Backlight driving circuit applied to liquid crystal display device, backlight module and display device

Abstract

The backlight driving circuit comprises a feedback current setting module which is connected with an LED driving module and used for providing feedback current setting signals for adjusting backlight current for the LED driving module, a positive input end of a comparator is electrically connected with an intermediate node of a first voltage dividing branch, and a negative input end of the comparator is electrically connected with a negative node of a second voltage dividing branch. A negative input end of the switching tube is electrically connected with an intermediate node of the second voltage dividing branch, a control end of the switching tube is electrically connected with an output end of the comparator, a first conduction end of the switching tube is electrically connected with an output end of a feedback current setting signal, and a first thermistor is connected in parallel between the first conduction end and a second conduction end of the switching tube; the first voltage dividing branch and the second voltage dividing branch comprise at least one second thermistor, so that when the environment temperature of the liquid crystal display device reaches a preset threshold value, high-low level conversion occurs to the output of the comparator, and the switching tube is controlled to be switched off. And the feedback current can be adjusted in real time according to the temperature.

Description

Technical Field

[0001] The utility model relates to the field of display technology, in particular to a backlight driving circuit, a backlight module and a display device applied to a liquid crystal display device. Background Art

[0002] Liquid crystal display (LCD) has many advantages such as thin body, power saving, no radiation, etc., and has been widely used. Most of the liquid crystal display devices on the current market are backlight type liquid crystal display devices, which include a liquid crystal panel and a backlight module. The working principle of the liquid crystal panel is to place liquid crystal molecules between two parallel glass substrates. There are many vertical and horizontal fine wires between the two glass substrates. The liquid crystal molecules are controlled to change direction by powering on or off, and the light of the backlight module is refracted to produce a picture. Since the liquid crystal panel itself does not emit light, it needs to rely on the light source provided by the backlight module to display the image normally. Therefore, the backlight module becomes one of the key components of the liquid crystal display device. The backlight module is divided into two types: side-entry backlight module and direct-down backlight module according to the different incident positions of the light source. The direct-down backlight module is to place a light source such as CCFL (Cold Cathode Fluorescent Lamp) or LED (Light Emitting Diode) behind the liquid crystal panel to directly form a surface light source to provide to the liquid crystal panel. The edge-type backlight module is a module in which the backlight LED light bar is placed on the edge of the back panel behind the LCD panel. The light emitted by the LED light bar enters the light guide plate (LGP) from the light incident surface on one side, and is emitted from the light exiting surface of the light guide plate after reflection and diffusion. It then passes through the optical film group to form a surface light source to be provided to the LCD panel.

[0003] LED has the advantages of high brightness, low operating voltage, low power consumption, etc., so it has been widely used in liquid crystal display devices. However, light-emitting diodes also have the characteristics of high heat generation and difficulty in heat dissipation, which leads to excessively high operating temperature of the liquid crystal display device, thereby causing problems such as deformation and damage of the reflector or light guide plate. Utility Model Content

[0004] In view of the above problems, the purpose of the present invention is to provide a backlight driving circuit, a backlight module and a display device for a liquid crystal display device, so as to avoid the operating temperature of the liquid crystal display device being too high, thereby causing deformation and damage of the reflective sheet or light guide plate, etc.

[0005] According to one aspect of the present invention, there is provided a backlight driving circuit for a liquid crystal display device, the backlight driving circuit comprising an LED driving module, for providing a driving voltage to drive an LED backlight source, and adjusting the driving voltage according to a backlight current fed back by the LED backlight source, the backlight driving circuit further comprising: a feedback current setting module, connected to the LED driving module, for providing a feedback current setting signal for adjusting the backlight current to the LED driving module, the feedback current setting module comprising a comparator, a switch tube, a first voltage dividing branch, and a second voltage dividing branch, the positive input terminal of the comparator being electrically connected to an intermediate node of the first voltage dividing branch, the negative input terminal being electrically connected to an intermediate node of the second voltage dividing branch, the control terminal of the switch tube being electrically connected to an output terminal of the comparator, the first conduction terminal of the switch tube being electrically connected to an output terminal of the feedback current setting signal, a first thermistor being connected in parallel between the first conduction terminal and the second conduction terminal of the switch tube, wherein the first voltage dividing branch and the second voltage dividing branch comprise at least one second thermistor, so that when the ambient temperature of the liquid crystal display device reaches a preset threshold, the output of the comparator undergoes a high-low level conversion, and the switch tube is controlled to be turned off.

[0006] Optionally, the first thermistor is a positive temperature coefficient thermistor, and when the switch tube is turned off, the output end current value of the feedback current setting signal changes in the opposite direction of the first thermistor.

