JP2009104950A - Inverter, backlight device, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter which drives a lamp so as to eliminate fixed luminance unevenness due to position relations of a plurality of lamps. <P>SOLUTION: The PWM signal output by a PWM control circuit 130 in the inverter is distributed into two by a pulse distribution circuit 1431 for every unit control period, and the pulse drive signal is generated by two drive signal generating circuits 1432 according to the distributed PWM signals. The voltage boosted by a first transformer 141 is given to one end of a lamp 11, and the voltage boosted by a second transformer 142 is given to the other end of the lamp 11. By this structure, the higher voltage side and the lower voltage side of the voltage given to the both ends of the lamp are switched over alternately, and thereby, the luminance of the lamp is averaged in time, and fixed luminance unevenness due to the arrangement position relations of the plurality of lamps can be eliminated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inverter that drives a plurality of lamps, a backlight device including these, and a display device including the same.

  2. Description of the Related Art Conventionally, liquid crystal display devices have been provided with a device called a backlight (hereinafter referred to as a “backlight device”) that uses a cold cathode fluorescent lamp (CCFL) or the like as a light source. There are two types of backlight devices, one called a “directly type” in which a plurality of light sources are arranged side by side on the back surface of a display unit, and the other called an “edge light method” in which a light source is arranged at one end of a display unit. The direct-type backlight device can easily increase the luminance, but since a plurality of light sources are used, uneven luminance tends to occur. On the other hand, an edge light type backlight device can be easily reduced in thickness, but it is difficult to increase brightness.

  By the way, some direct-type backlight devices employ a pseudo-U-shaped lamp in which two straight-tube lamps connected in series are arranged in a U-shape. FIG. 7 is a block diagram showing the arrangement of lamps in a conventional backlight device employing a pseudo U-shaped lamp. This backlight device is composed of k (k is an arbitrary natural number) pseudo-U-shaped lamps 91a to 91k, and an inverter board 92 on which circuits for driving these lamps are formed. Yes.

  Among these lamps, one pseudo-U-shaped lamp 91a is composed of two straight tube lamps and a conductive wire connecting them. The inverter board 12 includes lamp driving circuits 940a to 940k for driving the pseudo U-shaped lamps a to 91k, respectively, and a control circuit (not shown) for controlling these lamp driving circuits. Among these lamp driving circuits, one lamp driving circuit 940a includes a transformer and a switch circuit (not shown) for applying an AC voltage to one end of the corresponding straight tube lamp.

  In such a backlight device, an AC voltage is generated on the secondary side of the transformer when the switch circuit performs a switching operation in accordance with control by the control circuit, and thereby the lamp emits light. At this time, the current flowing through the secondary side of the transformer is rectified and smoothed by a current detection circuit (not shown). Then, based on the smoothed current value, the control circuit feedback-controls the operation of the switch circuit.

  Here, the pseudo-U-shaped lamps 91a to 91k shown in FIG. 7 are partially colored (by gradation) for the convenience of explanation, and the darker the colored portion is, the lower the luminance is. Is shown. For example, the two straight tube lamps included in the pseudo U-shaped lamp 91a are shown to be whiter, that is, have a higher luminance as they are closer to the lamp driving circuit 940a. This is because a high voltage is applied from the lamp driving circuit 940a to one end of each of the two straight tube lamps by a transformer. Therefore, the closer to the other end, the lower the luminance.

  In this way, the lamp tube has a high luminance on the side to which a high voltage is applied (hereinafter referred to as “high voltage side”) and has a low luminance on the side far from the high voltage side (hereinafter referred to as “low pressure side”). If all the high-voltage sides of the lamps 91a to 91k are arranged on the same side, luminance unevenness (brightness unevenness) occurs. Therefore, as shown in FIG. 7, when the lamp driving circuits 940a to 940k are arranged and connected so that the high voltage sides of the pseudo U-shaped lamps 91a to 91k are alternately arranged, the luminance unevenness is eliminated or suppressed.

