JP4966720B2 - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display with the dispersion of the lifetime of a light source suppressed. <P>SOLUTION: Combination of each lamp L and a transformer circuit applying AC voltage to the lamp L is switched by a switching part 22, whenever a predetermined switching timing comes, and thus AC voltage is applied sequentially to one lamp by a plurality of transformer circuits. Consequently, even in either cases where the transformer circuits have variance in circuit performance caused by manufacture variance or where AC voltage applied to each lamp L has dispersion due to factors other than the dispersion in the circuit performance of the transformer circuit, the influence of these dispersions can be dispersed to each lamp and the dispersion in the lifetime of each lamp L can be suppressed. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a liquid crystal display device having a light source and a liquid crystal display panel on which light emitted from the light source is incident.

  In a liquid crystal display device having a large liquid crystal display panel having a diagonal size of, for example, 30 inches or more, a plurality of fluorescent tubes are used as a light source of a backlight in order to keep the entire display screen at a desired luminance. Yes. An inverter circuit is electrically connected to each fluorescent tube. The inverter circuit supplies a voltage required for lighting the fluorescent tube to the fluorescent tube.

  Variations may occur in the signal output from the inverter circuit due to the influence of the accuracy of the parts constituting the inverter circuit and the difference in the environment of the mounting position of the inverter circuit. Due to the variation in the signal, the life of the fluorescent tube connected to the inverter circuit varies.

  If there is a variation in the life of fluorescent tubes, for example, fluorescent tubes that have reached the end of their life and fluorescent tubes that have not reached the end of life will coexist, causing the display screen brightness to deteriorate and the display quality of the liquid crystal display device to deteriorate. Arise. In order to prevent the occurrence of such problems, increase the number of operations to replace a fluorescent tube that has reached the end of its life, or replace a fluorescent tube that has reached its end of life with a new fluorescent tube. It is conceivable to replace the tube with a new fluorescent tube at the same time. However, there is a problem that increasing the number of fluorescent tube replacement work increases the labor of the operator who performs the replacement work, and if a fluorescent tube that has not reached the end of its life is replaced with a new fluorescent tube before reaching the end of its life, There is a problem that a fluorescent tube that has not reached the end of its life cannot be used effectively.

  The liquid crystal display device disclosed in Patent Document 1 includes a plurality of cold cathode fluorescent tubes functioning as a light source of a backlight and an inverter circuit having one inverter transformer, and a plurality of inverters are provided by one inverter transformer. The cold cathode fluorescent tube is driven.

JP 2001-350133 A

  In the liquid crystal display device disclosed in Patent Document 1, by driving a plurality of fluorescent tubes with a single inverter transformer, the driving power supply of all the cold cathode fluorescent tubes is made constant, and the life of the fluorescent tubes varies. The brightness of the display screen is stabilized so as not to occur. When the liquid crystal display device includes a relatively small liquid crystal display panel, it is possible to drive a plurality of fluorescent tubes with one inverter transformer as in Patent Document 1, but the liquid crystal display panel When the number of fluorescent tubes increases as the size of the fluorescent tube increases, the burden is increased with only one inverter transformer, and it is difficult to drive all the fluorescent tubes stably. Therefore, in order to drive all the fluorescent tubes, it is necessary to provide a plurality of inverter transformers. However, each inverter circuit having an inverter transformer has a variation in circuit performance due to manufacturing variations. Due to the variation in the circuit performance of the inverter circuit, the lifespan between fluorescent tubes driven by different inverter transformers is shortened. There is a problem that variations occur.

  The objective of this invention is providing the liquid crystal display device which can suppress the dispersion | variation in the lifetime of a light source.

The present invention includes a plurality of light sources that emit light by applying a driving voltage;
A liquid crystal display panel on which light emitted from each light source is incident;
A plurality of drive circuits for applying a drive voltage to each light source;
A liquid crystal display device comprising switching means for switching a combination of each light source and a driving circuit that applies a driving voltage to the light source each time a predetermined switching timing is reached.

Further, the present invention is characterized in that each drive circuit is configured to be connectable to all light sources.
According to the present invention, the switching means changes from a state where power supply from the power supply means for supplying power to the drive circuit is stopped to a state where power is supplied from the power supply means to the drive circuit. Each time it changes, it is judged that the switching timing has been reached.

  Further, the present invention is characterized in that the switching means determines that the switching timing has been reached each time a predetermined time is reached.

  Further, the present invention is characterized in that the switching means determines that the switching timing has been reached each time a predetermined time elapses.

  Further, the present invention is characterized in that the switching means determines that the switching timing has been reached based on an update of a display image displayed on the liquid crystal display panel.

  In the invention, it is preferable that the drive circuit starts applying the drive voltage to the light source after the combination of the light source and the drive circuit that applies the drive voltage to the light source is switched by the switching unit. And

  According to the present invention, the drive circuit stops applying the drive voltage to the light source before the combination of the light source and the drive circuit that applies the drive voltage to the light source is switched by the switching unit. The drive voltage is applied to the light source after the combination of the light source and the drive circuit that applies the drive voltage to the light source is switched.

  According to the present invention, the drive circuit applies a drive voltage to each light source. Thereby, a plurality of light sources emit light. Light emitted from a plurality of light sources that emit light when a drive voltage is applied enters the liquid crystal display panel. Thus, the light emitted from a plurality of light sources is incident on the liquid crystal display panel, so that the viewer who views the display image displayed on the liquid crystal display panel can view the display image. The combination of each light source and a drive circuit that applies a drive voltage to the light source is switched by the switching means every time a predetermined switching timing is reached.

  Therefore, one drive circuit that applied a drive voltage to one light source among the plurality of light sources before the switching operation by the switching unit is different from the one light source after the switching operation by the switching unit. This is a drive circuit that applies a drive voltage to the light source. In addition, after the switching operation by the switching unit, a driving voltage is applied to one light source by another driving circuit different from the one driving circuit.

  As described above, since a driving voltage is sequentially applied to one light source by a plurality of driving circuits, when there is a variation in circuit performance due to manufacturing variations in the driving circuit, and other than variations in circuit performance of the driving circuit In any case where the driving voltage applied to the light source varies due to a factor, the influence of these variations can be distributed to each light source. Therefore, it is possible to suppress variations in the lifetime of the light source. Thereby, a decrease in luminance in the liquid crystal display panel can be suppressed, and a decrease in display quality can be prevented.

  Further, according to the present invention, each drive circuit is configured to be connectable to all light sources, and therefore can be combined with all light sources. As a result, the switching means can switch each drive circuit to a combination selected from the combinations with all light sources, so that it depends on factors other than variations in circuit performance of the drive circuit and variations in circuit performance of the drive circuit. The influence of variations in driving voltage applied to the light sources can be distributed to all the light sources. Therefore, the variation in the lifetime of the light source can be further suppressed.

  In addition, according to the present invention, the switching unit switches the power supply unit from the state where the power supply unit to the drive circuit is stopped to the state where the power supply unit supplies power to the drive circuit. When it is determined that the timing has been reached, the combination of each light source and a drive circuit for applying a drive voltage to the light source is switched.

  In this way, when the combination of the light source and the drive circuit is switched according to the change in the power supply state, the change from the power supply stop state to the power supply state occurs at regular intervals. The combination of the light source and the drive circuit can be switched every fixed period. As a result, for example, the influence of variations in the circuit performance of the drive circuit on each light source can be averaged, so that variations in the life of the light source can be significantly suppressed.

  According to the present invention, each time a predetermined time is reached, the switching means determines that the switching timing has been reached, and the combination of each light source and a drive circuit that applies a drive voltage to the light source is switched. . In this way, by switching the combination of the light source and the drive circuit according to the predetermined time, the combination of the light source and the drive circuit can be switched at regular intervals. The light emission times of the light sources in the combination can be averaged.

  As a result, it is possible to prevent a light source having an extremely long light emission time from being generated for each combination, and to average the influence of variations in the circuit performance of the drive circuit on each light source, for example. As a result, it is possible to remarkably suppress variations in the life of the light source.

  According to the present invention, each time a predetermined time elapses, the switching means determines that the switching timing has been reached, and the combination of each light source and the drive circuit that applies a drive voltage to the light source is switched. It is done. In this way, by switching the combination of the light source and the drive circuit according to the predetermined time, when the light source emits light continuously, the light emission time of the light source in each combination can be averaged.

  As a result, it is possible to prevent a light source having an extremely long light emission time from being generated for each combination, and to average the influence of variations in the circuit performance of the drive circuit on each light source, for example. Thereby, it is possible to remarkably suppress the occurrence of variations in the life of the light source.

  Further, according to the present invention, based on the update of the display image displayed on the liquid crystal display panel, it is determined by the switching means that the switching timing has been reached, and each light source and driving for applying a driving voltage to the light source The combination with the circuit is switched. For example, when the display image is updated, or when the predetermined update count display image is updated, the combination of the light source and the drive circuit is switched.

  Accordingly, the possibility that the viewer recognizes the switching of the combination can be reduced as compared with the case where the combination is switched when one display image is displayed. This can prevent the switching operation of the combination from being mistaken as a failure of the liquid crystal display device.

  Further, according to the present invention, after the combination of the light source and the drive circuit that applies the drive voltage to the light source is switched by the switching unit, the drive circuit starts applying the drive voltage to the light source. That is, the combination of the light source and the drive circuit is switched in a state where no drive voltage is applied from the drive circuit to the light source.

  When the drive voltage is applied from the drive circuit to the light source, if the combination of the light source and the drive circuit is switched, a current suddenly flows between the drive circuit and the light source, and the drive circuit and the light source are connected. A large load is applied to the portion, for example, the drive circuit is damaged. In the present invention, since the combination of the light source and the drive circuit is switched in a state where no drive voltage is applied from the drive circuit to the light source, when the combination of the light source and the drive circuit is switched, for example, the drive circuit is damaged. Can be prevented.

  According to the invention, before the combination of the light source and the drive circuit for applying the drive voltage to the light source is switched by the switching means, the drive circuit stops applying the drive voltage to the light source. And the drive circuit for applying the drive voltage to the light source are switched, and then the drive voltage is applied to the light source by the drive circuit. That is, the combination of the light source and the drive circuit is switched in a state where no drive voltage is applied from the drive circuit to the light source.

  When the drive voltage is applied from the drive circuit to the light source, if the combination of the light source and the drive circuit is switched, a current suddenly flows between the drive circuit and the light source, and the drive circuit and the light source are connected. A large load is applied to the portion, for example, the drive circuit is damaged. In the present invention, since the combination of the light source and the drive circuit is switched in a state where no drive voltage is applied from the drive circuit to the light source, when the combination of the light source and the drive circuit is switched, for example, the drive circuit is damaged. Can be prevented.

  FIG. 1 is a block diagram showing an electrical configuration of a liquid crystal display device 10 according to an embodiment of the present invention. The liquid crystal display device 10 of the present embodiment is a transmissive liquid crystal display device, and has a large display screen whose diagonal dimension is 30 inches or more. The liquid crystal display device 10 is used for displaying information for an unspecified number of viewers. For example, the liquid crystal display device 10 is used for indoor and outdoor advertisement display, transportation schedule information display, movie theater screening, and vacant seat information display.

  The liquid crystal display device 10 includes a control unit 11, an ON / OFF switch unit 12, a power supply unit 13, an ON / OFF schedule storage unit 14, a communication unit 15, a display information storage unit 16, an inverter circuit 20, a switching drive unit 21, and a switching unit. A unit 22, a backlight unit 24, a display driving unit 26 and a liquid crystal display unit 27 are provided. The control unit 11 includes a timer unit 17 and a switching state storage unit 23.

