CN215009682U

CN215009682U - Electric tool and lithium battery protection circuit thereof

Info

Publication number: CN215009682U
Application number: CN202121170427.8U
Authority: CN
Inventors: 刘力丹; 雷飞; 刘晓东; 刘海春
Original assignee: Shanghai Qiwai Culture Technology Co ltd
Current assignee: Shanghai Qiwai Culture Technology Co ltd
Priority date: 2021-05-28
Filing date: 2021-05-28
Publication date: 2021-12-03
Anticipated expiration: 2031-05-28

Abstract

The application provides an electric tool and a lithium battery protection circuit thereof, wherein the lithium battery protection circuit comprises a lithium battery protection chip, a first MOSFET, a third MOSFET, first to third resistors, and first to third capacitors; the DO end of the lithium electric protection chip is connected with the grid of the first MOSFET, the CO end of the lithium electric protection chip is connected with the grid of the third MOSFET, the VM end of the lithium electric protection chip is connected with the negative electrode of the battery through a third capacitor, the VC end of the lithium electric protection chip is connected with the intermediate node of the battery through a second resistor, the V C end of the lithium electric protection chip is connected with the VSS end of the lithium electric protection chip through a second capacitor, the VDD end of the lithium electric protection chip is connected with the positive electrode of the battery through a first resistor, the VDD end of the lithium electric protection chip is connected with the negative electrode of the battery through a first capacitor, and the VSS end of the lithium electric protection chip is connected with the negative electrode of the battery; the source electrode of the first MOSFET is connected with the cathode of the battery, and the drain electrode of the first MOSFET is connected with the drain electrode of the third MOSFET; the source of the third MOSFET is grounded. Therefore, the on-off state of the battery loop can be controlled through the lithium battery protection circuit, and the protection is more comprehensive.

Description

Electric tool and lithium battery protection circuit thereof

Technical Field

The application relates to the technical field of electric tools, in particular to an electric tool and a lithium battery protection circuit thereof.

Background

Compared with the traditional electric tool adopting nickel-cadmium and nickel-hydrogen batteries, the electric tool adopting the lithium battery has the advantages of environmental protection, energy conservation, light weight, convenient use, high working efficiency, more working times in each charging and discharging period and the like.

However, lithium batteries have strict requirements for battery voltage, discharge current, etc. during charging and discharging due to their own characteristics, and if the requirements exceed the specifications, the battery may be damaged or shortened in charge and discharge cycle life, and if the requirements exceed the specifications, the battery may be damaged, or if the requirements exceed the specifications, safety accidents such as fire or explosion may occur. The lithium battery single-section protection circuit is designed for mobile phone digital products, charging and discharging currents are small during work, and the electric tool load is a direct current brush motor and has the characteristic of large discharging current, so that the lithium battery protection circuit adopting the mobile phone digital protection circuit as the electric tool has the defects of incomplete protection function, relatively low safety and reliability and the like.

Disclosure of Invention

An object of the application is to provide an electric tool and lithium electricity protection circuit thereof, solved electric tool's lithium electricity protection circuit protect function not comprehensive, safety and reliability relatively lower problem.

The purpose of the application is realized by adopting the following technical scheme:

in a first aspect, the present application provides a lithium battery protection circuit of an electric tool, the lithium battery protection circuit including a lithium battery protection chip, a first MOSFET, a third MOSFET, a first resistor, a second resistor, a third resistor, a first capacitor, a second capacitor, and a third capacitor; the DO end of the lithium electric protection chip is connected to the grid electrode of the first MOSFET, the CO end of the lithium electric protection chip is connected to the grid electrode of the third MOSFET, the VM end of the lithium electric protection chip is grounded through the third resistor, the VM end of the lithium electric protection chip is connected to a battery cathode through the third capacitor, the VC end of the lithium electric protection chip is connected to a battery intermediate node through the second resistor, the VC end of the lithium electric protection chip is connected to the VSS end of the lithium electric protection chip through the second capacitor, the VDD end of the lithium electric protection chip is connected to a battery anode through the first resistor, the VDD end of the lithium electric protection chip is connected to the battery cathode through the first capacitor, and the VSS end of the lithium electric protection chip is connected to the battery cathode; the source of the first MOSF ET is connected to the negative electrode of the battery, and the drain of the first MOSFET is connected to the drain of the third MO SFET; the source of the third MOSFET is grounded. The technical scheme has the beneficial effects that on one hand, the overcharge/overdischarge state of the rechargeable battery can be monitored by arranging the lithium battery protection chip, and the overcharge/overdischarge state is compared with the preset threshold value of the lithium battery protection chip. When the discharge voltage of the rechargeable battery is changed from high to low and is smaller than the overdischarge detection threshold, the DO end of the lithium battery protection chip is switched to a low level, so that the grid electrode of the first M OSFET is controlled, and the first MOSFET is cut off. When the discharge voltage of the rechargeable battery is changed from low to high and is higher than the overcharge detection threshold value, the CO end of the lithium battery protection chip is switched to a low level, and then the grid electrode of the third MOSFET is controlled, and the third MOSFET is cut off. On the one hand, first resistance, second resistance, first electric capacity, second electric capacity and third electric capacity play the effect of stabilizing lithium electricity protection chip supply voltage, first resistance with the second resistance plays the effect of lithium electricity protection chip supply voltage current-limiting partial pressure, first electric capacity filtering the clutter of the VDD end of lithium electricity protection chip, the second electric capacity filtering the clutter of the VC end of lithium electricity protection chip, the third electric capacity filtering the clutter of the VM end of lithium electricity protection chip. On the one hand, the third resistor plays a current limiting role, avoids reverse charging or damage caused by overlarge charging voltage of the charger, and protects the lithium battery protection chip.

