Liquid crystal handwriting board

Abstract

The invention discloses a liquid crystal handwriting board which comprises a power grid power output module, an energy storage battery, a power conversion circuit, a control circuit, an infrared sensor and a liquid crystal film. When the power grid normally supplies power, electric energy output by the power grid sequentially passes through the power grid power output module and the power conversion circuit to supply power to the liquid crystal film, the control circuit and the infrared sensor circuit. When the power grid is powered off, the energy storage battery supplies power to the liquid crystal film, the control circuit and the infrared sensor circuit through the power conversion circuit. When the infrared sensor circuit obtains a power supply, the infrared sensor circuit can send a received local erasing signal to the control circuit, so that the control circuit controls and executes a local erasing action on the liquid crystal handwriting board. When a power grid is powered off, the liquid crystal handwriting board can still achieve a local erasing function.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal films, and in particular to a liquid crystal handwriting board. Background Art

[0002] Currently, most of the LCD handwriting tablets with partial erase function are powered by adapter power, and some products retain a small battery inside for one-key erase function. In the event of a power outage, although the one-key erase function can be performed by this small battery, the partial erase function cannot be performed. Summary of the invention

[0003] The main purpose of the present invention is to provide a liquid crystal handwriting board, which aims to realize the local erasing function of the liquid crystal handwriting board when the power grid is out of power.

[0004] To achieve the above-mentioned purpose, the present invention proposes a liquid crystal handwriting board, comprising a power grid output module, a storage battery, a power conversion circuit, a control circuit, an infrared sensor and a liquid crystal film; when the power grid is supplying power normally, the electric energy output by the power grid is sequentially supplied through the power grid output module and the power conversion circuit to supply power to the liquid crystal film, the control circuit and the infrared sensor circuit respectively; when the power grid is out of power, the storage battery supplies power to the liquid crystal film, the control circuit and the infrared sensor circuit respectively through the power conversion circuit; when the infrared sensor circuit obtains power supply, the received local erasing signal can be sent to the control circuit, so that the control circuit controls the execution of a local erasing action on the liquid crystal handwriting board.

[0005] Preferably, the control circuit is also used to detect the remaining power of the grid power output module and the energy storage battery, and to control the power supply path of the infrared sensor circuit; when the grid is out of power and the control circuit detects that the remaining power of the energy storage battery is lower than a preset threshold, the power supply path of the infrared sensor circuit is cut off.

[0006] Preferably, the first output end of the grid power output module, the output end of the energy storage battery and the input end of the power conversion circuit are interconnected, and the power conversion circuit is used to output power supply to the liquid crystal film, the control circuit and the infrared sensor circuit; the first power detection end of the control circuit is connected to the power detection end of the grid power output module, the second power detection end of the control circuit is connected to the power detection end of the energy storage battery, and the first control end of the control circuit is connected to the controlled end of the infrared sensor circuit.

[0007] Preferably, the power conversion circuit includes a power conversion chip, a resistor R13, a resistor R14, a resistor R16, a resistor R17, a resistor R32, a resistor R60, a capacitor EC3, a capacitor C12, a capacitor C21, a capacitor C22, a capacitor C24, an inductor L1, a transistor Q8, a transistor Q9, a diode D1 and a diode D7; the anode of the diode D1 is used to connect to the grid power output module, the anode of the diode D7 is used to connect to the energy storage battery, the cathode of the diode D1, the cathode of the diode D7, the first end of the capacitor EC3, the first end of the resistor R16 and the source of the transistor Q9 are interconnected; the second end of the resistor R16, the first end of the resistor R60 and the collector of the transistor Q8 are interconnected, the base of the transistor Q8, the second end of the resistor R32 and the first end of the capacitor C12 are interconnected, and the first end of the resistor R32 is used to input a switch start signal; The drain of transistor Q9, the first end of resistor R13 and the VIN pin of the power conversion chip are interconnected, the SW pin of the power conversion chip, the first end of capacitor C24 and the first end of inductor L1 are interconnected, the second end of capacitor C24 is connected to the BST pin of the power conversion chip, the EN pin of the power conversion chip is connected to the second end of resistor R13, the FB pin of the power conversion chip, the second end of resistor R14 and the first end of resistor R17 are interconnected; the second end of inductor L1, the first end of resistor R14, the first end of capacitor C22 and the first end of capacitor C21 are interconnected, and their connection nodes are used to provide power supply for the control circuit and the infrared sensor circuit; the second end of capacitor EC3, the second end of capacitor C12, the GND pin of the power conversion chip, the second end of resistor R17, the second end of capacitor C22 and the second end of capacitor C21 are all grounded.

