JP2007200577A - Lighting device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting device which can prevent brightness unevenness from occurring, and a liquid crystal display device. <P>SOLUTION: A lighting device 21 comprises a plurality of light emitting elements T connected in series; a plurality of current bypass elements U connected in parallel to the light emitting elements T respectively; and a constant current source 25 which are connected in series to the plurality of light emitting elements T, and supplies a constant current to the plurality of light emitting elements T. A current bypass element U changes from a non-conducting state to a conducting state when a light emitting element T connected in parallel to the current bypass element U changes from a conducting state, where a current flows to a non-conducting state where a current does not flow. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lighting device and a liquid crystal display device including the lighting device.

  The transmissive and transflective liquid crystal display devices include a liquid crystal display panel and a backlight provided on the back surface of the liquid crystal display panel. The backlight is used as an illumination device that irradiates light to the liquid crystal display panel in order to improve the visibility of the liquid crystal display device. As this backlight, a cold cathode fluorescent lamp (abbreviated as CCFL) is widely used. Since the cold cathode fluorescent lamp has a large outer shape, it is difficult to reduce the size of the backlight. Further, since a drive circuit for driving the cold cathode fluorescent lamp requires a booster circuit and a ballast, there is a problem that the configuration of the backlight becomes complicated. In order to solve this problem, an illumination device using a light emitting diode (abbreviated as LED), which is easy to downsize as compared with a cold cathode fluorescent lamp and does not require a booster circuit or a ballast in a drive circuit. Has been proposed as a backlight.

  As a conventional lighting device, there is a lighting device configured by connecting a plurality of LEDs in series. Compared to a lighting device configured by connecting a plurality of LEDs in parallel, this lighting device has a larger combined resistance, which is a combination of the internal resistances of the LEDs, so the current flowing through the circuit is reduced and the power consumption of the lighting device is reduced. Can be reduced. However, when an LED ceases to emit light due to its lifespan or failure, it is normally electrically non-conductive, that is, an open mode. Therefore, when even one LED enters an open mode, all LEDs do not emit light. There is a problem.

  As a conventional lighting device, there is a lighting device configured by connecting a plurality of LEDs in parallel. In this lighting device, even when one LED is in the open mode, the remaining LEDs except for the LED in the open mode maintain the light emitting state. However, when the LEDs are connected in parallel, it is necessary to supply the total current flowing from the current source to each LED, and the current flowing from the current source increases, so that the power consumed in the intermediate wiring section is large. There is a problem of becoming.

  In order to solve the problems of the lighting device configured by connecting the plurality of LEDs described above in series or in parallel, there is a lighting device using both serial connection and parallel connection.

  FIG. 16 is a circuit diagram showing a circuit configuration of the illumination device 1 of the first conventional technique. The lighting device 1 includes a first series light emitting element array 2, a second series light emitting element array 3, and a constant current source 4.

  The first series light emitting element array 2 is configured by connecting four LEDs 5a to 5d in series. The second series light emitting element array 3 is configured by connecting four LEDs 6a to 6d in series. The first series light emitting element array 2 and the second series light emitting element array 3 are connected in parallel. The constant current source 4 is connected to the first series light emitting element array 2 and the second series light emitting element array 3 and supplies a constant current to the first series light emitting element array 2 and the second series light emitting element array 3.

  For example, when one LED 5a of the first series light emitting element array 2 enters the open mode, no current flows to the other three LEDs 5b, 5c, 5d, and all the LEDs of the first series light emitting element array 2 are turned off. Since the four LEDs 6a to 6d of the two-series light emitting element array 3 maintain the light emitting state, it is possible to prevent all the LEDs constituting the lighting device 1 from being turned off. In particular, by arranging the LEDs 5a to 5d of the first series light emitting element array 2 and the LEDs 6a to 6d of the second series light emitting element array 3 alternately in a straight line, the luminance unevenness of the illumination device 6 can be dispersed ( For example, see Patent Document 1).

  FIG. 17 is a circuit diagram showing a circuit configuration of the illumination device 7 of the second conventional technique. The illumination device 7 includes first to fourth parallel light emitting element arrays 8 to 11 and a constant current source 4.

  The first parallel light-emitting element array 8 is configured by connecting two LEDs 12a and 12b in parallel. The second parallel light emitting element array 9 is configured by connecting two LEDs 13a and 13b in parallel. The third parallel light emitting element array 10 is configured by connecting two LEDs 14a and 14b in parallel. The fourth parallel light emitting element array 11 is configured by connecting two LEDs 15a and 15b in parallel. The first to fourth parallel light emitting element arrays 8 to 11 are respectively connected in series. The constant current source 4 is connected to the first parallel light emitting element array 8 and the fourth parallel light emitting element array 11 and supplies a constant current to the first to fourth parallel light emitting element arrays 8 to 11.

  Even if one of the two LEDs of each of the first to fourth parallel light-emitting element arrays 8 to 11 is in the open mode due to a failure or a lifetime, the other LED is kept in the light emitting state, so that it is in the open mode. The remaining LEDs other than the LEDs emit light, and the luminance unevenness of the illumination device 7 can be minimized.

JP 2000-89224 A

  In the lighting device 1 of the first conventional technique, when one LED enters the open mode, all the LEDs in the series light emitting element array including the LEDs in the open mode do not emit light.

  The lighting device for a large liquid crystal display panel is configured to include about 1000 LEDs, and each series light emitting element array is configured by connecting 25 to 30 LEDs in series. Therefore, when one LED is in the open mode, 25 to 30 LEDs are turned off, resulting in uneven brightness in the liquid crystal display panel. Since there are variations in the life of LEDs, there are LEDs that reach the end of their life and turn off at an early stage, and from 25 to 30 LEDs turn off at an early stage, resulting in uneven brightness in the liquid crystal display panel.

