CN110379373A - Backlight drive circuit and its control method and liquid crystal display device - Google Patents
Backlight drive circuit and its control method and liquid crystal display device Download PDFInfo
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- CN110379373A CN110379373A CN201910516870.7A CN201910516870A CN110379373A CN 110379373 A CN110379373 A CN 110379373A CN 201910516870 A CN201910516870 A CN 201910516870A CN 110379373 A CN110379373 A CN 110379373A
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- 239000004973 liquid crystal related substance Substances 0.000 title claims abstract description 28
- 238000000034 method Methods 0.000 title claims abstract description 16
- 238000001514 detection method Methods 0.000 claims abstract description 38
- 238000010438 heat treatment Methods 0.000 claims description 15
- 238000012512 characterization method Methods 0.000 abstract 1
- 230000003068 static effect Effects 0.000 description 6
- 239000010409 thin film Substances 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 230000005669 field effect Effects 0.000 description 3
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- 230000017525 heat dissipation Effects 0.000 description 1
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- 239000000463 material Substances 0.000 description 1
- 239000012788 optical film Substances 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
- G09G3/3406—Control of illumination source
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Abstract
This application discloses a kind of backlight drive circuit and its control method and liquid crystal display devices, comprising: lamp bar；First driving chip and the second driving chip provide corresponding driving current to lamp bar when opening respectively；Temperature detecting module, it is disposed adjacent with the heater element in backlight drive circuit to detect the temperature of heater element, the detection voltage of output characterization temperature, and a control signal is generated according to detection voltage and reference voltage, switching control module, for opening the first driving chip when controlling signal and being the first level state and turning off the second driving chip, and the first driving chip and the second driving chip are opened when controlling signal and being second electrical level state, adaptively the working condition of the first driving chip and the second driving chip can be controlled according to Current Temperatures, the deformed damaged of adjacent elements caused by not only avoidable driving chip temperature is excessively high, and the quiescent dissipation of backlight drive circuit can be reduced.
Description
Technical Field
The present invention relates to the field of display technologies, and in particular, to a backlight driving circuit, a control method thereof, and a liquid crystal display device.
Background
A Liquid Crystal Display (LCD) is a Display device that changes the light transmittance of a light source by utilizing the phenomenon that the alignment direction of Liquid Crystal molecules changes under the action of an electric field. Liquid crystal display devices have been widely used in mobile terminals such as mobile phones and large-sized display panels such as flat panel televisions due to advantages of good display quality, small volume, and low power consumption.
Since the liquid crystal panel does not emit light, the backlight module is one of the key components of the liquid crystal display device because the light source provided by the backlight module is needed to normally display the image.
The backlight module is divided into a side-in type backlight module and a direct type backlight module according to different incident positions of the light source. In the direct type backlight module, a Light source such as a CCFL (Cathode Fluorescent Lamp) or an LED (Light Emitting Diode) is disposed behind a liquid crystal panel to directly form a surface Light source to provide to the liquid crystal panel. The edge of the back Plate at the rear side of the liquid crystal panel is provided with a backlight lamp bar (Light bar), Light rays emitted by the lamp bar enter the Light Guide Plate from a Light incident surface at one side of the Light Guide Plate (LGP), are emitted from a Light emitting surface of the Light Guide Plate after being reflected and diffused, and are formed into a surface Light source through the optical film group to be provided for the liquid crystal panel.
The LED has the advantages of high brightness, low operating voltage, low power consumption, and the like, and thus is widely applied to the liquid crystal display device, but the light emitting diode also has the characteristics of large heat productivity, difficulty in heat dissipation, and the like, and often causes the operating temperature of the liquid crystal display device to be too high.
Fig. 1 shows a circuit diagram of a backlight driving circuit in the prior art, and as shown in fig. 1, a backlight driving circuit 10 includes a light bar 11 and a driving chip 12. The driving chip 12 includes an input terminal Vin, an output terminal Vout, and a feedback terminal FB. The output terminal Vout is used for providing a voltage to the light bar 11 to drive the light bar 11. The driving chip 12 adjusts the output current of the driving chip by receiving a PWM (pulse width Modulation) signal inputted from the outside, and then adjusts the current on the light bar 11 to adjust the backlight brightness.