[0008] Preferably, the control circuit includes a control chip, a resistor R36, a resistor R37, a resistor R85, a resistor R86, a capacitor C1 and a capacitor C72, the first end of the resistor R36 is the first power detection end of the control circuit, the second end of the resistor R36, the first end of the resistor R37, the first end of the capacitor C1 and the first voltage detection pin of the control chip are interconnected, the first end of the resistor R85 is the second power detection end of the control circuit, the second end of the resistor R85, the first end of the resistor R86, the first end of the capacitor C72 and the second voltage detection pin of the control chip are interconnected, and the second end of the resistor R37, the second end of the capacitor C1, the second end of the resistor R86 and the second end of the capacitor C72 are all grounded.

[0009] Preferably, the infrared sensor circuit includes a resistor R15, a transistor Q11 and a diode D6, the first end of the resistor R15 is connected to the source of the transistor Q11, and its connection node is used to input the power supply of the infrared sensor circuit, the second end of the resistor R15 is connected to the gate of the transistor Q11, and its connection node is the controlled end of the infrared sensor circuit, the drain of the transistor Q11 is connected to the anode of the diode D6, and the cathode of the diode D6 is used to output the power supply of the infrared sensor.

[0010] Preferably, the liquid crystal handwriting board also includes a charging circuit for charging the energy storage battery, the input end of the charging circuit is connected to the second output end of the grid power output module, and the output end of the charging circuit is connected to the input end of the energy storage battery.

[0011] Preferably, the charging circuit includes a charging chip, a resistor R50, a capacitor C26 and a capacitor C28, a VIN pin of the charging chip, an EN pin of the charging chip, a first end of the resistor R50 and a first end of the capacitor C26 are interconnected, and a connection node is an input end of the charging circuit, a second end of the resistor R50 is connected to a CS pin of the charging chip, a BAT pin of the charging chip is connected to a first end of the capacitor C28, and a connection node is used to output charging power to the energy storage battery, and a second end of the capacitor C26, a GND pin of the charging chip and a second end of the capacitor C28 are all grounded.

[0012] Preferably, the charging circuit also includes a resistor R100 and a resistor R101, the first end of the resistor R100, the first end of the capacitor C26, the first end of the resistor R50, the VIN pin of the charging chip and the EN pin of the charging chip are interconnected, the second end of the resistor R100 is connected to the first end of the resistor R101, and the connection node is used to output a charging protection signal, and the second end of the resistor R101 is grounded.

[0013] Preferably, the grid power output module comprises a DC power adapter and a DC socket connected in sequence, the DC power adapter is used to input grid power, and the DC socket is used to output grid power.

[0014] Preferably, the liquid crystal handwriting board further includes a Schottky diode D2, which is connected in series between the grid power output module and the power conversion circuit, and the cathode of the Schottky diode D2 is connected to the power conversion circuit.

[0015] Preferably, the liquid crystal handwriting board further includes a Schottky diode D3, which is connected in series between the energy storage battery and the power conversion circuit, and the cathode of the Schottky diode D2 is connected to the power conversion circuit.

[0016] When the grid power output module of the present liquid crystal handwriting board is connected to the mains, the electric energy flows to the liquid crystal film, the control circuit and the infrared sensor circuit respectively through the grid power output module and the power conversion circuit, so that the control circuit and the infrared sensor circuit are powered on and work, and the liquid crystal handwriting board can realize the partial erasing function. When the grid power is cut off, the power supply path including the grid power output module is disconnected, and the energy storage battery provides power to the liquid crystal film, the control circuit and the infrared sensor circuit, so as to keep the infrared sensor circuit in the powered-on state. In this way, even if the grid power is cut off, the present liquid crystal handwriting board can realize the partial erasing function. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of an embodiment of a liquid crystal handwriting tablet of the present invention;

[0018] Figure 2 It is a structural schematic diagram of another embodiment of the liquid crystal handwriting tablet of the present invention;

[0019] Figure 3 It is a structural schematic diagram of another embodiment of the liquid crystal writing tablet of the present invention;

[0020] Figure 4 for Figure 2 A schematic diagram of the circuit structure of an embodiment of a power conversion circuit;