  In the illumination device 7 of the second conventional technique, even if one of the two LEDs in each light emitting element array is in the open mode, the other LED maintains the light emitting state. At this time, since the entire current flows through the other LED and the current flowing through the other LED doubles, the luminance increases and luminance unevenness occurs. Therefore, when one LED enters the open mode, there is a high possibility that the other LED will reach the end of its life and enter the open mode. When both LEDs of the parallel light emitting element array are in the open mode, there is a problem in that the LEDs of all the parallel light emitting element arrays connected in series to the parallel light emitting element array are turned off.

  Accordingly, an object of the present invention is to provide an illumination device and a liquid crystal display device that can suppress the occurrence of uneven brightness.

The present invention includes a plurality of light emitting elements connected in series to each other and emitting light by applying a voltage;
A power supply unit connected in series to the plurality of light emitting elements connected in series and supplying power to each light emitting element;
A conductive state in which a current flows from a non-conductive state where no current flows when a predetermined voltage higher than the voltage applied when each light emitting element is in a light emitting state is applied in parallel to each light emitting element. And a plurality of current diverting elements that change to a lighting device.

  According to the present invention, when the light emitting element is normal and capable of emitting light, the light emitting element is in a light emitting state in which power is supplied from the power supply unit to emit light. Since each light-emitting element is individually connected in parallel with a current bypass element, when the light-emitting element is in a light-emitting state, the same voltage as that applied to the light-emitting element is applied. If one of the light emitting elements is turned off due to a failure or the like and changes to a non-conductive state where no current flows, the current bypass element connected in parallel to the changed light emitting element changes to a non-conductive state. A voltage obtained by adding up the voltages applied to the remaining light emitting elements excluding the light emitting elements is temporarily applied. When this voltage becomes higher than a predetermined voltage, the current bypass element changes from a non-conductive state to a conductive state in which a current flows. That is, each current bypass element changes to a conductive state when a light emitting element connected in parallel changes to a non-conductive state.

  Even if the light emitting element changes to a non-conducting state due to the life or failure, the current flowing in the light emitting element flows around the current bypass element connected in parallel. Therefore, even if any one of the plurality of light emitting elements connected in series becomes non-conductive, the remaining light emitting elements other than the non-conductive light emitting elements remain conductive, Continue to emit light. As a result, even in a lighting device having a configuration in which a plurality of light emitting elements are connected in series, only the light emitting elements that have changed to a non-conductive state among the light emitting elements are turned off, and the normal light emitting elements maintain the light emitting state. .

  In addition, since the current bypass element is realized by a simple function that changes from a non-conductive state to a conductive state depending on the applied voltage, it is easy to create the current bypass element.

  In addition, since the light emitting elements are connected in series, when the same current is applied to each light emitting element, the same voltage is applied, and the luminance is the same, the current flowing near the power supply is less than when connected in parallel. Since the copper loss is reduced and the wiring can be thinned, the wiring of the circuit is not complicated.

In the present invention, the power supply unit includes a constant current source that supplies a constant current to the plurality of light emitting elements.
The current bypass element transitions from a non-conduction state to a conduction state when the predetermined voltage is applied.

  In addition, since the power supply unit is composed of a constant current source, even if the light emitting element becomes non-conductive and the current bypass element changes to the conductive state, the magnitude of the current flowing through each light emitting element in the light emitting state does not change, The voltage applied to each light emitting element does not change. That is, the power consumption of the light emitting element in the conductive state does not change. Therefore, even when any of the light-emitting elements changes to a non-conductive state, the conductive light-emitting element is not overloaded, and the lifetime of the conductive light-emitting element can be suppressed from being shortened.

  The current bypass element transitions from the non-conducting state to the conducting state when the predetermined voltage is applied. Therefore, even if the light emitting element returns from the non-conducting state to the conducting state, the current bypassing element maintains the conducting state. Since almost no voltage is applied to the conductive current bypass element, even if the light emitting element connected in parallel to the conductive current bypass element returns to the conductive state, this light emitting element receives almost no voltage, Does not emit light.

In the invention, it is preferable that the light emitting element is a light emitting diode.
According to the present invention, since the light emitting element is composed of a light emitting diode having a small forward voltage drop variation with respect to a current variation, it is possible to suppress variations in the voltage applied to each light emitting element. Therefore, the voltage applied to the light emitting element when the light emitting element is in the light emitting state can be prevented from exceeding a predetermined voltage, and the current bypassing element connected in parallel to the light emitting element is prevented from changing to the conductive state. be able to.

  In addition, since it is possible to adjust the light emission brightness simply by adjusting the magnitude of the current flowing through the light emitting diode, compared to a lighting device using a cold cathode fluorescent lamp that requires a booster circuit and a ballast in the drive circuit, The configuration of the lighting device is simplified. Further, since the size of the light emitting diode is very small compared to the size of the cold cathode fluorescent lamp, the size of the lighting device can be reduced.

The present invention also provides a liquid crystal display panel;
A liquid crystal display device comprising: the lighting device provided to face one surface in the thickness direction of the liquid crystal display panel.

  According to the present invention, the light from the lighting device that turns off only the light emitting element that has changed to the non-conducting state due to the lifetime or failure of the light emitting elements is irradiated to the liquid crystal display panel.

  According to the present invention, even in a lighting device having a configuration in which a plurality of light-emitting elements are connected in series, only the light-emitting elements that have changed to a non-conductive state due to the life or failure of the light-emitting elements are turned off and normal light emission is performed. The element maintains a light emitting state. A light emitting element that has changed to a non-conducting state due to a life or failure can prevent other light emitting elements from being turned off by affecting other light emitting elements, thereby suppressing unevenness in luminance of the lighting device. it can.

  In addition, since the current bypass element is realized by a simple function that changes from a non-conductive state to a conductive state depending on the applied voltage, it is easy to create the current bypass element.

  In addition, since the light emitting elements are connected in series, the combined resistance of the circuit in which the internal resistances of the respective light emitting elements are combined is increased and the current flowing in the circuit is reduced, so that the power consumption is reduced. be able to.

  In addition, even if a light-emitting element that is in a non-conducting state is generated, an overload is not applied to the light-emitting element that is in a conductive state. can do.