The existing backlight driving circuit has the following problems: the display brightness required by the existing liquid crystal display device is higher and higher, so that the output current of the driving chip is higher and higher, and the working temperature of the driving chip or the inductor is higher and higher. In the conventional lcd device, a Printed Circuit Board (PCB) integrated with a backlight driving Circuit is usually attached to the back of the backlight module, which may be deformed and damaged under the influence of high temperature for a long time, and thus may affect the display brightness and reduce the display effect of the display.
In order to reduce the temperature of the backlight driving circuit, two driving chips are used for driving the light bar of other existing backlight modules, but the static power consumption of the backlight driving circuit is increased, and the power consumption of the liquid crystal display device is increased.
Therefore, further improvement of the related art is expected to improve the display effect of the liquid crystal display device and also to reduce the power consumption of the liquid crystal display device.
Disclosure of Invention
In view of the foregoing, an object of the present invention is to provide a backlight driving circuit, a control method thereof and a liquid crystal display device, which can adaptively control the operating states of a first driving chip and a second driving chip according to the current temperature, so as to avoid the deformation and damage of the adjacent elements caused by the over-high temperature of the driving chips, and reduce the static power consumption of the backlight driving circuit.
According to a first aspect of the present invention, there is provided a backlight driving circuit comprising: a light bar; the first driving chip and the second driving chip respectively provide corresponding driving currents for the light bar when the light bar is started; the temperature detection module is arranged adjacent to a heating element in the backlight driving circuit to detect the temperature of the heating element, outputs detection voltage representing the temperature and generates a control signal according to the detection voltage and reference voltage; and the switching control module is used for turning on the first driving chip and turning off the second driving chip when the control signal is in a first level state, and turning on the first driving chip and the second driving chip when the control signal is in a second level state, wherein the heating element is positioned in the first driving chip.
Preferably, the light bar at least comprises a first LED lamp and a second LED lamp, wherein the first LED lamp receives the driving current provided by the first driving chip, the second LED lamp receives the driving current provided by the second driving chip when the control signal is in the second level state, and receives the driving current provided by the first driving chip when the control signal is in the first level state.
Preferably, the handover control module includes: the enabling control unit is used for providing an enabling signal for the second driving chip according to the control signal; and the connection control unit is used for receiving the driving current provided by the first driving chip through the connection control unit when the control signal is in a first level state, and disconnecting the connection between the second LED lamp and the first driving chip when the control signal is in a second level state.
Preferably, the switching control module further includes: the reference current control unit is used for providing reference current, and the first driving chip outputs corresponding driving current according to the reference current, wherein the reference current provided by the reference current control unit is larger than the reference current provided by the reference current control unit when the control signal is in a first level state.
Preferably, the reference current provided by the reference current control unit when the control signal is in the first level state is 2 times the reference current provided by the reference current control unit when the control signal is in the second level state.
Preferably, the temperature detection module includes: the circuit comprises a first resistor, a second resistor and a thermistor, wherein the first resistor, the second resistor and the thermistor are sequentially connected in series between a power supply voltage and a grounding end, and a node between the thermistor and the second resistor outputs a detection voltage; and the comparator comprises a normal phase input end, an inverted phase input end and an output end, wherein the normal phase input end of the comparator receives the reference voltage, the inverted phase input end of the comparator receives the detection voltage, and the output end of the comparator is used for outputting the control signal.
Preferably, the enable control unit includes a first transistor, a first pole of the first transistor is used for receiving the enable signal, a second pole of the first transistor is connected to the second driving chip, and a control pole of the first transistor is used for receiving the control signal.
Preferably, the connection control unit includes: a second transistor, a first pole of which is connected to the output end of the first driving chip and a second pole of which is connected to the anode of the second LED lamp; a third transistor, a first pole of which is connected to the feedback end of the first driving chip, a second pole of which is connected to the cathode of the second LED lamp, and a control pole of which is used for receiving the control signal; and a third resistor connected in series between the first electrode and the control electrode of the second transistor, wherein when the control signal is in a first level state, the second transistor and the third transistor are turned on, and when the control signal is in a second level state, the second transistor and the third transistor are turned off.
Preferably, the reference current control unit includes a fourth resistor, a fifth resistor, and a fourth transistor; the fourth resistor is connected between the reference end of the first driving chip and a grounding end; the fifth resistor and the fourth transistor are connected in series between the reference terminal of the first driving chip and a ground terminal, and a control electrode of the fourth transistor is used for receiving the control signal.