The control unit 11 includes an ON / OFF switch unit 12, a power supply unit 13, an ON / OFF schedule storage unit 14, a communication unit 15, a display information storage unit 16, an inverter circuit 20, and a switching drive unit 21 that configure the liquid crystal display device 10. And hardware resources including the display drive unit 26 are electrically connected to each other, and are configured to be able to transmit signals and information to each other. The control unit 11 is a processing circuit that comprehensively controls the aforementioned hardware resources based on a control program stored therein. In the present embodiment, the control unit 11 is a central processing unit (Central Processing Unit).
Unit; abbreviation: CPU) or the like.

  The ON / OFF switch unit 12 is realized by an operation start switch that is an ON switch and an operation end switch that is an OFF switch. The ON / OFF switch unit 12 gives an operation start command to the control unit 11 by operating the operation start switch. When the operation start command is given, the control unit 11 gives the power supply command to the power supply unit 13 that is a power supply unit. The power supply unit 13 supplies power to the control unit 11, the inverter circuit 20, the switching drive unit 21, and the display drive unit 26 when a power supply command is given. When the operation start command is given, the control unit 11 starts an image display operation using the power supplied from the power supply unit 13.

  The ON / OFF switch unit 12 gives an operation end command to the control unit 11 by operating the operation end switch. The control unit 11 gives a power supply stop command to the power supply unit 13 when the operation end command is given. The power supply unit 13 stops supplying power to the control unit 11, the inverter circuit 20, the switching drive unit 21, and the display drive unit 26 when a power supply stop command is given. The control unit 11 ends the image display operation when the operation end command is given.

The ON / OFF schedule storage unit 14 is a ROM (Read Only Memory) which is a nonvolatile storage circuit.
It is realized by. The ON / OFF schedule storage unit 14 stores information indicating a predetermined operation start time and information indicating a predetermined operation end time. The communication unit 15 receives information transmitted from an external device, for example, information representing a display image to be displayed on the liquid crystal display unit 27 (hereinafter, sometimes referred to as “display information”). The external device is realized by, for example, an image storage device such as a hard disk in which the display image to be displayed is stored, a communication device that receives the display image to be displayed, a photographing device that captures the display image to be displayed, and the like. . The external device provides display information to the liquid crystal display device 10 via the communication unit 15.

  The display information storage unit 16 is realized by a ROM (Read Only Memory) which is a nonvolatile storage circuit. The display information storage unit 16 stores display information currently displayed on the liquid crystal display unit 27. The control unit 11 compares the display information currently stored and stored in the display information storage unit 16 with the display information acquired from the external device via the communication unit 15. When the compared display information is different from each other, the control unit 11 determines that the display image to be displayed has been updated, and displays the display information acquired from the external device via the communication unit 15 as a display information storage unit. 16 to memorize.

  The timer unit 17 includes, for example, a real time clock (abbreviation: RTC) and measures the current time. The timer unit 17 also measures the relative elapsed time and counts the elapsed time (hereinafter referred to as “end elapsed time”) that has elapsed since the end of the image display operation. The control unit 11 determines whether or not the operation start time has elapsed based on the end elapsed time counted by the time measuring unit 17 and the operation start time stored in the ON / OFF schedule storage unit 14. The timer 17 counts the elapsed time (hereinafter referred to as “start elapsed time”) that has elapsed since the image display operation started. The control unit 11 determines whether or not the operation end time has elapsed based on the start elapsed time counted by the time measuring unit 17 and the operation end time stored in the ON / OFF schedule storage unit 14.

  The inverter circuit 20 includes a plurality of transformer circuits. When a fluorescent tube driving signal for driving a fluorescent tube included in the backlight unit 24 described later is supplied from the control unit 11, the transformer circuit as a driving circuit generates an AC voltage that is a driving voltage according to the fluorescent tube driving signal. . More specifically, the transformer circuit generates a high-frequency and high-voltage AC voltage according to the fluorescent tube driving signal, and applies the generated AC voltage to the fluorescent tube. The fluorescent tube emits light when an AC voltage is applied by a transformer circuit.

  The switching drive unit 21 issues a switching command to switch the combination of the fluorescent tube and the transformer circuit that applies an AC voltage to the fluorescent tube based on a signal representing a predetermined switching timing given from the control unit 11. To give. The switching unit 22 that is a switching unit switches the combination of a fluorescent tube and a transformer circuit that applies an AC voltage to the fluorescent tube in accordance with a switching command given from the switching drive unit 21.

  The switching state storage unit 23 is realized by a flash ROM that is a nonvolatile storage circuit. The switching state storage unit 23 stores a connection state between the fluorescent tube and the transformer circuit when the switching unit 22 switches the combination of the fluorescent tube of the backlight unit 24 and the transformer circuit included in the inverter circuit 20. When the combination of electrical connection between the two electrode terminals of the fluorescent tube and the output terminal and ground terminal of the transformer circuit is switched, the electrical connection state between the two electrode terminals and the output terminal and ground terminal Remember.

  The backlight unit 24 includes a lamp group 25 including a plurality of fluorescent tubes and a diffusing member. Hereinafter, the fluorescent tube may be referred to as a “lamp”. The lamp corresponds to a light source for use in liquid crystal display, a so-called backlight. Each lamp of the present embodiment is formed in a long bar shape and extends in parallel with each other. Each lamp is disposed on the opposite side of the liquid crystal display unit 27 with respect to the display surface, and is arranged in a predetermined parallel direction. In the present embodiment, with the liquid crystal display device 10 installed, the lamps extend in the horizontal direction and are aligned in the vertical direction. In the present embodiment, the lamp is realized by a cold cathode fluorescent lamp (abbreviation: CCFL).

  The light emitted from each lamp is incident on the diffusion member, and the incident light is diffused and emitted. The diffusing member is a translucent plate-like or sheet-like member that has translucency and light diffusing properties and scatters or diffuses light. When the light emitted from each lamp is incident on the diffusing member, the light emitted from the diffusing member has substantially uniform brightness over the entire emission surface of the diffusing member. The diffusion member is disposed between the lamp and a liquid crystal display unit 27 described later.

The liquid crystal display unit 27 is realized by a liquid crystal display panel in which a liquid crystal material is sealed between two glass substrates on which a thin film electrode circuit is formed. Hereinafter, the liquid crystal display panel is denoted by the same reference numeral “27” as that of the liquid crystal display unit. A thin film electrode circuit is, for example, a thin film transistor (Thin Film
Transistor (abbreviation: TFT). In order to display the display image on the liquid crystal display unit 27, the display driving unit 26 gives a liquid crystal drive signal corresponding to the display image to the thin film electrode circuit. The display drive unit 26 acquires display information representing a display image from the display information storage unit 16, and each thin film electrode formed on the liquid crystal display unit 27 so that the display image represented by the acquired display information can be displayed. Is selectively supplied with current. As a result, the light transmittance is adjusted by changing the alignment state of the liquid crystal molecules for each pixel region of the liquid crystal display unit 27. As a result, the liquid crystal display unit 27 can change the state of light passing therethrough, and can emit light corresponding to the image to be displayed from the display surface. The image displayed on the liquid crystal display unit 27 may be a moving image or a still image. The still image may be an image that is sequentially switched at a predetermined switching time.

  Next, switching operation of the combination of electrical connections between the transformer circuit of the inverter circuit 20 and each lamp of the lamp group 25 according to the embodiment of the present invention will be described. FIG. 2 is a block diagram showing an electrical configuration of the inverter circuit 20, the switching unit 22, and the lamp group 25 according to the first embodiment of the present invention. FIG. 3 is a timing chart showing the switching of the combination of electrical connections between the inverter circuit 20 and each lamp in the lamp group 25.

  The inverter circuit 20 includes a plurality of n (where n is a natural number of 2 or more) transformer circuits in the present embodiment. Each transformer circuit has an output section An (n is a natural number) having an output terminal an (n is a natural number) for outputting an AC voltage signal as a drive voltage signal and a ground terminal bn (n is a natural number) to which a ground potential is applied. Each is equipped. Hereinafter, when each output terminal is generically referred to and when an unspecified output terminal is indicated, it may be simply referred to as “output terminal a”. Further, when each ground terminal is generically referred to and when an unspecified ground terminal is indicated, it may be simply referred to as “ground terminal b”. In addition, when each output unit is collectively referred to and when an unspecified output unit is indicated, it may be simply referred to as “output unit A”. Each ground terminal b of each output unit A in the inverter circuit 20 is connected to the ground.

  The switching unit 22 includes m (m is a natural number) change-over switches S1, ..., Sm. The m-th changeover switch Sm is realized by a two-circuit two-contact switch having two switch parts, specifically, an (n-1) th switch part Bn-1 and an nth switch part Bn (n is a natural number of 2 or more). . Hereinafter, when each changeover switch is generically referred to and when an unspecified changeover switch is indicated, it may be simply referred to as “changeover switch S”. In addition, when the switch parts are collectively referred to and when an unspecified switch part is indicated, it may be simply referred to as “switch part B”. Each switch portion B includes a common contact c, a first individual contact d, and a second individual contact e.

  In each switch unit B, the switching mode is set so that the common contact c is electrically connected to one of the first and second individual contacts d and e in accordance with a switching command given from the switching drive unit 21. It is configured to be switched.

  The lamp group 25 includes a plurality of lamps L1, L2,..., Ln-1, Ln (n is a natural number of 2 or more) in the present embodiment. Hereinafter, when each lamp is generically referred to and when an unspecified lamp is indicated, it may be simply referred to as “lamp L”. Each lamp L has electrode terminals 25a and 25b at both ends in the longitudinal direction. The electrode terminals 25a and 25b correspond to electrodes. Of the electrode terminals of each lamp L, the other electrode terminal 25b is connected to the ground.

  In the present embodiment, the (n-1) -th output circuit an-1 (n is a natural number of 2 or more) of the n-1 transformer circuit (n is a natural number of 2 or more) in the inverter circuit 20 is connected to the m-th changeover switch Sm. It is electrically connected to a common contact c of the (n-1) th switch portion Bn-1 (n is a natural number of 2 or more). The first individual contact d of the (n-1) th switch unit Bn-1 is the one-side electrode terminal 25a of the n-1th lamp Ln-1 (n is a natural number of 2 or more) and the second individual contact of the nth switch unit Bn. It is electrically connected to the contact e. The second individual contact e of the n-1th switch unit Bn-1 is electrically connected to the one-side electrode terminal 25a of the nth lamp Ln and the first individual contact d of the nth switch unit Bn.

  The n-th output terminal an of the n-th transformer circuit in the inverter circuit 20 is electrically connected to the common contact c of the n-th switch part Bn of the m-th changeover switch Sm. The first individual contact d of the nth switch unit Bn is electrically connected to the one-side electrode terminal 25a of the nth lamp Ln and the second individual contact e of the n-1 switch unit Bn-1. The second individual contact e of the n-th switch part Bn is electrically connected to the one-side electrode terminal 25a of the n-1 lamp Ln-1 and the first individual contact d of the n-1 switch part Bn-1. ing.

  In the present embodiment, each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, each of the switch units Bn-1 and Bn of the m-th changeover switch Sm is common. The switching mode is switched so that the contact c is electrically connected to the first and second individual contacts d and e alternately.

