Power-off protection circuit based on lithium battery

Abstract

The utility model discloses a power-off protection circuit based on a lithium battery, which comprises the lithium battery, a charging circuit, a power supply multiplexing circuit, a sampling circuit, a power-off control circuit and a protection control circuit, and is characterized in that the sampling circuit is used for collecting the voltage of an input power supply VIN5V and transmitting the voltage to a power-off sampling end PR1; the power supply multiplexing circuit is used for conducting a first input end VIN1 and a multiplexing circuit output end VOUT in a default state; when the voltage collected by the sampling circuit is lower than a preset value, the second input end VIN2 and the output end VOUT of the multiplexing circuit are controlled to be conducted, and a power-off prompt signal is sent to the protection control circuit through a power-off prompt signal end ST; the protection control circuit is used for controlling two switch ends of the power-off control circuit to be switched on in a default state; when a power-off prompt signal sent by the power supply multiplexing circuit is received, a set action is executed, and the two switch ends of the power-off control circuit are controlled to be switched off after the set action is executed. The power supply state of the power supply can be inducted in time, and protection action can be performed in time after power failure.

Description

Technical Field

[0001] The utility model relates to a power-off protection circuit, in particular to a power-off protection circuit based on a lithium battery. Background Art

[0002] During the use of embedded system products, power outages may occur due to power failures or human negligence. In this case, the system will lose critical data and cannot recover it. It may also damage the running memory such as SDRAM, affecting the reliability of the product. Therefore, in this application scenario, the power failure protection circuit is an indispensable component of the circuit design. It can continue to provide short-term power to the embedded system after a sudden power failure, so that the system can successfully save critical data. Common power failure protection circuits include:

[0003] A circuit such as Figure 1 As shown, the power supply is switched through diodes, and only the one with higher supply voltage is selected. However, there are problems such as large diode voltage drop and high circuit power consumption. Once the voltage difference between VIN1 and VIN2 is large, there will be a reverse leakage current problem.

[0004] Another circuit such as Figure 2 As shown, Figure 1 Replacing the diode D in the circuit with two PMOS transistors can significantly reduce power consumption. VIN1 is the main power supply and VIN2 is the backup power supply. VIN1 cannot be less than VIN2-VGS(th), and there is still a diode voltage drop problem in the VIN1 input path.

[0005] The third circuit is Figure 3 As shown, VIN1 is the main power supply and VIN2 is the backup power supply. When both VIN1 and VIN2 are powered, VIN1 will be used. The voltage drop between input and output is very small, but there is a floating GND situation.

[0006] Since the above-mentioned existing technologies all have corresponding functional defects, it is difficult to provide timely and effective protection for embedded system products and cannot meet application requirements. Utility Model Content

[0007] The technical problem to be solved by the present invention is to provide a lithium battery-based power-off protection circuit that can timely sense the power supply status of the input power supply and take protective action in time after the input power supply is cut off, in response to the shortcomings of the existing technology.

[0008] In order to solve the above technical problems, the present utility model adopts the following technical solutions.

[0009] A power-off protection circuit based on a lithium battery, comprising a lithium battery, a charging circuit, a power multiplexing circuit, a sampling circuit, a power-off control circuit, and a protection control circuit. The input end of the charging circuit is connected to a preset input power supply VIN_5V, and the output end of the charging circuit is connected to the charging and discharging end of the lithium battery. The power multiplexing circuit comprises a first input end VIN1, a second input end VIN2, a power-off sampling end PR1, a power-off prompt signal end ST, and a multiplexing circuit output end VOUT. The first input end VIN1 is used to connect to the input power supply VIN_5V. The two switch ends of the power-off control circuit are connected between the charging and discharging end of the lithium battery and the second input end VIN2. The control end of the power-off control circuit is connected to the protection control circuit. The sampling circuit is connected to the input power supply VIN_5V and the power-off sampling end PR1. R1, the power-off prompt signal terminal ST is connected to the protection control circuit, wherein: the sampling circuit is used to collect the voltage of the input power supply VIN_5V and transmit it to the power-off sampling terminal PR1; the power multiplexing circuit is used to: in a default state, connect the first input terminal VIN1 and the output terminal VOUT of the multiplexing circuit; when the voltage collected by the sampling circuit is lower than a preset value, control the second input terminal VIN2 and the output terminal VOUT of the multiplexing circuit to be connected, and send a power-off prompt signal to the protection control circuit through the power-off prompt signal terminal ST; the protection control circuit is used to: in a default state, control the two switch terminals of the power-off control circuit to be turned on; execute a setting action when receiving the power-off prompt signal sent by the power multiplexing circuit, and control the two switch terminals of the power-off control circuit to be disconnected after the setting action is completed.