Such luminance unevenness occurs not only in the backlight device adopting the conventional direct method but also in the backlight device adopting the edge light method. Therefore, there is known a conventional backlight device in which pseudo U-shaped lamps are arranged on opposite side surfaces and arranged so that their high-pressure sides do not face each other (in a staggered manner) (see Patent Document 1).
JP-A-2002-231034

  However, as shown in FIG. 7, when dimming is performed so that the luminance of the backlight device is lowered, there is a problem that luminance unevenness occurs even if the lamps are alternately arranged as described above. In general, the brightness of the backlight device is appropriately changed according to the control for dimming from the outside of the device, but when dimming so that the brightness of the backlight device is lowered, While the luminance itself hardly changes, the low-luminance portion on the low-pressure side becomes wider. For this reason, if a fixed low-luminance portion is generated at the central portion, uneven luminance cannot be eliminated even if the lamps are alternately arranged.

  Therefore, an object of the present invention is to provide an inverter, a backlight device, and a display device that drive a lamp so as to eliminate fixed luminance unevenness due to the arrangement relationship of a plurality of lamps.

1st invention is an inverter which light-emits a lamp | ramp by applying an alternating voltage, Comprising:
First voltage generating means for generating a first AC signal whose effective value of voltage changes, and applying the first AC signal to one end of a lamp composed of one or more discharge tubes;
A second voltage generating means for generating a second AC signal whose effective voltage value is different from the first AC signal and applying the second AC signal to the other end of the lamp;
A first effective value which is a voltage effective value of the first AC signal is equal to or greater than a second effective value which is a voltage effective value of the second AC signal; and the first effective value is the first effective value. Switching control means for controlling the first and second voltage generating means so that the case where the value is less than the effective value of 2 is alternately and periodically switched.

According to a second invention, in the first invention,
The switching control means includes a case where the first effective value is equal to or greater than a reference voltage value near ground potential and the second effective value is the reference voltage value, and the first effective value is the reference voltage value. Control is performed so that the voltage value and the second effective value are larger than the reference voltage value alternately and periodically.

According to a third invention, in the first invention,
The switching control means includes
Voltage control means for generating a pulse width modulation signal for controlling the lamp to emit light at a predetermined brightness;
The first and second voltage generation means include distribution means for alternately distributing the pulse width modulation signal every predetermined period.

According to a fourth invention, in the third invention,
The distribution means distributes alternately every control unit period of the pulse width modulation signal or every integer multiple of the control unit period.

A fifth invention is a backlight device for irradiating light to a display unit of a display device,
The lamp;
It is provided with the inverter as described in any one invention from 1st to 4th.

According to a sixth invention, in the fifth invention,
A plurality of the lamps are provided, and each of the lamps is arranged on a predetermined plane to irradiate light from the back side of the display unit, and both ends thereof are arranged along the same side
The first and second voltage generating means provided in the inverter are arranged along the side.

A seventh invention is the sixth invention, wherein
Each of the plurality of lamps is a pseudo U-shaped lamp in which two cold cathode tubes are connected to each other by a conductive wire and arranged in a U shape.

The eighth invention is a display device having a display unit and illumination means for irradiating the display unit with light,
The backlight device according to any one of the fifth to seventh aspects is provided as the illumination unit.

  According to the first aspect, the switching control means alternately alternates between the case where the first effective value is greater than or equal to the second effective value and the case where the first effective value is less than the second effective value. The first and second voltage generating means are controlled so as to be switched periodically. As a result, the high-voltage side and the low-voltage side of the voltage applied to both ends of the lamp are alternately switched to average the luminance of the lamp in time, and fixed luminance unevenness due to the arrangement relationship of the plurality of lamps. Can be eliminated.

  According to the second aspect, at least one of the first effective value and the second effective value is set to the reference voltage value near the ground potential by the switching control means, so that power consumption can be reduced. .

  According to the third aspect of the invention, the pulse width modulation signal is generated by the voltage control means, and the pulse width modulation signal is alternately distributed every predetermined period by the distribution means, so that these are realized by a relatively simple digital circuit. Manufacturing cost can be reduced.