  The current bypass element transitions from the non-conducting state to the conducting state when the predetermined voltage is applied. Therefore, even if the light emitting element returns from the non-conducting state to the conducting state, the current bypassing element maintains the conducting state. Since almost no voltage is applied to the conductive current bypass element, even if the light emitting element connected in parallel to the conductive current bypass element returns to the conductive state, this light emitting element receives almost no voltage, Does not emit light. This can prevent the light emitting element from blinking.

  Further, according to the present invention, the light emitting element is composed of a light emitting diode having a small forward voltage drop fluctuation with respect to a current fluctuation, and therefore fluctuations in the voltage applied to each light emitting element can be suppressed. Therefore, the voltage applied to the light emitting element when the light emitting element is in the light emitting state can be prevented from exceeding a predetermined voltage, and the current bypass element connected in parallel to the light emitting element is prevented from changing to the conductive state. be able to. Accordingly, it is possible to prevent the light emitting element from being turned off despite being in a state where the light emitting element can emit light normally, and it is possible to suppress the occurrence of luminance unevenness of the lighting device.

  In addition, since it is possible to adjust the light emission brightness simply by adjusting the magnitude of the current flowing through the light emitting diode, compared to a lighting device using a cold cathode fluorescent lamp that requires a booster circuit and a ballast in the drive circuit, The configuration of the lighting device is simplified. Further, since the size of the light emitting diode is very small compared to the size of the cold cathode fluorescent lamp, the size of the lighting device can be reduced.

  In addition, according to the present invention, only the light emitting element that has changed to a non-conducting state due to the life or failure of the light emitting element is turned off, and the light from the lighting device in which the occurrence of luminance unevenness is suppressed is applied to the liquid crystal display panel. The Thereby, a liquid crystal display device in which the occurrence of luminance unevenness is suppressed is realized.

  FIG. 1 is a circuit diagram showing a partial circuit configuration of a lighting device 21 according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing the lighting device 21. FIG. 3 is a cross-sectional view schematically showing the lighting device 21. The illumination device 21 is used as a backlight in the liquid crystal display device 22. The illumination device 21 includes m (symbol m is a positive integer) light emitting units S1, S2,... Sm-1, Sm, a mounting board 23, and a printed wiring board 24. Each light emitting unit S1, S2,..., Sm-1, Sm has n (symbol n is an integer of 2 or more) light emitting elements T1, T2, ..., Tn-1, Tn and n current bypasses. .., Un−1, Un, and a constant current source 25 that is a constant current supply unit. A plurality of light emitting units S1, S2,..., Sm-1, Sm, light emitting elements T1, T2,..., Tn-1, Tn, current bypass elements U1, U2,. In some cases, and in the case of indicating unspecified ones, they may be simply referred to as light emitting unit S, light emitting element T, and current bypass element U.

  In the present embodiment, as an example, when m = 3 and n = 4, that is, there are three light emitting units S, and each of the light emitting units T and the current bypass elements U included in each light emitting unit S is four. Will be described.

  The lighting device 21 is provided with a printed wiring board 24 held on one surface 26 in the thickness direction of the mounting substrate 23, and the light emitting element T and the current bypass element U are mounted on the one surface 27 in the thickness direction of the printed wiring board 24. The protection unit 31 that surrounds the light emitting element T and the current bypass element U is provided.

  A predetermined land 32 is formed on one surface portion in the thickness direction of the printed wiring board 24. The land 32 is used for mounting and connecting electronic components, and is formed of a conductive conductor pattern.

  The light emitting elements T are arranged on the one surface 27 in the thickness direction of the printed wiring board 24 in a row. In the present embodiment, the light emitting elements T1, T2,..., Tn−1, Tn have an optical axis L that coincides with the thickness direction of the printed wiring board 24, and the light emission direction is opposite to the printed wiring board 24. The printed wiring board 24 is arranged and mounted in a straight line. The light emitting elements T1, T2,..., Tn-1, Tn are predetermined first in the order of T1, T2, ..., Tn-1, Tn-1, Tn from one side of the first direction X to the other. Are arranged with an interval W1. The first interval W1 is a distance between the optical axes L of the adjacent light emitting elements T. Hereinafter, a direction perpendicular to the first direction X and the optical axis L direction of the light emitting element T may be referred to as a second direction Y. In addition, the optical axis L direction of the light emitting element T may be referred to as a third direction Z.

  FIG. 4 is a cross-sectional view of the light emitting element T. In the present embodiment, the light emitting element T is composed of a light emitting diode (LED), and includes a cathode K, an n-type semiconductor layer 34 stacked on one surface 33 in the thickness direction of the cathode K, and an n-type semiconductor layer. The p-type semiconductor layer 36 is laminated on the one surface 35 in the thickness direction 34, and the anode A is laminated on the one surface 37 in the thickness direction of the p-type semiconductor layer 36. The anode A and the cathode K are formed of a conductive material such as a metal material and an alloy material. Specifically, gold (Au), an alloy of gold and germanium (AuGe), an alloy of gold and zinc (AuZn), nickel (Ni), aluminum (Al), and the like. The n-type semiconductor layer 34 and the p-type semiconductor layer 36 include gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), gallium nitride (GaN), aluminum gallium indium nitride (AlGaInN), zinc selenide (ZnSe), and indium gallium. It is formed by doping a semiconductor material such as phosphorus (InGaP) with impurities. In particular, when the lighting device 21 is used as a backlight of the liquid crystal display device 22, the light emitting element T is used in combination with light emitting elements of three primary colors of red, green, and blue in order to improve color rendering. The n-type semiconductor layer 34 and the p-type semiconductor layer 36 are formed by doping impurities into a semiconductor material (gallium arsenide for red and green and gallium nitride for blue) corresponding to the color of color.

