and in a direction of increasing when the temperature decreases. The initial voltage is changed corresponding to the temperature. That is, when the temperature of the cold cathode tube is low, the voltage of the lighting drive output becomes high, and lighting is ensured. Further, when the temperature of the cold cathode tube is not low, the voltage of the lighting drive output is lowered, and the voltage applied to the cold cathode tube is suppressed from becoming excessively high.

  In addition to the above configuration, the lighting control means changes the initial voltage application period corresponding to the temperature in a direction that decreases when the temperature detected by the temperature sensor increases and in a direction that increases when the temperature decreases. Let That is, when the temperature of the cold cathode tube is low, the period during which the voltage of the lighting drive output is high becomes long, and when the voltage of the lighting drive output drops to the normal voltage, the cold cathode tube is sufficiently warmed. . When the temperature of the cold cathode tube is not low, the voltage of the lighting drive output drops to the normal voltage in a short time.

  The liquid crystal display device according to the present invention includes an inverter circuit that generates a lighting drive output that lights a cold cathode tube that is a light source of a backlight of a liquid crystal panel, and a DC output that is an operation power source of the inverter circuit. A power supply unit that generates a first DC output that is an initial voltage higher than a normal voltage and a DC output that is an operating power supply for the inverter circuit, and that generates a second DC output that is a normal voltage. It is applied to the liquid crystal display device provided. Then, when starting the lighting of the cold cathode tube, the first DC output is supplied to the inverter circuit. After starting the lighting of the cold cathode tube, when the initial voltage application period which is a predetermined period has elapsed, the inverter Lighting control means for switching the DC output supplied to the circuit from the first DC output to the second DC output is provided.

  That is, the inverter circuit increases the voltage of the lighting drive output when the input DC output voltage is high. Accordingly, at the start of lighting, the voltage of the lighting drive output becomes high. For this reason, since the step-up transformer having a simplified configuration is used, even when the level of the ringing pulse at the start of lighting becomes low, the cold cathode tube can reliably start lighting even at a low temperature. A voltage is applied to obtain a possible glow discharge. Further, the control for switching the voltage of the DC output input to the inverter circuit from the first DC output to the second DC output is simple control.

  Further, in addition to the above configuration, a temperature sensor for detecting the temperature of the cold cathode tube is provided, and the lighting control means is configured to be shortened when the temperature detected by the temperature sensor is high, and to be long when the temperature is low. The initial voltage application period is changed corresponding to the temperature. That is, when the temperature of the cold cathode tube is low, the period during which the voltage of the lighting drive output is high becomes long, and when the voltage of the lighting drive output drops to the normal voltage, the cold cathode tube is sufficiently warmed. . When the temperature of the cold cathode tube is not low, the voltage of the lighting drive output drops to the normal voltage in a short time.

  According to the present invention, the voltage of the lighting drive output is high at the start of lighting. For this reason, since the step-up transformer having a simplified configuration is used, even when the level of the ringing pulse at the start of lighting becomes low, the cold cathode tube can reliably start lighting even at a low temperature. A voltage is applied to obtain a possible glow discharge. Further, the control for switching the voltage of the DC output input to the inverter circuit from the initial voltage to the normal voltage is simple control. In addition, when the temperature of the cold cathode tube is low, the voltage of the lighting drive output is increased to ensure lighting. Further, when the temperature of the cold cathode tube is not low, the voltage of the lighting drive output is lowered, and the voltage applied to the cold cathode tube is suppressed from becoming excessively high. In addition, when the temperature of the cold cathode tube is low, the period during which the voltage of the lighting drive output is high becomes long, and when the voltage of the lighting drive output drops to the normal voltage, the cold cathode tube is sufficiently warmed. . When the temperature of the cold cathode tube is not low, the voltage of the lighting drive output drops to the normal voltage in a short time. Further, when the voltage of the DC output input to the inverter circuit is changed stepwise, the voltage of the lighting drive output changes stepwise, so that the brightness of the cold cathode tube changes with a slight width. For this reason, even when a step-up transformer with a simplified configuration is used, the cold cathode tube can be reliably turned on even when the temperature is low, without complicating the electrical configuration, and the cold cathode Even when the start of lighting of the tube is ensured, the deterioration of the cold cathode tube caused by the high voltage of the lighting drive output can be suppressed, and after the start of lighting of the cold cathode tube Even when the lack of brightness is prevented, the deterioration of the cold cathode tube caused by the length of the high period of the voltage of the lighting drive output can be suppressed, and the change in the brightness of the displayed image is conspicuous It can not be.