In summary, by providing the lithium battery protection chip, the first MOSFET, the third MOSFET, the first resistor, the second resistor, the third resistor, the first capacitor, the second capacitor, and the third capacitor, the on-off states of the first MOSFET and the third MOSFET can be controlled according to whether the rechargeable battery is overcharged or overdischarged, so as to stably control the on-off between the negative electrode of the rechargeable battery and the negative electrode of the battery protection board, thereby realizing the protection of overcharge, overdischarge, short circuit, and overcurrent during the lithium battery charging, and having comprehensive protection function, safety, and high reliability.

In some optional embodiments, the lithium electric protection circuit further comprises a second MOSFET and a fourth MOSFET; the source of the first MOSFET is connected to the source of the second MOSFET, the gate of the first MOSFET is connected to the gate of the second MOSFET, and the drain of the first MOSFET is connected to the drain of the second MOSFET; the source of the third MOSFET is connected to the source of the fourth MOSFET, the gate of the third MOSFET is connected to the gate of the fourth MOSFET, and the drain of the third MOSFET is connected to the drain of the fourth MOSFET. The beneficial effects of this technical scheme lie in, through setting up second MOSFET and fourth MOSFET for the channel length of every MOSFET is for shortening, reducing channel resistance greatly, shortens the switching time, improves the protection efficiency.

In some optional embodiments, the lithium battery protection circuit further includes a fourth capacitor and a first diode; the first end of the fourth capacitor is grounded, and the second end of the fourth capacitor is connected to the positive electrode of the battery; the anode of the first diode is grounded, and the cathode of the first diode is connected to the anode of the battery. The technical scheme has the beneficial effects that the rechargeable battery and the lithium battery protection chip are prevented from being damaged by reverse voltage of an external circuit.

In some optional embodiments, the lithium battery protection circuit further includes a fourth resistor, a first end of the fourth resistor is grounded, and a second end of the fourth resistor is connected to the negative electrode of the battery protection board. The technical scheme has the beneficial effects that the fourth resistor plays a role in secondary protection of the lithium battery protection circuit.

In some optional embodiments, the lithium electric protection circuit further includes a fifth capacitor and a sixth capacitor, and the fifth capacitor and the sixth capacitor are sequentially connected in series between the first MOSFET and the source of the third MOSF ET. The technical scheme has the beneficial effects that the fifth capacitor and the sixth capacitor which are connected in series are provided, and the working state of the MOSFET is stabilized.

In some optional embodiments, the capacitance of the fifth capacitor is the same as that of the sixth capacitor, which has the advantage that the fifth capacitor and the sixth capacitor with the same capacitance operate more stably.

In some optional embodiments, the first MOSFET, the second MOSFET, the third MOSFET, and the fourth MOSFET all employ an N-channel enhancement type. Compared with other types of MOSFETs, the N-channel enhancement type MOSFET has the advantages of small on-resistance and easiness in control.

In some optional embodiments, the first to third resistances are patch resistances. The technical scheme has the advantages that the chip resistor is small in size, light in weight, easy to weld when a circuit is arranged, high in stability, and capable of reducing cost, saving materials and energy, and reducing manpower and working hours when the charging management circuit is manufactured.