[0007] Optionally, the second thermistor is a positive temperature coefficient thermistor, which is arranged in the first voltage divider branch, and the switch tube is an N-type switch tube.

[0008] Optionally, the first voltage divider branch includes: a first resistor and a second thermistor, the first ends of the first resistor and the second thermistor are respectively electrically connected to the positive input end of the comparator, the second end of the first resistor receives a power supply voltage, and the second end of the second thermistor is grounded.

[0009] Optionally, the second thermistor is a positive temperature coefficient thermistor, which is arranged in the second voltage dividing branch, and the switch tube is a P-type switch tube.

[0010] Optionally, the second voltage divider branch includes: a third resistor and a second thermistor, the first ends of the first resistor and the second thermistor are respectively electrically connected to the negative input end of the comparator, the second end of the first resistor receives a power supply voltage, and the second end of the second thermistor is grounded.

[0011] Optionally, the positive power supply terminal of the comparator receives a power supply voltage, the negative power supply terminal is grounded, and a feedback resistor is further provided between the output terminal and the negative input terminal of the comparator.

[0012] Optionally, a fifth resistor is further included, a first end of the fifth resistor is electrically connected to the second conduction end of the switch tube, and a second end of the fifth resistor is grounded.

[0013] According to another aspect of the present invention, there is provided a backlight module, comprising: a backlight driving circuit as described in any one of the above items; and a plurality of the LED backlight sources, each of the driving voltage output terminals being connected to the anodes of one or more corresponding LED backlight sources, and the cathodes of the one or more corresponding LED backlight sources being connected to the LED driving module.

[0014] According to another aspect of the present invention, a display device is provided, comprising: the above-mentioned backlight module.

[0015] The backlight driving circuit provided by the utility model has a feedback current IBF of a fixed value when the temperature is lower than a critical point, and when the temperature is higher than the critical point, the feedback current IBF decreases as the ambient temperature increases, and the LED driving module reduces the driving voltage provided to the backlight source according to the feedback current IFB, thereby reducing the backlight power consumption, reducing the heat generated by the backlight source, lowering the temperature, and preventing the problem of deformation of the light guide plate and the diaphragm. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other purposes, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0017] Figure 1 A schematic block diagram of a backlight module according to an embodiment of the utility model is shown.

[0018] Figure 2 A schematic diagram showing the structure of a feedback current setting module in a backlight driving circuit according to an embodiment of the present invention is shown.

[0019] Figure 3 A line graph showing the feedback current and temperature changes in the backlight driving module according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0020] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements or modules are represented by the same or similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0021] It should be understood that in the following description, a "circuit" may include a single or multiple combined hardware circuits, programmable circuits, state machine circuits, and / or elements capable of storing instructions executed by programmable circuits. When an element or circuit is said to be "connected to" another element or an element or circuit is said to be "connected between" two nodes, it may be directly coupled or connected to another element or there may be an intermediate element, and the connection between the elements may be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there is no intermediate element between the two.

[0022] At the same time, certain words are used in this patent specification and claims to refer to specific components. It should be understood by those skilled in the art that hardware manufacturers may use different terms to refer to the same component. This patent specification and claims do not use differences in names as a way to distinguish components, but rather use differences in components' functions as the criteria for distinction.

[0023] In addition, it should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements defined by the statement "comprise one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements.

[0024] Figure 1 A schematic block diagram of a backlight module according to an embodiment of the utility model is shown.

[0025] The backlight module 100 includes a backlight driving circuit 110 and a plurality of LED backlight sources 120. The backlight driving circuit 110 includes an LED driving module 111 and a feedback current setting module 112.

[0026] The LED driving module 111 is used to provide a driving voltage to drive the LED backlight source 120, and adjust the driving voltage according to the feedback current IFB of the LED backlight source 120. For example, in the case where the backlight module 100 has two LED backlight sources 120, the cathodes K1 and K2 of the LED backlight sources can be connected to the LED driving module 111 to feed back the backlight current.

[0027] The backlight driving circuit 110 further includes a feedback current setting module 112. The feedback current setting module 112 is connected to the LED driving module 111 and is used to provide the LED driving module 111 with a feedback current setting signal for adjusting the backlight current. The LED driving module 111 adjusts the feedback current IFB of the LED backlight source 120 according to the feedback current setting signal.

[0028] In addition, the above-mentioned backlight module includes a gating module (not shown in the figure), for example, it is arranged between the LED backlight source 120 and the output end of the LED driving module 111, and provides a driving voltage for the corresponding LED backlight source 120 according to the backlight source control signal. Through the gating module, each of the driving voltage output ends is connected to the anode of one or more corresponding LED backlight sources.

