CN110648635B - Backlight closing circuit and display device - Google Patents
Backlight closing circuit and display device Download PDFInfo
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- CN110648635B CN110648635B CN201911052990.2A CN201911052990A CN110648635B CN 110648635 B CN110648635 B CN 110648635B CN 201911052990 A CN201911052990 A CN 201911052990A CN 110648635 B CN110648635 B CN 110648635B
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- 239000003990 capacitor Substances 0.000 claims description 68
- 239000004973 liquid crystal related substance Substances 0.000 claims description 13
- 238000010586 diagram Methods 0.000 description 7
- 230000002093 peripheral effect Effects 0.000 description 3
- 230000005669 field effect Effects 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 230000011664 signaling Effects 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
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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
The invention provides a backlight turn-off circuit and a display device. The backlight closing circuit is applied to a backlight circuit of the display device and comprises a backlight control circuit and a closing control circuit, wherein the closing control circuit is used for outputting a closing control signal to the backlight control circuit through a closing control signal output end within preset time after a power line of the display device is pulled out to be powered off in a starting-up state; and the backlight control circuit is used for controlling to close the backlight circuit after receiving the closing control signal. In the invention, when the display device is in a starting state and the power line is pulled out, the backlight circuit is closed before the display screen is in a closed state, so that the phenomenon of flashing white screen at the moment of pulling out the power line in a normal working state is avoided.
Description
Technical Field
The invention relates to the technical field of display, in particular to a backlight turn-off circuit and a display device.
Background
When the power line is pulled out when the display device is in a starting state, the screen of the display screen is closed after suddenly emitting white light. Because the power source is not pulled out in the normal working state of the display device, the normal shutdown time sequence is that the backlight Voltage is firstly reduced to zero, then the Voltage drop of the LVDS (Low-Voltage Differential Signaling) is zero, and finally the Voltage drop of the display screen is zero. When the shutdown time sequence is not satisfied, the time point of the shutdown of the backlight circuit is later than the time period of the shutdown of the display screen, so that the phenomenon of screen flashing and white is likely to occur. In the display field, the main integrated circuit is uncontrolled at the moment of plugging and unplugging, so that the backlight circuit can not be controlled to be turned off at the moment of power failure of the display device. In the field of the existing display, a technical scheme for solving the problem of power supply flashing white screen by adding a peripheral circuit is not provided.
Disclosure of Invention
The invention mainly aims to provide a backlight turn-off circuit and a display device, and solves the problem that a power supply is pulled out to flash a white screen in a manner of adding a peripheral circuit in the prior art.
In order to achieve the above object, the present invention provides a backlight shutdown circuit applied to a backlight circuit of a display device, the backlight shutdown circuit including a backlight control circuit and a shutdown control circuit, wherein,
the closing control circuit is used for outputting a closing control signal to the backlight control circuit through the closing control signal output end within preset time after a power line is pulled out to be powered off when the display device is in a starting state;
and the backlight control circuit is used for controlling to close the backlight circuit after receiving the closing control signal.
In implementation, the shutdown control circuit comprises a storage capacitor circuit and a first control circuit;
the first end of the storage capacitor circuit is electrically connected with the first voltage end, and the second end of the storage capacitor circuit is electrically connected with the control end of the first control circuit;
the first end of the first control circuit is electrically connected with the second voltage end, and the second end of the first control circuit is electrically connected with the closing control signal output end;
the first voltage end is used for providing a first voltage, and the second voltage end is used for providing a second voltage;
the first control circuit is used for generating the closing control signal according to the first voltage and the second voltage within preset time after a power line of the display device is pulled out to be powered off in a starting state.
In implementation, the power supply voltage end is used for providing power supply voltage;
the first voltage end is the power supply voltage end, and the second voltage is obtained by converting the power supply voltage through a direct current converter; or,
the second voltage end is the power supply voltage end, and the first voltage is obtained by converting the power supply voltage through a direct current converter.
When the control circuit is implemented, the first control circuit comprises a first control switch tube;
the control electrode of the first control switch tube is the control end of the first control circuit, the first electrode of the first control switch tube is the first end of the first control circuit, and the second electrode of the first control switch tube is the second end of the first control circuit.
When the control circuit is implemented, the first control switch tube is a p-type switch tube; the first voltage end is a power supply voltage end, the power supply voltage end is used for providing power supply voltage, and the second voltage is obtained by converting the power supply voltage through a direct current converter;
when the display device is in a starting state and a power line is not pulled out, the power voltage is greater than the second voltage; after the power line is pulled out to cut off the power supply in the power-on state of the display device, the falling speed of the power supply voltage is greater than that of the second voltage.
When the control circuit is implemented, the first control switch tube is an n-type switch tube; the second voltage end is a power supply voltage end, the power supply voltage end is used for providing power supply voltage, and the first voltage is obtained by converting the power supply voltage through a direct current converter;
when the display device is in a starting state and a power line is not pulled out, the power voltage is greater than the first voltage; after the power line is pulled out to cut off the power supply in the power-on state of the display device, the falling speed of the power supply voltage is greater than that of the first voltage.