According to a second aspect of the present invention, a method for controlling a backlight driving circuit is provided, where the backlight driving circuit includes a first driving chip, a second driving chip, and a light bar, and the first driving chip and the second driving chip respectively provide corresponding driving currents to the light bar when the backlight driving circuit is turned on, where the method includes: detecting the temperature of a heating element in the backlight driving circuit, outputting a detection voltage representing the temperature, and generating a control signal according to the detection voltage and a reference voltage; and turning on the first driving chip and turning off the second driving chip when the control signal is in a first level state, and turning on the first driving chip and the second driving chip when the control signal is in a second level state, wherein the heating element is located inside the first driving chip.
According to a third aspect of the present invention, there is provided a liquid crystal display device comprising the backlight driving circuit described above.
The backlight driving circuit, the control method thereof and the liquid crystal display device provided by the invention have the following beneficial effects.
The backlight driving circuit comprises a thermistor arranged on a PCB integrated with the backlight driving circuit, the thermistor provides detection voltage according to the temperature change of the backlight driving circuit, the comparison module provides a control signal according to the detection voltage and the reference voltage, and the switching control module controls the working state of the first driving chip and the second driving chip according to the control signal.
The backlight driving circuit can adaptively control the working states of the first driving chip and the second driving chip according to the current temperature of the backlight driving circuit. When the temperature is too high, the backlight driving circuit works by the double driving chips, so that the output current of each driving chip is reduced, the working temperature of each driving chip is reduced, and the adjacent parts are prevented from being deformed and damaged; when the temperature is lower than the preset temperature, the backlight driving circuit works with the single driving chip, and the static power consumption of the backlight driving circuit is reduced. Similarly, the static power consumption of the liquid crystal display device adopting the backlight driving circuit is also obviously reduced.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:
FIG. 1 shows a circuit schematic of a backlight driving circuit according to the prior art;
fig. 2 shows a circuit schematic diagram of a backlight driving circuit provided according to a first embodiment of the present invention;
fig. 3 is a schematic view showing a structure of a liquid crystal display device provided according to a second embodiment of the present invention;
fig. 4 is a flow chart illustrating a control method of a backlight driving circuit according to a third embodiment of the invention.
Detailed Description
Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by the same or similar reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale.
In the following description, numerous specific details of the invention, such as structure, materials, dimensions, processing techniques and techniques of components, are set forth in order to provide a more thorough understanding of the invention. However, as will be understood by those skilled in the art, the present invention may be practiced without these specific details.
It should be understood that in the following description, a "circuit" refers to a conductive loop formed by at least one element or sub-circuit through an electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.
Fig. 2 is a circuit diagram of a backlight driving circuit according to a first embodiment of the invention, and as shown in fig. 2, the backlight driving circuit 20 includes a light bar 21, a first driving chip 22, a second driving chip 23, a temperature detecting module 24, and a switching control module.
The first driving chip 22 and the second driving chip 23 are used for providing driving current to the light bar 21 when being turned on.
In the present embodiment, the first driving chip 22 and the second driving chip 23 respectively include an input terminal Vin, an output terminal Vout, an enable terminal EN, a feedback terminal FB, and a reference terminal ISET. The light bar 21 is connected between the output terminals Vout and FB of the first and second driving chips 22 and 23.
Further, the light bar 21 at least includes a plurality of first LED lamps and a plurality of second LED lamps, anodes of the plurality of first LED lamps are connected to the output end of the first driving chip 22, and cathodes of the plurality of first LED lamps are connected to the feedback end of the first driving chip 22. Similarly, the anodes of the second LED lamps are connected to the output terminal of the second driving chip 23, and the cathodes are connected to the feedback terminal of the second driving chip 23.
The temperature detection module 24 is disposed adjacent to a heat generating element (e.g., a first driving chip or an inductor) in the backlight driving circuit, so as to detect a temperature of the heat generating element, output a detection voltage Vt representing the temperature, and generate a control signal sw according to the detection voltage Vt and a reference voltage Vref.
As a non-limiting example, the temperature detection module 24 includes a first resistor R1, a second resistor R2, and a thermistor Rt disposed on a PCB (Printed Circuit Board) integrated with a backlight driving Circuit. The first resistor R1, the thermistor Rt and the second resistor R2 are connected in series between the power supply voltage Vcc and the ground GND in this order. A node between the thermistor Rt and the second resistor R2 outputs a detection voltage Vt. Wherein,
the thermistor Rt may be a positive temperature coefficient thermistor or a negative temperature coefficient thermistor.