  According to the present invention, the voltage of the lighting drive output is high at the start of lighting. For this reason, since the step-up transformer having a simplified configuration is used, even when the level of the ringing pulse at the start of lighting becomes low, the cold cathode tube can reliably start lighting even at a low temperature. A voltage is applied to obtain a possible glow discharge. Further, the control for switching the voltage of the DC output input to the inverter circuit from the initial voltage to the normal voltage is simple control. For this reason, even when a step-up transformer with a simplified configuration is used, the cold cathode tube can be reliably lit even when the temperature is low, without complicating the electrical configuration.

  Further, when the temperature of the cold-cathode tube is low, the voltage of the lighting drive output is increased to ensure lighting. Further, when the temperature of the cold cathode tube is not low, the voltage of the lighting drive output is lowered, and the voltage applied to the cold cathode tube is suppressed from becoming excessively high. For this reason, even when the start of lighting of the cold cathode tube is ensured, deterioration of the cold cathode tube caused by a high voltage of the lighting drive output can be suppressed.

  Further, when the temperature of the cold cathode tube is low, the period during which the voltage of the lighting drive output is high is lengthened, and when the voltage of the lighting drive output drops to the normal voltage, the cold cathode tube is sufficiently warmed. ing. When the temperature of the cold cathode tube is not low, the voltage of the lighting drive output drops to the normal voltage in a short time. For this reason, when preventing the shortage of luminance after the start of lighting of the cold-cathode tube, it is possible to suppress the deterioration of the cold-cathode tube caused by the longer period during which the lighting drive output voltage is high.

  According to the present invention, the voltage of the lighting drive output is high at the start of lighting. For this reason, since the step-up transformer with a simplified configuration is used, even when the level of the ringing pulse at the start of lighting becomes low, the cold cathode tube reliably starts lighting even when the temperature becomes low. A voltage is applied to obtain a glow discharge that is possible. Further, the control for switching the voltage of the DC output input to the inverter circuit from the first DC output to the second DC output is simple control. For this reason, even when a step-up transformer with a simplified configuration is used, the cold cathode tube can be reliably lit even when the temperature is low, without complicating the electrical configuration.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 is a block diagram showing an electrical configuration of the first embodiment of the liquid crystal display device according to the present invention.

  In the figure, a backlight 31 is a rectangular surface light source provided behind a liquid crystal panel 32, and includes a cold cathode tube 2, a light guide plate (not shown), and the like. The signal processing circuit 33 outputs a control signal and a video signal obtained by performing predetermined processing on the video signal input from the outside to the drive circuit 34. The drive circuit 34 performs driving in the X direction (source driving) and driving in the Y direction (gate driving) of the liquid crystal panel 32 based on the control signal and the video signal output from the signal processing circuit 33, and thereby the liquid crystal panel. 32 displays an image.

  FIG. 1 is a block diagram showing an electrical configuration of a drive portion for driving the cold cathode tube 2 to light. Elements and blocks that are the same as those in the prior art shown in FIG. 9 are denoted by the same reference numerals as those in FIG. Has been granted.

  In the figure, there are roughly divided an inverter circuit 1, a cold cathode tube 2, a switching power supply (a power supply unit described in claims) 3, a microcomputer (hereinafter referred to as a microcomputer) 4, and a temperature sensor 5. Yes. The temperature sensor 5 detects the temperature of the cold cathode tube 2 (or the temperature in the vicinity of the cold cathode tube 2), and sends the detection result to the microcomputer 4. The microcomputer 4 and the temperature sensor 5 operate using a DC output (not shown) as an operating power source.

  The inverter circuit 1 generates a lighting drive output for lighting the cold cathode tube 2. For this purpose, a switching control circuit 11, a step-up transformer T1, transistors Q1, Q2, resistors R1, R2, and a capacitor C1 are provided.

  The step-up transformer T1 is a transformer in which the primary coil L1 and the secondary coil L2 are wound coaxially, and the primary coil L1 and the secondary coil L2 are closely coupled by a magnetic circuit without a gap that leaks magnetic flux. It has become. That is, since the structure is simple, the transformer has a low component cost.