In implementation, the shutdown control circuit further comprises a first current limiting resistor, a second current limiting resistor and a third current limiting resistor;
the control electrode of the first control switch tube is electrically connected with the second end of the storage capacitor circuit through the first current-limiting resistor, and the control electrode of the first control switch tube is electrically connected with the first electrode of the first control switch tube through the second current-limiting resistor;
and the second pole of the first control switch tube is electrically connected with the closing control signal output end through the third current limiting resistor.
In practice, the storage capacitor circuit includes a first storage capacitor and a second storage capacitor connected in parallel with each other.
In implementation, the backlight control circuit comprises a second control switch tube and a first pull-up resistor;
a control electrode of the second control switch tube is electrically connected with the closing control signal output end, a first electrode of the second control switch tube is electrically connected with a backlight enabling end of the backlight circuit, and a second electrode of the second control switch tube is electrically connected with a third voltage end; the third voltage end is used for providing a third voltage signal;
the first electrode of the second control switch tube is also electrically connected with a fourth voltage end through the first pull-up resistor;
the backlight circuit is used for being closed when the backlight enabling end of the backlight circuit is connected with the third voltage signal.
In practice, the backlight control circuit further comprises a filter capacitor, a second pull-up resistor and a fourth current limiting resistor, wherein,
the first end of the filter capacitor is electrically connected with the backlight enabling end, and the second end of the filter capacitor is electrically connected with a fifth voltage end;
the second pull-up resistor is connected between the backlight control terminal and the fourth voltage terminal;
the first end of the fourth current limiting resistor is electrically connected with the backlight control end, and the second end of the fourth current limiting resistor is electrically connected with the control electrode of the second control switch tube.
The invention also provides a display device, which comprises a backlight circuit and the backlight closing circuit;
the backlight closing circuit is used for closing the backlight circuit after a power line is pulled out to be powered off when the display device is in a power-on state.
Compared with the prior art, the backlight circuit is closed before the display screen is in a closed state after the power line is pulled out in the starting state of the display device, so that the phenomenon of screen flashing and white display at the moment of pulling out the power line in a normal working state is avoided.
Drawings
Fig. 1 is a block diagram of a backlight shutdown circuit according to an embodiment of the present invention;
fig. 2 is a block diagram of a backlight shutdown circuit according to another embodiment of the present invention;
fig. 3 is a block diagram of a backlight shutdown circuit according to another embodiment of the present invention;
fig. 4 is a block diagram of a backlight shutdown circuit according to still another embodiment of the present invention;
FIG. 5 is a circuit diagram of one embodiment of a backlight control circuit;
FIG. 6 is a circuit diagram of an embodiment of a backlight shutdown circuit according to the present invention;
fig. 7 is a waveform diagram of a power supply voltage provided by VDD and a voltage provided by VCC.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The switching tubes adopted in all the embodiments of the invention can be triodes, thin film switching tubes or field effect tubes or other devices with the same characteristics. In the embodiment of the invention, in order to distinguish the two poles of the switch except the control pole, one pole is called a first pole, and the other pole is called a second pole.
In actual operation, when the switching tube is a triode, the control electrode may be a base electrode, the first electrode may be a collector electrode, and the second electrode may be an emitter electrode; alternatively, the control electrode may be a base electrode, the first electrode may be an emitter electrode, and the second electrode may be a collector electrode.
In actual operation, when the switch tube is a thin film switch tube or a field effect transistor, the control electrode may be a gate electrode, the first electrode may be a drain electrode, and the second electrode may be a source electrode; alternatively, the control electrode may be a gate electrode, the first electrode may be a source electrode, and the second electrode may be a drain electrode.
The backlight shutdown circuit according to the embodiment of the present invention is applied to a backlight circuit of a display device, as shown in fig. 1, the backlight shutdown circuit includes a shutdown control circuit 11 and a backlight control circuit 12, wherein,
the turn-OFF control circuit 11 is configured to output a turn-OFF control signal to the backlight control circuit 12 through a turn-OFF control signal output terminal BL-OFF within a predetermined time after a power line of the display apparatus is pulled out to be powered OFF in a power-on state;
the backlight control circuit 12 is electrically connected to the turn-OFF control signal output end BL-OFF, and is configured to control to turn OFF the backlight circuit after receiving the turn-OFF control signal.
In the embodiment of the present invention, turning off the backlight circuit means: and controlling the backlight circuit not to emit light.
The backlight closing circuit of the embodiment of the invention is used for closing the backlight circuit before the liquid crystal display screen is in a liquid crystal closing state after the power line is pulled out when the display device is in a starting state so as to avoid the phenomenon of flashing white screen at the moment of pulling out the power line in a normal working state.
In an embodiment of the present invention, the power supply line is a voltage line for supplying power to the display device.
In specific implementation, the preset time can be selected according to actual conditions, and the preset time can be less than or equal to the closing time of the liquid crystal display;
the liquid crystal screen closing time refers to: the time period between the moment when the power cord is pulled out and the moment when the liquid crystal display screen starts to be in the liquid crystal closing state lasts.