[0010] Preferably, a DC-DC circuit is included, the input end of the DC-DC circuit is connected to the output end VOUT of the multiplexing circuit, and the output end of the DC-DC circuit serves as a VCC_3V3 power supply end.

[0011] Preferably, the power multiplexing circuit includes a power multiplexer chip U4, and the model of the power multiplexer chip U4 is TPS2116.

[0012] Preferably, the first input terminal VIN1 and the second input terminal VIN2 of the power multiplexing circuit are grounded via capacitors C10 and C11 respectively.

[0013] Preferably, the sampling circuit includes a resistor R10 and a resistor R11, which are sequentially connected in series and connected between the input power supply VIN_5V and ground, and a connection point between the resistor R10 and the resistor R11 is connected to the power-off sampling terminal PR1.

[0014] Preferably, the charging circuit includes a linear lithium-ion battery charging chip U1, and the model of the linear lithium-ion battery charging chip U1 is TP4065.

[0015] Preferably, the charging circuit includes an indicator light LED1, an anode of the indicator light LED1 is connected to the input power supply VIN_5V via a resistor R2, and a cathode of the indicator light LED1 is connected to the CHRG terminal of the linear lithium-ion battery charging chip U1.

[0016] Preferably, the power-off control circuit includes a comparator U3, an NPN tube Q2 and a PMOS tube Q1. The non-inverting end of the comparator U3 is grounded through a resistor R9, and the inverting end of the comparator U3 is connected to the protection control circuit through a resistor R5. The output end of the comparator U3 is connected to the base of the NPN tube Q2, the emitter of the NPN tube Q2 is grounded, the collector of the NPN tube Q2 is connected to the gate of the PMOS tube Q1, the source of the PMOS tube Q1 is connected to the charging and discharging end of the lithium battery, the drain of the PMOS tube Q1 is connected to the second input end VIN2, and a resistor R4 is connected between the source and gate of the PMOS tube Q1.

[0017] Preferably, the base of the NPN transistor Q2 is connected to the VCC_3V3 power supply terminal through a resistor R7.

[0018] Preferably, the DC-DC circuit includes a power supply chip U5, and the model of the power supply chip U5 is TPS63000DRCR.

[0019] In the lithium battery-based power-off protection circuit disclosed by the present invention, the input power supply and the backup lithium battery are switched through a power multiplexer, and then the power supply is stepped down to 3.3V by a step-down chip to power the embedded system. At the same time, the input power is charged to the lithium battery through a linear lithium-ion battery charging chip, so that the lithium battery maintains its charge. In normal mode, the system is powered by the input power supply. When the system suddenly loses power, the circuit automatically switches to the lithium battery to provide energy. After the system saves key data, it outputs a control signal to disconnect the lithium battery, and the entire system is powered off normally. Compared with the existing technology, the present invention can timely sense the power supply status of the input power supply and can take protective action in time after the input power supply is cut off, which better meets the application requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the first protection circuit in the prior art;

[0021] Figure 2 This is a schematic diagram of the second protection circuit in the prior art;

[0022] Figure 3This is a schematic diagram of the third protection circuit in the prior art;

[0023] Figure 4 This is a block diagram of the power-off protection circuit based on lithium batteries in this utility model;

[0024] Figure 5 This utility model is based on the principle of power-off protection circuit of lithium battery Figure 1 ;

[0025] Figure 6 This utility model is based on the principle of power-off protection circuit of lithium battery Figure 2 . DETAILED DESCRIPTION

[0026] The present invention will be described in more detail below with reference to the accompanying drawings and embodiments.