In some optional embodiments, the first to third capacitors are patch ceramic capacitors. The technical scheme has the beneficial effects that on one hand, the equivalent series impedance of the patch ceramic capacitor is small, the frequency characteristic is excellent, and the absorption effect on circuit noise is good; on the other hand, the patch ceramic capacitor has good tolerance to abnormal voltage, and the possibility of failure caused by insulation breakdown is greatly reduced when abnormal conditions occur.

In a second aspect, the present application provides an electric power tool including the lithium-ion electric protection circuit of any one of the electric power tools described above. The beneficial effects of this technical scheme lie in, can be applied to electric tool with electric tool's charge management circuit, promote electric tool lithium electricity protection's intellectuality.

Drawings

The present application is further described below with reference to the drawings and examples.

Fig. 1 is a schematic structural diagram of a lithium battery protection circuit of an electric power tool according to an embodiment of the present disclosure;

fig. 2 is a schematic structural diagram of an electric tool according to an embodiment of the present application.

In the figure: 10. a lithium battery protection chip; 1. a DO terminal of the lithium battery protection chip; 2. protecting a CO end of the chip by the lithium battery; 3. the VM end of the lithium battery protection chip; 4. the VC end of the lithium battery protection chip; 5. the VDD end of the lithium battery protection chip; 6. the VSS end of the lithium battery protection chip; r1, a first resistor; r2, a second resistor; r3, third resistor; r4, fourth resistor; r5, fifth resistor; c1, a first capacitance; c2, a second capacitor; c3, a third capacitance; c4, a fourth capacitance; c5, a fifth capacitance; c6, a sixth capacitor; d1, a first diode; b +, battery positive pole; b-, a battery cathode; BM, battery intermediate node; p-, the negative electrode of the battery protection board; m1, a first MOSFET; m2, a second MOSFET; m3, third MOSFET; m4, fourth MO SFET; GND and ground.

Detailed Description

The present application is further described with reference to the accompanying drawings and the detailed description, and it should be noted that, in the present application, the embodiments or technical features described below may be arbitrarily combined to form a new embodiment without conflict.

Referring to fig. 1, an embodiment of the present application provides a lithium electric protection circuit of an electric power tool, including a lithium electric protection chip 10, a first MOSFET M1, a third MOSFET M3, a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, and a third capacitor C3; the DO terminal 1 of the lithium electric protection chip is connected to the gate of the first MOSFET M1, the CO terminal 2 of the lithium electric protection chip is connected to the gate of the third MOSFET M3, the VM end 3 of the lithium electric protection chip is grounded through the third resistor R3, the VM end 3 of the lithium electric protection chip is also connected to the negative electrode B-of the battery through the third capacitor C3, the VC terminal 4 of the lithium battery protection chip is connected to the battery intermediate node BM through the second resistor R2, the VC terminal 4 of the lithium electrical protection chip is connected to the VSS terminal 6 of the lithium electrical protection chip through the second capacitor C2, the VDD terminal 5 of the lithium electric protection chip is connected to the battery anode B + through the first resistor R1, the VDD terminal 5 of the lithium battery protection chip is further connected to a battery cathode B-through a first capacitor C1, and the VSS terminal 6 of the lithium battery protection chip is connected to the battery cathode B-; the source of the first MOSFET M1 is connected to the battery cathode B-, the drain of the first MOSFET M1 is connected to the drain of the third MOSFET M3; the source of the third MOSFET M3 is grounded.

A Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), which is a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET).

In a specific application, the lithium battery protection circuit protects a battery formed by connecting two lithium batteries in series, and a point where the positive electrodes and the negative electrodes of the two lithium batteries are connected is a battery intermediate node. The network label of the positive electrode of the battery is, for example, B +, the network label of the negative electrode of the battery is, for example, B-, the network label of the middle node of the battery is, for example, BM, the network label of the negative electrode of the battery protection board is, for example, P-, and the network label of the ground terminal is, for example, GND.

The network label (net label) is an electrical connection point, generally composed of letters, symbols, numbers, etc., the electrical connection lines, pins and networks with the same network label are connected together, and the network labels are not connected.

The selection of the lithium battery protection chip 10 is not limited in the embodiments of the present application, and the model of the lithium battery protection chip 10 is, for example, R5460N214A, and R5460N214A may be used for overcharge and overdischarge protection of 2-cell series lithium batteries.