  Specifically, as shown in FIG. 3, for example, when the operation start switch of the ON / OFF switch unit 12 is operated at time t <b> 1 and an operation start command is given to the control unit 11, the mth changeover switch Sm The common contact c of the n-1 switch unit Bn-1 is electrically connected to the first individual contact d. As a result, the (n-1) th output terminal an-1 of the (n-1) th transformer circuit and the one-side electrode terminal 25a of the (n-1) th lamp Ln-1 are electrically connected, and the (n-1) th output terminal an The AC voltage signal output from -1 is applied to the one-side electrode terminal 25a of the (n-1) th lamp Ln-1. As a result, an AC voltage is applied to the (n-1) th lamp Ln-1, and the (n-1) th lamp Ln-1 emits light.

  When the operation start switch of the ON / OFF switch unit 12 is operated at time t1 and an operation start command is given to the control unit 11, the common contact c of the switch unit Bn of the m-th changeover switch Sm becomes the first individual contact d. And electrically connected. As a result, the n-th output terminal an of the n-th transformer circuit and the one-side electrode terminal 25a of the n-th lamp Ln are electrically connected, and the AC voltage signal output from the n-th output terminal an is converted into the n-th lamp. Ln is applied to one side electrode terminal 25a. As a result, an AC voltage is applied to the nth lamp Ln, and the nth lamp Ln emits light.

  Next, after the operation end switch of the ON / OFF switch unit 12 is operated at time t2 and an operation end command is given to the control unit 11, the operation start switch of the ON / OFF switch unit 12 is operated again at time t3. When the operation start command is given to the control unit 11, the common contact c of the (n-1) th switch unit Bn-1 of the mth changeover switch Sm is electrically connected to the second individual contact e. As a result, the (n-1) th output terminal an-1 of the (n-1) th transformer circuit and the one-side electrode terminal 25a of the nth lamp (Ln) are electrically connected and output from the (n-1) th output terminal an-1. The AC voltage signal thus applied is supplied to the one-side electrode terminal 25a of the nth lamp Ln. As a result, an AC voltage is applied to the nth lamp Ln, and the nth lamp Ln emits light.

  Further, the operation end switch of the ON / OFF switch unit 12 is operated at time t2 and an operation end command is given to the control unit 11, and then the operation start switch of the ON / OFF switch unit 12 is operated again at time t3. When the start command is given to the control unit 11, the common contact c of the switch unit Bn of the m-th changeover switch Sm is electrically connected to the second individual contact e. As a result, the n-th output terminal an of the n-th transformer circuit and the one-side electrode terminal 25a of the n-1th lamp Ln-1 are electrically connected, and the AC voltage signal output from the n-th output terminal an is obtained. , And supplied to the one-side electrode terminal 25a of the (n-1) th lamp Ln-1. As a result, an AC voltage is applied to the (n-1) th lamp Ln, and the (n-1) th lamp Ln-1 emits light.

  Thereafter, each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, each lamp L of the lamp group 25 and a transformer circuit that applies an AC voltage to the lamp L, In this embodiment, the combination of the one-side electrode terminal 25a of each lamp L and the output terminal a of the transformer circuit that applies an AC voltage to the lamp L is switched by the changeover switch S.

  More specifically, every time an operation start command is given to the control unit 11, the (n-1) th output terminal an-1 of the (n-1) th transformer circuit is connected to the one side electrode of the (n-1) th lamp Ln-1. The terminals 25a and the one-side electrode terminal 25a of the nth lamp Ln are alternately connected. Therefore, every time an operation start command is given to the control unit 11, the n-1th lamp Ln-1 and the nth lamp Ln are alternately supplied from the (n-1) th output terminal an-1 of the (n-1) th transformer circuit. An alternating voltage is applied. Each time an operation start command is given to the control unit 11, the n-th output terminal an of the n-th transformer circuit is connected to the one-side electrode terminal 25a of the n-th lamp Ln and the one-side electrode terminal of the n-1 lamp Ln-1. Alternately connected to 25a. Therefore, every time an operation start command is given to the control unit 11, an AC voltage is alternately applied from the nth output terminal an of the nth transformer circuit to the nth lamp Ln and the n−1th lamp Ln−1. .

  In other words, with respect to the one-side electrode terminal 25a of the n-1th lamp Ln-1, from the n-1st output terminal an-1 of the n-1th transformer circuit and the nth output terminal an of the nth transformer circuit. Alternating voltage is applied alternately. An alternating voltage is alternately applied from the n-th output terminal an of the n-th transformer circuit to the one-side electrode terminal 25a of the n-th lamp Ln and the n-1 output terminal an-1 of the n-1 transformer circuit. Is done.

  FIG. 4 is a flowchart showing a processing procedure of the control unit 11 regarding the switching control of the combination of the connection between the transformer circuit and each lamp L of the lamp group 25. The control unit 11 can perform switching control by executing a control program stored therein. In the flowchart shown in FIG. 4, when the image display is electrically connected, this processing starts and the process proceeds to step a1.

  In step a1, the control unit 11 determines whether or not an operation start command is given from the ON / OFF switch unit 12, and when the operation start command is given, the process proceeds to step a2 where the operation start command is given. If not, wait until an operation start command is given.

  In step a2, the connection state between the lamp L of the backlight unit 24 and the transformer circuit provided in the inverter circuit 20 previously switched by the switching unit 22 is read from the switching state storage unit 23, and the process proceeds to step a3. To do. In step a2, if the combination of the lamp L and the transformer circuit has not been switched by the switching unit 22 before, the information on the connection state in a predetermined initial state is read, and the process proceeds to step a3. .

  In step a <b> 3, the control unit 11 gives a signal indicating that a predetermined switching timing has been reached to the switching drive unit 21. The switching drive unit 21 gives the switching unit 22 a switching command for switching the combination of the lamp L and the transformer circuit based on the signal given from the control unit 11. The switching unit 22 switches the combination of the lamp L and a transformer circuit that applies an AC voltage to the lamp L in accordance with a switching command given from the switching drive unit 21. When the combination of the lamp L and the transformer circuit is switched by the switching unit 22, the process proceeds to step a4.

  In step a4, the transformer circuit of the inverter circuit 20 turns on the lamp L by applying an AC voltage between the electrodes of the lamp L newly connected by switching the combination of the lamp L and the transformer circuit in step a3. Let When the lamp L is turned on in step a4, the process proceeds to step a5.

  In step a5, the control unit 11 determines whether or not an operation end command is given from the ON / OFF switch unit 12. When the operation end command is given, the control unit 11 ends the switching control and follows a predetermined end procedure. The image display is terminated, and the process proceeds to step a6. If the operation end command is not given in step a5, the lamp L is lit while maintaining the connection state between the lamp L switched by the switching unit 22 in step a3 and the transformer circuit until the operation end command is given. .

  In step a6, the control unit 11 stores the connection state between the lamp L and the transformer circuit switched by the switching unit 22 in step a3 in the switching state storage unit 23 as the current connection state between the lamp L and the transformer circuit. Thus, all processing procedures relating to the switching control are completed.

  As described above, according to the first embodiment, each lamp L of the lamp group 25 emits light when an AC voltage is applied by a transformer circuit. Light emitted from the plurality of lamps L that emits light when an AC voltage is applied enters the liquid crystal display panel 27. Thus, the light emitted from the plurality of lamps L is incident on the liquid crystal display panel 27 so that the viewer who views the display image displayed on the liquid crystal display panel 27 can visually recognize the display image. The combination of each lamp L and a transformer circuit that applies an AC voltage to the lamp L is switched by the switching unit 22 every time a predetermined switching timing is reached.

  Therefore, one transformer circuit that has applied an AC voltage to one of the plurality of lamps L before the switching operation by the switching unit 22 is a single lamp after the switching operation by the switching unit 22. A transformer circuit for applying an AC voltage to another different lamp is obtained. In addition, after the switching operation by the switching unit 22, an alternating voltage is applied to one lamp by another transformer circuit different from the one transformer circuit. As described above, since an AC voltage is sequentially applied to one lamp by a plurality of transformer circuits, when there is a variation in circuit performance due to manufacturing variations in the transformer circuit, and other than variations in circuit performance of the transformer circuit In any case where the AC voltage applied to the lamp L varies due to a factor, the influence of these variations can be distributed to each lamp L. Therefore, variation in the life of the lamp L can be suppressed. As a result, a decrease in luminance in the liquid crystal display panel 27 can be suppressed and a decrease in display quality can be prevented.

  Further, according to the present embodiment, the control unit 11 receives an operation start command from the ON / OFF switch unit 12 and stops supplying power from the power supply unit 13 to the transformer circuit of the inverter circuit 20. Each time the power supply unit 13 changes to a state where power is supplied to the transformer circuit, the switching unit 22 determines that the switching timing has been reached, and applies an AC voltage to each lamp L and the lamp L. The combination with the transformer circuit is switched.

  In this way, by changing the combination of the lamp L and the transformer circuit in accordance with the change in the power supply state, a change from the state where the power supply is stopped to the state where the power is supplied occurs at regular intervals. In this case, the combination of the lamp L and the transformer circuit can be switched at regular intervals. As a result, for example, the influence of variations in circuit performance of the transformer circuit on each lamp L can be averaged, so that variations in the life of the lamp L can be remarkably suppressed.

  Further, according to the present embodiment, after the switching unit 22 switches the combination of the lamp L and the transformer circuit that applies an AC voltage to the lamp L, the application of the AC voltage to the lamp L by the transformer circuit is started. Is done. That is, the combination of the lamp L and the transformer circuit is switched in a state where no AC voltage is applied to the lamp L from the transformer circuit. When the combination of the lamp L and the transformer circuit is switched while an AC voltage is applied from the transformer circuit to the lamp L, a current suddenly flows between the transformer circuit and the lamp L, and the transformer circuit and the lamp are switched. A large load is applied to the connection portion with L, for example, the transformer circuit is damaged. In the present embodiment, since the combination of the lamp L and the transformer circuit is switched in a state where an AC voltage is not applied from the transformer circuit to the lamp L, when the combination of the lamp L and the transformer circuit is switched, For example, the transformer circuit can be prevented from being damaged.

  In the present embodiment, as shown in step a1 of the flowchart of FIG. 4 described above, the control unit 11 is given an operation start command from the ON / OFF switch unit 12, and the power supply unit 13 transfers to the transformer circuit of the inverter circuit 20. The switching unit 22 determines that the switching timing has been reached each time the power supply unit 13 changes to a state where power is supplied from the power supply unit 13 to the transformer circuit. However, the switching timing is not limited to such timing.

  For example, every time a predetermined time is reached, the switching unit 22 may determine that the switching timing has been reached, or every time a predetermined time elapses, the switching unit 22 has reached the switching timing. The switching unit 22 may determine that the switching timing has been reached based on the update of the display image displayed on the liquid crystal display panel 27.

  When the switching unit 22 determines that the switching timing has been reached each time a predetermined time is reached, whether or not the control unit 11 has reached the predetermined time in step a1 of FIG. You just have to judge. By switching the combination of the lamp L and the transformer circuit according to a predetermined time, the combination of the lamp L and the transformer circuit can be switched at regular intervals, so that when the lamp L emits light continuously, The light emission times of the lamps L in the combination can be averaged. As a result, it is possible to prevent the lamp L having an extremely long light emission time from occurring for each combination, and to average the influence of variations in circuit performance of the transformer circuit on each lamp L, for example. As a result, it is possible to remarkably suppress variations in the life of the lamp L.