As a non-limiting example, the temperature sensing module 24 further includes a comparator U1, the comparator U1 including a non-inverting input, an inverting input, and an output. Wherein, the positive phase input end of the positive phase U1 of the comparator is connected with the reference voltage Vref; the inverting input of the comparator U1 is connected to the sense voltage Vt. The output terminal of the comparator U1 is used for outputting the control signal sw.
The switching control module is configured to control the working states of the first driving chip 22 and the second driving chip 23 according to the level state of the control signal sw.
Further, when the temperature of the heating element is less than the preset temperature, the switching control module turns on the first driving chip 22 and turns off the second driving chip 23, and the first driving chip 22 provides driving current to the first LED lamps and the second LED lamps. When the temperature of the heating element is greater than or equal to the preset temperature, the switching control module turns on the first driving chip 22 and the second driving chip 23, the first driving chip 22 provides driving current for the plurality of first LED lamps, and the second driving chip 23 provides driving current for the plurality of second LED lamps.
In the present embodiment, the switching control module includes an enable control unit 25, a connection control unit 26, and a feedback control unit 27.
The enable control unit 25 is connected to an enable terminal of the second driver chip 23, and configured to provide an enable signal EN to the second driver chip 23 according to the control signal sw.
The connection control unit 26 is connected between the first driving chip 22 and the plurality of second LED lamps, and is configured to conduct a current path between the first driving chip 22 and the second LED lamps according to a level state of the control chip. When the temperature of the heating element is less than the preset temperature, the second LED lamp receives the driving current provided by the first driving chip 22 via the connection control unit 26; when the temperature of the heating element is greater than/equal to a preset temperature, the connection control unit 26 disconnects the current path between the second LED lamp and the first driving chip 22.
Further, the switching control module further includes a reference current control unit 29, where the reference current control unit 29 is connected to the reference terminal of the first driving chip 22, and is configured to adjust the reference current ISET of the first driving chip 22 according to the control signal sw, and the first driving chip 22 outputs a corresponding driving current according to the reference current ISET.
As a non-limiting example, the enable control unit 25 includes a first transistor M1, a first pole of the first transistor M1 is used for receiving the enable signal EN, a second pole is connected to the enable terminal of the second driving chip 23, and a control pole is used for receiving the control signal sw.
The connection control unit 26 includes a third resistor R3, and a second transistor M2 and a third transistor M3. A first pole of the second transistor M2 is connected to the output terminal of the first driving chip 22, a second pole is connected to the anodes of the plurality of second LED lamps, and a third resistor R3 is connected in series between the first pole and the control pole of the second transistor M2. The third transistor M3 has a first pole connected to the feedback terminal of the first driving chip 22, a second pole connected to the cathodes of the plurality of second LED lamps, and a control pole for receiving the control signal sw.
The reference current control unit 27 includes a fourth resistor R4, a fifth resistor R5, and a fourth transistor M4, the fourth resistor R4 is connected between the reference terminal of the first driving chip 22 and the ground terminal, the fifth resistor R5 and the fourth transistor M4 are connected in series between the reference terminal of the first driving chip 22 and the ground terminal, and a control electrode of the fourth transistor M4 is configured to receive the control signal sw.
In this embodiment, the first to fourth transistors M1-M4 may be transistors or field effect transistors, and the control electrode may be the base electrode of the transistor or the gate electrode of the field effect transistor; the first pole and the second pole can be an emitter or a collector of a triode, and can also be a source and a drain of a field effect transistor.
Fig. 3 is a schematic structural diagram of a liquid crystal display device according to a second embodiment of the invention, and as shown in fig. 3, the liquid crystal display device 200 includes a display panel 210, a source driving circuit 220, a gate driving circuit 230, a timing control circuit 240, and a backlight driving circuit 250.
The display panel 210 includes a plurality of scan lines and a plurality of data lines, and a plurality of pixel units (not shown) at intersections thereof, each including a thin film transistor and a pixel electrode, respectively. The grid electrodes of the thin film transistors of the pixel units positioned on the same row are connected to the same scanning line, and the source electrodes of the thin film transistors of the pixel units positioned on the same column are connected to the same data line.