In the prior art, when the power line is pulled out when the display device is in a power-on state, the screen of the display screen is turned off after emitting white light suddenly. Because the power source is not pulled out in the normal working state of the display device, the normal shutdown time sequence is that the backlight Voltage is firstly reduced to zero, then the Voltage drop of the LVDS (Low-Voltage Differential Signaling) is zero, and finally the Voltage drop of the display screen is zero. When the shutdown time sequence is not satisfied, the time point of the shutdown of the backlight circuit is later than the time period of the shutdown of the display screen, so that the phenomenon of screen flashing and white is likely to occur.
When the display screen is closed, all grid lines are opened to release residual charges, so that the liquid crystal is ensured not to be polarized, and normal display is ensured when the display screen is started next time. When the display screen is normally black, the display screen is in a liquid crystal open state when the charges are released, and a white picture is displayed; if the backlight voltage is not reduced to zero at this time, human eyes can see the backlight through the display screen, that is, when the backlight voltage is reduced to zero later than the voltage of the display screen, the phenomenon of screen flashing is generated.
The embodiment of the invention designs the peripheral circuit independently, can solve the problem of screen flashing and white display when the display is abnormally shut down without rapidly detecting and executing the command by the Scalar IC, and improves the product quality.
Specifically, the shutdown control circuit may include a storage capacitor circuit and a first control circuit;
the first end of the storage capacitor circuit is electrically connected with the first voltage end, and the second end of the storage capacitor circuit is electrically connected with the control end of the first control circuit;
the first end of the first control circuit is electrically connected with the second voltage end, and the second end of the first control circuit is electrically connected with the closing control signal output end;
the first voltage end is used for providing a first voltage, and the second voltage end is used for providing a second voltage;
the first control circuit is used for generating the closing control signal according to the first voltage and the second voltage within preset time after a power line of the display device is pulled out to be powered off in a starting state.
As shown in fig. 2, on the basis of the embodiment of the backlight turn-off circuit shown in fig. 1, the turn-off control circuit may include a storage capacitor circuit 111 and a first control circuit 112;
a first terminal of the storage capacitor circuit 111 is electrically connected to a first voltage terminal Vt1, and a second terminal of the storage capacitor circuit 111 is electrically connected to a control terminal of the first control circuit 112;
a first terminal of the first control circuit 112 is electrically connected to a second voltage terminal Vt2, and a second terminal of the first control circuit 112 is electrically connected to the shutdown control signal output terminal BL-OFF;
the first voltage terminal Vt1 is for providing a first voltage, the second voltage terminal Vt2 is for providing a second voltage;
the first control circuit 112 is configured to generate the shutdown control signal according to the first voltage and the second voltage within a predetermined time after the power line is pulled out to power off in the power-on state of the display device.
In the embodiment of the present invention, the shutdown control circuit 11 may include a storage capacitor circuit 111 and a first control circuit 112, and the first control circuit 112 generates a shutdown control signal according to the first voltage and the second voltage within a predetermined time by using a principle that a voltage difference between two ends of the storage capacitor circuit 111 cannot change abruptly, so as to control the backlight control circuit 12 to control the shutdown of the backlight circuit.
In specific implementation, the power supply voltage end is used for providing power supply voltage;
the first voltage end is the power supply voltage end, and the second voltage is obtained by converting the power supply voltage through the direct current converter, so that after a power line of the display device is pulled off in a starting state, the power failure speed of the power supply voltage provided by the power supply voltage end is greater than that of the second voltage; or,
the second voltage end is the power supply voltage end, the first voltage is obtained by converting the power supply voltage through the direct current converter, and therefore after the power line of the display device is pulled out in a starting state, the power failure speed of the power supply voltage provided by the power supply voltage end is larger than that of the first voltage.
According to a specific embodiment, the first voltage terminal may be a power supply voltage terminal;
when the first voltage terminal is a power supply voltage terminal, a second voltage provided by the second voltage terminal may be obtained by passing a power supply voltage through a dc converter (the power supply voltage terminal provides the power supply voltage), and the second voltage may be smaller than the power supply voltage; since the second voltage is converted from the power supply voltage, the power supply voltage drops at a rate greater than that of the second voltage when the power supply line is pulled out in the power-on state of the display device.
According to another specific embodiment, the second voltage terminal may be a power supply voltage terminal;
when the second voltage terminal is a power voltage terminal, a first voltage provided by the first voltage terminal may be obtained by passing a power voltage through a dc converter (the power voltage terminal provides the power voltage), and the first voltage may be smaller than the power voltage; since the first voltage is converted from the power supply voltage, the power supply voltage drops at a rate greater than that of the first voltage when the power supply line is pulled out in the power-on state of the display device.
Specifically, the first control circuit may include a first control switch tube;
the control electrode of the first control switch tube is the control end of the first control circuit, the first electrode of the first control switch tube is the first end of the first control circuit, and the second electrode of the first control switch tube is the second end of the first control circuit.