[0029] The LED driving module 111 may be an integrated circuit chip, such as TPS61181 purchased from Texas Instruments, USA. The feedback current setting module 112 is connected to the ISET pin of TPS61181, and the cathode of the LED backlight source 120 is connected to the IFB pin of the integrated circuit chip such as TPS61181.

[0030] Figure 2 A schematic diagram showing the structure of a feedback current setting module in a backlight driving circuit according to an embodiment of the present invention is shown.

[0031] like Figure 2 As shown, the feedback current setting module includes a comparator U1, a switch tube Q1 and a plurality of resistors, wherein the positive input terminal of the comparator U1 is electrically connected to the first ends of the resistors R1 and R2 respectively, the second end of the resistor R1 receives the power supply voltage VCC, and the second end of the resistor R2 is grounded. The negative input terminal of the comparator U1 is electrically connected to the first ends of the resistors R3 and R4 respectively, the second end of the resistor R3 receives the power supply voltage VCC, and the second end of the resistor R4 is grounded. A resistor R5 is electrically connected between the output terminal and the negative input terminal of the comparator U1. The positive power supply terminal of the comparator U1 receives the power supply voltage VCC, and the negative power supply terminal of the comparator U1 is grounded. The output terminal of the comparator U1 is electrically connected to the control terminal of the switch tube Q1.

[0032] A first end of the resistor R6 is electrically connected to the drain of the switch tube Q1 , a second end of the resistor R6 is grounded, and a resistor R7 is connected in parallel between the source and the drain of the switch tube Q1 .

[0033] In one embodiment, the resistor R2 and the resistor R7 are thermistors with positive temperature coefficients. When the temperature rises, the resistance of the resistor R2 and the resistor R7 increases. The switch tube Q1 is a P-type switch tube.

[0034] By setting the resistors R1, R2, R3 and R4, at normal temperature, the voltage at the middle node between the resistors R1 and R2 is smaller than the voltage at the middle node between the resistors R3 and R4. At this time, the output end of the comparator U1 outputs a low level, the switch tube Q1 is turned on, the ISET pin is only connected to the resistor R6, and the LED driving module 111 receives a fixed feedback current setting signal.

[0035] When the resistance value of resistor R1 changes with temperature and reaches a certain critical point (preset temperature threshold), the voltage at the middle node of resistors R1 and R2 is greater than the voltage at the middle node of resistors R3 and R4. At this time, the output end of comparator U1 outputs a high level, so that the switch tube Q1 is turned off, the ISET pin is connected to resistors R6 and R7, and the LED driving module 111 receives a feedback current setting signal that changes in the opposite direction with the resistance value of resistor R6.

[0036] In another embodiment, the resistor R3 and the resistor R7 are thermistors with positive temperature coefficients. When the temperature rises, the resistance of the resistor R3 and the resistor R7 increases. The switch tube Q1 is an N-type switch tube.

[0037] By setting the resistors R1, R2, R3 and R4, at normal temperature, the voltage at the middle node between the resistors R1 and R2 is smaller than the voltage at the middle node between the resistors R3 and R4. At this time, the output end of the comparator U1 outputs a high level, the switch tube Q1 is turned on, the ISET pin is only connected to the resistor R6, and the LED driving module 111 receives a fixed feedback current setting signal.

[0038] When the resistance value of resistor R3 changes with temperature and reaches a certain critical point (preset temperature threshold), the voltage at the middle node between resistors R1 and R2 is less than the voltage at the middle node between resistors R3 and R4. At this time, the output end of comparator U1 outputs a low level, so that the switch tube Q1 is turned off, the ISET pin is connected to resistors R6 and R7, and the LED driving module 111 receives a feedback current setting signal that changes in the opposite direction with the resistance value of resistor R6.

[0039] The LED driving module 111 adjusts the feedback current IFB of the LED backlight source 120 according to the feedback current setting signal. For example, the feedback current IBF is positively correlated with the feedback current setting signal Iset, so when the current value of the feedback current setting signal Iset decreases, the feedback current IBF also decreases accordingly.

[0040] Figure 3 A line graph showing the feedback current and temperature changes in the backlight driving circuit according to an embodiment of the present invention is shown.

[0041] like Figure 3 As shown above, Figure 2From the circuit diagram, it can be seen that when the temperature is lower than the critical point, the feedback current IBF is a fixed value, and when the temperature is higher than the critical point, the feedback current IBF decreases with the increase of the ambient temperature. The LED driving module 111 reduces the driving voltage provided to the backlight source according to the feedback current IFB, thereby reducing the backlight power consumption, reducing the heat generated by the backlight source, and lowering the temperature, thereby preventing the problem of deformation of the light guide plate and the diaphragm.