  Therefore, when the current flowing through the primary coil L1 is switched, the lighting drive output indicated by 42 in FIG. 3 appears in the secondary coil L2. If the level of the ringing pulse in the lighting drive output is indicated by V11 and the output voltage determined by the winding ratio between the primary coil L1 and the secondary coil L2 is indicated by V12, the coupling between the primary coil L1 and the secondary coil L2 Since the degree is large, the level of the ringing pulse is small, and the ratio (V11 / V12) is a small value. That is, the P-P value of the lighting drive output remains a value that is slightly larger than the output voltage V12 determined by the winding ratio between the primary coil L1 and the secondary coil L2.

  The secondary coil L2 that sends out the lighting drive output having the waveform described above is connected to the cold cathode tube 2 via the capacitor C1. A DC output 21 output from the switching power supply 3 is led to the center tap of the primary coil L1. Further, the end side terminal of the primary coil L1 is connected to the collectors of the corresponding transistors Q1 and Q2. The emitters of the transistors Q1 and Q2 are grounded. The outputs from the switching control circuit 11 are led to the bases of the transistors Q1 and Q2 via the corresponding resistors R1 and R2, respectively.

  The switching control circuit 11 turns off the transistor Q2 when the transistor Q1 is turned on, and turns on the transistor Q2 when the transistor Q1 is turned off. For this reason, the current flowing through the primary coil L1 is switched, and a lighting drive output for lighting the cold cathode tube 2 is generated in the secondary coil L2.

  The switching power supply 3 generates a DC output 21 serving as an operating power supply for the inverter circuit 1 using a commercial power supply (not shown) as a primary power supply. Note that the voltage of the DC output 21 is stabilized at a voltage instructed by the microcomputer 4. That is, when the instruction from the microcomputer 4 indicates 15V, the voltage control circuit 13 detects the voltage error of the DC output 21 with respect to 15V and feeds back to the primary side, thereby stabilizing the voltage of the DC output 21 to 15V. Let Further, when the instruction from the microcomputer 4 indicates 12V, the voltage error of the DC output 21 with respect to 12V is detected and fed back to the primary side, thereby stabilizing the voltage of the DC output 21 to 12V.

  The switching power supply 3 is configured to be able to stabilize the voltage of the DC output 21 to four types of voltages of 15V, 14V, 13V, and 12V in accordance with instructions from the microcomputer 4. Further, when the inverter circuit 1 is applied to, for example, a 15-inch liquid crystal panel 32, the effective value (rms) of the lighting drive output is obtained when the voltage of the DC output 21 is 12V (normal voltage). The standard value is 1180V.

  The microcomputer 4 controls main operations as a liquid crystal display device. Therefore, the operation of the switching power supply 3 is stopped when a power-off instruction is input to a remote controller (not shown), and the operation of the switching power supply 3 is started when a power-on instruction is input. Further, by controlling the operation of the signal processing circuit 33, the brightness and contrast of the image displayed on the liquid crystal panel 32 are set to the brightness and contrast designated by the user. Moreover, the lighting control means 15 is comprised by a part of the function.

  When a power-on instruction is input to a remote controller (not shown) and lighting of the cold cathode tube 2 is started, the lighting control unit 15 supplies the voltage of the DC output 21 supplied to the inverter circuit 1 by the switching power source 3 at a normal time. Set to the initial voltage that is higher than the voltage. Then, when a predetermined period has elapsed after the start of lighting of the cold cathode fluorescent lamp 2, the voltage of the DC output 21 is lowered stepwise toward the normal voltage by controlling the switching power supply 3 ( The change in the voltage of the DC output 21 will be described in detail later).

  Further, the lighting control means 15 changes the initial voltage in a direction that decreases when the temperature detected by the temperature sensor 5 increases, and in a direction that increases when the temperature decreases, corresponding to the detected temperature. . Further, an initial voltage application period (an initial voltage is applied to the inverter circuit 1) corresponding to the detected temperature in a direction in which the temperature detected by the temperature sensor 5 becomes shorter when the temperature becomes higher and in a direction that becomes longer when the temperature becomes lower. After the voltage is supplied, the period during which the voltage supplied to the inverter circuit 1 is reduced to the normal voltage is changed.