According to a specific embodiment, the first control switch tube may be a p-type switch tube; the first voltage end is a power supply voltage end, the power supply voltage end is used for providing power supply voltage, and the second voltage is obtained by converting the power supply voltage through a direct current converter;
when the display device is in a starting state and a power line is not pulled out, the power voltage is greater than the second voltage; after the power line is pulled out to cut off the power supply in the power-on state of the display device, the falling speed of the power supply voltage is greater than that of the second voltage.
In a specific implementation, the first control switch tube may be a p-type switch tube, and the first voltage end is a power supply voltage end, and the second voltage provided by the second voltage end may be obtained by passing a power supply voltage through a dc converter, and the second voltage may be smaller than the power supply voltage.
According to another specific embodiment, the first control switch tube may be an n-type switch tube; the second voltage end is a power supply voltage end, the power supply voltage end is used for providing power supply voltage, and the first voltage is obtained by converting the power supply voltage through a direct current converter;
when the display device is in a starting state and a power line is not pulled out, the power voltage is greater than the first voltage; after the power line is pulled out to cut off the power supply in the power-on state of the display device, the falling speed of the power supply voltage is greater than that of the first voltage.
As shown in fig. 3, based on the embodiment of the backlight turn-off circuit shown in fig. 2, the first control circuit 112 may include a first control transistor Q1;
a first end of the storage capacitor circuit 111 is electrically connected with a power supply voltage end VDD, and a second end of the storage capacitor circuit 111 is electrically connected with a base electrode of the first control triode Q1;
an emitting electrode of the first control triode Q1 is electrically connected with a high-voltage end VCC, and a collecting electrode of the first control triode Q1 is electrically connected with the turn-OFF control signal output end BL-OFF.
In the embodiment shown in fig. 3, Q1 is a PNP transistor.
In the embodiment shown in fig. 3, the first voltage terminal is a power voltage terminal VDD, and the second voltage terminal is a high voltage terminal VCC; when the display device is in a starting state and the power line is not pulled out, the power voltage can be 5V, and VCC can provide 3.3V; the 3.3V voltage provided by the VCC is obtained by converting the power supply voltage through a direct current converter;
after the display device is turned on and the power line is pulled out, since the 3.3V voltage provided by VCC is obtained by converting the power voltage through the dc converter, the speed of the voltage drop of the power voltage is greater than the speed of the voltage drop provided by VCC, and since the voltage difference between the two ends of the storage capacitor circuit 111 cannot change suddenly, Q1 will be turned on to control BL-OFF to output a turn-OFF control signal (in this embodiment, the turn-OFF control signal is a high level signal) to the backlight control circuit 12 to control the backlight control circuit 12 to turn OFF the backlight circuit;
when the display device is operating normally (i.e. the display device is in the on state, and the power line is not pulled out, and the display device is normally OFF), Q1 is turned OFF, and the potential of BL-OFF is not affected by VDD and VCC.
The normal shutdown of the display device refers to: the display device is normally powered off by the operator pressing a power-off key.
In a specific implementation, the first control switch tube may be an n-type switch tube, and the second voltage end is a power supply voltage end, and the first voltage provided by the first voltage end may be obtained by passing a power supply voltage through a dc converter, and the first voltage may be smaller than the power supply voltage.
As shown in fig. 4, on the basis of the embodiment of the backlight turn-off circuit shown in fig. 2, the first control circuit 112 may include a first control transistor Q1;
a first end of the storage capacitor circuit 111 is electrically connected with a high-voltage end VCC, and a second end of the storage capacitor circuit 111 is electrically connected with a base electrode of the first control triode Q1;
an emitter of the first control transistor Q1 is electrically connected to a power supply voltage terminal VDD, and a collector of the first control transistor Q1 is electrically connected to the shutdown control signal output terminal BL-OFF.
In the embodiment shown in fig. 4, Q1 is an NPN transistor.
In the embodiment shown in fig. 4, the second voltage terminal is the power voltage terminal VDD, and the first voltage terminal is the high voltage terminal VCC; when the display device is in a starting state and the power line is not pulled out, the power voltage can be 5V, and VCC can provide 3.3V; the 3.3V voltage provided by the VCC is obtained by converting the power supply voltage through a direct current converter;
after the display device is turned on and the power line is pulled out, since the 3.3V voltage provided by VCC is converted from the power voltage through the dc converter, the speed of the power voltage drop is greater than the speed of the voltage drop provided by VCC, and since the voltage difference between the two ends of the storage capacitor circuit 111 cannot change suddenly, the voltage difference between the base of Q1 and the emitter of Q1 is greater than the threshold voltage of Q1, Q1 is turned on to control BL-OFF to output a turn-OFF control signal (in this embodiment, the turn-OFF control signal is a high level signal) to the backlight control circuit 12, so as to control the backlight control circuit 12 to turn OFF the backlight circuit.