  In addition, since the combination of each lamp L and a transformer circuit that applies an AC voltage to the lamp L is switched at a predetermined time, a viewer viewing the display image can view the display image at a predetermined time. By setting the time at a low time, for example, at midnight, it is possible to reduce the possibility that the viewer can recognize the switching of the combination of each lamp L and the transformer circuit that applies an AC voltage to the lamp L. This prevents the switching operation from being mistaken as a failure of the liquid crystal display device 10.

  When the switching unit 22 determines that the switching timing has been reached each time a predetermined time elapses, the control unit 11 determines that the predetermined time has elapsed in step a1 of FIG. Or not. By switching the combination of the lamp L and the transformer circuit according to a predetermined time, when the lamp L emits light continuously, the light emission time of the lamp L in each combination can be averaged. As a result, it is possible to prevent the lamp L having an extremely long light emission time from occurring for each combination, and to average the influence of variations in circuit performance of the transformer circuit on each lamp L, for example. As a result, it is possible to remarkably suppress variations in the life of the lamp L.

  When the switching unit 22 is configured to determine that the switching timing has been reached based on the update of the display image displayed on the liquid crystal display panel 27, the control unit 11 in step a1 in FIG. It may be determined whether or not the display image displayed on the liquid crystal display panel 27 has been updated. For example, the combination of the lamp L and the transformer circuit is switched when the display image is updated or when the predetermined update count display image is updated. Accordingly, the possibility that the viewer recognizes the switching of the combination can be reduced as compared with the case where the combination is switched when one display image is displayed. Accordingly, it is possible to prevent the combination switching operation from being mistaken as a failure of the liquid crystal display device 10.

  When the switching timing reaches every predetermined time as described above, every time a predetermined time elapses, and every time a display image displayed on the liquid crystal display panel 27 is updated, the switching unit 22 causes the lamp L And the transformer circuit that applies an AC voltage to the lamp L are switched, the application of the AC voltage to the lamp L is stopped by the transformer circuit, and the switching unit 22 supplies the lamp L and the lamp L with an AC voltage. After the combination with the transformer circuit to which the voltage is applied is switched, an AC voltage is applied to the lamp L by the transformer circuit.

  In other words, the combination of the lamp L and the transformer circuit is switched in a state where no AC voltage is applied to the lamp L from the transformer circuit. When the combination of the lamp L and the transformer circuit is switched while an AC voltage is applied from the transformer circuit to the lamp L, a current suddenly flows between the transformer circuit and the lamp L, and the transformer circuit and the lamp L are switched. As a result, a large load is applied to the connecting portion, and for example, the transformer circuit is damaged. When the combination of the lamp L and the transformer circuit is switched by switching the combination of the lamp L and the transformer circuit in a state where no AC voltage is applied from the transformer circuit to the lamp L, for example, the transformer circuit is damaged. Can be prevented.

  Next, switching operation of the combination of electrical connections between the transformer circuit of the inverter circuit 20 and each lamp L of the lamp group 25 according to the second embodiment of the present invention will be described. FIG. 5 is a block diagram showing an electrical configuration of the inverter circuit 20, the switching unit 22, and the lamp group 25 according to the second embodiment of the present invention. FIG. 6 is a diagram for explaining switching of the combination of the eight lamps L and the inverter circuit 20. FIG. 7 is a timing chart showing switching of the electrical connection combination between the inverter circuit 20 of FIG. 5 and each lamp L of the lamp group 25. The inverter circuit, switching unit, and lamp group of the second embodiment are similar to the inverter circuit 20, switching unit 22, and lamp group 25 of the first embodiment shown in FIG. Therefore, in the present embodiment, only differences from the first embodiment will be described, the same reference numerals will be given to portions corresponding to the first embodiment, and common description will be omitted.

  The switching unit 22 includes one movable unit 30 that can be angularly displaced around a preset rotation axis X and n (n is a natural number of 2 or more) number of change-over switches S1, S2,..., Sn-1, Sn. This is realized by a rotary switch provided. Hereinafter, when each changeover switch is generically referred to and when an unspecified changeover switch is indicated, it may be simply referred to as “changeover switch S”. Each changeover switch S is stacked in a direction extending in parallel along a preset rotation axis X. 5 and 6 show a case where each changeover switch S is realized by a one-circuit eight-contact switch for easy understanding. Each changeover switch S includes a common contact c, a first individual contact d, a second individual contact e, a third individual contact f, a fourth individual contact g, a fifth individual contact h, a sixth individual contact i, and a seventh individual contact. j and the eighth individual contact k.

  In each change-over switch S, the common contact c is moved from the first to the eighth in accordance with the change command given from the change-over drive unit 21 by the angular displacement of the movable unit 30 around the preset rotation axis X by, for example, a motor. The switching mode is configured so as to be electrically connected to any one of the individual contacts d to k. In the present embodiment, the movable portion 30 is configured to be angularly displaced about the rotational axis X by a motor, but is configured to be angularly displaced about the rotational axis X by an electromagnet and a solenoid. May be.

  Each output terminal a of each transformer circuit in the inverter circuit 20 is electrically connected to a common contact c of each changeover switch S of the changeover unit 22. The first individual contact d of the first changeover switch S1 is electrically connected to the one-side electrode terminal 25a of the first lamp L1, and all changeover switches S other than the first changeover switch S1, specifically the second ,..., N-th switch S2,..., Sn are electrically connected to the first individual contacts d. The second individual contact e of the second changeover switch S2 is electrically connected to the one-side electrode terminal 25a of the second lamp L2, and all changeover switches S other than the second changeover switch S2, specifically the first , Third to n-1, nth changeover switches S1, S3,..., Sn-1 and Sn are electrically connected to second individual contacts e.

  The seventh individual contact j of the (n-1) th change switch Sn-1 is electrically connected to the one-side electrode terminal 25a of the (n-1) th lamp Ln-1, and other than the n-1th changeover switch Sn-1. All changeover switches S, specifically, the first,..., N-2th, nth changeover switches S1,..., Sn-2, Sn are electrically connected to the seventh individual contact j. The eighth individual contact k of the nth changeover switch Sn is electrically connected to the one-side electrode terminal 25a of the nth lamp Ln, and all changeover switches S other than the nth changeover switch Sn, specifically the first ,..., N-1 changeover switches S1,..., Sn-1 are electrically connected to the eighth individual contact k.

  In FIG. 6, for easy understanding, a switching unit 22 including eight changeover switches S1,..., S8 and a lamp group 25 including eight lamps L are shown. As shown in FIG. 6, when the changeover switch S of the switching unit 22 is eight, the electrical connection between the first to eighth individual contacts d to k and the first to eighth lamps L1 to L8 is as follows. It is like this.

  The first individual contact d of the first changeover switch S1 is electrically connected to the one-side electrode terminal 25a of the first lamp L1, and is electrically connected to the first individual contact d of the second to eighth changeover switches S2 to S8. It is connected to the. The second individual contact e of the second changeover switch S2 is electrically connected to the one-side electrode terminal 25a of the second lamp L2, and the second individual contact e of the first, third to eighth changeover switches S1, S3 to S8. It is electrically connected to the contact e. The third individual contact f of the third changeover switch S3 is electrically connected to the one-side electrode terminal 25a of the third lamp L3, and the first, second, fourth to eighth changeover switches S1, S2, S4 to It is electrically connected to the third individual contact f in S8. The fourth individual contact g of the fourth changeover switch S4 is electrically connected to the one-side electrode terminal 25a of the fourth lamp L4, and the first to third, fifth to eighth changeover switches S1 to S3, S5. It is electrically connected to the fourth individual contact g in S8.

  The fifth individual contact h of the fifth changeover switch S5 is electrically connected to the one-side electrode terminal 25a of the fifth lamp L5, and the first to fourth, sixth to eighth changeover switches S1 to S4, S6 to S6. It is electrically connected to the fifth individual contact h in S8. The sixth individual contact i of the sixth changeover switch S6 is electrically connected to the one-side electrode terminal 25a of the sixth lamp L6, and the first to fifth, seventh, and eighth changeover switches S1 to S5, S7, It is electrically connected to the sixth individual contact i in S8. The seventh individual contact j of the seventh selector switch S7 is electrically connected to the one-side electrode terminal 25a of the seventh lamp L7, and the seventh individual contacts j of the first to sixth and eighth selector switches S1 to S6, S8. It is electrically connected to the contact j. The eighth individual contact k of the eighth changeover switch S8 is electrically connected to the one-side electrode terminal 25a of the eighth lamp L8 and is electrically connected to the eighth individual contact k of the first to seventh changeover switches S1 to S7. It is connected to the.

  In the present embodiment, each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, the common contacts c of the first to eighth changeover switches S1 to S8 are The switching mode is configured to be switched so that the first to eighth individual contacts d to k are electrically connected in order.

  More specifically, as shown in FIG. 7, for example, when the operation start switch of the ON / OFF switch unit 12 is operated at time t <b> 1 and an operation start command is given to the control unit 11, the nth changeover switch Sn is common. The contact c is electrically connected to the eighth individual contact k. As a result, the n-th output terminal an of the n-th transformer circuit and the one-side electrode terminal 25a of the n-th lamp Ln are electrically connected, and the AC voltage signal output from the n-th output terminal an is converted into the n-th lamp. Ln is applied to one side electrode terminal 25a. As a result, an AC voltage is applied to the nth lamp Ln, and the nth lamp Ln emits light.

  Next, after the operation end switch of the ON / OFF switch unit 12 is operated at time t2 and an operation end command is given to the control unit 11, the operation start switch of the ON / OFF switch unit 12 is operated again at time t3. When the operation start command is given to the control unit 11, the common contact c of the nth changeover switch Sn is electrically connected to the seventh individual contact j. As a result, the n-th output terminal an of the n-th transformer circuit and the one-side electrode terminal 25a of the n-1th lamp Ln-1 are electrically connected, and the AC voltage signal output from the n-th output terminal an is obtained. , And supplied to the one-side electrode terminal 25a of the (n-1) th lamp Ln-1. As a result, an AC voltage is applied to the (n-1) th lamp Ln-1, and the (n-1) th lamp Ln-1 emits light.

  Thereafter, each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, each lamp L of the lamp group 25 and a transformer circuit that applies an AC voltage to the lamp L, In this embodiment, the combination of the one-side electrode terminal 25a of each lamp L and the output terminal a of the transformer circuit that applies an AC voltage to the lamp L is switched by the changeover switch S.

  More specifically, every time an operation start command is given to the controller 11, the n-th output terminal an of the n-th transformer circuit is connected to the one-side electrode terminal 25a of the n-th lamp Ln, the n-1th lamp Ln--. Are connected in sequence to one electrode terminal 25a of the first lamp L1. Therefore, each time an operation start command is given to the control unit 11, the nth lamp Ln, the n-1th lamp Ln-1,. An AC voltage is sequentially applied to the lamp L1. In this way, the n-th transformer circuit is configured to be connectable to all the lamps L constituting the lamp group 25, so that it can be combined with all the lamps L.

  As described above, according to the second embodiment, each transformer circuit of the inverter circuit 20 is configured to be connectable to all the lamps L, so that it can be combined with all the lamps L. As a result, the switching unit 22 can switch each transformer circuit to a combination selected from the combinations with all the lamps L. Therefore, other than the variation in the circuit performance of the transformer circuit and the variation in the circuit performance of the transformer circuit. The influence of variations in the AC voltage applied to the lamps L due to the factors can be distributed to all the lamps L. Therefore, the variation in the life of the lamp L can be further suppressed.