[0027] The utility model discloses a power-off protection circuit based on a lithium battery, combined with Figures 4 to 6 As shown, it includes a lithium battery 1, a charging circuit 2, a power multiplexing circuit 3, a sampling circuit 4, a power-off control circuit 5 and a protection control circuit. The input end of the charging circuit 2 is connected to a preset input power supply VIN_5V, and the output end of the charging circuit 2 is connected to the charging and discharging end of the lithium battery 1. The power multiplexing circuit 3 includes a first input end VIN1, a second input end VIN2, a power-off sampling end PR1, a power-off prompt signal end ST and a multiplexing circuit output end VOUT. The first input end VIN1 is used to connect the input power supply VIN_5V. The two switch ends of the power-off control circuit 5 are connected between the charging and discharging end of the lithium battery 1 and the second input end VIN2. The control end of the power-off control circuit 5 is connected to the protection control circuit. The sampling circuit 4 is connected between the input power supply VIN_5V and the power-off sampling end PR1. The power-off prompt signal end ST is connected to the protection control circuit, wherein:

[0028] The sampling circuit 4 is used to collect the voltage of the input power supply VIN_5V and transmit it to the power-off sampling terminal PR1;

[0029] The power multiplexing circuit 3 is used for:

[0030] In a default state, the first input terminal VIN1 is connected to the output terminal VOUT of the multiplexing circuit;

[0031] When the voltage collected by the sampling circuit 4 is lower than a preset value, the second input terminal VIN2 is controlled to be connected to the output terminal VOUT of the multiplexing circuit, and a power-off prompt signal is sent to the protection control circuit through the power-off prompt signal terminal ST;

[0032] The protection control circuit is used for:

[0033] In a default state, the two switch terminals of the power-off control circuit 5 are controlled to be turned on;

[0034] When receiving the power-off prompt signal sent by the power multiplexing circuit 3 , a setting action is executed, and after the setting action is completed, the two switch ends of the power-off control circuit 5 are controlled to be disconnected.

[0035] In the lithium battery-based power-off protection circuit disclosed by the present invention, the input power supply and the backup lithium battery are switched through a power multiplexer, and then the power supply is stepped down to 3.3V by a step-down chip to power the embedded system. At the same time, the input power is charged to the lithium battery through a linear lithium-ion battery charging chip, so that the lithium battery maintains its charge. In normal mode, the system is powered by the input power supply. When the system suddenly loses power, the circuit automatically switches to the lithium battery to provide energy. After the system saves key data, it outputs a control signal to disconnect the lithium battery, and the entire system is powered off normally. Compared with the existing technology, the present invention can timely sense the power supply status of the input power supply and can take protective action in time after the input power supply is cut off, which better meets the application requirements.

[0036] Regarding the working principle of the above circuit, the present utility model provides the following preferred embodiments.

[0037] Example 1

[0038] In this example, see Figure 1 The input power VIN_5V is used to charge the lithium battery through the lithium-ion charging circuit to keep the lithium battery charged. The lithium battery is connected to the VIN2 terminal of the power multiplexer chip TPS2116 through the normally closed switch Q1. The input power VIN_5V is connected to the VIN1 terminal of the power multiplexer chip TPS2116. The output terminal VOUT of the power multiplexer chip TPS2116 is connected to the input terminal of the DC-DCBUCK step-down chip. After passing through the step-down circuit, the VCC_3V3 power supply is output to power the embedded system.