[0042] In one embodiment, the present application also provides a display device, comprising the above-mentioned display module.

[0043] It should be noted that it will be understood by those skilled in the art that the words "during", "when" and "when ..." used in this article in connection with the operation of the circuit are not strict terms indicating an action that occurs immediately when the start-up action begins, but that there may be some small but reasonable one or more delays between it and the reaction action initiated by the start-up action, such as various transmission delays, etc. The words "approximately" or "substantially" used in this article mean that the element value has a parameter that is expected to be close to the declared value or position. However, as is well known in the art, there are always slight deviations that make it difficult for the value or position to be strictly the declared value. It has been properly determined in the art that a deviation of at least ten percent (10%) (for semiconductor doping concentrations, at least twenty percent (20%)) is a reasonable deviation from the accurate ideal target described. When used in conjunction with a signal state, the actual voltage value or logic state (e.g., "1" or "0") of the signal depends on whether positive logic or negative logic is used.

[0044] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the present invention to specific embodiments. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that technicians in the relevant technical field can make good use of the present invention and the modified use based on the present invention. The scope of protection of the present invention shall be based on the scope defined by the claims of the present invention and their equivalents.

Claims

1. A backlight driving circuit for a liquid crystal display device, the backlight driving circuit comprising an LED driving module, for providing a driving voltage to drive an LED backlight source, and adjusting the driving voltage according to a backlight current fed back by the LED backlight source, characterized in that: The backlight driving circuit further includes: A feedback current setting module is connected to the LED driving module and is used to provide the LED driving module with a feedback current setting signal for adjusting the backlight current. The feedback current setting module includes a comparator, a switch tube, a first voltage dividing branch, and a second voltage dividing branch. The positive input terminal of the comparator is electrically connected to the middle node of the first voltage dividing branch, and the negative input terminal of the comparator is electrically connected to the middle node of the second voltage dividing branch. The control end of the switch tube is electrically connected to the output end of the comparator, the first conduction end of the switch tube is electrically connected to the output end of the feedback current setting signal, and a first thermistor is connected in parallel between the first conduction end and the second conduction end of the switch tube. The first voltage-dividing branch and the second voltage-dividing branch include at least one second thermistor, so that when the ambient temperature of the liquid crystal display device reaches a preset threshold, the output of the comparator undergoes a high-low level conversion to control the switch tube to be turned off.

2. The backlight driving circuit according to claim 1, characterized in that: The first thermistor is a positive temperature coefficient thermistor. When the switch tube is turned off, the current value at the output end of the feedback current setting signal changes in the opposite direction of the first thermistor.

3. The backlight driving circuit according to claim 2, characterized in that: The second heat The sensitive resistor is a positive temperature coefficient thermistor, which is arranged in the first voltage dividing branch, and the switching tube is an N-type switching tube.

4. The backlight driving circuit according to claim 3, characterized in that: The first voltage dividing branch includes: a first resistor and a second thermistor, wherein the first ends of the first resistor and the second thermistor are electrically connected to the positive input end of the comparator respectively, the second end of the first resistor receives the power supply voltage, and the second end of the second thermistor is grounded.

5. The backlight driving circuit according to claim 2, characterized in that: The second heat The sensitive resistor is a positive temperature coefficient thermistor, which is arranged in the second voltage dividing branch, and the switching tube is a P-type switching tube.

6. The backlight driving circuit according to claim 4, characterized in that: The second voltage dividing branch includes: a third resistor and a second thermistor, wherein the first ends of the first resistor and the second thermistor are electrically connected to the negative input end of the comparator respectively, the second end of the first resistor receives the power supply voltage, and the second end of the second thermistor is grounded.

7. The backlight driving circuit according to claim 2, characterized in that: The positive power supply terminal of the comparator receives the power supply voltage, the negative power supply terminal is grounded, and a feedback resistor is arranged between the output terminal and the negative input terminal of the comparator.

8. The backlight driving circuit according to claim 2, characterized in that: It also includes a fifth resistor, a first end of the fifth resistor is electrically connected to the second conduction end of the switch tube, and a second end of the fifth resistor is grounded.

9. A backlight module, characterized in that: include: The backlight driving circuit according to any one of claims 1 to 8; And a plurality of the LED backlight sources, each of the driving voltage output terminals is connected to the anodes of one or more corresponding LED backlight sources, and the cathodes of the one or more corresponding LED backlight sources are connected to the LED driving module.

10. A display device, characterized in that: include: The backlight module as claimed in claim 9.

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