[0021] Figure 5 for Figure 3 A schematic diagram of the circuit structure of an embodiment of a charging circuit;

[0022] Figure 6 for Figure 2 A schematic diagram of the circuit structure of an embodiment of a control circuit;

[0023] Figure 7 for Figure 2 A schematic diagram of the circuit structure of an embodiment of a mid-infrared sensor circuit. DETAILED DESCRIPTION

[0024] The scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] See also Figure 1 and Figure 2The present invention proposes a liquid crystal handwriting board, comprising a power supply output module 100, a storage battery 200, a power conversion circuit 300, a control circuit 400, an infrared sensor 500 and a liquid crystal film (not shown in the figure); when the power supply of the power grid is normal, the electric energy output by the power grid is sequentially supplied to the liquid crystal film, the control circuit 400 and the infrared sensor circuit 500 through the power supply output module 100 and the power conversion circuit 300; when the power grid is out of power, the storage battery 200 supplies power to the liquid crystal film, the control circuit 400 and the infrared sensor circuit 500 through the power conversion circuit 300; when the infrared sensor circuit 500 obtains power supply, the received partial erasing signal can be sent to the control circuit 400, so that the control circuit 400 controls the execution of the partial erasing action on the liquid crystal handwriting board.

[0026] In a preferred embodiment, the control circuit 400 is also used to detect the remaining power of the grid power output module 100 and the energy storage battery 200, and to control the power supply path of the infrared sensor circuit 500; when the grid is out of power and the control circuit 400 detects that the remaining power of the energy storage battery 200 is lower than a preset threshold, the power supply path of the infrared sensor circuit 500 is cut off.

[0027] Specifically, the first output end of the grid power output module 100, the output end of the energy storage battery 200 and the input end of the power conversion circuit 300 are interconnected, and the power conversion circuit 300 is used to output power supply to the liquid crystal film, the control circuit 400 and the infrared sensor circuit 500; the first power detection end of the control circuit 400 is connected to the power detection end of the grid power output module 100, the second power detection end of the control circuit 400 is connected to the power detection end of the energy storage battery 200, and the first control end of the control circuit 400 is connected to the controlled end of the infrared sensor circuit 500.

[0028] In the present liquid crystal handwriting board, when the power grid power output module 100 is connected to the mains, the electric energy flows to the liquid crystal film, the control circuit 400 and the infrared sensor circuit 500 respectively through the power grid power output module 100 and the power conversion circuit 300, so that the control circuit 400 and the infrared sensor circuit 500 are powered on and work, the infrared sensor circuit 500 is kept in a powered-on state, and the infrared sensor (not shown) is powered on. The liquid crystal handwriting board can realize the local erasing function. When the power grid is out of power, the power supply path including the power grid power output module 100 is disconnected, and the energy storage battery 200 provides power to the liquid crystal film, the control circuit 400 and the infrared sensor circuit 500 through the power conversion circuit 300, and the infrared sensor circuit 500 is kept in a powered-on state and powered on. In this way, even if the power grid is out of power, the present liquid crystal handwriting board can realize the local erasing function.

[0029] In order to retain the local erasing function of the LCD handwriting board and maintain operation for a longer period of time when the power grid is outage, in the technical solution of the present invention, the control circuit 400 also detects the remaining power status of the grid power output module 100 and the energy storage battery 200, and controls the power supply path of the infrared sensor circuit 500.

[0030] When the power grid is in good condition, the control circuit 400 does not respond to the detected remaining power state.

[0031] When the power grid is out of power, the control circuit 400 detects that there is no remaining power in the power output module 100 of the power grid, and continues to detect the remaining power state of the energy storage battery 200, and does not respond to the detected remaining power state, until the control circuit 400 detects that the remaining power of the energy storage battery 200 reaches a preset threshold, the control circuit 400 controls the infrared sensor circuit 500 to enter a power-off state, stops supplying power to the infrared sensor, and temporarily shuts off the local erasing function of the liquid crystal handwriting board, thereby extending the working time of the liquid crystal handwriting board. In this embodiment, the control circuit detects the remaining power state of the energy storage battery 200 in a variety of ways, such as determining the remaining power of the energy storage battery 200 by detecting the output voltage of the energy storage battery 200, or configuring a special power detector (not shown) to detect the remaining power of the energy storage battery 200.