[0039] At the same time, the PR1 signal is input to the PR1 terminal of the power multiplexer chip TPS2116 and compared with the internal Vref_TPS2116 reference voltage, ultimately controlling the on / off of VIN1, VIN2, and VOUT. Furthermore, when VIN1 is connected to VOUT, the chip's ST signal output is open-drain. When VIN2 is connected to VOUT, the chip's ST signal output is low. This ST signal is output as the MCU's Power_Swicth_Signal signal, which the MCU can use to determine whether the input power is currently off.

[0040] In addition, the switch Q1 remains in a normally closed state, and the protection control circuit outputs a Battery_Control_Signal signal to compare with the reference voltage Vref_Comparer, and finally outputs a signal VBAT_ON / OFF to control the on / off of the switch Q1.

[0041] In normal mode, the system's main power supply, VCC_3V3, is generated by stepping down the input power supply, VIN_5V. When the input power fails, the circuit switches to the lithium battery, VIN_BAT, to generate energy. After the system saves critical data or completes the current operation, it outputs the Battery_Control_Signal signal, which is compared with the reference voltage, Vref_Comparer, by comparator U3. Finally, the VBAT_ON / OFF signal is output to turn off switch Q1, and the entire system powers down normally.

[0042] This embodiment includes a DC-DC circuit 6 , the input end of the DC-DC circuit 6 is connected to the output end VOUT of the multiplexing circuit, and the output end of the DC-DC circuit 6 serves as a VCC_3V3 power supply end.

[0043] The preferred chips used in each circuit of this embodiment are as follows:

[0044] The DC-DC circuit 6 includes a power supply chip U5, and the model of the power supply chip U5 is TPS63000DRCR;

[0045] The power multiplexing circuit 3 includes a power multiplexer chip U4, and the model of the power multiplexer chip U4 is TPS2116;

[0046] The charging circuit 2 includes a linear lithium-ion battery charging chip U1 , and the model of the linear lithium-ion battery charging chip U1 is TP4065.

[0047] In order to filter the input signal, in this embodiment, the first input terminal VIN1 and the second input terminal VIN2 of the power multiplexing circuit 3 are grounded via capacitors C10 and C11 respectively.

[0048] See Figure 4 and Figure 6 In this embodiment, the sampling circuit 4 includes a resistor R10 and a resistor R11. The resistors R10 and R11 are connected in series between the input power supply VIN_5V and ground. The connection point between the resistors R10 and R11 is connected to the power-off sampling terminal PR1. The resistors R10 and R11 act as a series voltage divider, and the divided voltage is transmitted to the power-off sampling terminal PR1.

[0049] To serve as a charging reminder, in this embodiment, the charging circuit 2 includes an indicator light LED1, the anode of the indicator light LED1 is connected to the input power supply VIN_5V through a resistor R2, and the cathode of the indicator light LED1 is connected to the CHRG terminal of the linear lithium-ion battery charging chip U1.

[0050] As a key power-off protection control circuit of this utility model, please refer to Figure 1 and Figure 2 The power-off control circuit 5 includes a comparator U3, an NPN transistor Q2, and a PMOS transistor Q1. The non-inverting terminal of the comparator U3 is grounded via a resistor R9, and the inverting terminal of the comparator U3 is connected to the protection control circuit via a resistor R5. The output terminal of the comparator U3 is connected to the base of the NPN transistor Q2, the emitter of the NPN transistor Q2 is grounded, the collector of the NPN transistor Q2 is connected to the gate of the PMOS transistor Q1, the source of the PMOS transistor Q1 is connected to the charge and discharge terminals of the lithium battery 1, the drain of the PMOS transistor Q1 is connected to the second input terminal VIN2, and a resistor R4 is connected between the source and gate of the PMOS transistor Q1. Furthermore, the base of the NPN transistor Q2 is connected to the VCC_3V3 power supply terminal via a resistor R7.

