JP4760093B2 - Separately excited inverter circuit for backlight device for liquid crystal television, and separately excited inverter circuit for backlight device - Google Patents

Description

  The present invention relates to a separately-excited inverter circuit for a direct backlight device that irradiates a liquid crystal panel from the back side.

  In a separately-excited inverter circuit using a ballast capacitor-less inverter transformer in a conventional separately-excited inverter circuit for a liquid crystal television backlight device, it is necessary to feedback control the current (tube current) flowing in the cold-cathode tube. . When this feedback control is performed using a control IC, the control IC performs feedback control via one or two control channels. Therefore, the number of cold cathode tubes subject to feedback control is only one or two of the cold cathode tubes constituting the backlight device, and feedback control is not performed on the remaining cold cathode tubes ( Uncontrolled). If a current exceeding the rated current is passed through the uncontrolled cold cathode tube, the life of the cold cathode tube is shortened. Therefore, it is necessary to avoid a current exceeding the rated current flowing through the cold cathode tube.

  Further, in the case of the two-channel control as described above, if the substrate used for mounting the components for the three cold cathode tubes and the components for mounting the four components for the cold cathode tubes are shared, When three cold-cathode tube components are mounted, it is difficult to stabilize the luminance at the center in the vertical direction of the screen, which must be most stabilized on the display screen of the liquid crystal television. For this reason, there is a problem that it is difficult to use a common substrate for mounting the three cold cathode tube components and the four cold cathode tube components.

Also, an optical sensor is provided for each light source provided in the backlight device, and the output value from the optical sensor is compared with the control value from the control unit. There is known a direct-type backlight device that outputs a control amount equal to the control value to a drive unit to display a target luminance value without unevenness of luminance due to a portion of a light emitting unit ( For example, see Patent Document 1). However, the invention described in Patent Document 1 cannot solve the above problem.
JP 2000-294026 A

  The present invention has been made to solve the above-described problem, and when feedback control of output current from a control IC to three or four cold-cathode tubes is performed via two control channels. However, it is possible to prevent a current exceeding the rated current from flowing through the cold cathode tube on the non-control side, and the board used for mounting the components for the three cold cathode tubes and the components for the four cold cathode tubes An object of the present invention is to provide a back-excited inverter circuit for a backlight device for a liquid crystal television and a back-excited inverter circuit capable of stabilizing the luminance at the center portion in the vertical direction of the screen even when the screen is shared. And

  In order to achieve the above-mentioned object, the invention of claim 1 is the invention of each of the three or four U-shaped cold-cathode tubes arranged in parallel in the left-right direction of the liquid crystal panel of the backlight device for a liquid crystal television. A MOS-FET (Metal Oxide Semiconductor Field Effect Transistor) provided for each U-shaped cold cathode tube, and a voltage to be output to each U-shaped cold cathode tube. A voltage for controlling the output current to each U-shaped cold cathode tube is applied to a plurality of component groups including a ballast capacitorless inverter transformer, etc. to be raised, and to the gates of the MOS-FETs in the plurality of component groups And a substrate on which the plurality of component groups and the control IC are mounted. The plurality of component groups are divided into two groups, and the control IC is divided into the two groups. of In order to feedback control the output current to each U-shaped cold cathode tube, a control voltage having a different duty ratio is applied to each channel. In a separately-excited inverter circuit for a backlight device for a liquid crystal television, the substrate is commonly used for mounting three U-shaped cold-cathode tube components and four U-shaped cold-cathode tube components. When the number of the U-shaped cold cathode tubes is three, the first group of the two groups is the first from the top of the three U-shaped cold cathode tubes. When the number of the U-shaped cold cathode tubes is four, which is composed of only parts corresponding to the U-shaped cold cathode tubes, the first of the four U-shaped cold cathode tubes from the top. From the top of the parts group corresponding to the U-shaped cold cathode tube The second group of the two groups is the first from the bottom of the three or four U-shaped cold cathode tubes. The control IC is composed of a part group corresponding to the second U-shaped cold cathode tube and a part group corresponding to the second U-shaped cold cathode tube from the bottom, and the control IC is one of the two control channels. From the first channel, a voltage for feedback control of the current flowing through the first U-shaped cold cathode tube from the top is applied to each component group included in the first group, and the 2 For feedback control of the current flowing through the second U-shaped cold-cathode tube from the bottom to each component group included in the second group from the second channel of the two control channels. Apply the voltage, the U-shaped cold shade When the number of polar tubes is 3, when the number of U-shaped cold cathode tubes is 4, among the four component groups mounted on the substrate, the second U-shaped cold cathode from the top is used. A component group corresponding to the cathode tube is not mounted on the substrate.