  Further, according to the present embodiment, the switching control of the combination of the connection between the transformer circuit and each lamp L of the lamp group 25 is performed according to the processing procedure shown in the flowchart of FIG. In the present embodiment, as in the first embodiment described above, every time a predetermined time is reached, every time a predetermined time elapses, and every time a display image displayed on the liquid crystal display panel 27 is updated. The switching unit 22 may determine that the switching timing has been reached, and an effect similar to that of the first embodiment described above can be obtained.

  Next, the switching operation of the combination of electrical connections between the transformer circuit of the inverter circuit 20 and each lamp L of the lamp group 25 according to the third embodiment of the present invention will be described. FIG. 8 is a block diagram showing an electrical configuration of the inverter circuit 20, the switching unit 22, and the lamp group 25 according to the third embodiment of the present invention. FIG. 9 is a timing chart showing the switching of the combination of electrical connections between the inverter circuit 20 of FIG. 8 and each lamp L of the lamp group 25. The inverter circuit, switching unit, and lamp group of the third embodiment are similar to the inverter circuit 20, switching unit 22, and lamp group 25 of the first embodiment shown in FIG. Therefore, in the present embodiment, only differences from the first embodiment will be described, the same reference numerals will be given to portions corresponding to the first embodiment, and common description will be omitted.

  The switching unit 22 includes n (n is a natural number) change-over switches S1,..., Sn. The n-th changeover switch Sn is realized by a two-circuit two-contact switch having two switch units, specifically, a k-1th switch unit Bk-1 and a kth switch unit Bk (k = 2 × n). Each switch portion B includes a common contact c, a first individual contact d, and a second individual contact e.

  In the present embodiment, the n-th output terminal an of the n-th transformer circuit (n is a natural number of 2 or more) in the inverter circuit 20 is the k-1 switch portion Bk-1 (k is 2 or more) of the n-th changeover switch Sn. (Natural number) of the common contact c. The first individual contact d of the k-1th switch unit Bk-1 is electrically connected to the one-side electrode terminal 25a of the nth lamp Ln and the second individual contact e of the kth switch unit Bk. The second individual contact e of the k-1th switch unit Bk-1 is electrically connected to the other electrode terminal 25b of the nth lamp Ln and the first individual contact d of the kth switch unit Bk.

  The n-th ground terminal bn of the n-th transformer circuit in the inverter circuit 20 is electrically connected to the common contact c of the k-th switch part Bk of the n-th changeover switch Sn. The first individual contact d of the k-th switch part Bk is electrically connected to the other electrode terminal 25b of the n-th lamp Ln and the second individual contact e of the k-1 switch part Bk-1. The second individual contact e of the k-th switch part Bk is electrically connected to the one-side electrode terminal 25a of the n-th lamp Ln and the first individual contact d of the k-1 switch part Bk-1.

  In the present embodiment, each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, each of the switch units Bk-1 and Bk of the nth changeover switch Sn is common. The switching mode is switched so that the contact c is electrically connected to the first and second individual contacts d and e alternately.

  Specifically, as shown in FIG. 9, for example, when the operation start switch of the ON / OFF switch unit 12 is operated at time t <b> 1 and an operation start command is given to the control unit 11, the nth changeover switch Sn is switched. The common contact c of the k-1 switch unit Bk-1 is electrically connected to the first individual contact d of the k-1 switch unit Bk-1, and the common contact of the kth switch unit Bk of the nth changeover switch Sn. c is electrically connected to the first individual contact d of the k-th switch part Bk. As a result, the n-th output terminal an of the n-th transformer circuit and the one-side electrode terminal 25a of the n-th lamp Ln are electrically connected, and the AC voltage signal output from the n-th output terminal an is converted into the n-th lamp. Ln is applied to one side electrode terminal 25a. The n-th ground terminal bn of the n-th transformer circuit and the other-side electrode terminal 25b of the n-th lamp Ln are electrically connected, and a ground potential is applied to the other-side electrode terminal 25b of the n-th lamp Ln. As a result, an AC voltage is applied to the nth lamp Ln, and the nth lamp Ln emits light.

  Next, after the operation end switch of the ON / OFF switch unit 12 is operated at time t2 and an operation end command is given to the control unit 11, the operation start switch of the ON / OFF switch unit 12 is operated again at time t3. When the operation start command is given to the control unit 11, the common contact c of the (k-1) th switch unit Bk-1 of the nth changeover switch Sn is connected to the second individual contact e of the (k-1) th switch unit Bk-1. The common contact c of the k-th switch part Bk of the n-th changeover switch Sn is electrically connected to the second individual contact e of the k-th switch part Bk. As a result, the n-th output terminal an of the n-th transformer circuit and the other-side electrode terminal 25b of the n-th lamp Ln are electrically connected, and the AC voltage signal output from the n-th output terminal an becomes the n-th lamp. Ln is provided to the other electrode terminal 25b of Ln. Further, the n-th ground terminal bn of the n-th transformer circuit and the one-side electrode terminal 25a of the n-th lamp Ln are electrically connected, and a ground potential is applied to the one-side electrode terminal 25a of the n-th lamp Ln. As a result, an AC voltage is applied to the nth lamp Ln, and the nth lamp Ln emits light.

  Thereafter, each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, one side and the other side electrode terminals 25a and 25b of each lamp L of the lamp group 25, and the inverter A combination of electrical connections between the output terminal a and the ground terminal b of each transformer circuit of the circuit 20 is switched by the changeover switch S.

  More specifically, each time an operation start command is given to the controller 11, the n-th output terminal an of the n-th transformer circuit and the one-side and other-side electrode terminals 25a, 25b of the n-th lamp Ln The nth ground terminals bn are alternately connected.

  As described above, according to the third embodiment, the transformer circuit has an output terminal a that outputs an AC voltage signal and a ground terminal b that is supplied with a ground potential. Of the two electrode terminals 25a and 25b of the lamp L, the output terminal a is electrically connected to one electrode terminal to receive an AC voltage signal, and the ground terminal is electrically connected to the other electrode terminal. To provide a ground potential. Based on an AC voltage signal applied from the output terminal a of the transformer circuit, an AC voltage is applied between the two electrode terminals of the lamp L, and the lamp L emits light. The light emitted from the emitted lamp L enters the liquid crystal display panel 27. Thus, when the light emitted from the lamp L is incident on the liquid crystal display panel 27, the viewer can visually recognize the display image displayed on the liquid crystal display panel 27.

  The combination of electrical connection between the two electrode terminals 25a and 25b of the lamp L and the output terminal a and the ground terminal b of the transformer circuit is switched by the switching unit 22 every time the above-described predetermined switching timing is reached. . For example, when the two electrode terminals 25a and 25b of the lamp L are the first electrode terminal 25a and the second electrode terminal 25b, respectively, the output terminal a is connected to the first electrode terminal 25a before the switching operation by the switching unit 22, When the ground terminal b is connected to the two-electrode terminal 25b, after the switching operation by the switching unit 22, the output terminal a is connected to the second electrode terminal 25b, and the ground terminal b is connected to the first electrode terminal 25a. .

  Thus, since the output terminal a and the ground terminal b of the transformer circuit are alternately connected to the electrode terminals 25a and 25b of the lamp L, the AC voltage signal output from the output terminal a of the transformer circuit is electrically Even when there is a large bias, the occurrence of an electrical bias within the lamp L can be suppressed as much as possible. Therefore, it is possible to prevent the life of the lamp L from being shortened due to electrical bias.

  Each transformer circuit of the present embodiment has a configuration having an output terminal a that outputs an AC voltage signal and a ground terminal b to which a ground potential is applied, but is not limited to such a configuration. A transformer circuit according to another embodiment of the present invention includes a first output terminal that outputs an AC voltage signal and a second output terminal that outputs an AC voltage signal having a phase opposite to that of the AC voltage signal output from the first output terminal. The structure which has these may be sufficient. When configured in this way, the following effects are obtained.

  Of the two electrode terminals 25a and 25b of the lamp L, one electrode terminal is electrically connected to the first output terminal to provide an AC voltage signal, and the other electrode terminal is electrically connected to the second output terminal. And an AC voltage signal having a phase opposite to that of the AC voltage signal output from the first output terminal is applied. Based on the AC voltage signal applied from the first and second output terminals of the transformer circuit, an AC voltage is applied between the two electrode terminals 25a and 25b of the lamp L, and the lamp L emits light. The light emitted from the emitted lamp L enters the liquid crystal display panel 27. Thus, when the light emitted from the lamp L is incident on the liquid crystal display panel 27, the viewer can visually recognize the display image displayed on the liquid crystal display panel 27.

  The combination of electrical connection between the two electrode terminals 25a and 25b of the lamp L and the first and second output terminals of the transformer circuit is switched by the switching unit 22 every time the above-described predetermined switching timing is reached. . For example, when the two electrode terminals 25a and 25b of the lamp L are the first electrode terminal 25a and the second electrode terminal 25b, respectively, the first output terminal is connected to the first electrode terminal 25a before the switching operation by the switching unit 22, When the second output terminal is connected to the second electrode terminal 25b, after the switching operation by the switching unit 22, the first output terminal is connected to the second electrode terminal 25b, and the second output terminal is connected to the first electrode terminal 25a. Will be connected.

  Since the first and second output terminals of the transformer circuit are alternately connected to the electrode terminals 25a and 25b of the lamp L in this way, the alternating currents output from the first and second output terminals of the transformer circuit, respectively. Even if an electrical bias occurs in the voltage signal, it is possible to suppress the electrical bias in the lamp L as much as possible. Therefore, it is possible to prevent the life of the lamp L from being shortened due to electrical bias.

  Further, according to the present embodiment, the switching control of the combination of the electrical connection between the two electrode terminals 25a and 25b of the lamp L and the output terminal a and the ground terminal b of the transformer circuit is performed in the flow chart of FIG. This is performed according to the processing procedure shown in FIG. In the present embodiment, as in the first embodiment described above, every time a predetermined time is reached, every time a predetermined time elapses, and every time a display image displayed on the liquid crystal display panel 27 is updated. The switching unit 22 may determine that the switching timing has been reached, and an effect similar to that of the first embodiment described above can be obtained.

  Next, the switching operation of the combination of electrical connections between the transformer circuit of the inverter circuit 20 and each lamp L of the lamp group 25 according to the fourth embodiment of the present invention will be described. FIG. 10 is a block diagram showing an electrical configuration of the inverter circuit 20, the first switching unit 31, the second switching unit 32, and the lamp group 25 according to the fourth embodiment of the present invention. FIG. 11 is a timing chart showing switching of the electrical connection combination between the inverter circuit 20 of FIG. 10 and each lamp L of the lamp group 25. The fourth embodiment is similar to the first embodiment shown in FIG. 2 and the third embodiment shown in FIG. Therefore, in the present embodiment, only differences from the first embodiment and the third embodiment will be described, and the same reference is made to portions corresponding to the first embodiment and the third embodiment. A common description is omitted by adding a reference numeral.

  The inverter circuit 20 includes a plurality of first and second transformer circuits in the present embodiment. The first transformer circuit includes a first output unit A1 having a first output terminal a1 that outputs an AC voltage signal and a first ground terminal b1 to which a ground potential is applied. The second transformer circuit includes a second output unit A2 having a second output terminal a2 that outputs an AC voltage signal and a second ground terminal b2 to which a ground potential is applied.