  According to the fourth aspect of the invention, since the pulse width modulation signal is alternately distributed every control unit period or every integer multiple of the control unit period, these can be realized by a relatively simple digital circuit, and manufactured. Cost can be reduced and desired luminance can be continuously displayed.

  According to the fifth aspect, the effect of the inverter according to any one of the first to fourth aspects can be exhibited in the backlight device.

  According to the sixth invention, both ends of the lamp are arranged along the same side, and the first and second voltage generating means provided in the inverter are arranged along the side. For example, the board on which the inverter is mounted However, it is possible to reduce the manufacturing cost of the apparatus because the configuration can be simplified such that only one lamp is required on one side of the lamp.

  According to the seventh aspect of the present invention, for example, by adopting a pseudo U-shaped lamp using two inexpensive straight-tube cold cathode tubes, the manufacturing cost of the apparatus can be reduced, and there is no gap. Since a plurality of lamps can be arranged (or with a small gap), the luminance per unit area can be increased.

  According to the eighth aspect, the effect of the backlight device according to any one of the fifth to seventh aspects can be exhibited in the display device.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

<1. Overall Configuration and Operation of Liquid Crystal Display Device>
FIG. 1 is a block diagram showing an overall configuration of a liquid crystal display device including a backlight device having an inverter according to an embodiment of the present invention. The liquid crystal display device includes a backlight device 100, a display control circuit 200, a source driver (video signal line driving circuit) 300, a gate driver (scanning signal line driving circuit) 400, and a display unit 500.

  The display unit 500 includes a plurality (n) of source bus lines (video signal lines) SL1 to SLn, a plurality (m) of gate bus lines (scanning signal lines) GL1 to GLm, and a plurality of these. A plurality (n × m) of pixel forming portions (not shown) provided corresponding to the intersections of the source bus lines SL1 to SLn and the plurality of gate bus lines GL1 to GLm are included. Each pixel formation portion includes a TFT as a switching element, a pixel electrode connected to the drain terminal of the TFT, a common electrode and auxiliary capacitance electrode provided in common to the plurality of pixel formation portions, and a pixel A liquid crystal capacitor formed by the electrode and the common electrode and an auxiliary capacitor formed by the pixel electrode and the auxiliary capacitor electrode are included. A pixel capacitor is formed by the liquid crystal capacitor and the auxiliary capacitor.

  The display control circuit 200 receives image data DAT sent from the outside, and receives a digital video signal DV, a source start pulse signal SSP for controlling image display on the display unit 500, a source clock signal SCK, a latch strobe signal LS, a gate A start pulse signal GSP, a gate clock signal GCK, and a backlight control signal BS for controlling the operation of the backlight device 100 are output.

  The source driver 300 receives the digital video signal DV, the source start pulse signal SSP, the source clock signal SCK, and the latch strobe signal LS output from the display control circuit 200, and supplies driving video signals to the source bus lines SL1 to SLn. Apply. Based on the gate start pulse signal GSP and the gate clock signal GCK output from the display control circuit 200, the gate driver 400 applies an active scanning signal to each of the gate bus lines GL1 to GLm in one vertical scanning period. Repeat as. The backlight device 100 irradiates light from the back surface of the display unit 500 based on the backlight control signal BS output from the display control circuit 200.

  As described above, the driving video signals are applied to the source bus lines SL1 to SLn, the scanning signals are applied to the gate bus lines GL1 to GLm, and the display unit 500 is irradiated with the light, thereby the display unit. An image is displayed at 500.

<2. Configuration and operation of backlight device>
FIG. 2 is a block diagram illustrating a configuration of the backlight device 100 according to the present embodiment. The backlight device 100 includes k (U is an arbitrary natural number) pseudo U-shaped lamps 11a to 11k and an inverter board 12 on which circuits for driving the lamps 11a to 11k are formed. The The inverter board 12 includes a pulse width modulation (hereinafter abbreviated as “PWM”) control circuit 130, and k lamp driving circuits 140a to 140k for driving the k lamps 11a to 11k, respectively. It is included.