The gate driving circuit 230 is connected to the plurality of scan lines for providing gate signals to sequentially scan the plurality of scan lines in each frame period to gate the corresponding thin film transistors. The source driving circuit 220 is connected to a plurality of data lines for applying gray scale voltages corresponding to the gray scale driving signals to the corresponding thin film transistors via the data lines.
The timing control circuit 240 is configured to obtain a timing signal and a gray-scale driving signal of each pixel unit according to the received image data, and provide the timing signal and the gray-scale driving signal to the source driving circuit 220 and the gate driving circuit 230.
The backlight driving circuit 250 is implemented by, for example, a backlight driving circuit shown in fig. 2, and adjusts an on/off time of the backlight according to a duty ratio of a received Pulse Width Modulation (PWM) signal, thereby controlling the backlight luminance.
Fig. 4 is a flowchart illustrating a control method of a backlight driving circuit according to a third embodiment of the present invention. The following describes a control method of the backlight driving circuit according to the present invention in detail with reference to fig. 2 to 4. As shown in fig. 4, the control method of the present embodiment includes steps S110 to S120.
In step S110, a temperature of a heat generating element in the backlight driving circuit is detected, a detection voltage representing the temperature is output, and a control signal is generated according to the detection voltage and a reference voltage.
In step S120, the first driving chip is turned on and the second driving chip is turned off when the control signal is in the first level state, and the first driving chip and the second driving chip are turned on when the control signal is in the second level state. Wherein the heating element is located inside the first driving chip.
Specifically, when the driving chip in the backlight driving circuit operates under the pulse width modulation signal with the duty ratio of 100% for a long time, the temperature of the heat generating element in the backlight driving circuit will gradually increase, and the temperature of the backlight driving circuit needs to be reduced in order to avoid the deformation and damage of the elements adjacent to the backlight driving circuit.
For convenience of explanation, the thermistor Rt is a negative temperature coefficient thermistor, and the first transistor M1 is a PNP transistor or a PMOS transistor, and the second transistor M2, the third transistor M3, and the fourth transistor M4 are NPN transistors or NMOS transistors.
As a non-limiting example, the temperature of the backlight driving circuit is reduced by reducing the duty ratio of the pulse width modulation signal, so that the deformation damage of the adjacent elements caused by the overhigh temperature of the backlight driving circuit is avoided.
As the temperature of the backlight driving circuit decreases, the resistance of the thermistor Rt gradually increases, and when the detection voltage Vt is less than the reference voltage Vref, the control signal sw output by the comparator U1 is at a high level, the first transistor M1 is in an off state, and the third transistor M3 and the fourth transistor M4 are in an on state. Since the first transistor M1 is in the off state, the enable terminal of the second driver chip 23 has no enable signal, and the second driver chip 23 does not operate. Since the fourth transistor M4 is in a conducting state, the fourth resistor R4 and the fifth resistor R5 are connected in parallel between the reference terminal ISET of the first driver chip 22 and the ground terminal GND, and the input current of the reference terminal ISET of the first driver chip 22 becomes large (for example, the reference current provided by the reference current control unit when the control signal is in a high state is 2 times the reference current provided by the reference current control unit when the control signal is in a low state), so that the output voltage of the first driver chip 22 becomes large and the second transistor M2 is turned on. The second and third transistors M2 and M3 turn on current paths between the plurality of second LED lamps and the output and feedback terminals of the first driving chip 22, and thus the first and second LED lamps are simultaneously supplied with driving currents by the first driving chip 22.
As another non-limiting example, as the temperature of the backlight driving circuit increases, the resistance value of the thermistor Rt gradually decreases and the detection voltage Vt gradually increases. When the detection voltage Vt is greater than the reference voltage Vref, the control signal sw output by the comparator U1 is at a low level, and the first transistor M1 is in a turned-on state, and the third transistor M3 and the fourth transistor M4 are in a turned-off state. The enable terminal of the second driver chip 23 receives the enable signal EN through the first transistor M1, and the second driver chip 23 starts to operate. And since the fourth transistor M4 is turned off, only the fourth resistor R4 is connected between the reference terminal ISET of the first driver chip 22 and the ground terminal GND, the input current of the reference terminal ISET of the first driver chip 22 becomes small, the output voltage of the first driver chip 22 becomes small, the second transistor M2 is turned off, and the current path between the plurality of second LED lamps and the feedback terminal and the output terminal of the first driver chip 22 is disconnected. Therefore, the first driving chip 22 supplies a driving current to the first LED lamp, and the second driving chip 23 supplies a driving current to the second LED lamp. Since the first driver chip 22 and the second driver chip 23 operate simultaneously and the input current of the reference terminal ISET of each driver chip becomes small, the amount of heat generated is small and the temperature is lowered.