Lithium protection chip 10 can contain 6 pins, lithium protection chip's first pin is DO end 1 of lithium protection chip promptly, lithium protection chip's second pin is CO end 2 of lithium protection chip promptly, lithium protection chip's third pin is VM end 3 of lithium protection chip promptly, lithium protection chip's fourth pin is VC end 4 of lithium protection chip promptly, lithium protection chip's fifth pin is VDD end 5 of lithium protection chip promptly, lithium protection chip's sixth pin is VSS end 6 of lithium protection chip promptly. The lithium battery protection chip 10 may further include other pins, which are not described herein.

In the embodiment of the present application, the selection of the first resistor R1, the second resistor R2, the third resistor R3, the first capacitor C1, the second capacitor C2, and the third capacitor C3 is not limited. The first resistor R1 has a resistance of 300 Ω, 330 Ω or 390 Ω, the second resistor R2 has a resistance of 300 Ω, 330 Ω or 390 Ω, and the third resistor R3 has a resistance of 1K Ω, 1.1K Ω or 1.2K Ω. The capacitance of the first capacitor C1 is, for example, 0.1 μ F, 0.2 μ F or 0.3 μ F. The capacitance of the second capacitor C2 is, for example, 0.1 μ F, 0.2 μ F or 0.3 μ F. The capacitance of the third capacitor C3 is, for example, 10 muf, 18 muf or 20 muf.

On one hand, by setting the lithium electric protection chip 10, the overcharge and overdischarge states of the rechargeable battery can be monitored and compared with the preset threshold value of the lithium electric protection chip 10. When the lithium electric protection chip 10 detects that the voltage between the VDD terminal 5 of the lithium electric protection chip and the VC terminal 4 of the lithium electric protection chip changes from high to low and is smaller than the overdischarge detection threshold, or that the voltage between the VC terminal 4 of the lithium electric protection chip and the VSS terminal 6 of the lithium electric protection chip changes from high to low and is smaller than the overdischarge detection threshold, the DO terminal 1 of the lithium electric protection chip is switched to a low level to control the gate of the first MOSFET M1, and the first MOSFET M1 for externally controlling discharge is turned off. When the lithium electric protection chip detects that the voltage between VDD terminal 5 of lithium electric protection chip and VC terminal 4 of lithium electric protection chip is changed up by low, is greater than overcharge detection threshold, or the voltage between VC terminal 4 of lithium electric protection chip and VSS terminal 6 of lithium electric protection chip is changed up by low, is greater than overcharge detection threshold, CO end 2 of lithium electric protection chip will switch to the low level, and then control third MOSFET M3's grid, the third MOSFET M3 that external control charges are closed. When the voltage of the VM end 3 of the lithium electric protection chip is greater than the threshold value of the load short-circuit voltage, the DO end 1 of the lithium electric protection chip is switched to a low level, so that the grid of the first MOSFET M1 is controlled, and the first MOSFET M1 is closed. When the battery is charged by using an improper charger, an excessive charging current may flow, which causes the voltage at the VM terminal 3 of the lithium electric protection chip to become lower than the overcharge detection voltage threshold, the CO terminal 2 of the lithium electric protection chip will be switched to a low level, and then the gate of the third MOSFET M3 is controlled, and the third MOSFET M3 for externally controlling charging is turned off, so that the excessive charging current is prevented from passing. On the one hand, first resistance R1, second resistance R2, first electric capacity C1, second electric capacity C2 and third electric capacity C3 can play the effect of stabilizing lithium electricity protection chip supply voltage, first resistance R1 with second resistance R2 plays the effect of lithium electricity protection chip supply voltage current-limiting partial pressure, first electric capacity C1 filtering the clutter of VDD end 5 of lithium electricity protection chip, second electric capacity C2 filtering the clutter of VC end 4 of lithium electricity protection chip, third electric capacity C3 filtering the clutter of VM end 3 of lithium electricity protection chip. On the one hand, the third resistor R3 plays a role in limiting current, avoids damage caused by reverse charging or overlarge charging voltage of the charger, and protects the lithium battery protection chip.

In summary, by providing the lithium battery protection chip 10, the first MOSFET M1, the third MOSFET M3, the first resistor R1, the second resistor R2, the third resistor R3, the first capacitor C1, the second capacitor C2, and the third capacitor C3, the on/off of the first MOSFET M1 and the third MOSFET M3 can be controlled according to whether the rechargeable battery is in a normal charging/discharging state, so as to stably control the on/off between the negative electrode B-of the rechargeable battery and the negative electrode P-of the battery protection board, thereby realizing the protection of lithium battery overcharge, overdischarge, short circuit, and overcurrent during charging, and having comprehensive protection function, safety, and high reliability.