[0051] The working principle of the above circuit is as follows:

[0052] See Figure 5 In this embodiment, the comparator U3 is powered by the VCC_3V3 power supply terminal. The non-inverting input terminal of the comparator U3 is connected to the midpoint of the voltage divider resistor R8 and the resistor R9 to set the reference voltage Vref_Comparer of the comparator. The inverting input terminal of the pin 1 is connected to the pull-down resistor R6 and is connected to the Battery_Control_Signal signal of the MCU through the resistor R5. The output terminal of the pin 4 is connected to the base of the transistor Q2; the base of the transistor Q2 is also connected to the pull-up resistor R7, the emitter is connected to GND, and the collector is connected to the gate of the PMOS transistor Q1; the drain of the PMOS transistor Q1 is connected to the lithium battery U2, and the source is connected to the VIN_BAT power supply. At the same time, a resistor R4 is connected between the drain and gate of the PMOS transistor Q1.

[0053] Linear lithium-ion battery charger chip U1's pin 3, BAT, is connected to the lithium battery. Pin 2, GND, is connected to GND. Pin 4, VCC, is connected to the input power supply VIN_5V via a current-limiting resistor R1. Pin 1, CHRG, is connected to the light-emitting diode LED1 and current-limiting resistor R2, which are connected to the input power supply VIN_5V. Pin 5, PROG, is connected to a pull-down resistor R3. LED1 indicates the charging status, and resistor R3 sets the lithium battery charging current. In this embodiment, resistors R8 and R9 are 10kΩ and 10kΩ, respectively. The comparator reference voltage is:

[0054] Vref_Comparer=VCC_3V3*R8 / (R8+R9)=1.65V.

[0055] See Figure 6 In this embodiment, pin 3 VIN1 and pin 5 MODE of the power multiplexer chip U4 are connected to the input voltage VIN_5V, pin 4 PR1 is connected to the midpoint of the voltage divider resistors R10 and R11 of the input voltage VIN_5V, pin 6 VIN2 is connected to the VIN_BAT power supply, pin 2 VOUT and pin 7 VOUT are connected to the input pin of the BUCK-BOOST power chip U5, pin 8 ST is connected to the pull-up resistor R12, and is connected to the Power_Swicth_Signal signal of the MCU through the resistor R16. Among them, resistors R10 and R11 are used to set the power switching threshold and compare it with the reference voltage of the non-inverting input of the internal comparator of the chip. The internal reference voltage of the chip Vref_TPS2116 = 1V, and the voltage at the chip's 4-pin PR1 VPR1 = VIN_5V*R11 / (R10+R11). When the chip's VOUT pin is switched to VIN1, the 8-pin ST outputs an open-drain state. When the chip's VOUT pin is switched to VIN2, the 8-pin ST output is a low-level state, and the 8-pin ST is connected to the pull-up resistor R12.

[0056] When the voltage VPR1>Vref_TPS2116=1V:

[0057] VOUT switches to VIN1, Power_Swicth_Signal is set to 1;

[0058] When the voltage VPR1 <Vref_TPS2116=1V:

[0059] VOUT switches to VIN2, and Power_Swicth_Signal is set to 0;

[0060] In this embodiment, the resistor R10 is 10 kΩ, the resistor R11 is 3 kΩ, and the power switching threshold voltage VPR1 is 1.15 V.

[0061] Figure 6 The power supply chip U5 is a buck-boost power supply chip, which is a typical application and is not described in detail in this embodiment. Resistors R14 and R15 are used to set the output voltage, calculated as Vout = 0.5V * (1 + R14 / R15). In this embodiment, resistor R14 is 1000kΩ, and resistor R15 is 178kΩ, resulting in an output voltage VCC_3V3 of 3.3V.

[0062] When the system is powered on for the first time, since the power supply VCC_3V3 has not been established yet, the output state of pin 4 of comparator U3 is in a high-impedance state. Transistor Q2 is turned on due to the existence of pull-up resistor R7. Then, the gate of PMOS transistor Q1 is pulled to GND. The drain-gate voltage VGS of PMOS transistor Q1 is the lithium battery voltage VBAT < VGS(th). Thus, PMOS transistor Q1 is also turned on, and the voltage VIN_BAT at PMOS transistor Q1 is the lithium battery voltage VBAT.