  The invention of claim 2 drives each of the cold cathode tubes provided for each of the cold cathode tubes among a plurality of cold cathode tubes arranged in parallel in the left-right direction of the liquid crystal panel of the backlight device. And a plurality of component groups, such as an inverter transformer for increasing the voltage output to each U-shaped cold cathode tube, and each U-shaped cold cathode in the switching circuit in the plurality of component groups. A control IC for applying a voltage for controlling an output current to the tube; and a substrate on which the plurality of component groups and the control IC are mounted. The control IC includes the U-shaped cold cathodes. In the back-excited inverter circuit that applies a control voltage to each of the switching circuits in order to perform feedback control of the output current to the tube, the plurality of component groups include one or more groups. The control IC is provided with a voltage for feedback control of the current flowing in the uppermost cold cathode tube among the cold cathode tubes corresponding to the component groups included in each group. This is applied to the switching circuit in each component group included in the group.

  According to a third aspect of the invention, in the back-excited inverter circuit of the backlight device according to the second aspect, the substrate can be shared for mounting different numbers of components for the cold cathode tube, and is included in each group. And the number of cold cathode tubes corresponding to these component groups is one, the number of parts included in each group and the number of cold cathode tubes corresponding to these component groups is two. At one time, of the two component groups mounted on the substrate, a component group corresponding to the lower cold cathode tube is not mounted on the substrate.

  According to a fourth aspect of the present invention, in the back-excited inverter circuit according to the second aspect, the plurality of cold-cathode tubes arranged in parallel in the left-right direction of the liquid crystal panel of the backlight device is 3 Or four U-shaped cold-cathode tubes, and the substrate is commonly used for mounting three U-shaped cold-cathode tube components and four U-shaped cold-cathode tube components. When the number of the U-shaped cold cathode tubes is three, among the four component groups mounted on the substrate when the number of the U-shaped cold cathode tubes is four, A component group corresponding to the second U-shaped cold cathode tube from the top is not mounted on the substrate.

  According to the first aspect of the present invention, the control IC feedback-controls the current flowing through the first U-shaped cold cathode tube from the top to each component group included in the first group from the first channel. The voltage for performing feedback control of the current flowing through the second U-shaped cold cathode tube from the bottom is applied to each component group included in the second group from the second channel. To do. As a result, among the first and second U-shaped cold cathode tubes from the top corresponding to each component group included in the first group, the upper U-shaped cold cathode tube (the first U-shape from the top). The current flowing in the first and second U-shaped cold-cathode tubes from the top can be feedback controlled based on the current flowing in the cold-cathode tube), and each component group included in the second group is supported. Of the first and second U-shaped cold cathode tubes from the bottom, the current flowing through the upper U-shaped cold cathode tube (the second U-shaped cold cathode tube from the bottom) is 1 from the bottom. The current flowing in the second and second U-shaped cold cathode tubes can be feedback controlled. Here, in general, for each cold cathode tube constituting the backlight device, the temperature of the upper cold cathode tube is more likely to rise than the lower cold cathode tube due to the heat generated by each cold cathode tube. Moreover, the current flowing through each cold cathode tube becomes easier to flow as the temperature of each cold cathode tube is higher. For this reason, the current flows more easily in the upper cold cathode tube than in the lower cold cathode tube. Therefore, of the two U-shaped cold cathode tubes arranged adjacent to each other in the vertical direction as described above, the current flowing in each cold cathode tube is determined based on the current flowing in the upper U-shaped cold cathode tube. By performing feedback control, it is possible to prevent a current exceeding the rated current from flowing not only through the upper U-shaped cold cathode tube on the control side but also through the lower U-shaped cold cathode tube on the non-control side.