[0032] See also Figure 3 In a preferred embodiment, the liquid crystal handwriting board further includes a charging circuit 600 for charging the energy storage battery 200, the input end of the charging circuit 600 is connected to the second output end of the grid power output module 100, and the output end of the charging circuit 600 is connected to the input end of the energy storage battery 200. Preferably, the energy storage battery 200 is a lithium battery.

[0033] It is easy to understand that when the grid power output module 100 is connected to the mains, in addition to providing power to the liquid crystal panel, the control circuit 400 and the infrared sensor circuit 500 through the power conversion circuit 300, the energy storage battery 200 can also be charged through the charging circuit 600. In this way, when the grid is out of power, the charged energy storage battery 200 can be directly used to provide power to the liquid crystal panel, the control circuit 400 and the infrared sensor circuit 500, which is very convenient.

[0034] See also Figure 5In a specific embodiment, preferably, the charging circuit 600 includes a charging chip U2, a resistor R50, a capacitor C26 and a capacitor C28, a VIN pin of the charging chip U2, an EN pin of the charging chip U2, a first end of the resistor R50 and a first end of the capacitor C26 are interconnected, and a connection node thereof is an input end of the charging circuit 600, a second end of the resistor R50 is connected to a CS pin of the charging chip U2, a BAT pin of the charging chip U2 is connected to a first end of the capacitor C28, and a connection node thereof is used to output charging power to the energy storage battery 200, and a second end of the capacitor C26, a GND pin of the charging chip U2 and a second end of the capacitor C28 are all grounded.

[0035] Furthermore, the charging circuit 600 also includes a resistor R100 and a resistor R101. The first end of the resistor R100, the first end of the capacitor C26, the first end of the resistor R50, the VIN pin of the charging chip U2, and the EN pin of the charging chip U2 are interconnected. The second end of the resistor R100 is connected to the first end of the resistor R101, and the connection node is used to output a charging protection signal. The second end of the resistor R101 is grounded.

[0036] Here, the charging chip U2 is a dedicated lithium battery charging integrated circuit with constant current, constant voltage and trickle charging functions. At the same time, it can display the charging status by connecting the CHRG pin and the STDBY pin to the light-emitting diode (not shown in the figure), such as a red LED light when charging and a green LED light when fully charged. In addition, the dedicated lithium battery charging circuit of the charging chip U2 also supports the safe charging of lithium batteries. It can be charged in the environment range of 0 to 45 degrees Celsius. Charging will be stopped outside this temperature range to ensure the safety of the lithium battery. The VIN pin of the charging chip U2 is connected to the grid power output module 100, and the EN pin of the charging chip U2 is an enable pin connected to the input power supply. The CS pin of the charging chip U2 is a current limiting control pin, and different charging currents can be set by adjusting the different resistance values ​​of the resistor R50. The BAT pin of the charging chip U2 is connected to the charging input of the lithium battery. When the lithium battery is within the normal voltage range and ambient temperature conditions, it can be charged normally. The TEMP pin of the charging chip U2 is connected to the negative temperature coefficient thermistor NTC. Usually, this negative temperature coefficient thermistor NTC is installed on the lithium battery so that the actual temperature of the lithium battery can be normally fed back to the TEMP pin of the charging chip U2.

[0037] See also Figure 4In a preferred embodiment, the power conversion circuit 300 includes a power conversion chip U5, a resistor R13, a resistor R14, a resistor R16, a resistor R17, a resistor R32, a resistor R60, a capacitor EC3, a capacitor C12, a capacitor C21, a capacitor C22, a capacitor C24, an inductor L1, a transistor Q8, a transistor Q9, a diode D1 and a diode D7; the anode of the diode D1 is used to connect to the grid power output module 100, the anode of the diode D7 is used to connect to the energy storage battery 200, the cathode of the diode D1, the cathode of the diode D7, the first end of the capacitor EC3, the first end of the resistor R16 and the source of the transistor Q9 are interconnected; the second end of the resistor R16, the first end of the resistor R60 and the collector of the transistor Q8 are interconnected, the base of the transistor Q8, the second end of the resistor R32 and the first end of the capacitor C12 are interconnected, and the first end of the resistor R32 is used to input a switch start signal; The drain of transistor Q9, the first end of resistor R13 and the VIN pin of power conversion chip U5 are interconnected, the SW pin of power conversion chip U5, the first end of capacitor C24 and the first end of inductor L1 are interconnected, the second end of capacitor C24 is connected to the BST pin of power conversion chip U5, the EN pin of power conversion chip U5 is connected to the second end of resistor R13, the FB pin of power conversion chip U5, the second end of resistor R14 and the first end of resistor R17 are interconnected; the second end of inductor L1, the first end of resistor R14, the first end of capacitor C22 and the first end of capacitor C21 are interconnected, and their connection nodes are used to provide power supply for control circuit 400 and infrared sensor circuit 500; the second end of capacitor EC3, the second end of capacitor C12, the GND pin of power conversion chip U5, the second end of resistor R17, the second end of capacitor C22 and the second end of capacitor C21 are all grounded.

