CN114420054B - Backlight constant current driving circuit, switching power supply and display device - Google Patents
Backlight constant current driving circuit, switching power supply and display device Download PDFInfo
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- CN114420054B CN114420054B CN202111594470.1A CN202111594470A CN114420054B CN 114420054 B CN114420054 B CN 114420054B CN 202111594470 A CN202111594470 A CN 202111594470A CN 114420054 B CN114420054 B CN 114420054B
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- 230000003287 optical effect Effects 0.000 claims description 4
- 239000011521 glass Substances 0.000 abstract description 8
- 238000005096 rolling process Methods 0.000 abstract description 8
- 238000010586 diagram Methods 0.000 description 5
- 238000004146 energy storage Methods 0.000 description 4
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- 230000008094 contradictory effect Effects 0.000 description 1
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- 230000000694 effects Effects 0.000 description 1
- 239000004973 liquid crystal related substance Substances 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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- 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
- G09G3/3413—Details of control of colour illumination sources
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Abstract
The invention discloses a backlight constant current driving circuit, a switching power supply and display equipment, wherein the backlight constant current driving circuit is connected with a main board and a lamp strip, and comprises: the constant current control module and the boost feedback module; the constant current control module is connected with the lamp strip and is used for detecting the cathode voltage of the lamp strip; the boost feedback module is respectively connected with the constant current control module and the lamp strip and is used for adjusting the power supply voltage of the lamp strip according to the cathode voltage of the lamp strip; the constant current control module is also connected with the main board and is used for outputting direct current dimming current to the lamp strip according to the enabling signal and the pulse width modulation signal output by the main board. The invention can ensure that the current flowing through the lamp bar is stable direct current, and no switch alternation exists, thereby avoiding the problem of rolling interference of the screen caused by asynchronous PWM dimming frequency and screen glass field frequency in the PWM dimming mode, i.e. avoiding the problem of screen flashing.
Description
Technical Field
The invention relates to the technical field of liquid crystal display, in particular to a backlight constant current driving circuit, a switching power supply and display equipment.
Background
At present, with the development of technology, the development of television display technology is gradually changed, and the current Light-Emitting Diode (LED) display device is one of the ways of better cost and higher luminous efficiency. According to the existing backlight technology, basically, pulse width modulation (Pulse Width Modulation, PWM) dimming is carried out, the frequency is in the range of 100-20KHz, the size of backlight current can be adjusted by adjusting PWM duty ratio, and the larger the duty ratio is, the larger the LED lamp strip current is, and the smaller the duty ratio is, the smaller the LED lamp strip current is.
However, when the PWM dimming frequency is not synchronized with the screen glass field frequency, a problem of rolling disturbance of the screen may occur.
Accordingly, the prior art is still in need of improvement and development.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention is directed to a backlight constant current driving circuit, a switching power supply and a display device, so as to solve the problem of rolling interference of a screen caused by that the PWM dimming frequency is not synchronous with the field frequency of a screen glass in the existing PWM dimming mode.
The technical scheme of the invention is as follows:
a backlight constant current driving circuit is connected with a main board and a lamp strip, and comprises: the constant current control module and the boost feedback module; wherein,,
the constant current control module is connected with the lamp strip and is used for detecting the cathode voltage of the lamp strip;
the boost feedback module is respectively connected with the constant current control module and the lamp strip, and is used for adjusting the power supply voltage of the lamp strip according to the cathode voltage of the lamp strip;
the constant current control module is also connected with the main board, and is used for outputting direct current dimming current to the lamp strip according to the enabling signal and the pulse width modulation signal output by the main board.
In the above technical scheme, the cathode voltage of the lamp strip is detected by the constant current control module, and the boost feedback module adjusts the power supply voltage of the lamp strip according to the cathode voltage of the lamp strip so as to provide proper power supply voltage for the lamp strip. Meanwhile, the constant current control module outputs direct current dimming current to the lamp strip according to the enabling signal and the pulse width modulation signal output by the main board so as to ensure that the current flowing through the lamp strip is stable direct current, and no switch alternation exists, so that the problem of rolling interference of a screen caused by asynchronous PWM dimming frequency and screen glass field frequency in a PWM dimming mode is avoided, and the problem of screen flashing is avoided.