When the temperature of the driving chip is again lower than the preset temperature, the detection voltage Vt output by the temperature detection module 24 is lower than the reference voltage Vref, the control signal sw output by the comparator U1 is at a high level, the first transistor M1 is in an off state, the second to fourth transistors M2-M4 are in an on state, and the first driving chip 22 provides driving currents to the first LED lamp and the second LED lamp of the light bar 21.
As another non-limiting example, the thermistor Rt may also be a ptc thermistor, the first transistor M1 and the second transistor M2 may be NPN transistors or NMOS transistors, and the third transistor M3 and the fourth transistor M4 may be PNP transistors or PMOS transistors.
Similarly, when the duty ratio of the pwm signal is decreased to lower the temperature of the driver chip, the resistance of the thermistor Rt is small, the detection voltage Vt is greater than the reference voltage Vref, the control signal sw output by the comparator U1 is low, the first transistor M1 is in an off state, and the third transistor M3 and the fourth transistor M4 are in an on state. Since the first transistor M1 is in the off state, the enable terminal of the second driver chip 23 has no enable signal, and the second driver chip 23 does not operate. Since the fourth transistor M4 is in a conducting state, the fourth resistor R4 and the fifth resistor R5 are connected in parallel between the reference terminal ISET of the first driver chip 22 and the ground terminal GND, so that the input current of the reference terminal ISET of the first driver chip 22 becomes large, the output voltage of the first driver chip 22 becomes large, and the second transistor M2 is turned on. The second and third transistors M2 and M3 turn on current paths between the plurality of second LED lamps and the output and feedback terminals of the first driving chip 22, and thus the first and second LED lamps are simultaneously supplied with driving currents by the first driving chip 22.
When the driving chip in the backlight driving circuit operates under the pulse width modulation signal with 100% duty ratio for a long time, the temperature of the backlight driving circuit gradually increases, the resistance value of the thermistor Rt increases along with the increase of the temperature, and the detection voltage Vt output by the temperature detection module 24 becomes smaller, when the detection voltage Vt is smaller than the reference voltage Vref, the control signal sw output by the comparator U1 is at a high level, the first transistor M1 is in a conducting state, and the third transistor M3 and the fourth transistor M4 are in a turning-off state. The enable terminal of the second driver chip 23 receives the enable signal EN through the first transistor M1, and the second driver chip 23 starts to operate. And since the fourth transistor M4 is turned off, only the fourth resistor R4 is connected between the reference terminal ISET of the first driver chip 22 and the ground terminal GND, the input current of the reference terminal ISET of the first driver chip 22 becomes small, the output voltage of the first driver chip 22 becomes small, the second transistor M2 is turned off, and the current path between the plurality of second LED lamps and the feedback terminal and the output terminal of the first driver chip 22 is disconnected. Therefore, the first driving chip 22 supplies a driving current to the first LED lamp, and the second driving chip 23 supplies a driving current to the second LED lamp. Since the input current of the reference terminal ISET of the first driver chip 22 becomes small, the driving current of the first driver chip 22 becomes small, the amount of heat generated is small, and the temperature is reduced.
When the temperature of the driving chip is again lower than the preset temperature, the detection voltage Vt is higher than the reference voltage Vref, the control signal sw output by the comparator U1 is at a low level, the first transistor M1 is in an off state, the second to fourth transistors M2-M4 are in an on state, and the first driving chip 22 provides driving currents to the first LED lamp and the second LED lamp of the light bar 21.
The backlight driving circuit provided by the invention comprises a thermistor arranged on a PCB integrated with the backlight driving circuit, the thermistor provides detection voltage according to the temperature change of the backlight driving circuit, a comparison module provides a control signal according to the detection voltage and a reference voltage, and a switching control module controls the working state of a first driving chip and a second driving chip according to the control signal.
The backlight driving circuit can adaptively control the working states of the first driving chip and the second driving chip according to the current temperature of the backlight driving circuit. When the temperature is too high, the backlight driving circuit works by the double driving chips, so that the output current of each driving chip is reduced, the working temperature of each driving chip is reduced, and the adjacent parts are prevented from being deformed and damaged; when the temperature is lower than the preset temperature, the backlight driving circuit works with a single driving chip, so that the static power consumption of the backlight driving circuit is reduced while the display image quality is improved. Similarly, the static power consumption of the liquid crystal display device adopting the backlight driving circuit is also obviously reduced.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.