  The PWM controller circuit 130 controls the operations of the k lamp driving circuits 140a to 140k. The lamp driving circuits 140a to 140k drive the lamps 11a to 11k based on the control by the PWM control circuit 130. The lamp driving circuits 140a to 140k also rectify (further smoothen) the current flowing to the high voltage side of the lamps 11a to 11k and feed back the current to the PWM control unit circuit 130. The lamps 11a to 11k emit light based on application of AC voltage by the lamp driving circuits 140a to 140k.

  FIG. 3 is a block diagram showing a detailed configuration of the pseudo U-shaped lamp and the lamp driving circuit. The pseudo U-shaped lamp 11, which is an arbitrary one of the pseudo U-shaped lamps 11 a to 11 k, includes a first lamp 111 and a second lamp 112 that are cold-cathode tubes, It is comprised by the conducting wire 113 which connects 112 mutually. In place of the pseudo U-shaped lamp, a U-shaped lamp in which one cold cathode tube is formed in a U shape may be used. However, since the pseudo U-shaped lamp can be composed of two straight tube type cold cathode tubes, the manufacturing cost of the apparatus can be reduced, and a plurality of lamps without gaps (or with less gaps) can be provided. Since it can arrange | position, it is suitable at the point which can raise the brightness | luminance per unit area.

  The lamp driving circuit 140, which is any one of the lamp driving circuits 140a to 140k, includes first and second transformers 141 and 142 for applying an AC voltage to the first and second lamps 111 and 112, respectively. And a switch circuit 143 that supplies a voltage to the primary side of the first and second transformers 141 and 142, and a current that flows to the secondary side of the first and second transformers 141 and 142 is half-wave rectified, respectively. First and second current detection circuits 144 and 145 are provided.

  In the configuration as described above, the first and second transformers 141 and 142 receive the low-voltage AC voltage signal supplied from the switch circuit 143 on the primary side, and thereby the first and second lamps on the secondary side. The voltage is boosted to an AC signal having a high voltage to be applied to 111 and 112.

  The switch circuit 143 includes an oscillation circuit that generates a high frequency of about 10 to 100 KHz. The PWM signal supplied from the PWM control circuit 130 is alternately allocated for each control unit period, and the high frequency is output during the ON period of the allocated PWM signal. And the burst signal not including the high frequency is generated in the off period. In the following, this burst signal is also referred to as a “pulse drive signal”, and its ON period is also referred to as a “pulse”. The frequency of the PWM signal is about several hundred Hz.

  The PWM control circuit 130 receives a voltage signal corresponding to the effective value of the input current from the first and second current detection circuits 144 and 145, and instructs the effective value of the input current not shown (determined display luminance) from the CPU. The feedback control is performed to adjust the voltage to be applied to the first and second lamps 111 and 112 so as to be equal to the calculated value. In other words, the switching operation of the switch circuit 143 generates an AC voltage on the secondary side of the first and second transformers 141 and 142. As a result, an AC voltage is applied to the first and second lamps 111 and 112, and the lamps 111 and 112 emit light. At this time, the currents flowing on the secondary sides of the first and second transformers 141 and 142 are half-wave rectified and smoothed by the first and second current detection circuits 144 and 145, respectively. The smoothed current is applied to the PWM control circuit 130, and the feedback control is performed. Such control is well known, and the PWM control circuit 130 can be configured by a relatively simple digital circuit, so that the manufacturing cost can be reduced. Next, the configuration and operation of the switch circuit 143 will be described with reference to FIG.

<3. Configuration and operation of switch circuit>
FIG. 4 is a block diagram for explaining the configuration and operation of the switch circuit 143. As shown in FIG. 4, the PWM control circuit 130 is configured so that the on-duty ratio of the PWM signal (specifically, the on-period and A duty ratio that is a ratio of an on period included in a unit control period including an off period is determined, and a PWM signal having the duty ratio is supplied to the switch circuit 143. In the figure, the unit control period is indicated by an arrow, and the PWM signal in the PWM control circuit 130 shown above has an equal length between the ON period and the OFF period included in the unit control period. It can be seen that the duty ratio is set to 50%. Although the PWM signal is shown only for two unit control periods here, the same waveform is repeatedly output as long as there is no change in the state.