[0063] The power switching threshold voltage VPR1 of power multiplexer chip U4 > Vref_TPS2116. The VOUT of U4 switches to VIN1, and the input power supply VIN_5V provides power to BUCK-BOOST power chip U5. After the power chip U5 performs BUCK bucking, it outputs the system main power supply VCC-3V3. At this time, comparator U3 has power and starts to work. The voltage Vref_Comparer at the non-inverting input terminal of the comparator is 1.65V, and the voltage at the inverting input terminal is 0V. The comparator U3 outputs a high level, and transistior Q2 and PMOS transistor Q1 continue to maintain the on state. The voltage VIN_BAT is the lithium battery voltage VBAT.

[0064] When the input power supply is cut off, the input power supply VIN_5V quickly drops to 0V. At this time, the power switching threshold voltage VPR1 of power multiplexer chip U4 < Vref_TPS2116. The VOUT of U4 switches to VIN2, and VIN_VABT provides power to BUCK-BOOST power chip U5. After the power chip U5 performs BUCK bucking, it continues to maintain the stability of the system main power supply VCC-3V3. At the same time, the ST level state of pin 8 of power multiplexer chip U4 changes to a low level and outputs this signal to the MCU signal Power_Swicth_Signal. After the MCU detects that the Power_Swicth_Signal signal changes to a low level, it saves the current running state or relevant key data. After completing the saving work, the MCU outputs the lithium battery control signal Battery_Control_Signal as a high level. At this time, this level Battery_Control_Signal > Vref_Comparer, and the comparator U3 outputs a low level. Transistor Q2 is turned off, and the gate level of PMOS transistor Q1 is pulled up to the VBAT voltage through resistor R4. The gate-drain voltage VGS > VGS(th), and PMOS transistor Q1 is turned off. The VIN_BAT at the source is quickly consumed and there is no new energy replenishment. The power supply VCC-3V3 output by the power chip U5 is turned off, and the system powers off normally.

[0065] The above embodiments are illustrated by taking the protection control circuit as an MCU, but in actual application it is not limited to this, that is, in other embodiments of the present invention, the protection control circuit can also be a circuit structure such as a timer or a delay device. For example: the main power offline signal ST output by the power switching switch chip TPS2116DRLR can be connected to the input end of the timer chip to start timing. After the timing is completed, the timer chip outputs a high-level signal to control the control signal VBAT_ON / OFF of the lithium battery to a low level, thereby cutting off the lithium battery; or, after detecting that the main power offline signal ST output by the power switching switch chip TPS2116DRLR is a low level, the control signal VBAT_ON / OFF of the lithium battery is controlled to a low level after passing through the RC delay circuit, thereby cutting off the lithium battery. All of the above alternatives fall within the scope of protection of the present invention.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements or improvements made within the technical scope of the present invention should be included in the scope of protection of the present invention.