  Also, two U-shaped cold cathode tubes (the first and second U-shaped cold cathode tubes from the top, and the first and second U-shaped cold cathode tubes from the bottom in the vertical direction) ) Has a smaller temperature difference than a U-shaped cold cathode tube that is separated in the vertical direction. Therefore, as described above, the control ICs have two U-shaped cold tubes arranged adjacent to each other in the vertical direction. By applying the same voltage for current control to the parts of the cathode tube through the same channel, the U-shaped cold cathode tube on the control side is added to the U-shaped cold cathode tube on the non-control side. It is possible to pass a current close to. Therefore, it is not necessary to reduce the luminance of the U-shaped cold cathode tube on the non-control side more than necessary.

  Further, when the number of U-shaped cold cathode tubes is three, the second U component from the top among the four component groups mounted on the substrate when the number of U-shaped cold cathode tubes is four. The group of parts corresponding to the letter-shaped cold cathode tube was not mounted on the substrate. As a result, when the number of U-shaped cold cathode tubes is three, feedback control is performed on the current flowing through the second U-shaped cold cathode tube from the top (second U-shaped cold cathode tube from the bottom). Therefore, it is possible to stabilize the luminance at the center portion in the vertical direction of the screen, which should be most stabilized on the display screen of the liquid crystal television. Further, when the number of U-shaped cold cathode tubes is three, the only U-shaped cold cathode tube on the non-control side is least susceptible to the heat generated by each cold cathode tube (the own tube emits). Since it can be the first U-shaped cold cathode tube from the bottom (which only receives heat), the luminance of the entire display screen of the liquid crystal television can be stabilized.

  According to the invention of claim 2, the control IC is included in each group based on the current flowing in the uppermost cold cathode tube among the cold cathode tubes corresponding to the component group included in each group. It is possible to feedback control all the cold-cathode tubes corresponding to the parts group. Here, in general, for each cold cathode tube constituting the backlight device, the temperature of the upper cold cathode tube is more likely to rise than the lower cold cathode tube due to the heat generated by each cold cathode tube. Moreover, the current flowing through each cold cathode tube becomes easier to flow as the temperature of each cold cathode tube is higher. For this reason, the current flows more easily in the upper cold cathode tube than in the lower cold cathode tube. Therefore, as described above, among the cold cathode tubes corresponding to the component groups included in each group, all the cold cathode tubes corresponding to the component groups included in each group are based on the current flowing in the uppermost cold cathode tube. By performing feedback control of the cathode tube, it is possible to prevent a current exceeding the rated current from flowing not only to the uppermost cold cathode tube on the control side but also to the cold cathode tube on the non-control side.

  According to the invention of claim 3, when the number of parts included in each group and the number of cold cathode tubes corresponding to these parts are one, the parts included in each group, and these When the number of cold cathode tubes corresponding to the component group is two, among the two component groups mounted on the substrate, the component group corresponding to the lower cold cathode tube which is the cold cathode tube on the non-control side Was not mounted on the board. As a result, the number of cold cathode tubes subject to feedback control can be increased as compared with the case where a component group corresponding to the upper cold cathode tube, which is the cold cathode tube on the control side, is not mounted on the substrate. .

  Further, when the number of U-shaped cold cathode tubes is three, the second U component from the top among the four component groups mounted on the substrate when the number of U-shaped cold cathode tubes is four. The group of parts corresponding to the letter-shaped cold cathode tube was not mounted on the substrate. As a result, when the number of U-shaped cold cathode tubes is three, feedback control is performed on the current flowing through the second U-shaped cold cathode tube from the top (second U-shaped cold cathode tube from the bottom). Therefore, it is possible to stabilize the luminance at the center portion in the vertical direction of the screen. Further, when the number of U-shaped cold cathode tubes is three, the only U-shaped cold cathode tube on the non-control side is least susceptible to the heat generated by each U-shaped cold cathode tube (automatically). Since the first U-shaped cold cathode tube from the bottom can receive only the heat generated by the tube, the luminance of the entire display screen can be stabilized.

  The best mode for carrying out the present invention will be described with reference to the drawings. The present invention relates to a separately-excited inverter circuit for a direct backlight device that irradiates a liquid crystal panel from the back side. In the following embodiments, an example in which the present invention is applied to a separately excited inverter circuit of a backlight device for a liquid crystal television will be described. In addition, embodiment described below does not cover this invention, and this invention is not limited only to the following form.