  The operation of the embodiment having the above configuration will be described.

  When a power-on instruction is input to a remote controller (not shown) or the like, the microcomputer 4 checks the temperature detected by the temperature sensor 5. And it is investigated which range is the detected temperature among the three types of ranges of 0 degrees to 10 degrees, 10 degrees to 20 degrees, and 20 degrees or more. And when it is the range of 0 degree-10 degree | times, the voltage of the DC output 21 is set so that it may be set to 15V, and the operation | movement of the switching power supply 3 is started. For this reason, the inverter circuit 1 is supplied with a DC output 21 of 15 V as an operating power source.

  Therefore, a voltage obtained by multiplying 1180 V by (15/12) is applied to the cold cathode tube 2. For this reason, even when the temperature of the tube is 0 to 10 degrees, the cold cathode tube 2 generates a stable glow discharge and starts to light up reliably. In addition, it emits light with sufficient brightness despite the low temperature of the tube. Then, the lighting control means 15 calculates a period determined corresponding to the temperature detected by the temperature sensor 5 (this period is calculated as a value that becomes shorter as the temperature becomes higher). The calculated value is, for example, 1 minute 30 seconds when the angle is 0 degree to 10 degrees, 30 seconds when the angle is 10 degrees to 20 degrees, and 10 seconds when the angle is 20 degrees or more.

  Then, the lighting control means 15 lowers the voltage of the DC output 21 from 15V to 14V when 1 minute 30 seconds elapses. Further, when 1 minute and 30 seconds have elapsed, the voltage of the DC output 21 is lowered from 14V to 13V. Further, when 1 minute and 30 seconds have elapsed, the voltage of the DC output 21 is lowered to 12 V, and thereafter, the voltage of the DC output 21 is maintained at 12 V (see voltage change indicated by 51 in FIG. 4). Accordingly, when the voltage of the DC output 21 drops to 12V (normal voltage), the temperature of the cold cathode tube 2 is sufficiently warmed, so that the cold cathode tube 2 has a standard value of 1180V lighting drive output, Emits light with sufficient brightness.

  Note that the initial voltage application period described in the claims is a period in which the voltage of the DC output 21 drops to 12 V, which is the normal voltage, after the DC output 21 of 15 V, which is the initial voltage, is sent out, When the above control is performed, the initial voltage application period is 4 minutes 30 seconds.

  The above-described operation was in the case where the temperature detected by the temperature sensor 5 was in the range of 0 degrees to 10 degrees, but when the temperature detected by the temperature sensor 5 was in the range of 10 degrees to 20 degrees, The voltage is set to 14V. Thereafter, every 30 seconds, the voltage of the DC output 21 drops from 14V to 13V and from 13V to 12V (refer to the voltage change indicated by 52 in FIG. 4). Therefore, at this time, the initial voltage application period is 1 minute.

  When the temperature detected by the temperature sensor 5 is in the range of 20 degrees or more, the initial voltage is set to 13V. When 10 seconds have elapsed, the voltage of the DC output 21 drops from 13 V to 12 V (see the voltage change indicated by 53 in FIG. 4). Accordingly, at this time, the initial voltage application period is 10 seconds.

  The second embodiment according to the present invention will be described below. FIG. 6 is a block diagram showing an electrical configuration of a drive portion that drives and drives the cold cathode fluorescent lamp 2 in the second embodiment. Elements and blocks that are the same as those in the embodiment shown in FIG. 1 are given the same reference numerals as those in FIG. Also, the overall configuration is the same as the configuration shown in FIG.

  The switching power supply (power supply unit) 8 is a direct current output serving as an operation power supply for the inverter circuit 1, and a first direct current output 61 whose voltage is an initial voltage higher than the normal voltage and the voltage is a normal voltage. A second DC output 62 is generated. The voltage of the first DC output 61 is 15V, and the voltage of the second DC output 62 is 12V.

  The lighting control means 9 supplies the first DC output 61 to the inverter circuit 1 to start lighting the cold cathode tube 2 when starting the lighting of the cold cathode tube 2. Then, when the initial voltage application period, which is a predetermined period, has elapsed after the cold cathode tube 2 is turned on, the DC output supplied to the inverter circuit 1 is supplied from the first DC output 61 to the second DC output. Switch to 62. In addition, the initial voltage application period is changed in correspondence with the temperature in a direction of shortening when the temperature detected by the temperature sensor 5 is high and in a direction of increasing when the temperature is low.