Specifically, the shutdown control circuit may further include a first current-limiting resistor, a second current-limiting resistor, and a third current-limiting resistor;
the control electrode of the first control switch tube is electrically connected with the second end of the storage capacitor circuit through the first current-limiting resistor, and the control electrode of the first control switch tube is electrically connected with the first electrode of the first control switch tube through the second current-limiting resistor;
and the second pole of the first control switch tube is electrically connected with the closing control signal output end through the third current limiting resistor.
In the embodiment of the invention, the first current limiting resistor, the second current limiting resistor and the third current limiting resistor play a role in limiting current, so that the triode is prevented from being damaged due to overlarge current.
In the embodiment of the present invention, the storage capacitor circuit may include a first storage capacitor and a second storage capacitor connected in parallel with each other, but is not limited thereto.
In a specific implementation, the storage capacitor circuit may include only one storage capacitor, or may include a plurality of storage capacitors connected in parallel, or may include a plurality of storage capacitors connected in series, and a specific structure of the storage capacitor circuit may be selected according to an actual situation.
In specific implementation, the shutdown control circuit is further configured to control the shutdown control circuit without passing through the shutdown control signal output terminal when the power line of the display device is not pulled out in the power-on state or the display device is normally shut down.
Specifically, the backlight control circuit may include a second control switch tube and a first pull-up resistor;
a control electrode of the second control switch tube is electrically connected with the closing control signal output end, a first electrode of the second control switch tube is electrically connected with a backlight enabling end of the backlight circuit, and a second electrode of the second control switch tube is electrically connected with a third voltage end; the third voltage end is used for providing a third voltage signal;
the first electrode of the second control switch tube is also electrically connected with a fourth voltage end through the first pull-up resistor;
the backlight circuit is used for being closed when the backlight enabling end of the backlight circuit is connected with the third voltage signal.
In the embodiment of the present invention, the third voltage signal may be a low voltage signal, or the third voltage terminal may be a ground terminal, but is not limited thereto.
In the embodiment of the present invention, the fourth voltage terminal may be a high-level terminal, but is not limited thereto.
In a specific implementation, the backlight control circuit may include a second control switch and a first pull-up resistor, and the second control switch is controlled to be turned on by a turn-off control signal, so as to control a potential of the backlight enable terminal to control the turn-off of the backlight circuit.
In a specific implementation, the backlight control circuit may further include a filter capacitor, a second pull-up resistor, and a fourth current limiting resistor, wherein,
the first end of the filter capacitor is electrically connected with the backlight enabling end, and the second end of the filter capacitor is electrically connected with a fifth voltage end;
the second pull-up resistor is connected between the backlight control terminal and the fourth voltage terminal;
the first end of the fourth current limiting resistor is electrically connected with the backlight control end, and the second end of the fourth current limiting resistor is electrically connected with the control electrode of the second control switch tube.
When the display device works normally, the potential of the backlight enabling end is controlled through the backlight control end, so that the backlight circuit is controlled to emit light or be closed.
In the embodiment of the present invention, the fifth voltage terminal may be a low voltage terminal or a ground terminal, but is not limited thereto.
As shown in fig. 5, an embodiment of the backlight control circuit may include a second control transistor Q2, a first pull-up resistor R105, a filter capacitor C113, a second pull-up resistor R106, and a fourth current limiting resistor R109;
the base electrode of the second control triode Q2 is electrically connected with the turn-OFF control signal output end BL-OFF, the collector electrode of the second control triode Q2 is electrically connected with the backlight enabling end BKL-EN of the backlight circuit, and the emitter electrode of the second control triode Q2 is electrically connected with the ground end GND;
the collector of the second control triode Q2 is also electrically connected with the high-level end through the first pull-up resistor R105; the high level end is used for providing a +5V voltage signal;
the backlight circuit is used for being closed when the potential of a backlight enabling end BKL-EN is low voltage, and emitting light when the potential of the backlight enabling end BKL-EN is high voltage;
a first end of the filter capacitor C113 is electrically connected with the backlight enable end BKL-EN, and a second end of the filter capacitor C113 is electrically connected with a ground end GND;
the second pull-up resistor R106 is connected between the backlight control terminal VBLCTRL and the high level terminal;
a first end of the fourth current limiting resistor R109 is electrically connected to the backlight control end VBLCTRL, and a second end of the fourth current limiting resistor R109 is electrically connected to a base of the second control triode Q2.
In the embodiment of the backlight control circuit shown in fig. 5, the Q2 is an NPN transistor, but not limited thereto.
When the embodiment of the backlight control circuit shown in fig. 5 is in operation, after the power line of the display device is pulled out in the power-on state, the potential of BL-OFF is high to control Q2 to be turned on, so that BKL-EN is connected to the ground to control the backlight circuit to be turned OFF;
after the power supply line is pulled out for a while, the potential of BL-OFF becomes a low voltage, and the display device is turned OFF.
When the embodiment of the backlight control circuit shown in fig. 5 works, the potential of BKL-EN is controlled by VBLCTRL when the display device works normally; when the potential of VBLCTRL is high voltage, Q2 is opened, the potential of BKL-EN is low level, and the backlight circuit is closed; when the potential of VBLCTRL is low voltage, Q2 is turned off, the potential of BKL-EN is high level, and the backlight circuit emits light.