  FIG. 1 shows a separately excited inverter circuit of the backlight device according to the present embodiment and four U-shaped cold cathode tubes connected to the separately excited inverter circuit. The backlight device 1 is a direct-type backlight device for a liquid crystal television, and mainly includes U-shaped cold cathode tubes 3a, 3b, 3c, 3d for irradiating the liquid crystal panel 4 for the liquid crystal television from the back side. , And a separately excited inverter circuit 2 for driving these U-shaped cold cathode tubes. As will be described in detail later, the substrate of the separately excited inverter circuit 2 can be shared for mounting three U-shaped cold cathode tube components and four U-shaped cold cathode tube components. it can.

  Next, referring to FIG. 1, when the number of U-shaped cold cathode tubes provided in the backlight device 1 is four, the control IC having two control channels is provided for each U. How to control the current flowing through the letter-shaped cold cathode tubes 3a, 3b, 3c, 3d will be described. The control IC controls the current flowing through the upper two U-shaped cold cathode fluorescent lamps 3a and 3b through one of the two control channels, and the lower through the other channel. The current flowing through the two U-shaped cold cathode fluorescent lamps 3c and 3d is controlled. More specifically, the control IC has 1 from the top based on the current flowing through the upper U-shaped cold cathode tube 3a among the first and second U-shaped cold cathode tubes 3a and 3b from the top. The current flowing through the second and second U-shaped cold cathode tubes 3a and 3b is feedback-controlled through the same channel, and the first and second U-shaped cold cathode tubes 3c and 3d from the bottom are: Based on the current flowing in the upper U-shaped cold cathode tube (second U-shaped cold cathode tube) 3c from the upper side, the current flowing in the first and second U-shaped cold cathode tubes 3c, 3d from the bottom Feedback control.

  Here, in general, for each cold cathode tube constituting the backlight device, the temperature of the upper cold cathode tube is more likely to rise than the lower cold cathode tube due to the heat generated by each cold cathode tube. Moreover, the current flowing through each cold cathode tube becomes easier to flow as the temperature of each cold cathode tube is higher. For this reason, the current flows more easily in the upper cold cathode tube than in the lower cold cathode tube. For example, for the upper two U-shaped cold cathode tubes 3a and 3b, as shown in FIGS. 2 (a) and 2 (b), the current value IA flowing through the upper cold cathode tube 3a It becomes larger than the current value IB flowing through the cathode tube 3b.

  Therefore, as described above, each of the cold cathodes is based on the current flowing through the upper U-shaped cold cathode tube in which the current flows more easily among the two U-shaped cold cathode tubes arranged adjacent to each other in the vertical direction. By feedback control of the current flowing in the tube, not only the upper U-shaped cold cathode tube on the control side but also the lower U-shaped cold cathode tube on the non-control side, the current exceeding the rated current flows. Can be prevented. For example, with respect to the upper two U-shaped cold cathode tubes 3a and 3b, as shown in FIG. 2A, the upper U-shaped cold cathode tubes 3a and 3b have an upper U-shaped cold cathode tube 3a and 3b. By feedback controlling the current flowing through the two U-shaped cold cathode tubes 3a and 3b based on the current flowing through the cathode tube 3a, not only the upper U-shaped cold cathode tube 3a on the control side but also the non-control side The lower U-shaped cold cathode fluorescent lamp 3b can be prevented from flowing a current higher than the rated current. On the other hand, as shown in FIG. 2B, of the two U-shaped cold cathode tubes 3a and 3b arranged adjacent to each other in the vertical direction, the lower U-shaped cold cathode tube is provided. Assuming that the current flowing through the two U-shaped cold cathode tubes 3a and 3b is feedback-controlled based on the current flowing through 3b, a current equal to or higher than the rated current flows through the lower U-shaped cold cathode tube 3b on the control side. However, it is difficult to prevent a current exceeding the rated current from flowing through the upper U-shaped cold cathode tube 3a on the non-control side due to the relationship of the current value IA> the current value IB. .

  In addition, as described above, the control IC has two U-shaped cold-cathode tubes (the upper two U-shaped cold-cathode tubes 3a and 3b and the lower two-shaped cold-cathode tubes 3a and 3b, and the lower two). The reason why the current flowing through the U-shaped cold cathode fluorescent lamps 3c and 3d) is feedback-controlled through the same channel is as follows. That is, the two U-shaped cold cathode tubes arranged adjacent to each other in the vertical direction have a smaller temperature difference than the U-shaped cold cathode tubes separated in the vertical direction. By applying the same voltage for current control through the same channel to a group of two U-shaped cold cathode tubes arranged adjacent to each other, a U-shaped cold cathode tube on the non-control side This is because a current having a value close to that of the U-shaped cold cathode tube on the control side can be passed, and the luminance of the U-shaped cold cathode tubes 3b and 3d on the non-control side does not have to be reduced more than necessary.