  The switch circuit 143 includes a pulse distribution circuit 1431 and two drive signal generation circuits 1432, and the PWM signal is supplied to the pulse distribution circuit 1431. The pulse distribution circuit 1431 distributes the received PWM signal to the two drive signal generation circuits 1432 alternately for each unit control period. Specifically, the pulse distribution circuit 1431 distributes the signal included in the first unit control period of the received PWM signals to one of the two drive signal generation circuits 1432, and in the second unit control period. The contained signal is distributed to the other of the two drive signal generation circuits 1432 and this operation is repeated alternately. Note that such a distribution circuit 1431 can be easily configured by a known digital circuit.

  As can be seen from FIG. 4, the signals in the first unit control period among the PWM signals are distributed to the upper drive signal generation circuit 1432 in the figure, and the lower stage in the figure that was not assigned at that time. The PWM signal of the drive signal generation circuit 1432 is in the off period during the first unit control period. Also, the PWM signal during the next unit control period is distributed to the lower drive signal generation circuit 1432 in the figure, and the PWM signal of the upper drive signal generation circuit 1432 in the figure that is not assigned at that time is 2 It is an off period during the first unit control period. When the signals are not distributed in this manner, the two drive signal generation circuits 1432 do not receive the PWM signal that is in the ON period at the same time, and one of them receives the PWM signal that includes the ON period. Always receives a PWM signal including an off period.

  Accordingly, the first and second transformers 141 and 142 receive burst-like pulse drive signals including pulses corresponding to the ON period only from one of the two drive signal generation circuits 1432. When a high voltage is applied to one end of each of the first and second lamps 111 and 112 shown in FIG. 3 according to the on-period, the other end must always be a low voltage (typically grounded) according to the off-period. Potential or a value near the potential). As described above, when a high voltage is applied to one end of the first and second lamps 111 and 112, a low voltage is applied to the other end, and conversely, when a high voltage is applied to the other end. A low voltage is applied to one end, and the high voltage side and the low voltage side are alternately switched. Thereby, luminance unevenness of the backlight device is eliminated or suppressed.

  FIG. 5 is a diagram illustrating that luminance unevenness is suppressed in the present apparatus. In the pseudo U-shaped lamps 11a to 11k shown on the right side of FIG. 5 (right side of the arrow in the figure), as described with reference to FIG. ) It is colored, and the darker the colored part, the lower the luminance.

  In the right side of the arrow shown in FIG. 5, the display states (luminance distributions) of the pseudo U-shaped lamps 11a to 11k during the first unit control period of the PWM signal are shown. The display states (luminance distributions) of the pseudo U-shaped lamps 11a to 11k during the second unit control period of the PWM signal are simply shown.

  Of the two straight tube lamps included in the pseudo-U-shaped lamp 11a shown on the right side of the arrow in FIG. 5, the upper straight tube lamp is disposed near both ends of the lamp (left side in the figure). It is shown that the colored portion is white, that is, the luminance is higher as it is closer to the lamp driving circuit 140a, and the lower straight tube type lamp is black as a whole, that is, the luminance is low. This is because a high voltage is applied to one upper end of the two straight tube lamps from the lamp driving circuit 940a, and a low voltage is applied to the other lower end. Accordingly, the closer to the other end, the lower the luminance.

  Thereafter, in the second unit control period, the display state (luminance distribution) of the two straight tube lamps included in the pseudo U-shaped lamp 11a shown on the left side of the arrow in FIG. Contrary to the case shown on the left side of FIG. 4, the upper straight tube lamp has a lower overall luminance, and the lower straight tube lamp has a higher luminance as it is closer to the lamp driving circuit 140a. This is because a low voltage is applied to one upper end of the two straight tube lamps from the lamp driving circuit 940a, and a low voltage is applied to the other upper end.

  As described above, since the two display states shown in FIG. 5 are alternately switched every unit control period, fixed luminance unevenness that occurs when these display states are not interchanged is eliminated or suppressed. That is, the frequency of the PWM control signal is about several hundred Hz and is faster than the frequency at which the luminance difference can be perceived. Therefore, when the display state is switched as described above, flickering is not perceived, and the intermediate luminance is constant. It feels like it is displayed. Accordingly, the luminance unevenness occurring in the two straight tube lamps is displayed such that one of them cancels out the other and the intermediate luminance between them. Therefore, luminance unevenness is eliminated or suppressed.