  The light emitting elements T1, T2,..., Tn−1, Tn are arranged such that the anode A of the light emitting element Ti (i is a positive integer equal to or less than n−1) and the cathode K of the light emitting element Ti + 1 are connected. T2,..., Tn-1, and Tn are connected in series with each other via the wiring 38. Specifically, the cathode K of the light emitting element Ti + 1 is directly connected to the land 32, and the anode A of the light emitting element Ti + 1 is a conductive wire to the land 32 to which the cathode K of the light emitting element Ti to be connected is connected. 41 is connected. The wiring 38 includes a land 32 and a wire 41. In this embodiment, since n = 4, the cathode K of the light emitting element T1 and the anode A of the light emitting element T2 are connected, and the cathode K of the light emitting element T2 and the anode A of the light emitting element T3 are connected to emit light. The cathode K of the element T3 and the anode A of the light emitting element T4 are connected. When a voltage equal to or higher than the diffusion potential is applied in the forward direction, the light emitting element T enters a short mode, that is, an electrically conductive state, and emits light. When the light emitting element T is broken due to a lifetime or failure and cannot emit light, it is normally in an open mode, that is, an electrically non-conductive state. Therefore, when the light emitting element T reaches the end of its life or breaks due to failure, the light emitting element T transitions from the short mode to the open mode. Since the light emitting elements T are connected in series, the combined resistance of the circuit in which the internal resistances of the respective light emitting elements T are combined is increased as compared with the case where they are connected in parallel. Electric power can be reduced.

  The light emitting element T emits light when current is supplied from the constant current source 25. The brightness of the LED changes depending on the magnitude of the flowing current, but the forward voltage drop V1 when emitting light has less fluctuation than the fluctuation of current. Therefore, the forward voltage drop V1 applied to the light emitting element T in the light emitting state hardly fluctuates even if the supplied current fluctuates. In addition, since the luminance of light emission can be adjusted only by adjusting the magnitude of the current flowing through the light emitting element T, compared with a lighting device using a cold cathode fluorescent lamp that requires a booster circuit and a ballast in the drive circuit. The configuration of the lighting device 21 is simplified. Moreover, since the size of the LED is very small compared to the size of the cold cathode fluorescent lamp, the lighting device 21 can be downsized.

  The light emitting units S1, S2,..., Sm-1, Sm are arranged in a line, and in the present embodiment, the light emitting elements T having the same numbers are arranged in a straight line in the second direction Y. The light emitting units S1, S2,..., Sm-1, Sm are spaced apart from each other in the order of S1, S2,. Arranged. The second interval W2 is a distance between the optical axes L of the light emitting elements T having the same number in the adjacent light emitting units S. In the present embodiment, since m = 3, the light emitting unit S1, the light emitting unit S2, and the light emitting unit S3 are arranged in this order from one to the other in the second direction Y. In the present embodiment, the light emitting elements T are arranged in an m × n matrix.

FIG. 5 is a cross-sectional view schematically showing the configuration of the current bypass element U. In the present embodiment, the current bypass element U is made of an antifuse, and includes one conductive layer 42, the other conductive layer 43, one polysilicon layer 44, the other polysilicon layer 45, and an electrical insulating layer 46. Consists of. On the other hand, the conductive layer 42 and the other conductive layer 43 are formed of a conductive material such as a metal material and an alloy material. Specifically, gold (Au), an alloy of gold and germanium (AuGe), gold and zinc Alloy (AuZn), nickel (Ni), aluminum (Al), and the like. On the other hand, the polysilicon layer 44 and the other polysilicon layer 45 are made of conductive polysilicon. The electrical insulating layer 46 has electrical insulation and is formed of silicon oxide (SiO ₂ ) or the like. In the current bypass element U, one polysilicon layer 44 is laminated on one surface 47 in the thickness direction of one conductive layer 42, and an electric insulation layer 46 is laminated on one surface 51 in the thickness direction of the polysilicon layer 44. The other polysilicon layer 45 is laminated on one surface 52 in the thickness direction 46, and the other conductive layer 43 is laminated on one surface 53 in the thickness direction of the other polysilicon layer 45. The current bypass element U is formed in a small size by a semiconductor process. By using such a small current bypass element U, the lighting device 21 can be downsized.

  The current bypass elements U1, U2,..., Un-1, Un are individually connected in parallel in this order to the light emitting elements T1, T2,. That is, the other conductive layer 43 of the current bypass element Uh (h is a positive integer) and the anode A of the light emitting element Th are connected, and the one conductive layer 42 of the current bypass element Uh and the cathode K of the light emitting element Th are connected. . Specifically, one conductive layer 42 of the current bypass element Uh is connected to the land 32 to which the cathode K of the light emitting element Th connected in parallel is connected, and the other conductive layer 43 of the current bypass element Uh is connected in parallel. A wire 41 is connected to the anode A of the light emitting element Th to be connected. In this embodiment, since n = 4, the current bypass element U1 is connected in parallel to the light emitting element T1, the current bypass element U2 is connected in parallel to the light emitting element T2, and the current bypass element U3 is the light emitting element T3. The current bypass element U4 is connected in parallel to the light emitting element T4.

  The current bypass element U has a function opposite to that of a fuse, and when a dielectric breakdown voltage V2 which is a predetermined voltage higher than the forward voltage drop V1 is applied, the electrical insulating layer 46 breaks down, and the open mode Transition from to short mode. The difference between the forward voltage drop V1 and the breakdown voltage V2 is selected to be larger than the fluctuation range of the forward voltage drop V1. Therefore, even if the current flowing through the light emitting element T fluctuates and the forward voltage drop V1 becomes large, the forward voltage drop V1 does not exceed the dielectric breakdown voltage V2. Therefore, when the light emitting element T emits light, The detour element U reliably maintains the open mode. The current bypass element U transitions from the open mode to the short mode when the light emitting element T connected in parallel transitions from the short mode to the open mode. Since the current bypass element U is realized by a simple function of transitioning from a non-conducting state to a conducting state by an applied voltage, the current bypass element U can be easily created and the lighting device can be easily created.

  The protection unit 31 is formed so as to cover the light emitting element T, the current bypass element U, and the wire 41 after the light emitting element T and the current bypass element U are mounted and electrically connected in parallel by the wire 41. The The protection part 31 is formed of a resin material having translucency. The protection unit 31 has a function of protecting the light emitting element T, the current bypass element U, and the wire 41 from oxidation, dust, water, and the like.