  Further, when the number of U-shaped cold cathode tubes arranged in the backlight device 1 is three, the same channel is used as in the case where the number of U-shaped cold cathode tubes is four. Of the two U-shaped cold-cathode tubes controlled via the upper U-shaped cold-cathode tube, the current flowing in each cold-cathode tube is feedback-controlled based on the current flowing in the upper U-shaped cold-cathode tube. In addition to the U-shaped cold cathode tube, the lower U-shaped cold cathode tube on the non-control side can be prevented from flowing a current higher than the rated current.

  Next, the substrate of the separately excited inverter circuit 2 will be described with reference to FIGS. FIG. 3A shows the arrangement of each component group on the substrate of the separately excited inverter circuit 2 when the number of U-shaped cold cathode tubes is four, and FIG. An arrangement of each component group on the substrate of the separately excited inverter circuit 2 when the number of cold cathode tubes is three is shown. In these drawings, parts groups A, B, C, and D are parts groups corresponding to the U-shaped cold cathode tubes 3a, 3b, 3c, and 3d in FIG. , C and D are all MOS-FETs (Metal Oxide Semiconductor Field Effect Transistors) for driving each U-shaped cold cathode tube, and no ballast capacitor is used to increase the voltage output to each U-shaped cold cathode tube.・ It is composed of an inverter transformer. Further, a common component group 23 in FIGS. 3A and 3B is a component group that is commonly used for driving all the U-shaped cold cathode tubes 3a, 3b, 3c, and 3d, and this common component group. 23 includes the control IC 22 described above. This control IC 22 has a voltage for controlling the output current to each U-shaped cold cathode tube 3a, 3b, 3c, 3d at the gate of each MOS-FET in the above component group A, B, C, D. Is applied to feedback control the current flowing through each of the U-shaped cold cathode tubes 3a, 3b, 3c, 3d.

  Further, as shown in FIGS. 3A and 3B, when the number of U-shaped cold cathode tubes is three, it is mounted on the substrate 21 when the number of U-shaped cold cathode tubes is four. Among the four component groups A, B, C, and D, the component group B corresponding to the second U-shaped cold cathode tube 3b from the top is not mounted on the substrate 21 (the component group on the substrate 21). Area 24 where B is to be mounted was opened). As a result, when the number of U-shaped cold cathode tubes is three, feedback control is performed on the current flowing through the second U-shaped cold cathode tube from the top (second U-shaped cold cathode tube from the bottom) 3c. Therefore, it is possible to stabilize the luminance at the center in the vertical direction of the screen, which should be most stabilized on the display screen of the liquid crystal television. Further, when the number of U-shaped cold cathode tubes is three, the only U-shaped cold cathode tube on the non-control side has the most heat generated by each of the cold cathode tubes 3a, 3b, 3c, 3d. Since it can be the first U-shaped cold cathode tube 3d from the bottom that is difficult to receive (only receives the heat generated by its own tube), the luminance of the entire display screen of the liquid crystal television can be stabilized.

  On the other hand, in the case where the number of U-shaped cold cathode tubes is three, when the number of U-shaped cold cathode tubes is four, the four component groups A, B, Of C and D, the component group D corresponding to the lowermost U-shaped cold cathode tube 3d is not mounted on the substrate 21, and the control IC 22 is connected to the upper U-shaped cold cathode via one channel. When the current flowing through the tube 3a and the middle U-shaped cold cathode tube 3b is controlled and the lower U-shaped cold cathode tube 3c is controlled through the other channel, the middle U-shaped cold cathode tube 3c is controlled. Since the U-shaped cold cathode tube 3b hits the lower U-shaped cold cathode tube among the U-shaped cold cathode tubes 3a and 3b controlled through the same channel, the control is not performed. Therefore, it is impossible to stabilize the luminance at the center portion in the vertical direction of the screen, which must be most stabilized on the display screen of the liquid crystal television.