In some embodiments, the lithium battery protection circuit may further include a second MOSFET M2 and a fourth MOSFET M4; the source of the first MOSFET M1 is connected to the source of the second MOSFET M2, the gate of the first MOSFET M1 is connected to the gate of the second MOSFET M2, and the drain of the first MOSFET M1 is connected to the drain of the second MOSFET M2; the source of the third MOSFET M3 is connected to the source of the fourth MOSFET M4, the gate of the third MO SFET M3 is connected to the gate of the fourth MOSFET M4, and the drain of the third MOSFET M3 is connected to the drain of the fourth MOSFET M4.

Therefore, by arranging the second MOSFET M2 and the fourth MOSFET M4, the length of a channel of each MOSF ET is greatly shortened, the channel resistance is reduced, the switching time is shortened, and the protection efficiency is improved.

In some embodiments, the lithium protection circuit may further include a fourth capacitor C4 and a first diode D1; a first end of the fourth capacitor C4 is grounded, and a second end of the fourth capacitor C4 is connected to the battery anode B +; the anode of the first diode D1 is grounded, and the cathode of the first diode D1 is connected to the battery positive electrode B +.

The capacitance of the fourth capacitor C4 is not limited in the embodiments of the present application, and the capacitance of the fourth capacitor C4 is, for example, 0.1 μ F, 0.2 μ F, or 0.3 μ F.

The first diode D1 is not limited in the embodiments of the present application, and the first diode D1 is, for example, DO-214AA UF 2G.

Therefore, by arranging the fourth capacitor C4 and the first diode D1, if an external circuit is suddenly powered off, reverse voltage can be generated on an external circuit energy storage component, on one hand, the reverse voltage and the first diode D1 circuit form a current path and are clamped by the diodes, reverse overvoltage cannot be generated on a power supply to damage the power supply, and on the other hand, the fourth capacitor C4 filters out residual high-frequency signals and protects the first diode D1 from breakdown. The fourth capacitor C4 and the first diode D1 are arranged to prevent the reverse voltage of the external circuit from damaging the rechargeable battery and the lithium battery protection chip.

In some embodiments, the lithium battery protection circuit may further include a fourth resistor R4, a first end of the fourth resistor R4 is grounded, and a second end of the fourth resistor R4 is connected to the battery protection board negative electrode P-.

Therefore, the charge accumulation between the negative electrode P-of the battery protection board and the ground end GND can damage the lithium battery protection circuit, and the charge is released through the fourth resistor R4 to eliminate the voltage difference between the negative electrode P-and the ground end GND, so that the secondary protection effect of the lithium battery protection circuit is achieved. A fifth resistor R5 can be arranged in parallel with the fourth resistor R4, so that the resistance is reduced to reduce the loss of circuit energy and improve the safety of protection.

In some embodiments, the lithium battery protection circuit may further include a fifth capacitor C5 and a sixth capacitor C6, and the fifth capacitor C5 and the sixth capacitor C6 are sequentially connected in series between the sources of the first MOSFET M1 and the third MOSFET M3.

Therefore, the fifth capacitor C5 and the sixth capacitor C6 which are connected in series are arranged to form a capacitor bank, the two capacitors can generate voltage division, and further, the loss resistors of the fourth capacitor C4 and the fifth capacitor C5 are also in a series state, so that the equivalent loss resistor, namely the loss value of the whole capacitor is increased, noise waves are introduced into the ground terminal GND, the effect of restraining oscillation is achieved, and the working state of the MOSFET is stabilized. When the capacitance selected by the fifth capacitor C5 and the capacitance selected by the sixth capacitor C6 are the same, the voltage at the two ends of the capacitor bank is equally distributed to the two capacitors, and the capacitors are more stably used.

In some embodiments, the first MOSFET M1, the second MOSFET M2, the third MOSFET M3, and the fourth MOSFET M4 may all employ N-channel enhancement.

Compared with a P-channel enhancement type MOSFET, the N-channel enhancement type MOSFET has the advantages of small on-resistance, low price and the like. Compared with a consumption type MOSFET, the N-channel enhancement type MOSFET is not easy to trigger an MOS tube by mistake and is easy to control when equipment is started in practical application.

In some embodiments, the first to fifth resistors R1 to R5 may be chip resistors.