  The constant current source 25 is connected in series to an electric circuit including the light emitting element T and the current bypass element U, and supplies power to the light emitting element T. In the present embodiment, the constant current source 25 is configured by a current mirror circuit, and supplies a constant current to the light emitting element T. One end 48 on the high potential side of the constant current source 25 is connected to the anode A of the light emitting element T1 via the wiring 38, and the other end 49 on the low potential side of the constant current source 25 is connected to the light emitting element Tn via the wiring 38. To the cathode K. In this embodiment, since n = 4, one end 48 on the high potential side of the constant current source 25 is connected to the anode A of the light emitting element T1 via the wiring 38, and the other end on the low potential side of the constant current source 25. 49 is connected to the cathode K of the light emitting element T4 via the wiring 38. The direction in which the current supplied from the constant current source 25 flows is the direction from the anode A to the cathode K of the light emitting element T. Hereinafter, an electric circuit composed of the light emitting element T and the current bypass element U viewed from the constant current source 25 may be referred to as a load resistor 54. The impedance of the load resistor 54 is the impedance of the circuit between the anode A of the light emitting element T1 and the cathode K of the light emitting element Tn.

  FIG. 6 is a circuit diagram showing a circuit configuration of the constant current source 25. The constant current source 25 includes a first transistor 55, a second transistor 56, and a resistor 57. The first transistor 55 and the second transistor 56 are pnp bipolar transistors and have substantially the same electrical characteristics. In FIG. 6, an electric circuit composed of the light emitting element T and the current bypass element U viewed from the constant current source 25 is shown as a load resistor 54.

  The base of the first transistor 55 and the base of the second transistor 56 are connected to each other. The same voltage Vcc is applied to the emitter of the first transistor 55 and the emitter of the second transistor 56. The collector of the first transistor is connected to the resistor 57. This resistor 57 is connected to the ground. The base and collector of the first transistor are connected to each other. The collector of the second transistor 56 is connected to the load resistor 54 as described above. This load resistor 54 is connected to the ground.

  Since the fluctuation of the voltage between the base and the emitter when the emitter-collector of the bipolar transistor is in a conductive state is small, the base voltage is determined by the emitter voltage Vcc applied to the emitter. Since the resistor 57 is connected to this base, the voltage applied to the resistor 57 is determined by the emitter voltage Vcc. Therefore, when the emitter voltage Vcc is fixed, the magnitude of the current I1 flowing through the resistor 57 can be adjusted by adjusting the resistance value of the resistor 57. The current I1 flowing through the resistor 57 is substantially equal to the current flowing into the first transistor 55.

  Since the voltage between the base and the emitter of the first transistor 55 is equal to the voltage between the base and the emitter of the second transistor 56, the first transistor 55 and the second transistor 56 have substantially the same electrical characteristics. The current flowing into the transistor 55 and the current flowing into the second transistor 56 are substantially equal. Therefore, a current I 2 that is substantially equal to the current I 1 flowing through the resistor 57 flows through the load resistor 54. Since the current flowing into the first transistor 55 is determined by the resistance value of the resistor 57 when the emitter potential Vcc is fixed, even if the impedance of the load resistor 54 changes, the current I2 flowing through the load resistor 54 is large. There is no change. That is, the constant current source 25 supplies a constant current I2 to the load resistor 54.

  When the load resistor 54 is in the open mode, no current flows through the load resistor 54, so that the collector voltage of the second transistor 56 is close to the emitter voltage Vcc. Specifically, the voltage close to the emitter voltage Vcc is a voltage obtained by subtracting the voltage between the emitter and the collector when no current flows into the collector of the second transistor from the voltage Vcc applied to the emitter. Therefore, when the load resistor 54 is in the open mode, a voltage close to the emitter voltage Vcc is applied to the load resistor 54.

  FIG. 7 is a circuit diagram showing a circuit configuration of the light emitting unit S at the moment when the light emitting element T1 transitions from the short mode to the open mode. FIG. 8 is a diagram illustrating a circuit configuration of the light emitting unit S after the current bypass element U1 transitions from the open mode to the short mode.

  When all the light emitting elements T are normally emitting light, a forward voltage drop V1 is applied to each of the current bypass elements U connected in parallel to the light emitting elements T, but the breakdown voltage V2 is Since it is higher than the directional voltage drop V1, the current bypass element U maintains the open mode. Therefore, the current flows through the light emitting element T without flowing through the current bypass element U.

  Since the fluctuation of the forward voltage drop V1 of the LED is small with respect to the fluctuation of the current flowing through the LED, the fluctuation of the voltage applied to the current bypass element U connected in parallel to the light emitting element T composed of this LED is also small. Therefore, when the light emitting element T emits light normally, the forward voltage drop V1 can be prevented from exceeding the dielectric breakdown voltage V2, and the current bypass element U can be prevented from transitioning to the short mode. . Accordingly, it is possible to prevent the light emitting element T from being turned off despite being in a state where the light emitting element T can normally emit light, and to suppress occurrence of luminance unevenness of the lighting device.

  When all the light emitting elements T are normally emitting light, one light emitting element T is broken and extinguished, and when the short mode is switched to the open mode, the light emitting elements T are connected in series. No current flows through the light emitting elements T, and all the light emitting elements T are turned off. At this time, the total of the forward voltage drops V1 applied to the remaining light emitting elements T excluding the light emitting elements T that have transitioned to the open mode, to the current bypass elements U connected in parallel to the light emitting elements T that have transitioned to the open mode. The voltage [(n−1) × V1] is applied. In practice, a voltage close to the emitter voltage Vcc of the first and second transistors 55 and 56 of the constant current source 25 is applied to the light emitting element T connected in parallel to the light emitting element T that has transitioned to the open mode. When the voltage [(n−1) × V1] applied to the current bypass element U connected in parallel to the light emitting element T transitioned to the open mode exceeds the dielectric breakdown voltage V2, the current bypass element U is in the open mode. Transition from to short mode. When the current bypass element U transitions from the open mode to the short mode, the current supplied from the constant current source 25 flows around the current bypass element U that has transitioned to the open mode. A current also flows through the remaining normal light emitting elements T, and the normal light emitting elements T enter a light emitting state. That is, only the broken light emitting element T in the light emitting unit S is turned off.