  In the present embodiment, unlike the first and third embodiments, two switching units, specifically, a first switching unit 31 and a second switching unit 32 are provided. The first switching unit 31 and the second switching unit 32 correspond to switching means. The first switching unit 31 includes a first changeover switch M1 and a second changeover switch M2. The first changeover switch M1 has a first switch part N1 and a second switch part N2, and the second changeover switch M2 has a third switch part N3 and a fourth switch part N4. Each switch part N1-N4 contains the common contact c, the 1st separate contact d, and the 2nd separate contact e. The first and second changeover switches M1 and M2 of the first changeover unit 31 are realized by a two-circuit two-contact switch. Hereinafter, when the change-over switches M1 and M2 of the first switching unit 31 are collectively referred to and when an unspecified change-over switch of the first switching unit 31 is indicated, it may be simply referred to as a “switch M”.

  The second switching unit 32 includes a first changeover switch P1 and a second changeover switch P2. The first changeover switch P1 has a first switch part Q1 and a second switch part Q2, and the second changeover switch P2 has a third switch part Q3 and a fourth switch part Q4. Each switch part Q1-Q4 contains the common contact c, the 1st separate contact d, and the 2nd separate contact e. The first and second changeover switches P1 and P2 of the second changeover unit 32 are realized by a two-circuit two-contact switch. Hereinafter, when the changeover switches P1 and P2 of the second switching unit 32 are collectively referred to and when an unspecified changeover switch of the second switching unit 32 is indicated, it may be simply referred to as “changeover switch P”. The lamp group 25 includes a plurality of first lamps L1 and second lamps L2 in the present embodiment.

  Each time the first and second switching units 31 and 32 of the present embodiment reach a predetermined switching timing, the combination of each lamp L of the lamp group 25 and the transformer circuit of the inverter circuit 20, and each lamp L It is configured to switch at least one of the combination of electrical connection between the two electrode terminals 25a and 25b and the output terminal a and the ground terminal b of the transformer circuit.

  In the present embodiment, the first output terminal a1 of the first transformer circuit in the inverter circuit 20 is electrically connected to the common contact c of the first switch unit N1 of the first switch M1 of the first switch unit 31. Yes. The first individual contact d of the first switch part N1 of the first changeover switch M1 is connected to the second individual contact e of the second switch part N2 of the first changeover switch M1 and the first changeover switch P1 of the second changeover part 32. The first switch part Q1 is electrically connected to the common contact c.

  The second individual contact e of the first switch portion N1 of the first changeover switch M1 is the same as that of the first individual contact d of the second switch portion N2 of the first changeover switch M1 and the second changeover switch P2 of the second changeover portion 32. It is electrically connected to the common contact c of the third switch part Q3.

  The first ground terminal b1 of the first transformer circuit is electrically connected to the common contact c of the third switch unit N3 of the second switch M2 of the first switch unit 31. The second output terminal a2 of the second transformer circuit is electrically connected to the common contact c of the second switch unit N2 of the first switch M1 of the first switch unit 31. The first individual contact d of the second switch portion N2 of the first changeover switch M1 is the second individual contact e of the first switch portion N1 of the first changeover switch M1 and the second changeover switch P2 of the second changeover portion 32. It is electrically connected to the common contact c of the third switch part Q3. The second individual contact e of the second switch part N2 of the first changeover switch M1 is the same as that of the first individual contact d of the first switch part N1 of the first changeover switch M1 and the first changeover switch P1 of the second changeover part 32. The first switch part Q1 is electrically connected to the common contact c.

  The second ground terminal b2 of the second transformer circuit is electrically connected to the common contact c of the fourth switch unit N4 of the second switch M2 of the first switch unit 31. The first individual contact d of the third switch part N3 of the second changeover switch M2 is the same as that of the second individual contact e of the fourth switch part N4 of the second changeover switch M2 and the first changeover switch P1 of the second changeover part 32. The second switch part Q2 is electrically connected to the common contact c. The second individual contact e of the third switch portion N3 of the second changeover switch M2 is the same as that of the first individual contact d of the fourth switch portion N4 of the second changeover switch M2 and the second changeover switch P2 of the second changeover portion 32. It is electrically connected to the common contact c of the fourth switch part Q4.

  The first individual contact d of the fourth switch portion N4 of the second changeover switch M2 is the second individual contact e of the third switch portion N3 of the second changeover switch M2 and the second changeover switch P2 of the second changeover portion 32. It is electrically connected to the common contact c of the fourth switch part Q4. The second individual contact e of the fourth switch portion N4 of the second changeover switch M2 is the same as that of the first individual contact d of the third switch portion N3 of the second changeover switch M2 and the first changeover switch P1 of the second changeover portion 32. The second switch part Q2 is electrically connected to the common contact c.

  The first individual contact d of the first switch part Q1 of the first changeover switch P1 of the second changeover part 32 is the first electrode terminal 25a of the first lamp L1 and the second switch part Q2 of the first changeover switch P1. 2 are electrically connected to the individual contacts e. The second individual contact e of the first switch portion Q1 of the first changeover switch P1 is electrically connected to the other electrode terminal 25b of the first lamp L1 and the first individual contact d of the second switch portion Q2 of the first changeover switch P1. Connected. The first individual contact d of the second switch part Q2 of the first changeover switch P1 is electrically connected to the second individual contact e of the first switch part Q1 of the first changeover switch P1 and the other electrode terminal 25b of the first lamp L1. Connected. The second individual contact e of the second switch part Q2 of the first changeover switch P1 is electrically connected to the one-side electrode terminal 25a of the first lamp L1 and the first individual contact d of the first switch part Q1 of the first changeover switch P1. Connected.

  The first individual contact d of the third switch part Q3 of the second changeover switch P2 of the second changeover part 32 is connected to the first electrode terminal 25a of the second lamp L2 and the fourth switch part Q4 of the second changeover switch P2. 2 are electrically connected to the individual contacts e. The second individual contact e of the third switch part Q3 of the second changeover switch P2 is electrically connected to the other electrode terminal 25b of the second lamp L2 and the first individual contact d of the fourth switch part Q4 of the second changeover switch P2. Connected. The first individual contact d of the fourth switch part Q4 of the second changeover switch P2 is electrically connected to the other electrode terminal 25b of the second lamp L2 and the second individual contact e of the third switch part Q3 of the second changeover switch P2. Connected. The second individual contact e of the fourth switch part Q4 of the second changeover switch P2 is electrically connected to the one-side electrode terminal 25a of the second lamp L2 and the first individual contact d of the third switch part Q3 of the second changeover switch P2. Connected.

  In the present embodiment, the switching state storage unit 23 is configured to be able to further store switching state identification information for identifying the switching states of the switching switch M of the first switching unit 31 and the switching switch P of the second switching unit 32, respectively. Is done. The switching state identification information is represented by a 2-digit binary number. The first digit of the switching state identification information represents the switching state of the changeover switch P, and the second digit of the switching state identification information represents the switching state of the changeover switch M.

  If the value of each digit represented by the binary number of the switching state identification information is “0”, the common contact c of each of the switch portions N1 to N4 and Q1 to Q4 of each changeover switch M and P is the first individual contact. It is electrically connected to d. If the value of each digit represented by the binary number of the switching state identification information is “1”, the common contact c of each of the switch portions N1 to N4 and Q1 to Q4 of each of the switches M and P is the second individual. It means being electrically connected to the contact e.

  In this embodiment, after the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, the operation end switch of the ON / OFF switch unit 12 is operated and the operation end command is operated. Each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11 after the series of operations given to the control unit 11 occur twice in succession, the first switching unit Each of the common contacts c of the switch parts N1, N2 of the first changeover switch M1 and the switch parts N3, N4 of the second changeover switch M2 of the first changeover part 31 are connected to the first and second individual contacts d, e. And the switching mode is switched so that they are electrically connected to each other alternately.

  Further, in the present embodiment, each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, each switch unit Q1 of the first changeover switch P1 of the second changeover unit 32. , Q2 and each common contact c of each switch part Q3, Q4 of the second changeover switch P2 of the second changeover part 32 are electrically connected to the first and second individual contacts d, e alternately. The switching mode is switched.

  Specifically, as shown in FIG. 11, for example, when the operation start switch of the ON / OFF switch unit 12 is operated at time t <b> 1 and an operation start command is given to the control unit 11, each of the first switching units 31. The common contact c of each switch part N1 to N4 of the changeover switch M is electrically connected to the first individual contact d of each switch part N1 to N4, and each switch part Q1 of each changeover switch P of the second switch part 32. The common contact c of .about.Q4 is electrically connected to the first individual contact d of each of the switch portions Q1 to Q4.

  As a result, the first output terminal a1 of the first transformer circuit and the one-side electrode terminal 25a of the first lamp L1 are electrically connected, and the AC voltage signal output from the first output terminal a1 is converted into the first lamp. L1 is applied to one side electrode terminal 25a. Further, the first ground terminal b1 of the first transformer circuit and the other electrode terminal 25b of the first lamp L1 are electrically connected, and a ground potential is applied to the other electrode terminal 25b of the first lamp L1. As a result, an AC voltage is applied to the first lamp L1, and the first lamp L1 emits light.

  Next, after the operation end switch of the ON / OFF switch unit 12 is operated at time t2 and an operation end command is given to the control unit 11, the operation start switch of the ON / OFF switch unit 12 is operated again at time t3. When the operation start command is given to the control unit 11, the switching mode of the first switching unit 31 is not switched, but the switching mode of the second switching unit 32 is switched as follows. That is, the common contact c of each switch part Q1-Q4 of each changeover switch P of the 2nd switching part 32 is electrically connected with the 2nd separate contact e of each switch part Q1-Q4.

  As a result, the first output terminal a1 of the first transformer circuit and the other electrode terminal 25b of the first lamp L1 are electrically connected, and the AC voltage signal output from the first output terminal a1 is converted into the first lamp. L1 is applied to the other electrode terminal 25b. Further, the first ground terminal bn of the first transformer circuit and the one side electrode terminal 25a of the first lamp L1 are electrically connected, and a ground potential is applied to the one side electrode terminal 25a of the first lamp L1. As a result, an AC voltage is applied to the first lamp L1, and the first lamp L1 emits light.

  Next, the operation end switch of the ON / OFF switch unit 12 is operated at time t4, and after the operation end command is given to the control unit 11, the operation start switch of the ON / OFF switch unit 12 is operated again at time t5. When an operation start command is given to the control unit 11, the common contact c of each switch unit N1 to N4 of each changeover switch M of the first switch unit 31 is electrically connected to the second individual contact e of each switch unit N1 to N4. The common contact c of each switch part Q1 to Q4 of each changeover switch P of the second switch part 32 is electrically connected to the first individual contact d of each switch part Q1 to Q4.

  As a result, the first output terminal a1 of the first transformer circuit and the one-side electrode terminal 25a of the second lamp L2 are electrically connected, and the AC voltage signal output from the first output terminal a1 is converted into the second lamp. It is given to one side electrode terminal 25a of L2. Further, the first ground terminal b1 of the first transformer circuit and the other side electrode terminal 25b of the second lamp L2 are electrically connected, and a ground potential is applied to the other side electrode terminal 25b of the second lamp L2. As a result, an AC voltage is applied to the second lamp L2, and the second lamp L2 emits light.

  Next, the operation end switch of the ON / OFF switch unit 12 is operated at time t6, and after the operation end command is given to the control unit 11, the operation start switch of the ON / OFF switch unit 12 is operated again at time t7. When the operation start command is given to the control unit 11, the switching mode of the first switching unit 31 is not switched, but the switching mode of the second switching unit 32 is switched as follows. That is, the common contact c of each switch part Q1-Q4 of each changeover switch P of the 2nd switching part 32 is electrically connected with the 2nd separate contact e of each switch part Q1-Q4.