According to a further arrangement of the invention, the boost feedback module comprises: the first resistor, the second resistor, the third resistor, the fourth resistor, the first capacitor and the voltage stabilizing source; wherein,,
one end of the first resistor is connected to the power supply voltage of the lamp strip and is connected with the lamp strip, and the other end of the first resistor is respectively connected with one end of the second resistor, one end of the third resistor and one end of the fourth resistor;
the other end of the second resistor is grounded;
the other end of the third resistor is connected with the voltage feedback end of the constant current control module;
the other end of the fourth resistor is connected with one end of the first capacitor;
the other end of the first capacitor is connected with the negative electrode of the voltage stabilizing source, the positive electrode of the voltage stabilizing source is grounded, and the reference end of the voltage stabilizing source is connected with the common connection ends of the first resistor, the second resistor and the third resistor.
According to a further arrangement of the invention, the boost feedback module further comprises: fifth resistor, sixth resistor and optocoupler; wherein,,
one end of the fifth resistor is connected with the power supply voltage of the optocoupler, and the other end of the fifth resistor is connected with one end of the sixth resistor and the first pin of the optocoupler respectively;
the other end of the sixth resistor is respectively connected with one end of the first capacitor, the negative electrode of the voltage stabilizing source and the second pin of the optical coupler;
and the third pin and the fourth pin of the optocoupler are respectively connected with the switching power supply chip.
According to a further arrangement of the invention, the constant current control module comprises: a constant current control chip; the constant current control chip is provided with a voltage feedback pin, an enabling signal pin, a pulse width modulation signal pin and a plurality of power supply pins;
the voltage feedback pin of the constant current control chip is connected with the other end of the third resistor and is used for detecting the cathode voltage of the lamp strip;
the enabling signal pin is connected with the main board and is used for receiving an enabling signal output by the main board;
the pulse width modulation signal pin is connected with the main board and is used for receiving a pulse width modulation signal output by the main board;
and the power pin is connected with the cathode of the lamp strip.
According to a further arrangement of the invention, the constant current control chip comprises: the digital-to-analog conversion unit is respectively connected with the main board and the lamp strip and is used for converting pulse width modulation signals output by the main board into direct current dimming currents.
The digital-to-analog conversion unit of the present invention further comprises: the device comprises a comparator, a first switch, a second switch, a seventh resistor and a plurality of switching tubes; wherein,,
the reverse input end of the comparator is connected with a pulse width modulation signal, the non-inverting input end of the comparator is used for being connected with the first switch, and the output end of the comparator is used for being connected with the second switch;
the first switch and the second switch are connected with one end of the seventh resistor;
the control end of the switching tube is connected with the other end of the seventh resistor, the first end of the switching tube is connected with the cathode of the lamp strip, and the second end of the switching tube is grounded.
According to a further arrangement of the invention, the constant current control module further comprises: one end of the second capacitor is connected with the other end of the seventh resistor and the control end of the switching tube respectively, and the other end of the second capacitor is grounded.
According to the further arrangement of the invention, the control end of the switching tube is conducted when being connected with a high-level signal.
Based on the same inventive concept, the present invention also provides a switching power supply, comprising: the backlight constant current driving circuit comprises a filtering module, a rectifying module, a first transformer, a second transformer and the backlight constant current driving circuit; wherein,,
the filtering module is connected with the rectifying module and is used for filtering the input alternating current and outputting the alternating current to the rectifying module;
the rectification module is respectively connected with the first transformer and the second transformer and is used for respectively outputting the direct current obtained after rectification to the first transformer and the second transformer;
the first transformer is used for being connected with a main board and providing power supply voltage for the main board;
the second transformer is respectively connected with the lamp strip and the backlight constant current driving circuit, and is used for providing power supply voltage for the lamp strip.
In the technical scheme, one path of input alternating current is output to the main board through the first transformer after filtering and rectifying, the other path of second transformer is used for supplying power to the lamp bar in a direct-pushing mode, and the power supply voltage of the lamp bar is regulated through the backlight constant current driving circuit, so that a primary DC/DC circuit can be omitted, the energy conversion energy efficiency is improved, and the power supply cost is reduced.
Based on the same inventive concept, the present invention also provides a display device comprising the switching power supply as described above.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained from the structures shown in these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of a switching power supply of the present invention.
Fig. 2 is a schematic circuit diagram of a backlight constant current driving circuit in the present invention.
Fig. 3 is a schematic circuit diagram of the constant current control module in the present invention.
Fig. 4 is a schematic diagram of a conventional PWM dimming current.
Fig. 5 is a schematic diagram of a dc dimming current according to the present invention.