[0038] In this embodiment, in the normal power supply state, the voltage of the grid power output module 100 is higher than that of the lithium battery, so in the normal power supply state, the grid power output module 100 is mainly used for power supply. Transistor Q8 and transistor Q9 form an electronic switch circuit. The base of transistor Q8 is connected to the control pin of the control chip (not shown) through resistor R32. The collector of transistor Q8 is connected to the gate of transistor Q9 through resistor R60. When the power is turned on, the control chip gives a high level through resistor R32. After transistor Q8 is turned on, the collector voltage becomes a low level, so the gate of transistor Q9 becomes a low level, so that the drain and source of transistor Q9 are turned on, and the input power enters the VIN pin of the power conversion chip U5. The power conversion chip U5 is a DC to DC conversion chip. The power input voltage is converted into +5V for use by the control chip and the infrared sensor circuit 500. The inductor L1 is an inductor coil. The resistor R14 and the resistor R17 are connected in series to form a voltage divider circuit. The middle connection point is input to the FB pin of the power conversion chip U5 to form a positive feedback circuit, so that the output voltage is constant to +5V. The capacitor EC3, the capacitor C22, the capacitor C21, etc. are input and output capacitors to stabilize and filter.

[0039] See also Figure 6 In a preferred embodiment, the control circuit 400 includes a control chip, a resistor R36, a resistor R37, a resistor R85, a resistor R86, a capacitor C1 and a capacitor C72, the first end of the resistor R36 is the first power detection end of the control circuit 400, the second end of the resistor R36, the first end of the resistor R37, the first end of the capacitor C1 and the first voltage detection pin GPIO1 of the control chip are interconnected, the first end of the resistor R85 is the second power detection end of the control circuit 400, the second end of the resistor R85, the first end of the resistor R86, the first end of the capacitor C72 and the second voltage detection pin GPIO2 of the control chip are interconnected, and the second end of the resistor R37, the second end of the capacitor C1, the second end of the resistor R86 and the second end of the capacitor C72 are all grounded.

[0040] Here, resistors R85 and R86 are connected in series to form a voltage divider circuit, and the connection point is input to the GPIO2 pin of the control chip after voltage stabilization and filtering by capacitor C72. This GPIO2 pin has an analog-to-digital AD conversion function, and the voltage of the lithium battery can be obtained after AD analog-to-digital conversion. Resistors R36 and R37 are connected in series to form a voltage divider circuit, and the connection point is input to the GPIO1 pin of the control chip after voltage stabilization and filtering by capacitor C1. This GPIO1 pin has an analog-to-digital AD conversion function, and the output voltage of the grid power output module 100 can be obtained after AD analog-to-digital conversion. If the power grid is out of power, a low voltage will be obtained at the GPIO1 port (for example: the maximum voltage of the lithium battery is 8.4V, and the output voltage of the power grid output module 100 is 12V). In this way, the control chip knows that the lithium battery is currently powering the device. In conjunction with the above lithium battery detection circuit, the power supply of the infrared sensor circuit 500 can be controlled. When the lithium battery voltage drops to a certain voltage, the control chip can turn off the power supply path of the infrared sensor. In this way, the LCD handwriting board will enter the one-key clear mode from the local erase function mode, ensuring that the LCD handwriting board still has the one-key clear function after the lithium battery voltage drops to a certain value.

[0041] See also Figure 7 In a preferred embodiment, the infrared sensor circuit 500 includes a resistor R15, a transistor Q11 and a diode D6. The first end of the resistor R15 is connected to the source of the transistor Q11, and its connection node is used to input the power supply of the infrared sensor circuit 500. The second end of the resistor R15 is connected to the gate of the transistor Q11, and its connection node is the controlled end of the infrared sensor circuit 500. The drain of the transistor Q11 is connected to the anode of the diode D6, and the cathode of the diode D6 is used to output the power supply of the infrared sensor.