  FIG. 4 shows a schematic circuit configuration of the backlight device 1 when the number of U-shaped cold cathode tubes is four. In the drawing, each U-shaped cold cathode tube 3a, 3b, 3c, 3d is represented by the same shape as a straight tube type cold cathode tube for simplification. Each component group A, B, C, D mainly includes switching circuits (SW circuits) 31, 33, 35, 37 for driving the U-shaped cold cathode tubes 3a, 3b, 3c, 3d, It comprises ballast capacitorless inverter transformers (capacitorless inverter transformers) 32, 34, 36, 38 for increasing the voltage output to the U-shaped cold cathode tubes 3a, 3b, 3c, 3d. The SW circuits 31, 33, 35, and 37 are mainly composed of MOS-FETs.

  Between the above-mentioned parts groups A, B, C, D and the control IC 22, a line L41 (for applying a control voltage from the control IC 22 to the parts groups A, B, C, D) ( A line L42 (corresponding to the second channel in claim 1) and a line L42 are provided. Further, between the control IC 22 and the U-shaped cold cathode tube 3a, and between the control IC 22 and the U-shaped cold cathode tube 3c, for feedback control of the current flowing through the U-shaped cold cathode tube 3a, respectively. Line L43 and a line L44 for feedback control of the current flowing through the U-shaped cold cathode tube 3c. The control IC 22 detects the current value flowing through the U-shaped cold cathode tube 3a via the line L43, and is necessary for feedback control of the current flowing through the U-shaped cold cathode tube 3a based on the detected current value. In addition to determining the duty ratio of the waveform of the correct voltage, a voltage having a waveform corresponding to the determined duty ratio is applied to the SW circuits 31 and 33 from the line L41. The control IC 22 detects the current value flowing through the U-shaped cold cathode tube 3c via the line L44, and feedback-controls the current flowing through the U-shaped cold cathode tube 3c based on the detected current value. In addition, the duty ratio of the waveform of the voltage necessary for the above is obtained, and the voltage of the waveform corresponding to the obtained duty ratio is applied from the line L42 to the SW circuits 35 and 37 (the gate side of the MOS-FET in the line). The SW circuits 31, 33, 35, and 37 output a voltage corresponding to the duty ratio of the waveform of the input voltage to the ballast capacitorless inverter transformers 32, 34, 36, and 38. The ballast capacitorless inverter transformers 32, 34, 36, and 38 amplify (increase) the voltage output from the SW circuits 31, 33, 35, and 37, and the U-shaped cold cathode tubes 3a, 3b, and 3c. 3d.

  As described above, according to the separately excited inverter circuit 2 of the backlight device 1 of the present embodiment, the control IC 22 has the SW corresponding to the two U-shaped cold cathode tubes 3a and 3b located above the line L41. A voltage for feedback control of the current flowing through the first U-shaped cold cathode tube 3a from the top is applied to the circuits 31 and 33, and the two U-shaped cold cathode tubes 3c on the lower side from the line L42 are applied. A voltage for feedback control of the current flowing through the U-shaped cold cathode tube 3c, which is the second from the bottom, is applied to 3d. As a result, of the first and second U-shaped cold cathode tubes 3a and 3b from the top, the current flowing in the upper U-shaped cold cathode tube (first U-shaped cold cathode tube) 3a is used as a reference. In addition, the current flowing through the first and second U-shaped cold cathode tubes 3a and 3b from the top can be feedback controlled, and the first and second U-shaped cold cathode tubes 3c and 3d from the bottom Based on the current flowing through the upper U-shaped cold cathode tube (second U-shaped cold cathode tube) 3c, the current flowing through the first and second U-shaped cold cathode tubes 3c and 3d from the bottom Can be feedback controlled. Here, in general, for each cold cathode tube constituting the backlight device, the temperature of the upper cold cathode tube is more likely to rise than the lower cold cathode tube due to the heat generated by each cold cathode tube. Moreover, the current of each cold cathode tube becomes easier to flow as the temperature of each cold cathode tube is higher. For this reason, the current flows more easily in the upper cold cathode tube than in the lower cold cathode tube. Therefore, as described above, of the two U-shaped cold cathode tubes 3a and 3b (or 3c and 3d) arranged adjacent to each other in the vertical direction, the upper U-shaped cold cathode tube 3a ( Alternatively, the current flowing in each U-shaped cold cathode tube 3a, 3b (or 3c, 3d) is feedback-controlled based on the current flowing in 3c), so that the upper U-shaped cold cathode tube 3a (or In addition to 3c), it is possible to prevent a current exceeding the rated current from flowing in the U-shaped cold cathode tube 3b (or 3d) on the lower side of the non-control side.