Therefore, when the first resistor R1-the fifth resistor R5 adopt chip resistors, the chip resistors have the advantages of small size, light weight, easiness in welding during circuit arrangement and strong stability, and can play the roles of reducing cost, saving materials, saving energy and reducing manpower and working hours during manufacturing of the charging management circuit.

In some embodiments, the first through sixth capacitors C1-C6 may be patch ceramic capacitors.

Therefore, when the first capacitor to the sixth capacitor are patch ceramic capacitors, the patch ceramic capacitors have small equivalent series impedance, excellent frequency characteristics and good circuit noise absorption effect; and secondly, the resistance of the chip ceramic capacitor to abnormal voltage is good, and the possibility of failure caused by insulation breakdown is greatly reduced when abnormal conditions occur.

Referring to fig. 2, an embodiment of the present application further provides an electric tool including a lithium-ion protection circuit of any one of the electric tools described above. Therefore, the lithium battery protection circuit of the electric tool can be applied to the electric tool, and the intelligence of lithium battery protection of the electric tool is improved.

The electric tool is, for example, an electric inflator, electric scissors, an electric drill, an electric screwdriver, or a hair dryer.

While the present application is described in terms of various aspects, including exemplary embodiments, the principles of the invention should not be limited to the disclosed embodiments, but are also intended to cover various modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Claims

1. The lithium battery protection circuit of the electric tool is characterized by comprising a lithium battery protection chip, a first MOSFET, a third MOSFET, a first resistor, a second resistor, a third resistor, a first capacitor, a second capacitor and a third capacitor;

the DO end of the lithium electric protection chip is connected to the grid electrode of the first MOSFET, the CO end of the lithium electric protection chip is connected to the grid electrode of the third MOSFET, the VM end of the lithium electric protection chip is grounded through the third resistor, the VM end of the lithium electric protection chip is connected to a battery cathode through the third capacitor, the VC end of the lithium electric protection chip is connected to a battery intermediate node through the second resistor, the VC end of the lithium electric protection chip is connected to the VSS end of the lithium electric protection chip through the second capacitor, the VDD end of the lithium electric protection chip is connected to a battery anode through the first resistor, the VDD end of the lithium electric protection chip is connected to the battery cathode through the first capacitor, and the VSS end of the lithium electric protection chip is connected to the battery cathode;

the source electrode of the first MOSFET is connected to the negative electrode of the battery, and the drain electrode of the first MOSFET is connected to the drain electrode of the third MOSFET;

the source of the third MOSFET is grounded.

2. The lithium-ion power protection circuit of claim 1, wherein the lithium-ion power protection circuit further comprises a second MOSFET and a fourth MOSFET;

the source of the first MOSFET is connected to the source of the second MOSFET, the gate of the first MO SFET is connected to the gate of the second MOSFET, and the drain of the first MOSFET is connected to the drain of the second MOSFET;

the source of the third MOSFET is connected to the source of the fourth MOSFET, the gate of the third MO SFET is connected to the gate of the fourth MOSFET, and the drain of the third MOSFET is connected to the drain of the fourth MOSFET.

3. The lithium-ion protection circuit for an electric tool of claim 1, wherein the lithium-ion protection circuit further comprises a fourth capacitor and a first diode;

the first end of the fourth capacitor is grounded, and the second end of the fourth capacitor is connected to the positive electrode of the battery;

the anode of the first diode is grounded, and the cathode of the first diode is connected to the anode of the battery.

4. The lithium protection circuit for an electric tool according to claim 1, further comprising a fourth resistor, wherein a first end of the fourth resistor is connected to ground, and a second end of the fourth resistor is connected to a negative electrode of the battery protection board.

5. The lithium-ion protection circuit for an electric power tool of claim 1, further comprising a fifth capacitor and a sixth capacitor, wherein the fifth capacitor and the sixth capacitor are serially connected in series between the sources of the first MOSFET and the third MOSFET.

6. The lithium-ion protection circuit for an electric power tool according to claim 5, wherein the capacitance of the fifth capacitor is the same as that of the sixth capacitor.

7. The lithium protection circuit for an electric tool according to claim 2, wherein the first MOSFET, the second MOSFET, the third MOSFET and the fourth MOSFET T are all of N-channel enhancement type.

8. The lithium-ion protection circuit of claim 1, wherein the first resistor to the third resistor are chip resistors.

9. The lithium-ion protection circuit of claim 1, wherein the first capacitor to the third capacitor are ceramic capacitors.

10. An electric power tool characterized by comprising the lithium electric protection circuit of the electric power tool according to any one of claims 1 to 9.