[0042] In this embodiment, when the power supply is normal, the GPIO3 pin of the control chip outputs a low level, the source and drain of the transistor Q11 are turned on, and the +5V power supply is supplied to the infrared sensor (not shown) through the transistor Q11 and the diode D6. When the power supply of the grid is normal, the transistor Q11 is always turned on to supply power. When the power supply of the grid is off, the control chip Figure 5 The voltage detection circuit shown starts to detect the voltage of the lithium battery. When the lithium battery voltage is higher than a certain value, the transistor Q11 continues to be turned on to power the infrared sensor. The LCD handwriting board has a local erase function. When the lithium battery voltage drops to a certain value, the GPIO3 port of the control chip outputs a high level, the transistor Q11 is disconnected, and the +5V power supply cannot power the infrared sensor. At this time, the local erase function of the LCD handwriting board is turned off, and the LCD handwriting board still retains the one-key clear function.

[0043] See also Figure 3In a preferred embodiment, the grid power output module 100 includes a DC power adapter 110 and a DC socket 120 connected in sequence, the DC power adapter 110 is used to input grid power, and the DC socket 120 is used to output grid power.

[0044] It is worth mentioning that, in order to enhance the circuit stability, the present liquid crystal handwriting board further includes a Schottky diode D2, which is connected in series between the grid power output module 100 and the power conversion circuit 300, and the cathode of the Schottky diode D2 is connected to the power conversion circuit 300. Similarly, the present liquid crystal handwriting board further includes a Schottky diode D3, which is connected in series between the energy storage battery 200 and the power conversion circuit 300, and the cathode of the Schottky diode D2 is connected to the power conversion circuit 300.

[0045] This technical solution uses a Schottky diode to connect the DC power adapter 110 and the lithium battery, samples and detects the voltage of the DC power adapter 110 and the lithium battery, and intelligently controls the power supply to the infrared sensor by setting appropriate interval values, so that the LCD handwriting board can continue to be partially erased for several hours after the power grid is cut off. When the battery voltage drops to a certain value, the partial erasing function is turned off, and the LCD handwriting board continues to provide the one-key clearing function for dozens of hours. The LCD handwriting board can continue to perform partial erasing and one-key clearing after a power outage.

[0046] It should be noted that the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0047] The above description is only a partial or preferred embodiment of the present invention. Neither the text nor the drawings can limit the scope of protection of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the overall concept of the present invention, or direct / indirect application in other related technical fields are included in the scope of protection of the present invention.

Claims

1. A liquid crystal writing tablet, characterized in that: It includes a grid power output module, an energy storage battery, a power conversion circuit, a control circuit, an infrared sensor and a liquid crystal film; When the power grid is supplying power normally, the power output by the power grid is sequentially supplied to the liquid crystal film, the control circuit and the infrared sensor circuit through the power grid power output module and the power conversion circuit respectively; When the power grid fails, the energy storage battery supplies power to the liquid crystal film, the control circuit and the infrared sensor circuit respectively through the power conversion circuit; When the infrared sensor circuit obtains power supply, the received partial erasing signal can be sent to the control circuit, so that the control circuit controls the execution of the partial erasing action on the liquid crystal handwriting board.

2. The liquid crystal writing tablet according to claim 1, characterized in that: The control circuit is also used to detect the remaining power of the grid power output module and the energy storage battery, and to control the power supply path of the infrared sensor circuit; When the power grid fails and the control circuit detects that the remaining power of the energy storage battery is lower than a preset threshold, the power supply path of the infrared sensor circuit is cut off.

3. The liquid crystal writing tablet according to claim 1, characterized in that: The first output end of the grid power output module, the output end of the energy storage battery and the input end of the power conversion circuit are interconnected, and the power conversion circuit is used to output power supply to the liquid crystal film, the control circuit and the infrared sensor circuit; The first power detection end of the control circuit is connected to the power detection end of the grid power output module, the second power detection end of the control circuit is connected to the power detection end of the energy storage battery, and the first control end of the control circuit is connected to the controlled end of the infrared sensor circuit.

