CN109003585B - Liquid crystal screen anti-smear circuit and liquid crystal screen - Google Patents
Liquid crystal screen anti-smear circuit and liquid crystal screen Download PDFInfo
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- CN109003585B CN109003585B CN201810852460.5A CN201810852460A CN109003585B CN 109003585 B CN109003585 B CN 109003585B CN 201810852460 A CN201810852460 A CN 201810852460A CN 109003585 B CN109003585 B CN 109003585B
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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
- G09G3/36—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 using liquid crystals
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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
- G09G2320/00—Control of display operating conditions
- G09G2320/02—Improving the quality of display appearance
- G09G2320/0257—Reduction of after-image effects
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- Theoretical Computer Science (AREA)
- Control Of Indicators Other Than Cathode Ray Tubes (AREA)
- Liquid Crystal Display Device Control (AREA)
Abstract
The invention discloses a liquid crystal screen and an anti-smear circuit thereof. This liquid crystal display screen anti-smear circuit includes: DC boost circuit and switch chip, DC boost circuit's output connects to the light source in a poor light through switch chip, and the switch chip extinguishes the light source in a poor light in order to eliminate the smear when the liquid crystal upset, still includes: the filter capacitor is connected between the output end of the direct current booster circuit and the ground, and the voltage stabilization control circuit is used for stabilizing the power supply voltage; the voltage stabilization control circuit is connected to the direct current booster circuit, and controls the direct current booster circuit to intermittently boost the power supply voltage to the working voltage of the backlight light source in the power-on stage of the liquid crystal screen anti-smear circuit, so that the problem that the liquid crystal screen anti-smear circuit affects the stability of the power supply voltage is solved.
Description
Technical Field
The invention relates to the technical field of liquid crystal display, in particular to a liquid crystal screen anti-smear circuit.
Background
With the development of technologies such as virtual reality, people have higher and higher requirements on screen display effects. For example, in a virtual reality helmet, a screen is a very critical device, and if the screen refresh rate is insufficient, discomfort such as dizziness may occur to the viewer. At present, in order to meet the display requirements, some devices select to use an Organic Light-Emitting Diode (OLED) screen to meet the requirements of virtual reality helmets and the like for quick response and quick refresh of the screen, but the OLED screen has high cost and difficult screen resolution improvement, which results in strong screen sense.
Therefore, some devices use a fast-response liquid crystal screen to replace the OLED screen, but because the liquid crystal needs time to turn over, the turning over process is prone to generate a smear problem, which affects the viewing experience of the user, and therefore, it is also necessary to use a "black insertion" technology to overcome the smear problem, that is, insert a black frame image or turn off a backlight source after the image frame is displayed. However, in the conventional scheme for turning off the backlight source, the operating voltage of the backlight source is periodically cut off, which may cause a large voltage ripple, and affect the stability of the power supply voltage.
Disclosure of Invention
In view of the problem of unstable voltage fluctuation in the smear circuit of the prior art liquid crystal screen turn-off backlight, the invention provides an anti-smear circuit of a liquid crystal screen and a liquid crystal screen, so as to overcome the problem or at least partially solve the problem.
In order to achieve the purpose, the invention adopts the following technical scheme:
according to an aspect of the present invention, there is provided an anti-smear circuit for a liquid crystal display, including: direct current boost circuit and switch chip, direct current boost circuit's output connects to the light source in a poor light through switch chip, and switch chip extinguishes the backlight source of LCD screen in order to eliminate the smear when the liquid crystal upset, and the anti smear circuit of LCD screen still includes: the filter capacitor is connected between the output end of the direct current booster circuit and the ground, and the voltage stabilization control circuit is used for stabilizing the power supply voltage; the voltage stabilization control circuit is connected to the direct current booster circuit, and controls the direct current booster circuit to intermittently boost the power supply voltage to the working voltage of the backlight light source in the electrifying stage of the liquid crystal screen anti-smear circuit.
Optionally, the filter capacitor is an electrolytic capacitor.
Optionally, the voltage regulation control circuit comprises: a switch control circuit connected between the power supply voltage and the DC booster circuit; the switch control circuit collects the voltage value of the power supply voltage, when the voltage value of the power supply voltage is lower than a first preset voltage, the connection between the power supply voltage and the direct current booster circuit is disconnected, and when the voltage value of the power supply voltage is higher than a second preset voltage, the connection between the power supply voltage and the direct current booster circuit is recovered.