The backlight shutdown circuit of the present invention is described below with reference to an embodiment.
As shown in fig. 6, an embodiment of the backlight shutdown circuit according to the present invention includes a shutdown control circuit and a backlight control circuit 12, wherein,
the shutdown control circuit includes a storage capacitor circuit 111 and a first control circuit 112;
the storage capacitor circuit 111 comprises a first storage capacitor C602 and a second storage capacitor C603 which are connected in parallel with each other;
a first end of the first storage capacitor C602 and a first end of the second storage capacitor C603 are electrically connected to a power supply voltage terminal VDD;
the first control circuit 112 comprises a first control triode Q1, a first current-limiting resistor R605, a second current-limiting resistor R604 and a third current-limiting resistor R607;
the base of the first control triode Q1 is electrically connected to the second end of the first storage capacitor R602 through the first current limiting resistor R605, and the base of the first control triode Q1 is electrically connected to the emitter of the first control triode Q1 through the second current limiting resistor R604; a second end of the first storage capacitor R602 is electrically connected to a second end of the second storage capacitor C603;
the collector of the first control triode Q1 is electrically connected with the OFF control signal output end BL-OFF through the third current limiting resistor R607;
an emitting electrode of the first control triode Q1 is electrically connected with a high-voltage end VCC;
one embodiment of the backlight control circuit may include a second control transistor Q2, a first pull-up resistor R105, a filter capacitor C113, a second pull-up resistor R106, and a fourth current limiting resistor R109;
the base electrode of the second control triode Q2 is electrically connected with the turn-OFF control signal output end BL-OFF, the collector electrode of the second control triode Q2 is electrically connected with the backlight enabling end BKL-EN of the backlight circuit, and the emitter electrode of the second control triode Q2 is electrically connected with the ground end GND;
the collector of the second control triode Q2 is also electrically connected with the high-level end through the first pull-up resistor R105; the high level end is used for providing a +5V voltage signal;
the backlight circuit is used for being closed when the potential of a backlight enabling end BKL-EN is low voltage, and emitting light when the potential of the backlight enabling end BKL-EN is high voltage;
a first end of the filter capacitor C113 is electrically connected with the backlight enable end BKL-EN, and a second end of the filter capacitor C113 is electrically connected with a ground end GND;
the second pull-up resistor R106 is connected between the backlight control terminal VBLCTRL and the high level terminal;
a first end of the fourth current limiting resistor R109 is electrically connected to the backlight control end VBLCTRL, and a second end of the fourth current limiting resistor R109 is electrically connected to a base of the second control triode Q2.
In the embodiment of the backlight turn-off circuit shown in fig. 6, Q1 is a PNP transistor and Q2 is an NPN transistor.
In the embodiment of the backlight shutdown circuit shown in fig. 6, when the display device is in the power-on state and the power line is not pulled out, the power voltage may be 5V, and VCC may provide 3.3V; the 3.3V voltage provided by the VCC is obtained by converting the power supply voltage through a direct current converter;
after the display device is turned on and the power line is pulled out, since the 3.3V voltage provided by VCC is obtained by converting the power voltage through the dc converter, the speed of the voltage drop of the power voltage is greater than the speed of the voltage drop provided by VCC, and since the voltage difference between the two ends of the storage capacitor circuit 111 cannot change suddenly, Q1 will be turned on to control BL-OFF to output a turn-OFF control signal (in this embodiment, the turn-OFF control signal is a high level signal) to the backlight control circuit 12 to control the backlight control circuit 12 to turn OFF the backlight circuit;
when the display device is operating normally (i.e. the display device is in the on state, and the power line is not pulled out, and the display device is normally OFF), Q1 is turned OFF, and the potential of BL-OFF is not affected by VDD and VCC.
In the embodiment of the backlight turn-off circuit shown in figure 6,
c602 is a 10uF/25V patch capacitor, the function of C602 is to isolate VDD from VCC, when the external power supply is disconnected, the voltage of the base of Q1 begins to drop due to the discharge characteristic of the capacitor;
c603 is an electrolytic capacitor of 10uF/50V, C602 has the function of isolating VDD from VCC, and when the external power supply is disconnected, the voltage of the base of Q1 begins to drop due to the discharge characteristic of the capacitor;
the resistance value of R605 and the resistance value of R604 are 10 kilo-ohms, and the function of R605 and the function of R604 are current limiting;
q1 is PNP type triode model PMBS3906, Q1 is used as a switching tube, and Q1 is conducted when the voltage difference between the base voltage of Q1 and the emitter electrode of Q1 is smaller than-0.7V;
the resistance value of R607, the resistance value of R105, the resistance value of R106 and the resistance value of R109 are 47 kilo-ohms, and R607 and R109 are used for limiting current and preventing Q1 from being damaged by overlarge current; r105 and R106 are pull-up resistors, and the pull-up is to clamp an uncertain signal at a high level through one resistor, and the resistors play a role in current limiting at the same time; on a lead connected with a pull-up resistor, if an external component is not started, the pull-up resistor weakly pulls up an input voltage signal; when the external component is not connected, the outside appears to be high-impedance to the input; at this time, the voltage at the input port can be pulled up to a high level by the pull-up resistor. If the external component is enabled, the high level set by the pull-up resistor is canceled, and the pull-up resistor can ensure that the pin can keep a certain logic level even when the external component is not connected;
c113 is a 0.1uF/16V patch capacitor which is used for filtering and filtering noise waves in the circuit;
the Q2 is an NPN type triode with the model of MMBT3904 and is used as a switching tube; q2 is turned on when the voltage difference between the base of Q2 and the emitter of Q2 is greater than 0.7V.