The marks in the drawings are as follows: 100. a filtering module; 200. a rectifying module; 300. a first transformer; 400. a second transformer; 500. a backlight constant current driving circuit; 501. a constant current control module; 5011. a digital-to-analog conversion unit; 502. a boost feedback module; 600. a main board; 700. a light bar.
Detailed Description
The invention provides a backlight constant current driving circuit, a switching power supply and display equipment, which are used for making the purposes, the technical scheme and the effects of the invention clearer and more definite, and the invention is further described in detail below by referring to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In the description and claims, unless the context specifically defines the terms "a," "an," "the," and "the" include plural referents. If there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature.
It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or wirelessly coupled. The term "and/or" as used herein includes all or any element and all combination of one or more of the associated listed items.
It will be understood by those skilled in the art that all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs unless defined otherwise. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present invention.
According to the research of the inventor, according to the existing backlight technology, basically pulse width modulation (Pulse Width Modulation, PWM) dimming is carried out, the frequency is in the range of 100-20KHz, the size of backlight current can be adjusted by adjusting PWM duty ratio, and the larger the duty ratio is, the larger the LED lamp strip current is, and the smaller the duty ratio is, the smaller the LED lamp strip current is. However, PWM dimming current control has the following problems; when the PWM dimming frequency is not synchronous with the screen glass field frequency, the problem of rolling interference of the screen can be caused; the light efficiency of the backlight lamp bar in the PWM dimming mode is low; during PWM high-frequency dimming, energy storage inductors in Boost circuits are noisy at different frequency points; when the PWM dimming mode is turned on, a certain overshoot exists, and a certain influence is exerted on the lamp strip; the PWM dimming method is uncomfortable for the eyes to see for a long time, such as dryness.
In order to solve the technical problems, the invention provides the backlight constant-current driving circuit, which detects the cathode voltage of the lamp strip through the constant-current control module, and adjusts the power supply voltage of the lamp strip through the boosting feedback module according to the cathode voltage of the lamp strip so as to provide proper power supply voltage for the lamp strip, thereby avoiding the problem that the energy storage inductance in the Boost circuit is noisy at different frequency points during PWM high-frequency dimming. Meanwhile, the constant current control module outputs direct current dimming current to the lamp strip according to an enabling signal and a pulse width modulation signal output by the main board so as to ensure that the current flowing through the lamp strip is stable direct current, and no switch alternation exists, so that the problem of rolling interference of a screen caused by asynchronous PWM dimming frequency and screen glass field frequency in a PWM dimming mode is avoided, namely, the problem of screen flashing is avoided, and uncomfortable feeling such as dryness and the like caused by long-time watching of human eyes in the PWM dimming mode is avoided. Meanwhile, the problem that a certain overshoot is generated when the PWM dimming mode is turned on to generate a certain influence on the lamp strip can be avoided. In addition, experiments show that the light efficiency of the backlight lamp bar in the PWM dimming mode can be improved by adopting direct current dimming.
Referring to fig. 1 to 5, the present invention provides a preferred embodiment of a backlight constant current driving circuit.
As shown in fig. 1, the present invention further provides a switching power supply connected to the main board 600 and the light bar 700, the switching power supply comprising: the backlight constant current driving circuit 500 includes a filter module 100, a rectifier module 200, a first transformer 300, a second transformer 400, and a backlight constant current driving circuit. The filtering module 100 is connected with the rectifying module 200, and the filtering module 100 is configured to filter the input ac and output the filtered ac to the rectifying module 200; the rectifying module 200 is connected to the first transformer 300 and the second transformer 400, respectively, and is configured to output the rectified dc power to the first transformer 300 and the second transformer 400, respectively; the first transformer 300 is used for being connected with a main board 600, and the first transformer 300 is used for providing power supply voltage for the main board 600; the second transformer 400 is respectively connected to the light bar 700 and the backlight constant current driving circuit 500, the second transformer 400 is configured to provide a supply voltage for the light bar 700, the backlight constant current driving circuit 500 is configured to adjust the supply voltage of the light bar 700 to provide a suitable supply voltage for the light bar 700, and is configured to output a dc dimming current to the light bar 700 according to an enable signal and a pulse width modulation signal output by the main board 600, so that a current flowing through the light bar 700 is a dc current.