Claims (10)
1. A backlight driving circuit, comprising:
a light bar;
the first driving chip and the second driving chip respectively provide corresponding driving currents for the light bar when the light bar is started;
the temperature detection module is arranged adjacent to a heating element in the backlight driving circuit to detect the temperature of the heating element, outputs detection voltage representing the temperature and generates a control signal according to the detection voltage and reference voltage; and
a switching control module for turning on the first driving chip and turning off the second driving chip when the control signal is in a first level state, and turning on the first driving chip and the second driving chip when the control signal is in a second level state,
wherein the heating element is located inside the first driving chip.
2. The backlight driving circuit of claim 1, wherein the light bar comprises at least a first LED light and a second LED light,
wherein the first LED lamp receives the driving current provided by the first driving chip,
the second LED lamp receives the driving current provided by the second driving chip when the control signal is in a second level state, and receives the driving current provided by the first driving chip when the control signal is in a first level state.
3. The backlight driving circuit according to claim 2, wherein the switching control module comprises:
the enabling control unit is used for providing an enabling signal for the second driving chip according to the control signal; and
and the connection control unit is used for receiving the driving current provided by the first driving chip by the second LED lamp when the control signal is in a first level state, and disconnecting the connection between the second LED lamp and the first driving chip when the control signal is in a second level state.
4. The backlight driving circuit according to claim 3, wherein the switching control module further comprises:
a reference current control unit for providing a reference current, the first driving chip outputting a corresponding driving current according to the reference current,
when the control signal is in a first level state, the reference current provided by the reference current control unit is larger than the reference current provided by the reference current control unit when the control signal is in a second level state.
5. The backlight driving circuit according to claim 1, wherein the temperature detecting module comprises:
the circuit comprises a first resistor, a second resistor and a thermistor, wherein the first resistor, the second resistor and the thermistor are sequentially connected in series between a power supply voltage and a grounding end, and a node between the thermistor and the second resistor outputs a detection voltage; and
a comparator including a positive input terminal, a negative input terminal, and an output terminal,
the positive phase input end of the comparator receives the reference voltage, the negative phase input end of the comparator receives the detection voltage, and the output end of the comparator is used for outputting the control signal.
6. The backlight driving circuit according to claim 3, wherein the enable control unit comprises a first transistor having a first pole for receiving the enable signal, a second pole connected to the second driving chip, and a control pole for receiving the control signal.
7. The backlight driving circuit according to claim 3, wherein the connection control unit comprises:
a second transistor, a first pole of which is connected to the output end of the first driving chip and a second pole of which is connected to the anode of the second LED lamp;
a third transistor, a first pole of which is connected to the feedback end of the first driving chip, a second pole of which is connected to the cathode of the second LED lamp, and a control pole of which is used for receiving the control signal; and
a third resistor connected in series between the first electrode and the control electrode of the second transistor,
when the control signal is in a first level state, the second transistor and the third transistor are turned on, and when the control signal is in a second level state, the second transistor and the third transistor are turned off.
8. The backlight driving circuit according to claim 4, wherein the reference current control unit comprises a fourth resistor, a fifth resistor, and a fourth transistor;
the fourth resistor is connected between the reference end of the first driving chip and a grounding end;
the fifth resistor and the fourth transistor are connected in series between the reference terminal of the first driving chip and a ground terminal, and a control electrode of the fourth transistor is used for receiving the control signal.
9. A control method of a backlight driving circuit, the backlight driving circuit comprises a first driving chip, a second driving chip and a light bar, the first driving chip and the second driving chip respectively provide corresponding driving currents for the light bar when the backlight driving circuit is started, and the control method comprises the following steps:
detecting the temperature of a heating element in the backlight driving circuit, outputting a detection voltage representing the temperature, and generating a control signal according to the detection voltage and a reference voltage; and
turning on the first driving chip and turning off the second driving chip when the control signal is in a first level state, and turning on the first driving chip and the second driving chip when the control signal is in a second level state,
wherein the heating element is located inside the first driving chip.
10. A liquid crystal display device comprising the backlight driving circuit according to any one of claims 1 to 8.
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| CN110379373B (en) | 2021-03-09 |
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