In the embodiment of the backlight shutdown circuit shown in fig. 6, the external power supply disconnection finger may be, but is not limited to, a power supply line being unplugged.
The operation principle of the backlight turn-off circuit shown in fig. 6 is as follows:
when the display device is in a normal working state, the system is in a stable state, the base voltage of Q1 and the emitter voltage of Q1 are both 3.3V, Q1 is turned OFF, and the potential of BL-OFF is controlled by VBLCTRL; when the potential of VBLCTRL is high voltage, the potential of BL-OFF is high voltage, Q2 is turned on, the potential of BKL-EN is low voltage, and the backlight circuit is turned OFF; when the potential of BLCTRL is low voltage, the potential of BL-OFF is low voltage, Q2 is turned OFF, the potential of BKL-EN is high voltage, the backlight circuit emits light, and the backlight circuit is in an open state;
when the power line of the display device is unplugged in a power-on state, the voltage provided by VCC is obtained by converting the power voltage provided by VDD through the direct current converter, so that the falling speed of the power voltage provided by VDD at the moment of power failure is greater than that of the voltage provided by VCC; when the power voltage provided by VDD is reduced, the voltage at two ends of the capacitor cannot change suddenly, so that the base voltage of Q1 is instantaneously smaller than 3.3V, when the voltage difference value between the base voltage of Q1 and the emitter voltage of Q1 is smaller than-0.7V, Q1 is conducted, the voltage of BL-OFF is high voltage, so that Q2 is conducted, and the voltage of BKL-EN is low voltage, so as to close the backlight circuit;
after the power line of the display device is unplugged for a period of time in the power-on state, when the power voltage provided by VDD and the voltage provided by VCC both drop to 0V, Q1 and Q2 are both turned off, and the display device is turned off.
In fig. 7, the solid line indicates the potential of VDD, and the dotted line indicates the potential of VCC.
The potential of VDD in fig. 7 is: when the backlight turn-off circuit shown in fig. 6 of the present invention is in operation, when the power line of the display device is pulled out and the power is turned off in the power-on state, the potential of the power voltage provided by VDD is increased;
the potential of VCC in fig. 7 is: when the backlight turn-off circuit shown in fig. 6 of the present invention is in operation, when the power line of the display device is pulled out and the power is turned off in the power-on state, the voltage level supplied by VCC is high.
As can be seen from fig. 7, the power supply voltage supplied by VDD drops faster than the voltage supplied by VCC.
The display device comprises a backlight circuit, and the display device also comprises the backlight closing circuit;
the backlight closing circuit is used for closing the backlight circuit after a power line is pulled out to be powered off when the display device is in a power-on state.
In the embodiment of the present invention, the display device may be a liquid crystal display device, but is not limited thereto. And the liquid crystal display device further comprises a liquid crystal display screen.
The display device provided by the embodiment of the invention can be any product or component with a display function, such as a mobile phone, a tablet personal computer, a television, a display device, a notebook computer, a digital photo frame, a navigator and the like.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A backlight shutdown circuit applied to a backlight circuit of a display device is characterized in that the backlight shutdown circuit comprises a backlight control circuit and a shutdown control circuit, wherein,
the closing control circuit is used for outputting a closing control signal to the backlight control circuit through the closing control signal output end within preset time after a power line of the display device is pulled out to be powered off in a starting-up state and before the liquid crystal display screen is in a liquid crystal closing state;
the backlight control circuit is used for controlling the backlight circuit to be closed after receiving the closing control signal;
the closing control circuit comprises a storage capacitor circuit and a first control circuit;
the first end of the storage capacitor circuit is electrically connected with the first voltage end, and the second end of the storage capacitor circuit is electrically connected with the control end of the first control circuit;
the first end of the first control circuit is electrically connected with the second voltage end, and the second end of the first control circuit is electrically connected with the closing control signal output end;
the first voltage end is used for providing a first voltage, and the second voltage end is used for providing a second voltage;
the first control circuit is used for generating the closing control signal according to the first voltage and the second voltage within preset time after a power line of the display device is pulled out to be powered off in a starting state.