In the above technical solution, after the input AC is rectified and filtered, one path of AC is output to the motherboard 600 through the first transformer 300 to supply power, for example, 12V and 24V to the motherboard 600, and the other path of AC is directly pushed to supply power to the light bar 700 through the second transformer 400, and the power supply voltage of the light bar 700 is regulated by the backlight constant current driving circuit 500, so that a primary DC/DC circuit is omitted, energy conversion efficiency is improved, and power supply cost is reduced.
As shown in fig. 1, in some embodiments, the backlight constant current driving circuit 500 includes: a constant current control module 501 and a boost feedback module 502. The constant current control module 501 is connected with the light bar 700, and the constant current control module 501 is used for detecting the cathode voltage of the light bar 700; the boost feedback module 502 is respectively connected with the constant current control module 501 and the light bar 700, and the boost feedback module 502 is used for adjusting the power supply voltage of the light bar 700 according to the cathode voltage of the light bar 700; the constant current control module 501 is further connected to the motherboard 600, and the constant current control module 501 is configured to output a direct current dimming current to the light bar 700 according to an enable signal and a pulse width modulation signal output by the motherboard 600.
Specifically, during the ac startup, the second transformer 400 outputs a supply voltage Vled, which is the winding voltage of the second transformer 400, and the supply voltage Vled directly provides a stable dc voltage to the light bar 700 after rectifying and filtering. The light bar 700 is an LED light bar 700, and the light bar 700 may be a single channel or multiple channels. The constant current control module 501 can detect the cathode voltage of the light bar 700, and the Boost feedback module 502 adjusts the power supply voltage of the light bar 700 according to the cathode voltage of the light bar 700 so as to provide an appropriate power supply voltage for the light bar 700, so that the problem that the energy storage inductance in the Boost circuit is noisy at different frequency points during PWM high-frequency dimming is avoided. Meanwhile, the constant current control module 501 outputs a direct current dimming current to the light bar 700 according to the enable signal and the pulse width modulation signal output by the main board 600, so as to ensure that the current flowing through the light bar 700 is a stable direct current, and no switch alternation exists, thereby avoiding the problem of rolling interference of a screen caused by that the PWM dimming frequency is not synchronous with the screen glass field frequency in the PWM dimming mode, that is, avoiding the problem of screen flashing, and avoiding uncomfortable feeling such as dryness and the like caused by long-time watching of human eyes in the PWM dimming mode. Meanwhile, the problem that a certain overshoot is generated when the PWM dimming mode is turned on to generate a certain influence on the lamp strip 700 can be avoided. In addition, experiments show that the light efficiency of the backlight bar 700 in the PWM dimming mode can also be improved by adopting the dc dimming.
Referring to fig. 1 and 2, in a further implementation of an embodiment, the boost feedback module 502 includes: the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, the first capacitor C1 and the regulated power supply U1. One end of the first resistor R1 is connected to the power supply voltage Vled of the light bar 700 and is connected to the light bar 700, and the other end of the first resistor R1 is connected to one end of the second resistor R2, one end of the third resistor R3 and one end of the fourth resistor R4, respectively; the other end of the second resistor R2 is grounded; the other end of the third resistor R3 is connected with the voltage feedback end of the constant current control module 501; the other end of the fourth resistor R4 is connected with one end of the first capacitor C1; the other end of the first capacitor C1 is connected with the negative electrode of the voltage stabilizing source U1, the positive electrode of the voltage stabilizing source U1 is grounded, and the reference end of the voltage stabilizing source U1 is connected with the common connection end of the first resistor R1, the second resistor R2 and the third resistor R3.
With continued reference to fig. 1 and fig. 2, further, the constant current control module 501 includes: a constant current control chip U3; the constant current control chip U3 is provided with a voltage feedback pin FB, an enabling signal pin ENA, a pulse width modulation signal pin PWM and a plurality of power supply pins (LED 1-LEDN); the voltage feedback pin FB of the constant current control chip U3 is connected to the other end of the third resistor R3, and the voltage feedback pin FB is configured to detect the cathode voltage of the light bar 700; the enable signal pin ENA is connected with the motherboard 600, and the enable signal pin ENA is used for receiving an enable signal output by the motherboard 600; the PWM signal pin PWM is connected to the motherboard 600, and is configured to receive a PWM signal output by the motherboard 600; the power pin is connected to the cathode of the light bar 700.