Claims

1. A power-off protection circuit based on a lithium battery, characterized in that: The invention comprises a lithium battery (1), a charging circuit (2), a power multiplexing circuit (3), a sampling circuit (4), a power-off control circuit (5) and a protection control circuit, wherein the input end of the charging circuit (2) is connected to a preset input power supply VIN_5V, the output end of the charging circuit (2) is connected to the charging and discharging end of the lithium battery (1), the power multiplexing circuit (3) comprises a first input end VIN1, a second input end VIN2, a power-off sampling end PR1, a power-off prompt signal end ST and a multiplexing circuit output end VOUT, the first input end VIN1 is used to connect to the input power supply VIN_5V, the two switch ends of the power-off control circuit (5) are connected between the charging and discharging end of the lithium battery (1) and the second input end VIN2, the control end of the power-off control circuit (5) is connected to the protection control circuit, the sampling circuit (4) is connected between the input power supply VIN_5V and the power-off sampling end PR1, the power-off prompt signal end ST is connected to the protection control circuit, wherein: The sampling circuit (4) is used to collect the voltage of the input power supply VIN_5V and transmit it to the power-off sampling terminal PR1; The power multiplexing circuit (3) is used for: In a default state, the first input terminal VIN1 is connected to the output terminal VOUT of the multiplexing circuit; When the voltage collected by the sampling circuit (4) is lower than a preset value, the second input terminal VIN2 is controlled to be connected to the output terminal VOUT of the multiplexing circuit, and a power-off prompt signal is sent to the protection control circuit through the power-off prompt signal terminal ST; The protection control circuit is used for: In a default state, the two switch terminals of the power-off control circuit (5) are controlled to be turned on; When a power-off prompt signal sent by the power multiplexing circuit (3) is received, a setting action is executed, and after the setting action is completed, the two switch ends of the power-off control circuit (5) are controlled to be disconnected.

2. The power-off protection circuit based on a lithium battery according to claim 1, characterized in that: It comprises a DC-DC circuit (6), the input end of the DC-DC circuit (6) is connected to the output end VOUT of the multiplexing circuit, and the output end of the DC-DC circuit (6) serves as a VCC_3V3 power supply end.

3. The power-off protection circuit based on a lithium battery according to claim 1, characterized in that: The power multiplexing circuit (3) includes a power multiplexer chip U4, and the model of the power multiplexer chip U4 is TPS2116.

4. The power-off protection circuit based on a lithium battery according to claim 1, characterized in that: The first input terminal VIN1 and the second input terminal VIN2 of the power multiplexing circuit (3) are grounded via capacitors C10 and C11 respectively.

5. The power-off protection circuit based on a lithium battery according to claim 1, characterized in that: The sampling circuit (4) comprises a resistor R10 and a resistor R11, wherein the resistor R10 and the resistor R11 are sequentially connected in series and connected between the input power supply VIN_5V and the ground, and the connection point between the resistor R10 and the resistor R11 is connected to the power-off sampling terminal PR1.

6. The power-off protection circuit based on a lithium battery according to claim 1, characterized in that: The charging circuit (2) comprises a linear lithium-ion battery charging chip U1, and the model of the linear lithium-ion battery charging chip U1 is TP4065.

7. The power-off protection circuit based on a lithium battery according to claim 6, characterized in that: The charging circuit (2) comprises an indicator light LED1, an anode of the indicator light LED1 is connected to the input power supply VIN_5V via a resistor R2, and a cathode of the indicator light LED1 is connected to the CHRG terminal of the linear lithium-ion battery charging chip U1.

8. The power-off protection circuit based on a lithium battery as claimed in claim 2, characterized in that: The power-off control circuit (5) includes a comparator U3, an NPN transistor Q2, and a PMOS transistor Q1. The in-phase terminal of the comparator U3 is grounded via a resistor R9, the inverting terminal of the comparator U3 is connected to the protection control circuit via a resistor R5, the output terminal of the comparator U3 is connected to the base of the NPN transistor Q2, the emitter of the NPN transistor Q2 is grounded, the collector of the NPN transistor Q2 is connected to the gate of the PMOS transistor Q1, the source of the PMOS transistor Q1 is connected to the charge and discharge terminals of the lithium battery (1), the drain of the PMOS transistor Q1 is connected to the second input terminal VIN2, and a resistor R4 is connected between the source and gate of the PMOS transistor Q1.

9. The power-off protection circuit based on a lithium battery according to claim 8, characterized in that: The base of the NPN transistor Q2 is connected to the VCC_3V3 power supply terminal through the resistor R7.

10. The power-off protection circuit based on a lithium battery according to claim 2, characterized in that: The DC-DC circuit (6) includes a power supply chip U5, and the model of the power supply chip U5 is TPS63000DRCR.

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