  Therefore, the lighting control unit 9 includes a diode D1, transistors Q3 and Q4, resistors R3 and R4, and a microcomputer 7. Then, the second DC output 62 is led to the anode of the diode D1, and the cathode is led to the power input of the inverter circuit 1. Further, the first DC output 61 is led to the emitter of the transistor Q3, and the collector is connected to the cathode of the diode D1. The base of the transistor Q3 is connected to the collector of the transistor Q4 via the resistor R3, and a control signal from the microcomputer 7 is guided to the base of the transistor Q4 via the resistor R4. The emitter of the transistor Q4 is grounded.

  For this reason, when the microcomputer 7 sets the control signal to the H level, both the transistor Q4 and the transistor Q3 are turned on, and the first DC output 61 of 15 V is led to the inverter circuit 1. When the control signal is set to the L level, both the transistor Q4 and the transistor Q3 are turned off, and the 12V second DC output 62 is guided to the inverter circuit 1.

  The operation of the embodiment having the above configuration will be described.

  When a power-on instruction is input to a remote controller (not shown) or the like, the microcomputer 7 starts the operation of the switching power supply 8. Further, the first DC output 61 is supplied to the inverter circuit 1 by setting the control signal to the H level. For this reason, a voltage obtained by multiplying 1180 V by (15/12) is applied to the cold cathode tube 2. As a result, the cold-cathode tube 2 generates a stable glow discharge even when the temperature of the tube reaches a low temperature around 0 ° C., and starts to light up reliably. In addition, it emits light with sufficient brightness despite the low temperature of the tube.

  Thereafter, the microcomputer 7 calculates a period determined in accordance with the temperature detected by the temperature sensor 5 (this period is calculated as a value that decreases as the temperature increases). The calculated value is, for example, 5 minutes when the angle is 0 degrees to 10 degrees, 1 minute when the angle is 10 degrees to 20 degrees, and 10 seconds when the angle is 20 degrees or more.

  For this reason, when the temperature detected by the temperature sensor 5 is in the range of 0 to 10 degrees, the microcomputer 7 sets the control signal to the L level when 5 minutes have elapsed, thereby supplying the direct current to the inverter circuit 1. The output voltage is lowered from 15V to 12V, and this state is maintained thereafter. Accordingly, when the voltage of the DC output 21 drops to 12V, the temperature of the cold cathode tube 2 is sufficiently warmed, so that the cold cathode tube 2 has sufficient brightness by the lighting drive output of 1180V which is a standard value. Emits light.

  When the temperature detected by the temperature sensor 5 is in the range of 10 degrees to 20 degrees, the microcomputer 7 supplies the inverter circuit 1 when one minute has elapsed after starting the lighting of the cold cathode tube 2. The voltage of the DC output is lowered from 15V to 12V, and this state is maintained thereafter. Accordingly, when the voltage of the DC output 21 drops to 12V, the temperature of the cold cathode tube 2 is sufficiently warmed, so that the cold cathode tube 2 has sufficient brightness by the lighting drive output of 1180V which is a standard value. Emits light.

  When the temperature detected by the temperature sensor 5 is in the range of 20 ° C. or more, the microcomputer 7 starts the lighting of the cold cathode tube 2 and when 10 seconds have elapsed, the DC output supplied to the inverter circuit 1 The voltage is reduced from 15V to 12V, and this state is maintained thereafter. Therefore, when the voltage of the DC output 21 drops to 12V, the cold cathode fluorescent lamp 2 emits light with sufficient brightness by the lighting drive output of 1180V which is a standard value.

  In addition, this invention is not limited to the said embodiment, About the voltage of the DC output which switching power supply 3 and 8 outputs, it can be set as other voltages. Further, the voltage of the lighting drive output can be set to other voltages.

  Moreover, although the case where it was set as the structure which can change the voltage of the direct-current output 21 in 4 steps | paragraphs, it can be made into arbitrary steps numbers, such as 3 steps | paragraphs or 5 steps | paragraphs.