Specifically, the power pin is connected to the cathode of the light bar 700, when the ac is turned on, the second transformer 400 outputs Vled voltage, and the constant current control chip U3 is controlled by the PWM dimming signal and the enable signal provided by the main board 600. When the enable signal ENA is not present, the constant current control chip U3 does not operate, the voltage feedback pin FB of the constant current control chip U3 does not generate a pull current, the third resistor R3 is equivalent to an open circuit, the I3 current is 0, and at this time, the voltage vled=2.5 (r1+r2)/R2 of the light bar 700 is determined by the resistance values of the first resistor R1 and the second resistor R2. When the enable signal ENA is present, the constant current control chip U3 starts to work normally, the voltage feedback pin FB of the constant current control chip U3 starts to generate a pull current I3, the current flows through the third resistor R3 to the inside of the constant current control chip U3 to form a loop, the constant current control chip U3 adjusts the current flowing through the third resistor R3 according to the current feedback of the lamp strip 700, so that Vled outputs a suitable voltage, vled=2.5 (r1+r2)/r2+i3R 1, and the voltage of the lamp strip 700 is determined by the values of the first resistor R1 and the second resistor R2, and the current flowing through the third resistor R3 is also related. I1 When I3 current increases, I1 increases accordingly, and the output Vled voltage increases, whereas the output Vled decreases, thereby providing the appropriate supply voltage for the light bar 700.
With continued reference to fig. 1 and 2, in a further implementation of an embodiment, the boost feedback module 502 further includes: fifth resistor R5, sixth resistor R6, and optocoupler U2. One end of the fifth resistor R5 is connected to the power supply voltage 12V of the optocoupler U2, and the other end of the fifth resistor R5 is connected to one end of the sixth resistor R6 and the first pin of the optocoupler U2 respectively; the other end of the sixth resistor R6 is respectively connected with one end of the first capacitor C1, the negative electrode of the voltage stabilizing source U1 and the second pin of the optical coupler U2; and a third pin and a fourth pin of the optical coupler U2 are respectively connected with the switching power supply chip.
Specifically, the power supply voltage 12V of the optocoupler U2 supplies power to the optocoupler U2 through the fifth resistor R5. The optocoupler U2 receives the supply voltage Vled, controls the current of the optocoupler U2, and feeds back the current to the primary side, so as to control the output voltage of the second transformer 400 through the switching power supply chip, thereby adjusting the power supply low voltage Vled.
Referring to fig. 2 and 3, in a further implementation manner of an embodiment, the constant current control chip includes: the digital-to-analog conversion unit 5011, the digital-to-analog conversion unit 5011 is respectively connected with the motherboard 600 and the light bar 700, and the digital-to-analog conversion unit 5011 is used for converting the pulse width modulation signal output by the motherboard 600 into a direct current dimming current.
Specifically, the digital-to-analog conversion unit 5011 includes: the device comprises a comparator U1A, a first switch K1, a second switch K2, a seventh resistor R7 and a plurality of switching tubes. The non-inverting input end of the comparator U1A is connected with the pulse width modulation signal PWM, the non-inverting input end of the comparator U1A is used for being connected with the first switch K1, and the output end of the comparator U1A is used for being connected with the second switch K2; the first switch K1 is also connected with one end of the seventh resistor R7; the second switch K2 is also connected with one end of the seventh resistor R7; the control end of the switching tube is connected with the other end of the seventh resistor R7, the first end of the switching tube is connected with the cathode of the lamp strip 700, and the second end of the switching tube is grounded.
Specifically, the control end of the switching tube is turned on when being connected to a high-level signal, and in some embodiments, the switching tube is an N-type MOS tube. After normal operation, when the PWM is at a low level, the pin 2 of the comparator U1A is at a voltage of 0, the comparator does not operate, the first switch K1 is connected to the point a, the second switch K2 is suspended, and the dc voltage passes through the seventh resistor R7 to the filter end LPF of the constant current control chip, and meanwhile, dc level is provided for the driving G pole of the MOS tube of the cathode of the light bar 700, so that the MOS tube is in an on state. When PWM is high level, the first switch K1 is connected to the B point, the output end (3 rd leg) of the comparator U1A is high level, the second switch K2 is connected to the C point, that is, the 3 rd leg of the comparator, the comparator U1A starts to work, the 1 st leg of the comparator U1A outputs high level, the high level passes through the seventh resistor R7 to the filter end LPF of the constant current control U3 chip, and meanwhile, provides dc level for the driving G pole of the MOS tube of the cathode of the light bar 700, so that the MOS tube is in the on state. In this way, the PWM is a dc current throughout the light bar 700 regardless of whether it is low or high, and there is no switching alternation, so that dimming of the dc current is achieved, and the problem of screen flicker is avoided, as shown in fig. 4 and 5.