<4. Effect>
As described above, according to this embodiment, the PWM signal output from the PWM control circuit 130 is divided into two by the pulse distribution circuit 1431 for each unit control period, and two drives are performed according to the distributed PWM signal. A pulse drive signal is generated by the signal generation circuit 1432 and a voltage boosted by a transformer is applied to both ends of the lamp. With this configuration, the high voltage side and the low voltage side of the voltage applied to both ends of the lamp are alternately switched, so that the lamp luminance is averaged over time, and fixed luminance unevenness due to the arrangement relationship of a plurality of lamps. Can be eliminated.

<5. Modification>
In the above embodiment, the k lamp driving circuits 140a to 140k are arranged to be collected on one inverter board 12 (that is, aligned on one side of the lamps 11a to 11k). The arrangement configuration shown in FIG.

  FIG. 6 is a block diagram showing an arrangement configuration of the pseudo U-shaped lamp and its driving circuit. As can be seen from FIG. 6, both end portions of the lamp are alternately arranged in the left-right direction of the drawing, and lamp driving circuits corresponding to the vicinity thereof are arranged so that voltage can be supplied to both end portions. Has been. Therefore, as shown in FIG. 6, even when the light emission luminance of the device is lowered, the portions where the lamp luminance is low (near the side far from the both ends to which the voltage is applied) are alternately arranged along the vertical direction of the drawing. Therefore, the luminance unevenness in the left-right direction in the figure is eliminated or reduced. However, in the arrangement configuration of the above-described embodiment, only one inverter board 12 is required on one side, so that the manufacturing cost of the device can be reduced.

  Further, in the above embodiment and the modification shown in FIG. 6, when a high voltage is applied to the upper end of the figure among the corresponding lamp ends by a certain lamp driving circuit, all other lamp driving circuits are also used. Similarly, the arrangement is such that a high voltage is applied to the upper end of the figure, but these may be arranged so as to be reversed in the lamp driving circuits adjacent in the vertical direction.

  Although the above embodiment is a backlight device that employs a direct method, luminance unevenness can also be eliminated by a similar configuration in a backlight device that employs an edge light method. For example, in the case where pseudo U-shaped lamps are respectively arranged on the side surfaces immediately below the opposing display units, it is necessary to arrange them so that their high-voltage sides do not face each other as in the conventional backlight device described above. Instead, the voltage applied to both ends of the lamp is alternately switched between the high voltage side and the low voltage side for each unit control period, whereby the luminance is averaged to eliminate or suppress the luminance unevenness.

  In the above embodiment, when a low voltage is applied to the first and second lamps 111 and 112, a high frequency of about 10 to 100 KHz supplied from the switch circuit 143 is not included. Although it is a neighborhood value, the signal given in this off period is not necessarily the ground potential, and may be a voltage lower than the high-frequency voltage given when a high voltage is applied. For example, a configuration in which a high-frequency signal having a voltage lower than that of the high-frequency signal is given may be used. However, in the configuration of this embodiment in which the ground potential or a value near the ground potential is applied during the off period, power consumption can be reduced.

  In the above embodiment, the PWM signal is distributed for each unit control period of the PWM signal by the pulse distribution circuit 1431. However, the PWM signal may be distributed for every integral multiple of the unit control period. In this way, since it can be configured by a simple digital circuit, the manufacturing cost can be suppressed and the duty ratio of the PWM signal is not partially changed, so that a desired luminance can be obtained. Displayed continuously. However, since the desired luminance is continuously reproduced if observed for a period longer than the above period, the unit period for distributing the PWM signal is not necessarily limited to the unit control period or an integral multiple thereof. is not. However, the period is preferably set to be higher than the frequency at which flicker is perceived (for example, about 60 Hz).