Optionally, the switch control circuit includes a voltage division sampling circuit, a comparator, a switching tube controller and a switching tube, and the switching tube is connected in series between the power supply voltage and the dc boost circuit;
the output end of the voltage division sampling circuit is connected with the input end of the comparator;
the output end of the comparator is connected with the switching tube controller;
and the switching tube controller controls the switching tube to be switched off or switched on according to the comparison result of the comparator.
Optionally, the comparator is a hysteretic comparator.
Optionally, the voltage regulation control circuit comprises: and the output end of the signal output circuit is connected to the enabling end of the direct current booster circuit, and the signal output circuit outputs a pulse width modulation signal to control the direct current booster circuit to boost intermittently in the electrifying stage of the liquid crystal screen anti-smear circuit.
Optionally, the signal output circuit adjusts the boosting process of the dc boost circuit by adjusting the frequency and/or duty ratio of the output pulse width modulation signal.
Optionally, after the liquid crystal screen anti-smear circuit is powered on, the signal output circuit outputs a stable voltage control signal to control the direct current boost circuit to continuously work.
Optionally, the signal output circuit comprises: a microcontroller.
According to another aspect of the invention, a liquid crystal screen is provided, and the liquid crystal screen is provided with the liquid crystal screen anti-smearing circuit.
In conclusion, the beneficial effects of the invention are as follows:
in the liquid crystal display technology, based on a scheme that a backlight light source is turned off by a switch chip to eliminate smear, a filter capacitor is arranged at the output end of a direct current booster circuit to reduce ripples generated by the fact that the switch chip is turned on and off continuously; meanwhile, a voltage stabilization control circuit is arranged, and the direct current booster circuit is controlled to boost voltage discontinuously in the power-on stage, so that the phenomenon that the power supply voltage is excessively reduced due to the fact that an accessed filter capacitor needs to be charged is avoided.
Drawings
FIG. 1 is a schematic diagram of a conventional anti-smear circuit of a liquid crystal display using a black insertion technique;
fig. 2 is a schematic structural diagram of an anti-smear circuit of a liquid crystal display according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a liquid crystal display anti-smear circuit with a filter capacitor added;
FIG. 4 is a circuit diagram of the embodiment of FIG. 3 with the addition of a switch control circuit;
FIG. 5 is a diagram of the voltage waveform for powering up a DC boost circuit using normal high level control;
fig. 6 is a schematic diagram of a power-on voltage waveform when the PWM signal is used to control the dc boost circuit.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Firstly, the anti-smear technology of the liquid crystal screen in the prior art is introduced. Fig. 1 is a schematic diagram of an anti-smear circuit of a conventional liquid crystal display panel using black insertion technology, and as shown in fig. 2, a dc boost circuit includes a dc boost chip and a resistor, an inductor, a diode, and the like. A switch chip (model TL4242) is arranged between the output end of the direct current booster circuit and an LED (light emitting diode) backlight light source, and the switch chip stops outputting voltage when the liquid crystal is turned over under the control of a PWM (Pulse Width Modulation) dimming signal to extinguish the backlight light source, so that the phenomenon of smear caused by the turning over of the liquid crystal is avoided.
However, in practical applications, due to the existence of the black insertion technique, the backlight light source is turned on for a short time, such as one-tenth of a period, during the display period, resulting in a decrease in screen brightness. In order to solve the problem of low screen brightness, the current value of the light emitting diode needs to be adjusted to be large (100mA-200mA), and in this case, when the switch chip is turned on and off continuously, a large ripple is generated on the output voltage due to insufficient response speed of the dc boost chip. This ripple is fed back to the supply voltage VBUS through the diode and the inductor, causing large fluctuations in the supply voltage VBUS. For example, in a practical circuit, the frequency of the PWM dimming signal is 70Hz (same as the screen refresh frequency), and a ripple having a peak-to-peak value of 1.36V and 70Hz is fed back to the supply voltage VBUS (about 5V) along with the dc boost circuit, and the lowest point of the ripple is already lower than 4V, which may cause other devices powered by the supply voltage VBUS to operate abnormally.
In order to solve the problem that the power supply voltage of the liquid crystal screen anti-smear circuit is interfered, the liquid crystal screen anti-smear circuit is provided.
The technical idea of the application is as follows: based on the scheme that the backlight light source is turned off by using the switch chip to eliminate the smear, the filter capacitor is arranged at the output end of the direct current booster circuit to reduce ripples generated by the continuous turning on and off of the switch chip and stabilize the power supply voltage in the normal working stage; meanwhile, a voltage stabilization control circuit is arranged, and the direct current booster circuit is controlled to boost voltage discontinuously in the power-on stage, so that the filter capacitor is prevented from being charged quickly, the power supply voltage is prevented from being excessively lowered due to the generation of large charging current, and the power supply voltage in the power-on stage is stabilized.