It should be noted that, the number of the MOS transistors corresponds to the number of the light bars 700, that is, one of the light bars 700 corresponds to one MOS transistor. The MOS tubes may be disposed inside the constant current control chip U3, and may also be disposed outside the constant current control chip U3, and in this embodiment, the MOS tubes are set to 4 (Q1-Q4) and disposed in the constant current control chip U3. In addition, the plurality of light bars 700 may be connected to the same constant current control chip, or one light bar 700 may correspond to each constant current control chip, and in this embodiment, the plurality of light bars 700 are connected to the same constant current control chip.
Referring to fig. 1 to 3, in a further implementation manner of an embodiment, the constant current control module 501 further includes: and one end of the second capacitor C2 is respectively connected with the other end of the seventh resistor R7 and the control end of the switching tube, and the other end of the second capacitor C2 is grounded.
Specifically, when PWM is low, the 2 pin of the comparator U1A is 0 voltage, the comparator U1A does not work, the first switch K1 is connected to the point a, the second switch K2 is suspended, the dc voltage is filtered and charged by the seventh resistor R7 to the filter end LPF of the constant current control chip U3 and the second capacitor C2, and at the same time, the dc level is provided to the driving G pole of the MOS tube of the cathode of the light bar 700, so that the MOS tube is in the on state. When PWM is high, the first switch K1 is connected to the point B, the 3 pin of the comparator U1A is high, the second switch K2 is connected to the point C, that is, the 3 rd pin of the comparator U1A, the comparator U1A starts to work, the 1 pin of the comparator U1A outputs high level, the high level passes through the seventh resistor R7 to the filter end LPF of the constant current control chip U3, and simultaneously provides dc level for the driving G pole of the MOS transistor of the cathode of the light bar 700, and the second capacitor C2 filters and charges the dc level to make the MOS transistor in an on state. The second capacitor C2 can filter out the ripple and noise at the LPF end, and maintain the voltage at the LPF end stable, so that the capacitance of the LPF end is at uF level, and thus the current flowing through the light bar 700 is ensured to be dc.
In some embodiments, the present invention also provides a display device comprising a switching power supply as described above. In particular, the embodiment of a switching power supply is described, and will not be described herein.
In summary, according to the backlight constant current driving circuit, the switching power supply and the display device provided by the invention, the cathode voltage of the lamp strip is detected through the constant current control module, and the power supply voltage of the lamp strip is regulated through the Boost feedback module according to the cathode voltage of the lamp strip, so that the proper power supply voltage is provided for the lamp strip, and the problem that the energy storage inductance in the Boost circuit is noisy at different frequency points during PWM high-frequency dimming is avoided. Meanwhile, the constant current control module outputs direct current dimming current to the lamp strip according to an enabling signal and a pulse width modulation signal output by the main board so as to ensure that the current flowing through the lamp strip is stable direct current, and no switch alternation exists, so that the problem of rolling interference of a screen caused by asynchronous PWM dimming frequency and screen glass field frequency in a PWM dimming mode is avoided, namely, the problem of screen flashing is avoided, and uncomfortable feeling such as dryness and the like caused by long-time watching of human eyes in the PWM dimming mode is avoided.
It is to be understood that the invention is not limited in its application to the examples described above, but is capable of modification and variation in light of the above teachings by those skilled in the art, and that all such modifications and variations are intended to be included within the scope of the appended claims.
Claims (9)
1. A backlight constant current driving circuit connected with a main board and a lamp strip, which is characterized by comprising: the constant current control module and the boost feedback module; wherein,,
the constant current control module is connected with the lamp strip and is used for detecting the cathode voltage of the lamp strip;
the boost feedback module is respectively connected with the constant current control module and the lamp strip, and is used for adjusting the power supply voltage of the lamp strip according to the cathode voltage of the lamp strip;
the constant current control module is also connected with the main board and is used for outputting direct current dimming current to the lamp strip according to an enabling signal and a pulse width modulation signal output by the main board;
the boost feedback module includes: the first resistor, the second resistor, the third resistor, the fourth resistor, the first capacitor and the voltage stabilizing source; wherein,,
one end of the first resistor is connected to the power supply voltage of the lamp strip and is connected with the lamp strip, and the other end of the first resistor is respectively connected with one end of the second resistor, one end of the third resistor and one end of the fourth resistor;
the other end of the second resistor is grounded;
the other end of the third resistor is connected with the voltage feedback end of the constant current control module;
the other end of the fourth resistor is connected with one end of the first capacitor;
the other end of the first capacitor is connected with the negative electrode of the voltage stabilizing source, the positive electrode of the voltage stabilizing source is grounded, and the reference end of the voltage stabilizing source is connected with the common connection ends of the first resistor, the second resistor and the third resistor.