It is a block diagram which shows the electrical constitution of the block which lights the cold cathode tube of 1st Embodiment of the liquid crystal display device which concerns on this invention. It is a block diagram which shows the electric constitution of embodiment of a liquid crystal display device. It is explanatory drawing which shows the waveform of a lighting drive output. It is explanatory drawing which shows the voltage change of the DC output supplied to an inverter circuit. It is explanatory drawing which shows the specification of the voltage of the lighting drive output which lights a cold cathode tube. It is a block diagram which shows the electric constitution of the block which lights the cold cathode tube of 2nd Embodiment. It is a circuit diagram which shows the electrical structure of a prior art. It is explanatory drawing which shows the waveform of the lighting drive output in a prior art. It is a circuit diagram which shows the electrical structure of a prior art.

Explanation of symbols

1 Inverter circuit 2 Cold cathode tube 3, 8 Switching power supply (power supply)
5 Temperature sensors 9, 15 Lighting control means 21 DC output 31 Backlight 32 Liquid crystal panel 61 First DC output 62 Second DC output T1 Step-up transformer

Claims (6)

An inverter circuit for generating a lighting drive output for lighting a cold cathode tube serving as a light source of a backlight of a liquid crystal panel;
In a liquid crystal display device including a power supply unit that generates a DC output serving as an operating power supply and supplies it to an inverter circuit,
A temperature sensor for detecting the temperature of the cold cathode tube;
Set the DC output voltage supplied to the inverter circuit by the power supply to the initial voltage, which is higher than the normal voltage, start the cold cathode tube lighting, and gradually start the cold cathode tube lighting. When the initial voltage application period, which is a predetermined period, has elapsed since the start of lighting of the cold cathode fluorescent lamp by reducing the DC output voltage, the DC output voltage supplied to the inverter circuit by the power supply unit during normal operation Lighting control means to be a voltage,
The lighting control means changes the initial voltage corresponding to the temperature in a direction that decreases when the temperature detected by the temperature sensor increases, and increases when the temperature decreases, and increases the temperature. A liquid crystal display device, wherein the initial voltage application period is changed in accordance with the temperature in a direction that becomes shorter when the temperature becomes lower and in a direction that becomes longer when the temperature becomes lower. An inverter circuit for generating a lighting drive output for lighting a cold cathode tube serving as a light source of a backlight of a liquid crystal panel;
In a liquid crystal display device including a power supply unit that generates a DC output serving as an operating power supply and supplies it to an inverter circuit,
When starting the cold-cathode tube lighting, the DC output voltage supplied to the inverter circuit by the power supply is set to the initial voltage that is higher than the normal voltage, and after starting the cold-cathode tube lighting, the predetermined voltage is set. A liquid crystal display device comprising lighting control means for reducing the voltage of the DC output supplied to the inverter circuit by the power supply unit to the normal voltage when the initial voltage application period, which is the period of, elapses. It has a temperature sensor that detects the temperature of the cold cathode tube,
The lighting control means changes the initial voltage in accordance with the temperature in a direction that decreases when the temperature detected by the temperature sensor increases and in a direction that increases when the temperature decreases. Item 3. A liquid crystal display device according to Item 2.   The lighting control means changes the initial voltage application period corresponding to the temperature in a direction that decreases when the temperature detected by the temperature sensor increases and in a direction that increases when the temperature decreases. The liquid crystal display device according to claim 2. An inverter circuit for generating a lighting drive output for lighting a cold cathode tube serving as a light source of a backlight of a liquid crystal panel;
It is a direct current output that serves as an operating power supply for the inverter circuit, and is a first direct current output that is an initial voltage whose voltage is higher than the normal voltage, and a direct current output that serves as an operating power supply for the inverter circuit. In a liquid crystal display device including a power supply unit that generates a second DC output that is a temporal voltage,
When starting the lighting of the cold cathode tube, the first DC output is supplied to the inverter circuit. After starting the lighting of the cold cathode tube, when the initial voltage application period, which is a predetermined period, has passed, A liquid crystal display device comprising lighting control means for switching a DC output to be supplied from a first DC output to a second DC output. It has a temperature sensor that detects the temperature of the cold cathode tube,
The lighting control means changes the initial voltage application period corresponding to the temperature in a direction that becomes shorter when the temperature detected by the temperature sensor becomes higher and becomes longer when the temperature becomes lower. The liquid crystal display device according to claim 5.

Images