Fig. 2 is a schematic structural diagram of a liquid crystal panel anti-smear circuit according to an embodiment of the present invention, and as shown in fig. 2, the liquid crystal panel anti-smear circuit includes: the output end of the direct current booster circuit is connected to the backlight light source through the switch chip, and the switch chip extinguishes the backlight light source to eliminate the smear when the liquid crystal is turned over.
Meanwhile, the liquid crystal display panel anti-smear circuit of the embodiment shown in fig. 2 further includes: the filter capacitor is connected between the output end of the direct current booster circuit and the ground, and the voltage stabilization control circuit is used for stabilizing the power supply voltage; the voltage stabilization control circuit is connected to the direct current booster circuit, and controls the direct current booster circuit to intermittently boost the power supply voltage to the working voltage of the backlight light source in the electrifying stage of the liquid crystal screen anti-smear circuit.
Referring to fig. 3, by providing the filter capacitor C1 at the output end of the dc boost circuit, a complementary current can be provided when the switch chip is closed by the energy storage function of the filter capacitor C1, so as to solve the problem of insufficient response speed of the dc boost circuit, thereby reducing ripples generated during black insertion of the anti-smear circuit and reducing adverse effects on the power supply voltage.
In addition, considering that the connected filter capacitor needs to be charged in the power-on stage, the power supply voltage can be pulled down, and the effect is more obvious when the capacitance value of the filter capacitor is larger, so that the power supply voltage is possibly too low, even the circuit protection is triggered, and the anti-smear circuit cannot be normally powered on to work. Therefore, the embodiment of the anti-smear circuit shown in fig. 2 of the present application is further provided with a voltage stabilization control circuit, and the voltage stabilization control circuit controls the dc boost circuit to boost voltage discontinuously in the power-on stage, so that an excessive current generated by the rapid charging of a large-capacity filter capacitor is avoided, and the power voltage is prevented from being excessively lowered.
In one embodiment of the present application, as shown with reference to fig. 4, the voltage stabilization control circuit includes: a switch control circuit connected between the power supply voltage and the DC booster circuit; the switch control circuit collects the voltage value of the power supply voltage, when the voltage value of the power supply voltage is lower than a first preset voltage, the connection between the power supply voltage and the direct current booster circuit is disconnected, and when the voltage value of the power supply voltage is higher than a second preset voltage, the connection between the power supply voltage and the direct current booster circuit is recovered. The first preset voltage and the second preset voltage are set according to specific conditions such as power supply voltage and current of the anti-smear circuit. When the power supply voltage is reduced to a first preset voltage, the connection between the power supply voltage and the direct current booster circuit is cut off, and the pull-down action of the charging current on the power supply voltage is interrupted, so that the power supply voltage gradually recovers to be increased; and when the power supply voltage is recovered to the second preset voltage, the power supply voltage and the direct current booster circuit are switched on again, and the filter capacitor with large capacity is charged continuously.
Specifically, referring to fig. 4, the switch control circuit includes a voltage division sampling circuit (including voltage division resistors R4 and R5), a comparator U1, a switching tube controller U2, and a switching tube Q1, which are connected in sequence, and the switching tube Q1 is connected in series between the power supply voltage VBUS and the dc boost circuit.
The voltage value of the power supply voltage VBUS is acquired through voltage division of the voltage division sampling circuit, and the output end of the voltage division sampling circuit, namely the connecting end of the voltage division resistors R4 and R5, is connected with one input end of the comparator U1.
The comparator U1 compares the voltage value collected by the voltage division sampling circuit with a first preset voltage and a second preset voltage, and the output end of the comparator U1 is connected with the switching tube controller U2.
The switching tube controller U2 controls the switching tube Q1 to turn off or on according to the comparison result of the comparator U1, so as to turn off or on the power supply voltage and the dc boost circuit.
In the circuit shown in fig. 4, the first predetermined voltage is lower than the second predetermined voltage, and the comparator U1 is a hysteresis comparator to avoid oscillation during the comparison of the voltages.