  Also, two U-shaped cold cathode tubes (the first and second U-shaped cold cathode tubes 3a and 3b from the top, and the first and second U-shaped from the bottom) arranged adjacent to each other in the vertical direction. Since the cold cathode tubes 3c, 3d) have a smaller temperature difference than the U-shaped cold cathode tubes separated in the vertical direction, the control ICs 22 are arranged adjacent to each other in the vertical direction as described above. By applying the same voltage for current control to the component groups of the two U-shaped cold cathode tubes 3a, 3b (or 3c, 3d) via the same line L41 (or L42), A current close to that of the U-shaped cold cathode tube 3a (or 3c) on the control side can be passed through the U-shaped cold cathode tube 3b (or 3d) on the non-control side. Therefore, it is not necessary to reduce the luminance of the U-shaped cold cathode tube 3b (or 3d) on the non-control side more than necessary.

  Further, when the number of U-shaped cold cathode tubes is three, the four component groups A, B, C, and D mounted on the substrate 21 when the number of U-shaped cold cathode tubes is four. Among them, the component group B corresponding to the second U-shaped cold cathode tube 3 b from the top is not mounted on the substrate 21. As a result, when the number of U-shaped cold cathode tubes is three, feedback control is performed on the current flowing through the second U-shaped cold cathode tube from the top (second U-shaped cold cathode tube from the bottom). Therefore, it is possible to stabilize the luminance at the center portion in the vertical direction of the screen, which should be most stabilized on the display screen of the liquid crystal television. Further, when the number of U-shaped cold cathode tubes is three, the only U-shaped cold cathode tube on the non-control side is least susceptible to the heat generated by each cold cathode tube (the own tube emits). Since it can be the first U-shaped cold cathode tube from the bottom (which only receives heat), the luminance of the entire display screen of the liquid crystal television can be stabilized.

  In addition, this invention is not restricted to the said embodiment, Various deformation | transformation are possible. For example, in the above embodiment, an example in which the present invention is applied to a separately excited inverter circuit of a backlight device for a liquid crystal television has been described. However, a separately excited inverter circuit of a backlight device to which the present invention is applied. Is not limited to a liquid crystal television, but may be a back-excited inverter circuit for a liquid crystal monitor of a personal computer. Moreover, although the said embodiment demonstrated the example at the time of applying this invention to the back-excited type inverter of the backlight apparatus which has three or four U-shaped cold cathode tubes, it becomes an application object of this invention. The separately excited inverter is not limited to this, and may be, for example, a separately excited inverter of a backlight device having two or three U-shaped cold cathode tubes. In the above embodiment, an example in which the SW circuits 31, 33, 35, and 37 are configured using MOS-FETs is shown. However, switches such as SIT (Static Induction Transistor) and SI (Static Induction) thyristors are used. The SW circuit may be configured using

The figure which shows the four U-shaped cold cathode tubes connected to the separately excited inverter circuit of the backlight apparatus by one Embodiment of this invention, and this separately excited inverter circuit. (A) and (b) are the U and U values when the current flowing through the upper U-shaped cold cathode tube is controlled as a reference and when the current flowing through the lower U-shaped cold cathode tube is controlled as a reference. The figure which shows the magnitude relationship of the electric current value which flows into a letter-shaped cold cathode tube. (A) is a figure which shows arrangement | positioning of each component group on the board | substrate of a separately excited inverter circuit when the number of the U-shaped cold cathode tubes in the said backlight apparatus is four, (b) is U-shaped The figure which shows arrangement | positioning of each component group on the board | substrate of a separately excited inverter circuit in case the number of type | mold cold cathode tubes is three. The schematic circuit block diagram of a backlight apparatus in case the number of the U-shaped cold cathode tubes in the said backlight apparatus is four.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight apparatus 2 Separately excited inverter circuit 3a, 3b, 3c, 3d U-shaped cold cathode tube 4 Liquid crystal panel 21 Substrate 22 Control IC
31, 33, 35, 37 SW circuit (switching circuit, MOS-FET)
32, 34, 36, 38 Ballast capacitorless inverter transformer A, B, C, D Parts group L41 line (first channel)
L42 line (second channel)