2. The backlight constant current driving circuit according to claim 1, wherein the boost feedback module further comprises: fifth resistor, sixth resistor and optocoupler; wherein,,
one end of the fifth resistor is connected with the power supply voltage of the optocoupler, and the other end of the fifth resistor is connected with one end of the sixth resistor and the first pin of the optocoupler respectively;
the other end of the sixth resistor is respectively connected with one end of the first capacitor, the negative electrode of the voltage stabilizing source and the second pin of the optical coupler;
and the third pin and the fourth pin of the optocoupler are respectively connected with the switching power supply chip.
3. The backlight constant current driving circuit according to claim 1, wherein the constant current control module comprises: a constant current control chip; the constant current control chip is provided with a voltage feedback pin, an enabling signal pin, a pulse width modulation signal pin and a plurality of power supply pins;
the voltage feedback pin of the constant current control chip is connected with the other end of the third resistor and is used for detecting the cathode voltage of the lamp strip;
the enabling signal pin is connected with the main board and is used for receiving an enabling signal output by the main board;
the pulse width modulation signal pin is connected with the main board and is used for receiving a pulse width modulation signal output by the main board;
and the power pin is connected with the cathode of the lamp strip.
4. A backlight constant current driving circuit according to claim 3, wherein the constant current control chip comprises: the digital-to-analog conversion unit is respectively connected with the main board and the lamp strip and is used for converting pulse width modulation signals output by the main board into direct current dimming currents.
5. A backlight constant current driving circuit according to claim 4, wherein the digital-to-analog conversion unit comprises: the device comprises a comparator, a first switch, a second switch, a seventh resistor and a plurality of switching tubes; wherein,,
the reverse input end of the comparator is connected with a pulse width modulation signal, the non-inverting input end of the comparator is used for being connected with the first switch, and the output end of the comparator is used for being connected with the second switch;
the first switch and the second switch are connected with one end of the seventh resistor;
the control end of the switching tube is connected with the other end of the seventh resistor, the first end of the switching tube is connected with the cathode of the lamp strip, and the second end of the switching tube is grounded.
6. The backlight constant current driving circuit according to claim 5, wherein the constant current control module further comprises: one end of the second capacitor is connected with the other end of the seventh resistor and the control end of the switching tube respectively, and the other end of the second capacitor is grounded.
7. The backlight constant current driving circuit according to claim 6, wherein the control terminal of the switching tube is turned on when a high level signal is inputted.
8. A switching power supply, comprising: a filter module, a rectifier module, a first transformer, a second transformer, and a backlight constant current driving circuit according to any one of claims 1 to 7; wherein,,
the filtering module is connected with the rectifying module and is used for filtering the input alternating current and outputting the alternating current to the rectifying module;
the rectification module is respectively connected with the first transformer and the second transformer and is used for respectively outputting the direct current obtained after rectification to the first transformer and the second transformer;
the first transformer is used for being connected with a main board and providing power supply voltage for the main board;
the second transformer is respectively connected with the lamp strip and the backlight constant current driving circuit, and is used for providing power supply voltage for the lamp strip.
9. A display device comprising the switching power supply of claim 8.
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| CN107464533B (en) * | 2017-08-21 | 2019-10-11 | 深圳创维－Rgb电子有限公司 | A kind of constant-current drive circuit and television set |
| CN108231014B (en) * | 2018-02-08 | 2020-08-04 | 深圳创维－Rgb电子有限公司 | Regional dimming constant current control circuit, driving power supply and television |
| CN211457466U (en) * | 2019-12-25 | 2020-09-08 | 深圳创维－Rgb电子有限公司 | Multi-channel output compatible circuit of backlight constant-current control system and television |
| CN212519510U (en) * | 2020-06-24 | 2021-02-09 | 合肥惠科金扬科技有限公司 | Backlight driving circuit and backlight driving device |
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