2. The backlight shutdown circuit of claim 1, wherein the supply voltage terminal is to provide a supply voltage;
the first voltage end is the power supply voltage end, and the second voltage is obtained by converting the power supply voltage through a direct current converter; or,
the second voltage end is the power supply voltage end, and the first voltage is obtained by converting the power supply voltage through a direct current converter.
3. The backlight shutdown circuit of claim 1, wherein the first control circuit comprises a first control switch tube;
the control electrode of the first control switch tube is the control end of the first control circuit, the first electrode of the first control switch tube is the first end of the first control circuit, and the second electrode of the first control switch tube is the second end of the first control circuit.
4. The backlight shutdown circuit of claim 3, wherein the first control switch is a p-type switch; the first voltage end is a power supply voltage end, the power supply voltage end is used for providing power supply voltage, and the second voltage is obtained by converting the power supply voltage through a direct current converter;
when the display device is in a starting state and a power line is not pulled out, the power voltage is greater than the second voltage; after the power line is pulled out to cut off the power supply in the power-on state of the display device, the falling speed of the power supply voltage is greater than that of the second voltage.
5. The backlight shutdown circuit of claim 3, wherein the first control switch is an n-type switch; the second voltage end is a power supply voltage end, the power supply voltage end is used for providing power supply voltage, and the first voltage is obtained by converting the power supply voltage through a direct current converter;
when the display device is in a starting state and a power line is not pulled out, the power voltage is greater than the first voltage; after the power line is pulled out to cut off the power supply in the power-on state of the display device, the falling speed of the power supply voltage is greater than that of the first voltage.
6. The backlight shutdown circuit of claim 3, wherein the shutdown control circuit further comprises a first current limiting resistor, a second current limiting resistor, and a third current limiting resistor;
the control electrode of the first control switch tube is electrically connected with the second end of the storage capacitor circuit through the first current-limiting resistor, and the control electrode of the first control switch tube is electrically connected with the first electrode of the first control switch tube through the second current-limiting resistor;
and the second pole of the first control switch tube is electrically connected with the closing control signal output end through the third current limiting resistor.
7. The backlight shutdown circuit of any of claims 1 to 6, wherein the storage capacitor circuit comprises a first storage capacitor and a second storage capacitor connected in parallel with each other.
8. The backlight shutdown circuit of any one of claims 1 to 6, wherein the backlight control circuit comprises a second control switch tube and a first pull-up resistor;
a control electrode of the second control switch tube is electrically connected with the closing control signal output end, a first electrode of the second control switch tube is electrically connected with a backlight enabling end of the backlight circuit, and a second electrode of the second control switch tube is electrically connected with a third voltage end; the third voltage end is used for providing a third voltage signal;
the first electrode of the second control switch tube is also electrically connected with a fourth voltage end through the first pull-up resistor;
the backlight circuit is used for being closed when the backlight enabling end of the backlight circuit is connected with the third voltage signal.
9. The backlight shutdown circuit of claim 8, wherein the backlight control circuit further comprises a filter capacitor, a second pull-up resistor, and a fourth current limiting resistor, wherein,
the first end of the filter capacitor is electrically connected with the backlight enabling end, and the second end of the filter capacitor is electrically connected with a fifth voltage end;
the second pull-up resistor is connected between the backlight control terminal and the fourth voltage terminal;
the first end of the fourth current limiting resistor is electrically connected with the backlight control end, and the second end of the fourth current limiting resistor is electrically connected with the control electrode of the second control switch tube.
10. A display device comprising a backlight circuit, characterized in that the display device further comprises a backlight shutdown circuit as claimed in any one of claims 1 to 9;
the backlight closing circuit is used for closing the backlight circuit after a power line is pulled out to be powered off when the display device is in a power-on state.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201911052990.2A CN110648635B (en) | 2019-10-31 | 2019-10-31 | Backlight closing circuit and display device |
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| Application Number | Priority Date | Filing Date | Title |
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| CN201911052990.2A CN110648635B (en) | 2019-10-31 | 2019-10-31 | Backlight closing circuit and display device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH08328672A (en) * | 1995-06-02 | 1996-12-13 | Tokimec Inc | Stabilized dc voltage circuit and switching power supply with the circuit |
| JP4819353B2 (en) * | 2004-12-20 | 2011-11-24 | Ｎｅｃディスプレイソリューションズ株式会社 | Display device |
| KR20080039587A (en) * | 2006-11-01 | 2008-05-07 | 엘지디스플레이 주식회사 | Back light unit and liquid crystal display device having the same and start driving method of thereof |
| CN101308630B (en) * | 2007-05-18 | 2011-12-14 | 群康科技(深圳)有限公司 | LCD device |
| CN202634566U (en) * | 2012-06-04 | 2012-12-26 | 深圳创维－Rgb电子有限公司 | Reset control circuit and television |
| CN103905756B (en) * | 2014-03-26 | 2017-02-01 | 深圳创维－Rgb电子有限公司 | Television set failure processing device and television set |
| CN206506602U (en) * | 2017-03-06 | 2017-09-19 | 康佳集团股份有限公司 | One kind shutdown power-off sequential control circuit and television set |
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