The working principle of the above-described embodiment of the present application is described with reference to fig. 2 to 4:
referring to fig. 3, the present application connects a filter capacitor C1 between the output of the dc boost circuit and ground. Preferably, the filter capacitor is an electrolytic capacitor, and has a larger capacitance value, so as to provide sufficient current for the LED backlight light source with high current and high brightness when the switch chip is closed, for example, in fig. 3, the filter capacitor C1 is an aluminum electrolytic capacitor of 470 uF/50V. This filter capacitor C1 can be when the switch chip is closed in the twinkling of an eye, and the electric charge that stores through self supplements for the LED of rear end rapidly and uses, has compensatied the not enough condition of direct current boost circuit response speed, surveys after optimizing, and the ripple on the supply voltage VBUS of fig. 3 has been controlled within 200mV to guarantee that supply voltage VBUS remains stable, guarantee other with electrical apparatus normal work.
Meanwhile, after the filter capacitor C1 is connected, because the capacitance value of the filter capacitor C1 is large, in the process that the direct current booster circuit boosts the power supply voltage VBUS (about 5V) to the working voltage of the LED (about 30V), according to the current formula at two ends of the capacitorIt can be seen that the current Ic flowing through the filter capacitor C1 is a relatively large value, which may pull the power supply voltage VBUS low, and even pull it low to trigger the power protection when it is severe, thereby causing the circuit to fail to operate normally.
In contrast, with the switch control circuit shown in fig. 4, by adjusting the resistance values of R4 and R5, when the VBUS voltage is lower than the first preset voltage, the output of the comparator U1 is low, thereby controlling the Q1(N-MOS transistor) to be turned off, after the turn-off, the VBUS current cannot be supplied to the dc boost chip at the rear end, the boost stops, at this time, the fluctuation on VBUS decreases, the VBUS voltage value increases, when the VBUS voltage value increases to the second preset voltage, the divided voltage value entering the comparator U1 through the dividing resistors R4 and R5 is higher than the second preset voltage, the comparator U1 outputs a high level, thereby controlling the Q1 to be turned on, the drain (D) is conducted with the source (S), and the VBUS continues to supply power to the rear-end circuit. The switch and the close of the Q1 realize that the power is supplied to the back end direct current booster circuit discontinuously, thereby prolonging the boosting time of the direct current booster circuit, ensuring that the VBUS voltage is always above a safe voltage value and ensuring the normal work of the VBUS.
In another embodiment of the present application, a regulator control circuit includes: and the output end of the signal output circuit is connected to an enable end of the direct current boost circuit, for example, an enable end EN of a direct current boost chip shown in fig. 1. In the power-on stage of the liquid crystal screen smear-resistant circuit, the signal output circuit controls the DC booster circuit to intermittently boost voltage by outputting a pulse width modulation signal.
After the liquid crystal screen smear-resistant circuit is powered on, the signal output circuit continues to output stable voltage control signals to control the direct-current booster circuit to work continuously.
As shown in fig. 5, in general, the enable terminal EN of the dc boost chip is enabled to start normal operation by changing from low level to high level, so as to output the voltage required by the system at the output terminal Vout. However, when a large capacitor is connected to the output terminal, such as the 470uF aluminum electrolytic capacitor C1 used in fig. 3, because the voltage across the capacitor cannot change suddenly, the instantaneous current is very large, for example, 2-3A or even higher, which results in large power supply voltage ripple, and the system cannot operate normally, and the waveform of the power-on voltage at this time can be referred to as shown in fig. 5.
And because instantaneous current is too big, when mains voltage provides through the USB mouth of PC or notebook, USB of PC or notebook can appear surge phenomenon, leads to USB unable normal use, if mains voltage is that the battery provided, because instantaneous current is too big, can lead to the battery automatic protection, stops the power supply.
In order to solve the above problem, as shown in fig. 6, in the present embodiment, the enable terminal EN signal of the dc boost circuit is changed to: and an EN signal at the power-on stage adopts a PWM control mode, and after a rear-end filter capacitor is fully charged, PWM is changed into high level. Similar to the embodiment shown in fig. 4, the boosting process of the dc boost circuit is intermittently implemented, so that an excessive charging current is prevented from being generated, and the power voltage is prevented from being excessively pulled down, and the voltage waveform of the power-on voltage at this time is as shown in fig. 6.
On the basis of the above embodiments of the present application, the signal output circuit adjusts the boosting process of the dc boost circuit by adjusting the frequency and/or duty ratio of the output pwm signal, so as to adjust according to the needs of the system and the size of the capacitor.
The signal output circuit described above is implemented using a microcontroller, for example.
In addition, the application also discloses a liquid crystal screen, and the liquid crystal screen is provided with the liquid crystal screen anti-smear circuit.
While the foregoing is directed to embodiments of the present application, other modifications and variations of the present application may be devised by those skilled in the art in light of the above teachings. It should be understood by those skilled in the art that the foregoing detailed description is for the purpose of better explaining the present application, and the scope of protection of the present application shall be subject to the scope of protection of the claims.