  In the above embodiment, the PWM signal from the PWM control circuit 130 is distributed by the pulse distribution circuit 1431. However, instead of this configuration, the corresponding pulse is supplied to one drive signal generation circuit 1432 without distributing the PWM signal. A configuration may be provided in which a circuit for generating a drive signal and distributing the generated pulse drive signal to the first and second transformers 141 and 142 is newly provided.

  In addition, the PWM signal is not simultaneously distributed to the two drive signal generation circuits 1432 to generate a corresponding pulse drive signal, and any of the first and second transformers 141 and 142 to which the generated pulse drive signal corresponds. The cutting circuit for stopping transmission of one of the two pulse drive signals may be newly provided so that only one of them is supplied.

  Further, the PWM signal is simultaneously given to the two drive signal generation circuits 1432 without being distributed, and only one of these two circuits is operated alternately so that one of the first and second transformers 141 and 142 is operated. Alternatively, a selection control circuit for supplying the pulse drive signal only to the above may be newly provided.

It is a block diagram which shows the structure of the liquid crystal provided with the backlight apparatus which has an inverter which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the backlight apparatus in the said embodiment. It is a block diagram which shows the detailed structure of the pseudo U-shaped lamp | ramp and lamp drive circuit in the said embodiment. It is a block diagram for demonstrating the structure and operation | movement of a switch circuit in the said embodiment. It is a figure explaining a brightness nonuniformity being suppressed in the said embodiment. It is a block diagram which shows the arrangement configuration of the pseudo-U-shaped lamp and its drive circuit in a modification of the embodiment. In the conventional example, it is a block diagram which shows the structure of the backlight apparatus which employ | adopts a pseudo-U-shaped lamp.

Explanation of symbols

11a to 11k ... pseudo U-shaped lamp 12 ... inverter board 13 ... conducting wire 100 ... backlight device 111, 112 ... lamp 130 ... control circuit 140a-110k ... lamp drive circuit 141, 142 ... transformer 143 ... switch circuit 144, 145 ... Current detection circuit 1431 ... Pulse distribution circuit 1432 ... Drive signal generation circuit

Claims (8)

An inverter that causes a lamp to emit light by applying an alternating voltage,
First voltage generating means for generating a first AC signal whose effective value of voltage changes, and applying the first AC signal to one end of a lamp composed of one or more discharge tubes;
A second voltage generating means for generating a second AC signal whose effective voltage value is different from the first AC signal and applying the second AC signal to the other end of the lamp;
A first effective value which is a voltage effective value of the first AC signal is equal to or greater than a second effective value which is a voltage effective value of the second AC signal; and the first effective value is the first effective value. And an switching control means for controlling the first and second voltage generating means so that the case of being less than the effective value of 2 is alternately and periodically switched.   The switching control means includes a case where the first effective value is equal to or greater than a reference voltage value near ground potential and the second effective value is the reference voltage value, and the first effective value is the reference voltage value. 2. The inverter according to claim 1, wherein the inverter is controlled such that a voltage value and the second effective value is larger than the reference voltage value alternately and periodically. 3. The switching control means includes
Voltage control means for generating a pulse width modulation signal for controlling the lamp to emit light at a predetermined brightness;
The inverter according to claim 1, further comprising a distribution unit that alternately distributes the pulse width modulation signal at predetermined intervals in the first and second voltage generation units.   The inverter according to claim 3, wherein the distribution unit distributes alternately every control unit period of the pulse width modulation signal or every integer multiple of the control unit period. A backlight device for irradiating light to a display unit of a display device,
The lamp;
A backlight device comprising the inverter according to any one of claims 1 to 4. A plurality of the lamps are provided, and each of the lamps is arranged on a predetermined plane to irradiate light from the back side of the display unit, and both ends thereof are arranged along the same side
The backlight device according to claim 5, wherein the first and second voltage generating means provided in the inverter are arranged along the side.   The backlight device according to claim 6, wherein each of the plurality of lamps is a pseudo-U-shaped lamp in which two cold cathode tubes are connected to each other by a conductive wire and arranged in a U shape. A display device having a display unit and illumination means for irradiating the display unit with light,
A display device comprising the backlight device according to claim 5 as the illumination unit.

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