  As a result, the first output terminal a1 of the first transformer circuit and the other electrode terminal 25b of the second lamp L2 are electrically connected, and the AC voltage signal output from the first output terminal a1 becomes the second lamp. L2 is applied to the other electrode terminal 25b. Further, the first ground terminal b1 of the first transformer circuit and the one side electrode terminal 25a of the second lamp L2 are electrically connected, and a ground potential is applied to the one side electrode terminal 25a of the second lamp L2. As a result, an AC voltage is applied to the second lamp L2, and the second lamp L2 emits light.

  Thereafter, each time the operation start switch of the ON / OFF switch unit 12 is operated and an operation start command is given to the control unit 11, each lamp L of the lamp group 25 and a transformer circuit that applies an AC voltage to the lamp L At least one of a combination and a combination of electrical connection between the one-side and other-side electrode terminals 25a and 25b of each lamp L of the lamp group 25 and the output terminal a and the ground terminal b of each transformer circuit of the inverter circuit 20 One of them is switched by the selector switch S.

  More specifically, after an operation start command is given to the control unit 11, a series of operations in which an operation end command is given to the control unit 11 occurs twice in succession, and then the operation start command is sent to the control unit 11. Whenever given, the first output terminal a1 of the first transformer circuit is alternately connected to the one-side electrode terminal 25a of the first lamp L1 and the one-side electrode terminal 25a of the second lamp L2. Therefore, after the series of operations has occurred twice in succession, each time an operation start command is given to the control unit 11, the first lamp L1 and the second lamp L2 are supplied from the first output terminal a1 of the first transformer circuit. An alternating voltage is alternately applied, and the first lamp L1 and the second lamp L2 are alternately lit.

  In addition, after the series of operations has occurred twice in succession, each time an operation start command is given to the control unit 11, the second output terminal a2 of the second transformer circuit is connected to the one-side electrode terminal 25a of the second lamp L2 and The first lamp L1 is alternately connected to one side electrode terminal 25a. Therefore, after the series of operations has occurred twice in succession, each time an operation start command is given to the control unit 11, the second output terminal a2 of the second transformer circuit supplies the second lamp L2 and the first lamp L1. An alternating voltage is alternately applied, and the second lamp L2 and the first lamp L1 are alternately lit.

  Each time an operation start command is given to the control unit 11, one side and the other side electrode terminals 25a, 25b of the first lamp L1 with respect to the first output terminal a1 and the first ground terminal b1 of the first transformer circuit, Alternatively, one side and the other side electrode terminals 25a and 25b of the second lamp L2 are alternately connected.

  Each time an operation start command is given to the control unit 11, one side and the other side electrode terminals 25a, 25b of the second lamp L2 with respect to the second output terminal a2 and the second ground terminal b2 of the second transformer circuit, Alternatively, the one side and the other side electrode terminals 25a and 25b of the first lamp L1 are alternately connected.

  FIG. 12 is a flowchart showing a processing procedure of the control unit 11 regarding other switching control of the combination of the connection between the transformer circuit and each lamp L of the lamp group 25. The control unit 11 can perform another switching control different from the switching control shown in FIG. 4 by executing a control program stored therein. In the flowchart shown in FIG. 12, when the image display is electrically connected, this process starts and the process proceeds to step b1.

  In step b1, the control unit 11 determines whether or not an operation start command is given from the ON / OFF switch unit 12. When the operation start command is given, the process proceeds to step b2 where the operation start command is given. If not, wait until an operation start command is given.

  In step b2, the connection state between the lamp L of the backlight unit 24 and the transformer circuit provided in the inverter circuit 20 previously switched by the switching unit 22, the one side and the other side electrode terminals 25a and 25b of the lamp L The electrical connection state between the output terminal a and the ground terminal b of the transformer circuit and the switching state identification information stored in the variable R are read from the switching state storage unit 23, and the process proceeds to step b3. In step b2, the switching unit 22 previously uses the combination of the lamp L and the transformer circuit and the electrical connection between the one side and the other side electrode terminals 25a and 25b of the lamp L and the output terminal a and the ground terminal b of the transformer circuit. If the combination of various connections has not been switched, information on the state of the combination in a predetermined initial state is read, and the process proceeds to step b3. The initial value of the switching state identification information is that each digit value represented by a binary number is “0”, that is, “00”.

  In step b3, the control unit 11 newly adds a value obtained by adding 1 to the value of the switching state identification information read in step b2 and stored in the variable R to the variable R. When the value obtained by adding the variables R and 1 is newly entered in the variable R, the process proceeds to step b4.

  The value of the switching state identification information changes to “01”, “10”, and “11” every time 1 is sequentially added to the initial value “00”. In the present embodiment, when the value of the switching state identification information is “11” and “1” is newly added, “00” is set. Accordingly, the value of the switching state identification information repeats “00”, “01”, “10”, and “11”.

  When the value of the first digit of the switching state identification information changes from “0” to “1”, or from “1” to “0”, the connection state of each of the switch units Q1 to Q4 of the switch P is switched. . Specifically, when the value of the first digit changes from “0” to “1”, the connection state between the common contact c and the first individual contact d of each of the switch portions Q1 to Q4 of the changeover switch P. Is switched to the connection state of the common contact c and the second individual contact e of each switch unit Q1 to Q4, and when the value of the first digit changes from “1” to “0”, The connection state between the common contact c of the switch parts Q1 to Q4 and the second individual contact e is switched to the connection state between the common contact c and the first individual contact d of each switch part Q1 to Q4.

  Further, when the value of the second digit of the switching state identification information changes from “0” to “1” or “1” to “0”, the connection state of each of the switch portions N1 to N4 of the changeover switch M is switched. Do. Specifically, when the value of the second digit changes from “0” to “1”, the connection state between the common contact c and the first individual contact d of each of the switch portions N1 to N4 of the changeover switch M. Is switched to the connection state between the common contact c and the second individual contact e of each of the switch sections N1 to N4, and when the value of the second digit changes from “1” to “0”, The connection state between the common contact c of the switch parts N1 to N4 and the second individual contact e is switched to the connection state between the common contact c and the first individual contact d of each switch part N1 to N4.

  When the value of each digit of the switching state identification information does not change such as “0” to “0” and “1” to “1”, the switch units N1 to N4 of the changeover switches M and P4. The connection state of Q1 to Q4 is maintained, and switching is not performed.

  In step b4, the control unit 11 provides the switching drive unit 21 with a signal indicating that a predetermined switching timing has been reached and switching state identification information. Based on the signal and the switching state identification information given from the control unit 11, the switching drive unit 21 connects the lamp L and the transformer circuit, and one side and the other side electrode terminals 25a and 25b of the lamp L. A switching command for switching at least one of the electrical connection states between the output terminal a and the ground terminal b of the transformer circuit is given to the switching unit 22. The switching unit 22 switches at least one of the connection states described above according to a switching command given from the switching drive unit 21. When the connection state is switched by the switching unit 22, the process proceeds to step b5.

  In step b5, each transformer circuit of the inverter circuit 20 turns on the lamp L by applying an AC voltage between the electrodes of the lamp L newly connected by switching the connection state described above in step b4. When the lamp L is turned on in step b5, the process proceeds to step b6.

  In step b6, the control unit 11 determines whether or not an operation end command is given from the ON / OFF switch unit 12. When the operation end command is given, the control unit 11 ends the switching control and follows a predetermined end procedure. The image display is terminated and the process proceeds to step b7. If the operation end command is not given in step b6, the lamp L is turned on while maintaining the above-described connection state switched by the switching unit 22 in step b4 until the operation end command is given.

  In step b7, the control unit 11 stores the switching state identification information put in the variable R in step b3 in the switching state storage unit 23 as the current switching state identification information, and the switching unit 22 switches in step b4. The above-described connection state is stored in the switching state storage unit 23 as the current connection state, and all processing procedures related to switching control are completed.

  As described above, according to the fourth embodiment, each transformer circuit has an output terminal a that outputs an AC voltage signal and a ground terminal b to which a ground potential is applied. Of the two electrode terminals 25a and 25b of each lamp L, one electrode terminal is electrically connected to an output terminal a of one transformer circuit selected from a plurality of transformer circuits, and an AC voltage signal is applied. The other electrode terminal is electrically connected to the ground terminal b of the transformer circuit and given with a ground potential. Based on an AC voltage signal applied from the output terminal a of the transformer circuit, an AC voltage is applied between the two electrode terminals 25a and 25b of each lamp L, and the lamp L emits light. Light emitted from each of the emitted lamps L enters the liquid crystal display panel 27. Thus, the light emitted from each lamp L is incident on the liquid crystal display panel 27, so that the viewer viewing the display image displayed on the liquid crystal display panel 27 can view the display image.

  In the present embodiment, among combinations of lamps L and transformer circuits, and combinations of electrical connections between the two electrode terminals 25a and 25b of each lamp L and output terminals a and ground terminals b of the transformer circuits. Each time at least one of them reaches a predetermined switching timing, the first and second switching units 31 and 32 are switched.

  For example, when the combination of each lamp L and the transformer circuit is switched, before the switching operation by the first and second switching units 31 and 32, the output is output to the two electrode terminals 25a and 25b of one lamp among the plurality of lamps L. The one transformer circuit to which the terminal a and the ground terminal b are connected has two electrode terminals 25a and 25b of another lamp different from the one lamp after the switching operation by the first and second switching units 31 and 32. Are connected to the output terminal a and the ground terminal b. The two electrode terminals 25a and 25b of one lamp are connected to an output terminal a and a ground terminal b of another transformer circuit different from the one transformer circuit. As described above, since the output terminal a and the ground terminal b of the plurality of transformer circuits are sequentially connected to the two electrode terminals 25a and 25b of one lamp, variations in circuit performance due to manufacturing variations occur in the transformer circuit. Even in some cases, the influence of this variation can be distributed to each lamp L, so that the variation in the life of the lamp L can be suppressed.

  When the combination of electrical connection between the two electrode terminals 25a and 25b of each lamp L and the output terminal a and ground terminal b of the transformer circuit is switched, the switching operation by the first and second switching units 31 and 32 is performed. Thus, the output terminal a and the ground terminal b of the transformer circuit are alternately connected to the electrode terminals 25a and 25b of the lamp L. As a result, even if an electrical bias occurs in the AC voltage signal output from the output terminal a of the transformer circuit, it is possible to suppress the electrical bias from occurring inside the lamp L as much as possible. It is possible to prevent the life of the lamp L from being shortened due to electrical bias.

  As described above, at least one of the combination of each lamp L and the transformer circuit, and the combination of electrical connection between the two electrode terminals 25a and 25b of each lamp L and the output terminal a and the ground terminal b of the transformer circuit. By switching one of them, the variation in the life of the lamp L can be suppressed, so that the luminance in the liquid crystal display panel 27 can be prevented from undesirably decreasing, and the display quality can be prevented from decreasing.

  Each transformer circuit of the present embodiment has a configuration having an output terminal a that outputs an AC voltage signal and a ground terminal b to which a ground potential is applied, but is not limited to such a configuration. A transformer circuit according to another embodiment of the present invention includes a first output terminal that outputs an AC voltage signal and a second output terminal that outputs an AC voltage signal having a phase opposite to that of the AC voltage signal output from the first output terminal. The structure which has these may be sufficient. When configured in this way, the following effects are obtained.