Claims (9)
1. An anti-smear circuit of a liquid crystal display, comprising: a DC booster circuit and a switch chip, the output end of the DC booster circuit is connected to the backlight source through the switch chip, the switch chip extinguishes the backlight source of the liquid crystal screen to eliminate the smear when the liquid crystal is turned over,
the liquid crystal screen anti-smear circuit further comprises: the filter capacitor is connected between the output end of the direct current booster circuit and the ground, and the voltage stabilization control circuit is used for stabilizing the power supply voltage; the voltage stabilizing control circuit is connected to the direct current booster circuit, and controls the direct current booster circuit to intermittently boost the power supply voltage to the working voltage of the backlight light source in the power-on stage of the liquid crystal screen anti-smear circuit;
the voltage stabilization control circuit includes: a switch control circuit connected between the power supply voltage and the DC boost circuit; the switch control circuit collects the voltage value of the power supply voltage, when the voltage value of the power supply voltage is lower than a first preset voltage, the connection between the power supply voltage and the direct current booster circuit is disconnected, and when the voltage value of the power supply voltage is higher than a second preset voltage, the connection between the power supply voltage and the direct current booster circuit is recovered.
2. The liquid crystal screen anti-smear circuit according to claim 1,
the filter capacitor is an electrolytic capacitor.
3. The liquid crystal screen anti-smear circuit according to claim 1,
the switch control circuit comprises a voltage division sampling circuit, a comparator, a switch tube controller and a switch tube, wherein the switch tube is connected between the power supply voltage and the direct current booster circuit in series;
the output end of the voltage division sampling circuit is connected with the input end of the comparator;
the output end of the comparator is connected with the switching tube controller;
and the switching tube controller controls the switching tube to be switched off or switched on according to the comparison result of the comparator.
4. The liquid crystal screen anti-smear circuit according to claim 3,
the comparator is a hysteresis comparator.
5. The liquid crystal screen anti-smear circuit according to claim 1 or 2,
the voltage stabilization control circuit includes: and the output end of the signal output circuit is connected to the enabling end of the direct current booster circuit, and the signal output circuit outputs a pulse width modulation signal to control the direct current booster circuit to boost intermittently in the electrifying stage of the liquid crystal screen anti-smear circuit.
6. The liquid crystal screen anti-smear circuit according to claim 5,
the signal output circuit adjusts the boosting process of the direct current boosting circuit by adjusting the frequency and/or duty ratio of the output pulse width modulation signal.
7. The liquid crystal screen anti-smear circuit according to claim 5,
after the liquid crystal screen anti-smear circuit is powered on, the signal output circuit outputs a stable voltage control signal to control the direct current booster circuit to continuously work.
8. The liquid crystal screen anti-smear circuit according to claim 5,
the signal output circuit includes: a microcontroller.
9. A liquid crystal panel characterized in that the liquid crystal panel is provided with the liquid crystal panel anti-smear circuit according to any one of claims 1 to 8.
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CN101315748A (en) * | 2007-05-31 | 2008-12-03 | 中华映管股份有限公司 | Driving mechanism and method of display equipment |
CN103325345A (en) * | 2012-03-23 | 2013-09-25 | 索尼公司 | Light emitting element drive device, light emitting element drive method, and display apparatus |
CN106981272A (en) * | 2017-05-26 | 2017-07-25 | 京东方科技集团股份有限公司 | Backlight driving method, device and the display panel of display panel |
CN207516649U (en) * | 2017-12-15 | 2018-06-19 | 潍坊歌尔电子有限公司 | Head-mounted display |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
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TW499666B (en) * | 2001-04-10 | 2002-08-21 | Winbond Electronics Corp | Control circuit and method for eliminating liquid crystal panel residual image |
JP5720266B2 (en) * | 2011-01-21 | 2015-05-20 | ソニー株式会社 | Light emitting element driving circuit, light emitting device, display device, and light emission control method |
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Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
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CN101315748A (en) * | 2007-05-31 | 2008-12-03 | 中华映管股份有限公司 | Driving mechanism and method of display equipment |
CN103325345A (en) * | 2012-03-23 | 2013-09-25 | 索尼公司 | Light emitting element drive device, light emitting element drive method, and display apparatus |
CN106981272A (en) * | 2017-05-26 | 2017-07-25 | 京东方科技集团股份有限公司 | Backlight driving method, device and the display panel of display panel |
CN207516649U (en) * | 2017-12-15 | 2018-06-19 | 潍坊歌尔电子有限公司 | Head-mounted display |
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