  When the light emitting element T transitions from the short mode to the open mode, and the current bypass element U connected in parallel to the light emitting element T transitions from the open mode to the short mode, a load that combines the light emitting element T and the current bypass element U The impedance of the resistor 54 changes. Specifically, the impedance of the load resistor 54 decreases. Since the constant current source 25 supplies a constant current to the load resistor 54 even when the impedance of the load resistor 54 changes, the magnitude of the current flowing through each light emitting element T does not change, and the forward voltage drop V1. Will not change. That is, the power consumption of each light emitting element T does not fluctuate. Even if any one of the light emitting elements T transitions to the open mode, the power consumption of the light emitting elements T can be kept constant. Therefore, it is possible to prevent each light emitting element T from being overloaded and to reduce the lifetime of each light emitting element T. Shortening can be suppressed. Thereby, the lifetime of the illuminating device 21 can be lengthened.

  In this embodiment, since n = 4, for example, when the light emitting element T1 transitions from the short mode to the open mode, the current bypass element U1 connected in parallel to the light emitting element T1 has a numerical value 3 in the forward voltage drop V1. Is applied (3 × V1). In the present embodiment, the breakdown voltage V2 is selected to be about twice the forward voltage drop V1. Therefore, when the light emitting element T1 transitions to the open mode, the voltage (3 × V1) applied to the current bypass element U1 exceeds the breakdown voltage V2, and the current bypass element U1 transitions from the open mode to the short mode. As a result, the current flowing through the light emitting element T1 flows around the current bypass element U1, the current flows through the remaining light emitting elements T2, T3, T4 except the light emitting element T1, and the light emitting elements T2, T3, T4 The light emission state is activated. Thus, the broken light-emitting element T1 affects the normal light-emitting element T, and the normal light-emitting element T can be prevented from turning off, and the occurrence of uneven brightness in the lighting device 21 can be suppressed.

  Once the current bypass element U is changed to the short mode, the short circuit mode is maintained even if the light emitting elements T connected in parallel return from the open mode to the short mode. Since almost no voltage is applied to the short-mode current bypass element U, even if the light-emitting element T connected in parallel to the short-mode current bypass element U returns to the short mode, the light-emitting element T has almost no voltage. It is not applied and does not emit light. This can prevent the light emitting element T from blinking.

  FIG. 9 is a diagram schematically showing the direction dependency of the light intensity of the light emitting element T. FIG. In FIG. 9, the direction dependency of the light intensity of the light emitting element T is shown using a broken line 61. This broken line 61 represents that the longer the distance from the light emitting element T, the stronger the light intensity in that direction. In the present embodiment, the light emitting element T is configured by an LED having a large beam divergence angle. The light emitting diode usually has the highest light intensity in the optical axis direction, and has a light intensity direction dependency such that the light intensity monotonously decreases as the light intensity deviates from the optical axis direction. T has a low light intensity in the optical axis direction, and the light intensity in the direction inclined from the optical axis L on the virtual plane perpendicular to the third direction Z direction including the optical axis L is in the optical axis L direction. It has direction dependency of light intensity that becomes stronger than light intensity.

  FIG. 10 is a cross-sectional view schematically showing the direction dependency of the light intensity of the illumination device 21 when all the light emitting elements T of the light emitting unit S emit light. FIG. 11 is a cross-sectional view schematically showing the direction dependency of the light intensity of the illumination device 21 when the light emitting element T2 of the light emitting unit S is turned off. As described above, the light emitting elements T included in the light emitting unit S are provided with a first interval W1 in the first direction X with respect to the adjacent light emitting elements T. The first interval W1 is a light emitting element Tj-1 (j is 2 or more and less than n on a virtual irradiation surface perpendicular to the third direction Z assumed as one of the third directions Z of the lighting device 21. The interval is selected such that the light from the integer), the light from the light emitting element Tj, and the light from the light emitting element Tj + 1 overlap. In the present embodiment, the first interval W1 is such that the region of strong light intensity among the light from the light emitting elements Tj−1, j + 1 on the virtual irradiation surface is the optical axis L between the virtual irradiation surface and the light emitting element Tj. It is chosen to overlap in the vicinity of the intersection with. By selecting the first interval W1 in this way, even when the light emitting element Tj is turned off, for example, on the virtual irradiation surface, the irradiation region of the light emitting element Tj is caused by the light from the light emitting elements Tj−1, j + 1. It can be prevented from becoming completely dark. Thereby, it is possible to suppress the occurrence of luminance unevenness on the virtual irradiation surface. For example, when the light emitting element T2 is turned off, a darkened area is generated on the virtual irradiation surface. However, since the light from the light emitting elements T1 and 3 irradiates the irradiation area of the light emitting element T2, luminance unevenness is minimized. be able to.

  In the present embodiment, the predetermined second interval W2 that is the interval between the light emitting elements T adjacent in the second direction Y is selected to be the same distance as the above-described predetermined first interval. Thereby, the light from the light emitting element Tj of the light emitting unit Sk (k is an integer of 2 or more and less than n) overlaps with the light from the light emitting element Tj of the light emitting units Sk-1, k + 1, and further the light emission of the light emitting unit Sk. It overlaps with the light from the elements Tj−1, j + 1. For example, even if the light emitting element Tj of the light emitting unit Sk is turned off, the light from the light emitting element Tj is emitted from the light emitting unit Sk-1, Sk + 1 and the light emitting element Tj− of the light emitting unit Sk on the virtual irradiation surface. Complemented by light from four light emitting elements T, 1 and j + 1. Thereby, it is possible to suppress the occurrence of luminance unevenness on the virtual irradiation surface.