  Of the two electrode terminals 25a and 25b of each lamp L, one electrode terminal is electrically connected to a first output terminal of one transformer circuit selected from a plurality of transformer circuits, and an AC voltage signal is applied. The second output terminal is electrically connected to the other electrode terminal, and an AC voltage signal having a phase opposite to that of the AC voltage signal output from the first output terminal is applied. Based on the AC voltage signals given from the first and second output terminals of the transformer circuit, an AC voltage is applied between the two electrode terminals 25a and 25b of each lamp L, and the lamp L emits light. Light emitted from each of the emitted lamps L enters the liquid crystal display panel 27. Thus, the light emitted from each lamp L is incident on the liquid crystal display panel 27, so that the viewer viewing the display image displayed on the liquid crystal display panel 27 can view the display image.

  In the present embodiment, a combination of each lamp L and a transformer circuit, and a combination of electrical connection between the two electrode terminals 25a and 25b of each lamp L and the first output terminal and the second output terminal. At least one of them is switched by the first and second switching units 31 and 32 every time a predetermined switching timing is reached.

  For example, when the combination of each lamp L and the transformer circuit is switched, before the switching operation by the first and second switching units 31 and 32, the second electrode terminals 25a and 25b of one lamp among the plurality of lamps L The one transformer circuit to which the first and second output terminals are connected has two electrode terminals 25a and 25b of other lamps different from the one lamp after the switching operation by the first and second switching units 31 and 32. Are connected to the first and second output terminals. Also, the first and second output terminals of another transformer circuit different from the one transformer circuit are connected to the two electrode terminals 25a and 25b of the one lamp.

  Thus, since the first and second output terminals of the plurality of transformer circuits are sequentially connected to the two electrode terminals 25a and 25b of one lamp, variations in circuit performance due to manufacturing variations occur in the transformer circuit. Even in some cases, the influence of this variation can be distributed to each lamp L, so that the variation in the life of the lamp L can be suppressed.

  When the combination of electrical connection between the two electrode terminals 25a and 25b of each lamp L and the first and second output terminals of the transformer circuit is switched, the switching operation by the first and second switching units 31 and 32 is performed. Thus, the first and second output terminals of the transformer circuit are alternately connected to the electrode terminals 25a and 25b of the lamp L. As a result, even if an electrical bias occurs in the AC voltage signals output from the first and second output terminals of the transformer circuit, it is possible to suppress the electrical bias in the lamp L as much as possible. Therefore, it is possible to prevent the life of the lamp L from being shortened due to electrical bias.

  As described above, at least one of the combination of each lamp L and the transformer circuit and the combination of electrical connection between the two electrode terminals 25a and 25b of each lamp L and the first and second output terminals of the transformer circuit. By switching one of them, the variation in the life of the lamp L can be suppressed, so that the luminance in the liquid crystal display panel 27 can be prevented from undesirably decreasing, and the display quality can be prevented from decreasing.

  Further, according to the present embodiment, every time the power supply unit 13 changes from a state where the supply of power to the transformer circuit of the inverter circuit 20 is stopped to a state where power is supplied from the power supply unit 13 to the transformer circuit. On the other hand, it is determined by the first and second switching units 31 and 32 that the switching timing has been reached, and the electrical connection between the two electrode terminals 25a and 25b of the lamp L and the output terminal a and the ground terminal b of the transformer circuit. Or a combination of electrical connections between the two electrode terminals 25a and 25b of the lamp L and the first and second output terminals of the transformer circuit, or any one of these combinations The combination of the lamp L and the transformer circuit is switched.

  As described above, when the above-described combination is switched according to the change in the power supply state to the transformer circuit, the change from the power supply stop state to the power supply state occurs at regular intervals. The above-mentioned combination can be switched at regular intervals. As a result, for example, the influence of the electrical bias of the output terminal of the transformer circuit on each of the electrode terminals 25a and 25b of the lamp L can be averaged. Can be suppressed. Further, for example, the influence of variations in circuit performance of the transformer circuit on each lamp L can be averaged. Therefore, it is possible to remarkably suppress the variation in the life of the lamp L.

  In the present embodiment, as shown in step b1 of the flowchart of FIG. 12 described above, the control unit 11 is given an operation start command from the ON / OFF switch unit 12, and the power supply unit 13 transfers to the transformer circuit of the inverter circuit 20. The switching timing has been reached by the first and second switching units 31 and 32 each time the power supply unit 13 changes from the state where the power supply is stopped to the state where power is supplied from the power supply unit 13 to the transformer circuit. However, the switching timing is not limited to such timing.

  For example, the first and second switching units 31 and 32 may determine that the switching timing has been reached each time a predetermined time is reached, or the first and second times each time a predetermined time elapses. It may be determined by the switching units 31 and 32 that the switching timing has been reached, or the first and second switching units 31 and 32 perform switching based on the update of the display image displayed on the liquid crystal display panel 27. It may be determined that the timing has been reached.

  When the first and second switching units 31 and 32 are configured to determine that the switching timing has been reached each time the predetermined time is reached, in step b1 in FIG. It may be determined whether or not a predetermined time has come. According to a predetermined time, a combination of electrical connection between the two electrode terminals 25a and 25b of the lamp L and the output terminal a and the ground terminal b of the transformer circuit, or the two electrode terminals 25a and 25b of the lamp L By switching the combination of electrical connection with the first and second output terminals of the transformer circuit, or any one of these combinations, and the combination of the lamp L and the transformer circuit, every fixed period Since the combinations described above can be switched to each other, when the lamp L emits light continuously, the light emission time of the lamp L in each combination can be averaged. As a result, it is possible to prevent the lamp L having an extremely long light emission time from occurring for each combination, and to average the influence of variations in circuit performance of the transformer circuit on each lamp L, for example. As a result, it is possible to remarkably suppress variations in the life of the lamp L.

  When the first and second switching units 31 and 32 are configured to determine that the switching timing has been reached each time a predetermined time elapses, in step b1 in FIG. It may be determined whether or not a predetermined time has elapsed. Depending on the predetermined time, a combination of electrical connection between the two electrode terminals 25a and 25b of the lamp L and the output terminal a and the ground terminal b of the transformer circuit, or the two electrode terminals 25a and 25b of the lamp L By switching the combination of electrical connection with the first and second output terminals of the transformer circuit, or one of these combinations, and the combination of the lamp L and the transformer circuit, the lamp L When light is emitted continuously, the light emission times of the lamps L in each combination can be averaged. As a result, it is possible to prevent the lamp L having an extremely long light emission time from occurring for each combination, and to average the influence of variations in circuit performance of the transformer circuit on each lamp L, for example. As a result, it is possible to remarkably suppress variations in the life of the lamp L.

  When the first and second switching units 31 and 32 are configured to determine that the switching timing has been reached based on the update of the display image displayed on the liquid crystal display panel 27, the steps in FIG. In b1, the control part 11 should just judge whether the display image displayed on the liquid crystal display panel 27 was updated. For example, when the display image is updated, or when a predetermined update count display image is updated, the aforementioned combination is switched. Accordingly, the possibility that the viewer recognizes the switching of the combination can be reduced as compared with the case where the combination is switched when one display image is displayed. Accordingly, it is possible to prevent the combination switching operation from being mistaken as a failure of the liquid crystal display device 10.

  Each of the above-described embodiments is merely an example of the present invention, and the configuration can be changed within the scope of the invention. For example, in each of the above-described embodiments, the liquid crystal display device 10 including the backlight unit 24 including the lamp L formed in the shape of a long bar has been described. It may be formed in a U shape. Even when the lamp L is formed in an I-shape or a U-shape, the same effects as those of the above-described embodiments can be obtained.

  In each of the above-described embodiments, the liquid crystal display device 10 using a fluorescent tube as a light source has been described. However, a light emitting diode (abbreviation: LED) may be used as the light source.

It is a block diagram which shows the electric constitution of the liquid crystal display device 10 which is one Embodiment of this invention. It is a block diagram which shows the electrical structure of the inverter circuit 20, the switching part 22, and the lamp group 25 of the 1st Embodiment of this invention. 4 is a timing chart showing switching of a combination of electrical connections between the inverter circuit 20 and each lamp of the lamp group 25. 7 is a flowchart showing a processing procedure of the control unit 11 relating to switching control of a combination of connections between the transformer circuit and each lamp L of the lamp group 25. It is a block diagram which shows the electrical structure of the inverter circuit 20, the switch part 22, and the lamp group 25 of the 2nd Embodiment of this invention. It is a figure for demonstrating switching of the combination of the eight lamps L and the inverter circuit 20. FIG. 6 is a timing chart showing switching of a combination of electrical connections between the inverter circuit 20 of FIG. 5 and each lamp L of the lamp group 25. FIG. It is a block diagram which shows the electrical structure of the inverter circuit 20, the switching part 22, and the lamp group 25 of the 3rd Embodiment of this invention. FIG. 9 is a timing chart showing switching of a combination of electrical connections between the inverter circuit 20 of FIG. 8 and each lamp L of the lamp group 25. FIG. It is a block diagram which shows the electrical structure of the inverter circuit 20, the 1st switching part 31, the 2nd switching part 32, and the lamp group 25 of the 4th Embodiment of this invention. 11 is a timing chart showing switching of a combination of electrical connections between the inverter circuit 20 of FIG. 10 and each lamp L of the lamp group 25. 10 is a flowchart showing a processing procedure of the control unit 11 regarding other switching control of a combination of connection between the transformer circuit and each lamp L of the lamp group 25.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 11 Control part 12 ON / OFF switch part 13 Power supply part 14 ON / OFF schedule memory | storage part 15 Communication part 16 Display information memory | storage part 17 Time measuring part 20 Inverter circuit 21 Switching drive part 22 Switching part 23 Switching state memory | storage part 24 backlight unit 25 lamp group 26 display drive unit 27 liquid crystal display unit 31 first switching unit 32 second switching unit

Claims (8)

A plurality of light sources that emit light by applying a driving voltage;
A liquid crystal display panel on which light emitted from each light source is incident;
A plurality of drive circuits for applying a drive voltage to each light source;
A liquid crystal display device comprising switching means for switching a combination of each light source and a driving circuit for applying a driving voltage to the light source each time a predetermined switching timing is reached.   2. The liquid crystal display device according to claim 1, wherein each drive circuit is configured to be connectable to all light sources.   Each time the switching means changes from a state where power supply from the power supply means for supplying power to the drive circuit is stopped to a state where power is supplied from the power supply means to the drive circuit, 3. The liquid crystal display device according to claim 1, wherein it is determined that the switching timing has been reached.   3. The liquid crystal display device according to claim 1, wherein the switching unit determines that the switching timing has been reached each time a predetermined time is reached.   3. The liquid crystal display device according to claim 1, wherein the switching unit determines that the switching timing has been reached each time a predetermined time elapses.   3. The liquid crystal display device according to claim 1, wherein the switching unit determines that the switching timing has been reached based on an update of a display image displayed on the liquid crystal display panel.   4. The drive circuit starts to apply a drive voltage to the light source after a combination of a light source and a drive circuit that applies a drive voltage to the light source is switched by the switching unit. The liquid crystal display device described.   The driving circuit stops applying the driving voltage to the light source before the switching unit switches the combination of the light source and the driving circuit that applies the driving voltage to the light source. The liquid crystal display device according to claim 4, wherein the driving voltage is applied to the light source after the combination with the driving circuit that applies the driving voltage to the light source is switched.

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