4. The liquid crystal writing board according to claim 3, characterized in that: The power conversion circuit includes a power conversion chip, a resistor R13, a resistor R14, a resistor R16, a resistor R17, a resistor R32, a resistor R60, a capacitor EC3, a capacitor C12, a capacitor C21, a capacitor C22, a capacitor C24, an inductor L1, a transistor Q8, a transistor Q9, a diode D1 and a diode D7; The anode of the diode D1 is used to connect to the grid power output module, the anode of the diode D7 is used to connect to the energy storage battery, the cathode of the diode D1, the cathode of the diode D7, the first end of the capacitor EC3, the first end of the resistor R16 and the source of the transistor Q9 are interconnected; the second end of the resistor R16, the first end of the resistor R60 and the collector of the transistor Q8 are interconnected, the base of the transistor Q8, the second end of the resistor R32 and the first end of the capacitor C12 are interconnected, and the first end of the resistor R32 is used to input a switch start signal; The drain of the transistor Q9, the first end of the resistor R13 and the VIN pin of the power conversion chip are interconnected, the SW pin of the power conversion chip, the first end of the capacitor C24 and the first end of the inductor L1 are interconnected, the second end of the capacitor C24 is connected to the BST pin of the power conversion chip, the EN pin of the power conversion chip is connected to the second end of the resistor R13, and the FB pin of the power conversion chip, the second end of the resistor R14 and the first end of the resistor R17 are interconnected; The second end of the inductor L1, the first end of the resistor R14, the first end of the capacitor C22 and the first end of the capacitor C21 are interconnected, and the connection node is used to provide power supply for the control circuit and the infrared sensor circuit; the second end of the capacitor EC3, the second end of the capacitor C12, the GND pin of the power conversion chip, the second end of the resistor R17, the second end of the capacitor C22 and the second end of the capacitor C21 are all grounded.

5. The liquid crystal writing board according to claim 3, characterized in that: The control circuit includes a control chip, a resistor R36, a resistor R37, a resistor R85, a resistor R86, a capacitor C1 and a capacitor C72. The first end of the resistor R36 is the first power detection end of the control circuit. The second end of the resistor R36, the first end of the resistor R37, the first end of the capacitor C1 and the first voltage detection pin of the control chip are interconnected. The first end of the resistor R85 is the second power detection end of the control circuit. The second end of the resistor R85, the first end of the resistor R86, the first end of the capacitor C72 and the second voltage detection pin of the control chip are interconnected. The second end of the resistor R37, the second end of the capacitor C1, the second end of the resistor R86 and the second end of the capacitor C72 are all grounded.

6. The liquid crystal writing board according to claim 3, characterized in that: The infrared sensor circuit includes a resistor R15, a transistor Q11 and a diode D6. The first end of the resistor R15 is connected to the source of the transistor Q11, and its connection node is used to input the power supply of the infrared sensor circuit. The second end of the resistor R15 is connected to the gate of the transistor Q11, and its connection node is the controlled end of the infrared sensor circuit. The drain of the transistor Q11 is connected to the anode of the diode D6, and the cathode of the diode D6 is used to output the power supply of the infrared sensor.

7. The liquid crystal writing board according to claim 3, characterized in that: The liquid crystal writing board also includes a charging circuit for charging the energy storage battery, the input end of the charging circuit is connected to the second output end of the grid power output module, and the output end of the charging circuit is connected to the input end of the energy storage battery.

8. The liquid crystal writing board according to claim 7, characterized in that: The charging circuit includes a charging chip, a resistor R50, a capacitor C26 and a capacitor C28. The VIN pin of the charging chip, the EN pin of the charging chip, the first end of the resistor R50 and the first end of the capacitor C26 are interconnected, and their connection node is the input end of the charging circuit. The second end of the resistor R50 is connected to the CS pin of the charging chip, and the BAT pin of the charging chip is connected to the first end of the capacitor C28. The connection node is used to output charging power to the energy storage battery. The second end of the capacitor C26, the GND pin of the charging chip and the second end of the capacitor C28 are all grounded.

9. The liquid crystal writing board according to claim 8, characterized in that: The charging circuit also includes a resistor R100 and a resistor R101. The first end of the resistor R100, the first end of the capacitor C26, the first end of the resistor R50, the VIN pin of the charging chip, and the EN pin of the charging chip are interconnected. The second end of the resistor R100 is connected to the first end of the resistor R101, and the connection node is used to output a charging protection signal. The second end of the resistor R101 is grounded.

10. The liquid crystal writing tablet according to any one of claims 1 to 9, characterized in that: The grid power output module comprises a DC power adapter and a DC socket connected in sequence, the DC power adapter is used to input grid power, and the DC socket is used to output the grid power.

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