  FIG. 12 is a front view showing a basic configuration of a liquid crystal television receiver 62 including the above-described lighting device 21 of the present embodiment. The liquid crystal television receiver 62 includes a cabinet 63, a stand 64, a speaker unit 65, a receiving unit connected to an antenna, a control unit, a driving unit, and a liquid crystal display device 22.

  The stand 64 supports the cabinet 63. The speaker unit 65, the receiving unit, the control unit, and the driving unit are housed and provided in the cabinet 63. The speaker units 65 are disposed on both sides of the cabinet 63, respectively.

  The control unit controls the speaker unit 65, the receiving unit, and the driving unit. The control unit is realized including, for example, a central processing unit (abbreviated as CPU). The receiving unit selects and receives a radio wave captured by the antenna and amplifies the received television signal. The television signal includes an audio signal and a video signal. The audio signal is given to the speaker unit 65. The video signal is given to the drive unit. The speaker unit 65 amplifies the given audio signal based on a command from the control unit and displays it audibly. The drive unit drives the liquid crystal display device 22 based on a command from the control unit, and displays the given video signal visually. The driving unit is realized by a driving driver IC (Integrated Circuit).

  FIG. 13 is a perspective view schematically showing the liquid crystal display device 22. The liquid crystal display device 22 includes a first back shield 66, a lighting device 21 provided on one surface in the thickness direction of the first back shield 66, a diffusion plate 67 provided on one surface in the thickness direction of the lighting device 21, and a diffusion. A diffusion sheet 71 provided on one surface in the thickness direction of the plate 67, a prism sheet 72 provided on one surface in the thickness direction of the diffusion sheet 71, and a reflection / polarization sheet 73 provided on one surface in the thickness direction of the prism sheet 72. And a spacer 74 provided on the peripheral edge of one surface in the thickness direction of the reflection / polarization sheet 73, and a liquid crystal display panel 76 provided to face the reflection / polarization sheet 73 with the spacer 74 interposed therebetween.

  The lighting device 21 is provided to face one surface of the liquid crystal display panel 76 in the thickness direction. The illuminating device 21 includes a light emitting element T composed of a white LED that emits white light, and functions as a so-called backlight that emits white light and irradiates the liquid crystal display panel 76. The illuminating device 21 is arranged so that the above-described virtual irradiation surface coincides with the diffusion plate 67. By arranging the illuminating device 21 in this manner, even if some of the light emitting elements T are turned off, the unevenness of the luminance of the light from the illuminating device 21 in the diffusing plate 67 can be suppressed to the minimum, and the diffusion The plate 67 is irradiated with light having a uniform light intensity.

  The first back shield 66 protects the liquid crystal display device 22 from mechanical shocks and the like. The diffusion plate 67 and the diffusion sheet 71 are each composed of a translucent plate and a sheet that scatter and diffuse light passing therethrough. The diffuser plate 67 is irradiated with light with less luminance unevenness, and this light passes through the diffuser plate 67 and the diffuser sheet 71, thereby further uniforming the luminance on a virtual plane perpendicular to the thickness direction of the illumination device 21. The light is less uneven. The light that has passed through the diffusion sheet 71 passes through the prism sheet 72, and only the desired polarization component is transmitted by the reflection / polarization sheet 73 and is condensed on the liquid crystal display panel 76.

  The liquid crystal display panel 76 is driven by an active matrix driving method, and includes a liquid crystal layer, a pair of alignment films, a pair of transparent electrodes, a pair of glass substrates, a color filter, and a pair of polarizing filters. Consists of including. The liquid crystal layer is filled between a pair of alignment films arranged to face each other with a spacer interposed therebetween. The transparent electrodes are arranged to face each other with a pair of alignment films interposed therebetween. The color filter is provided on one surface in the thickness direction that is separated from the illumination device 21 in the pair of alignment films. The pair of glass substrates are disposed to face each other with the color filter and the other alignment film interposed therebetween. The pair of polarizing filters are provided to face each other with a pair of glass substrates interposed therebetween.

  The drive unit controls the voltage applied to the transparent electrode based on a command from the control unit, thereby selectively transmitting a part of the light emitted from the illumination device 21 through the liquid crystal display panel 76. The video signal is displayed in the visual display 76.

  FIG. 14 is a cross-sectional view schematically showing a light emitting unit S of a lighting device 21 according to another embodiment of the present invention. FIG. 15 is a plan view of the semiconductor wafer 81 on which the light emitting element T and the current bypass element U are formed. In another embodiment of the present invention, the light emitting element T and the current bypass element U of the above-described embodiment are integrally formed as one module 82 with an electric insulating portion 83 having electric insulating properties interposed therebetween.

  The module 82 has a substantially rectangular parallelepiped shape, and includes one electrode layer 84, the other electrode layer 85, a current bypass element U, a light emitting element T, and an electrical insulating portion 83. On the other hand, the electrode layer 84 has conductivity and forms the other surface portion in the thickness direction of the module 82. The other electrode layer 85 has conductivity and constitutes one surface portion in the thickness direction of the module 82.

  The current bypass element U is formed at one corner of the four corners of the square from one end in the thickness direction of the module 82 from one end to the other end in the thickness direction of the module 82. One conductive layer 42 of the current bypass element U constitutes a part of one electrode layer 84, and the other conductive layer 43 constitutes a part of the other electrode layer 85.

  The electric insulating portion 83 includes the one electrode layer 84 and the other one so as to cover the surfaces of the current bypass element U in the direction perpendicular to the thickness direction of the one polysilicon layer 44, the other polysilicon layer 45, and the electric insulating layer 46. It is formed between the electrode layers 85.

  The light emitting element T constitutes the remaining part of the module 82 excluding the current bypass element U and the electrical insulating portion 83. The n-type semiconductor layer 34 and the p-type semiconductor layer 36 of the light emitting element T are electrically insulated from the one polysilicon layer 44, the electrical insulation layer 46, and the other polysilicon layer 45 by the electrical insulation portion 83. The cathode K constitutes a part of the one electrode layer 84. That is, the one electrode layer 84 is formed as a common electrode for the cathode K of the light emitting element T and the one conductive layer 42 of the current bypass element U, and the cathode K and the one electrode layer 84 are electrically connected. The anode A constitutes a part of the other electrode layer 85. That is, the other electrode layer 85 is formed as a common electrode for the anode A of the light emitting element T and the other conductive layer 43 of the current bypass element U, and the anode A and the other conductive layer 43 are electrically connected.