Claims (4)

Each of the U-shaped cold cathode tubes provided among the three or four U-shaped cold cathode tubes arranged in parallel in the left-right direction of the liquid crystal panel of the backlight device for the liquid crystal television. A plurality of components including a MOS-FET (Metal Oxide Semiconductor Field Effect Transistor) for driving a U-shaped cold cathode tube, a ballast capacitorless inverter transformer, and the like for increasing a voltage output to each U-shaped cold cathode tube Group,
A control IC for applying a voltage for controlling an output current to each U-shaped cold cathode tube to the gates of the MOS-FETs in the plurality of component groups;
A board on which the plurality of component groups and the control IC are mounted,
The plurality of parts groups are divided into two groups,
The control IC has two control channels corresponding to each of the two groups, and for each feedback control of the output current to each U-shaped cold cathode tube, In a separately excited inverter circuit for a backlight device for a liquid crystal television that applies a control voltage with a different duty ratio to
The board can be shared for mounting three U-shaped cold cathode tube components and four U-shaped cold cathode tube components,
When the number of the U-shaped cold cathode tubes is three, the first group of the two groups is the first U-shaped from the top of these three U-shaped cold cathode tubes. When the number of U-shaped cold-cathode tubes is four, which is composed of only parts corresponding to the cold-cathode tubes, the first U-shaped one from the top of these four U-shaped cold-cathode tubes A component group corresponding to the cold cathode tube and a component group corresponding to the second U-shaped cold cathode tube from the top;
The second group of the two groups includes a component group corresponding to the first U-shaped cold cathode tube from the bottom of the three or four U-shaped cold cathode tubes and the second group from the bottom. And a group of parts corresponding to the U-shaped cold cathode tube,
The control IC changes from the first channel of the two control channels to the first U-shaped cold cathode tube from the top with respect to each component group included in the first group. A voltage for feedback control of the flowing current is applied, and from the second channel of the two control channels, the second group from the bottom is applied to each component group included in the second group. Apply a voltage for feedback control of the current flowing in the U-shaped cold cathode tube,
When the number of U-shaped cold cathode tubes is three, the second from the top among the four component groups mounted on the substrate when the number of U-shaped cold cathode tubes is four A separately excited inverter circuit for a backlight device for a liquid crystal television, wherein a component group corresponding to the U-shaped cold cathode tube is not mounted on the substrate. A switching circuit for driving each cold cathode tube provided for each of the cold cathode tubes among a plurality of cold cathode tubes arranged in parallel in the left-right direction of the liquid crystal panel of the backlight device, A plurality of component groups consisting of inverter transformers and the like for increasing the voltage output to each cold cathode tube ;
A control IC for applying a voltage for controlling an output current to each of the cold cathode tubes to a switching circuit in the plurality of component groups;
A board on which the plurality of component groups and the control IC are mounted;
The control IC is a back-excited inverter circuit that applies a control voltage to each switching circuit in order to feedback control the output current to each cold cathode tube .
The plurality of parts groups are divided into two or more groups,
The control IC includes, among the cold cathode tubes corresponding to the component groups included in each group, a voltage for feedback control of the current flowing in the uppermost cold cathode tube, and each component included in the corresponding group. A separately-excited inverter circuit for a backlight device applied to a switching circuit in the group. The substrate can be shared for mounting components for different numbers of cold cathode tubes,
When the number of parts included in each group and the number of cold cathode tubes corresponding to these parts are one, the number of parts included in each group and the cold cathode tubes corresponding to these parts 3. A component group corresponding to a lower cold-cathode tube among the two component groups mounted on the substrate when the number is two is not mounted on the substrate. A back-excited inverter circuit as described in 1. The plurality of cold cathode tubes arranged in parallel in the left-right direction of the liquid crystal panel of the backlight device are three or four U-shaped cold cathode tubes,
The substrate can be shared for mounting three U-shaped cold cathode tube components and four U-shaped cold cathode tube components,
When the number of U-shaped cold cathode tubes is three, the second from the top among the four component groups mounted on the substrate when the number of U-shaped cold cathode tubes is four. 3. The back-excited inverter circuit according to claim 2, wherein a component group corresponding to a U-shaped cold cathode tube is not mounted on the substrate.

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