  A plurality of modules 82 are formed on the semiconductor wafer 81 using a semiconductor process. Thus, the module 82 is created by separating the plurality of modules 82 formed on the semiconductor wafer 81 into one module 82.

  Since the light emitting element T and the current bypass element U are integrally formed, the light emitting element T and the current bypass element U can be mounted on the printed wiring board 24 in one step. Further, the step of connecting the anode K of the light emitting element T and the other conductive layer 43 of the current bypass element U with the wire 41 can be omitted. As a result, the number of steps can be reduced as compared with the case of separately mounting on the printed wiring board 24, and the cost for creating the lighting device 21 can be reduced.

  Further, by integrally forming the light emitting element T and the current bypass element U, the module 82 can be miniaturized, and the lighting device 21 can be miniaturized.

  In still another embodiment of the present invention, the above-described current bypass element U is not limited to an antifuse, and is configured by an element that transitions from an open mode to a short mode when a dielectric breakdown voltage V2 is applied. The current bypass element U is realized by a tantalum electrolytic capacitor, for example. In this case, the anode of the tantalum electrolytic capacitor is electrically connected to the anode A of the light emitting element T, and the cathode of the tantalum electrolytic capacitor is electrically connected to the cathode K of the light emitting element T. Since the tantalum electrolytic capacitor transitions from the open mode to the short mode when the dielectric breakdown voltage V2 is applied, as described above, when the light emitting element T transitions to the open mode, the tantalum electrolytic capacitor is connected in parallel to the light emitting element T. The tantalum electrolytic capacitor transitions to the short mode. Since the current bypass element U constituted by the tantalum electrolytic capacitor also functions as a capacitor, the fluctuation of the forward voltage drop V1 of the light emitting elements T connected in parallel is reduced. Thereby, electrical noise generated from the light emitting element T can be removed.

  In still another embodiment of the present invention, the light emitting elements T are not limited to a matrix shape and may be arranged in any manner. For example, the light emitting elements T may be arranged in a staggered pattern.

  In still another embodiment of the present invention, the number m of the light emitting units S is not limited to the numerical value 3, and the number n of the light emitting elements T is not limited to the numerical value n and may be any numerical value. For example, the illuminating device 21 composed of 1000 light emitting elements T in which the number m of the light emitting units S is 40 and the number n of the light emitting elements T is 25 may be configured. Even in this case, since only the broken light emitting element T is turned off, the illumination device 21 with less luminance unevenness is realized.

  In the present embodiment, the illumination device 21 is used as a backlight of the liquid crystal display device 22, but is not limited to the backlight, and is also used for a transmissive display device or a transflective display device including a transmissive display element. Preferably used.

  In the present embodiment, the light emitting element T is composed of LEDs. However, the light emitting elements T are not limited to LEDs, and may be composed of lighting devices such as fluorescent lamps, halogen lamps, and light bulbs that are driven by a DC voltage.

It is a circuit diagram which shows the one part circuit structure of the illuminating device 21 of one Embodiment of this invention. FIG. 3 is a perspective view schematically showing the illumination device 21. FIG. 3 is a cross-sectional view schematically showing the illumination device 21. 3 is a cross-sectional view of a light emitting element T. FIG. 3 is a cross-sectional view schematically showing a configuration of a current bypass element U. FIG. 3 is a circuit diagram showing a circuit configuration of a constant current source 25. FIG. 3 is a circuit diagram illustrating a circuit configuration of a light emitting unit S at a moment when the light emitting element T1 transitions from a short mode to an open mode. FIG. It is a figure which shows the circuit structure of the light emission unit S after the electric current bypass element U1 changes from an open mode to a short mode. It is a figure which shows typically the direction dependence of the light intensity of the light emitting element T. FIG. It is sectional drawing which shows typically the direction dependence of the light intensity of the illuminating device 21 when all the light emitting elements T of the light emission unit S are light-emitting. It is sectional drawing which shows typically the direction dependence of the light intensity of the illuminating device 21 when the light emitting element T2 of the light emission unit S is light-extinguishing. It is a front view which shows the basic composition of the liquid crystal television receiver 62 provided with the illuminating device 21 of this Embodiment. 3 is a perspective view schematically showing a liquid crystal display device 22. FIG. It is sectional drawing which shows typically the light emission unit S of the illuminating device 21 of other embodiment of this invention. It is a top view of the semiconductor wafer 81 in which the light emitting element T and the current detour element U were formed. It is a circuit diagram which shows the circuit structure of the illuminating device 1 of the 1st prior art. It is a circuit diagram which shows the circuit structure of the illuminating device 7 of the 2nd prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Illuminating device 22 Liquid crystal display device 25 Constant current source 31 Protection part 32 Land 41 Wire 62 Liquid crystal television receiver 76 Liquid crystal display panel S Light emitting unit T Light emitting element U Current bypass element

Claims (4)

A plurality of light emitting elements connected in series with each other and emitting light by applying a voltage;
A power supply unit connected in series to the plurality of light emitting elements connected in series and supplying power to each light emitting element;
A conductive state in which a current flows from a non-conductive state where no current flows when a predetermined voltage higher than the voltage applied when each light emitting element is in a light emitting state is applied in parallel to each light emitting element. A lighting device comprising: a plurality of current bypass elements that change to The power supply unit includes a constant current source that supplies a constant current to the plurality of light emitting elements,
The lighting device according to claim 1, wherein the current bypass element transitions from a non-conductive state to a conductive state when the predetermined voltage is applied.   The lighting device according to claim 1, wherein the light emitting element includes a light emitting diode. A liquid crystal display panel;
A liquid crystal display device comprising: the lighting device according to claim 1 provided to face one surface in a thickness direction of the liquid crystal display panel.

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