Automatic charging power-off protection circuit for lithium ion battery pack

Abstract

An automatic charging power-off protection circuit for a lithium ion battery pack is composed of four cells, the lithium ion battery pack is connected with a charging interface and a discharging interface through a charging main loop and a discharging main loop, and the automatic charging power-off protection circuit is characterized by comprising a main control chip U1 with the model of BQ40Z50, a voltage acquisition circuit, a current acquisition circuit and a primary protection circuit, and the voltage acquisition circuit, the current acquisition circuit and the primary protection circuit are connected with the main control chip U1. The automatic charging power-off protection circuit of the lithium ion battery pack is composed of an integrated circuit BQ40Z50 (a main control unit and an accurate electric quantity algorithm) and a peripheral circuit thereof, and supports the use of 1-4 strings of lithium cells, including voltage, current and temperature protection, electric quantity display and the like; each battery cell is independently monitored, and when the charging / discharging voltage or the charging / discharging current exceeds a protection threshold value, turn-off can be quickly realized, so that the control precision is high; according to the automatic charging power-off protection circuit of the lithium ion battery pack, an integrated circuit BQ40Z50 is adopted, so that a peripheral circuit is simple in design and low in cost, and miniaturization design of devices is facilitated.

Description

Technical Field

[0001] The utility model relates to the technical field of application circuits of lithium-ion battery packs, and particularly relates to an automatic charging and power-off protection circuit for a lithium-ion battery pack. Background Art

[0002] As a new type of secondary clean and renewable energy source, lithium-ion batteries have the advantages of high working voltage, light weight, large energy density, etc., and have been widely used in fields such as power tools, digital cameras, mobile phones, laptop computers, etc., and show a strong development trend. Due to the characteristics of lithium-ion battery packs themselves, lithium-ion battery packs are very sensitive to voltage, current and temperature. Overcharging and over-discharging will cause irreversible damage to lithium-ion battery packs and even pose a risk of explosion. Therefore, the research and development of automatic charging and power-off protection for lithium-ion battery packs is particularly important. Automatic charging and power-off protection for lithium-ion battery packs is an indispensable part of the application of lithium-ion battery packs. Summary of the Utility Model

[0003] Based on this, the utility model provides an automatic charging and power-off protection circuit for a lithium-ion battery pack to solve the problems of inaccurate charge and discharge protection and power monitoring in traditional lithium battery packs.

[0004] To achieve the above object, the utility model provides an automatic charging and power-off protection circuit for a lithium-ion battery pack. The lithium-ion battery pack is composed of four battery cells. The lithium-ion battery pack is connected to a charge and discharge interface through a charge and discharge main circuit. It is characterized in that it includes a main control chip U1 of model BQ40Z50 and a voltage acquisition circuit, a current acquisition circuit and a primary protection circuit connected to the main control chip U1;

[0005] The voltage acquisition circuit is connected to each battery cell of the lithium-ion battery pack to acquire the voltage of each battery cell;

[0006] The current acquisition circuit is connected in series with a sampling resistor R19 in the negative bus of the charge and discharge main circuit of the lithium-ion battery pack to acquire the current of the lithium-ion battery pack during the charge and discharge process;

[0007] In the primary protection circuit, there are MOS transistor Q1, charging MOS transistor Q2, discharging MOS transistor Q3 and MOS transistor Q4. The charging MOS transistor Q2 and the discharging MOS transistor Q3 are connected in series in the positive bus of the charging and discharging main circuit of the lithium-ion battery pack. The BAT pin of the main control chip U1 is connected to the positive pole of the lithium-ion battery pack. The MOS transistor Q1 is connected in parallel with the MOS transistor Q2 after passing through the connection resistor R1. The MOS transistor Q4 is connected in parallel with the discharging MOS transistor Q3. One end of the charging MOS transistor Q2 connected to the positive pole of the lithium-ion battery pack is connected to the control end of the charging MOS transistor Q2 through the resistor R2. One end of the discharging MOS transistor Q3 connected to the positive pole of the charging and discharging interface is connected to the control end of the discharging MOS transistor Q3 through the resistor R3. The control end of the MOS transistor Q4 is grounded through the resistor R4. The equipotential point in series between the charging MOS transistor Q2 and the discharging MOS transistor Q3 is connected to the control end of the MOS transistor Q1 through the resistor R5;

[0008] The control end of the charging MOS transistor Q2 is connected to the CHG pin of the main control chip U1 through the resistor R7. The control end of the MOS transistor Q1 is connected to the PCHG pin of the main control chip U1 through the resistor R8. The control end of the discharging MOS transistor Q3 is connected to the VCC pin of the main control chip U1 through the resistor R9. The drain of the MOS transistor Q4 is connected to the DSG pin of the main control chip U1 through the resistor R10.

[0009] As a further preferred technical solution of the present invention, the primary protection circuit further includes a capacitor C1 and a capacitor C2. The capacitor C1 and the capacitor C2 are connected in series and then form a parallel connection structure with the series-connected charging MOS transistor Q2 and discharging MOS transistor Q3.

[0010] As a further preferred technical solution of the present invention, the voltage acquisition circuit includes resistors R20, R21, R22, R23. The VC4 pin of the main control chip U1 is connected to the fourth battery cell of the lithium-ion battery pack through the resistor R20. The VC3 pin of the main control chip U1 is connected to the third battery cell of the lithium-ion battery pack through the resistor R21. The VC2 pin of the main control chip U1 is connected to the second battery cell of the lithium-ion battery pack through the resistor R20. The VC4 pin of the main control chip U1 is connected to the first battery cell of the lithium-ion battery pack through the resistor R23.

[0011] As a further preferred technical solution of the present invention, a capacitor C14 is connected between the VC4 pin and the VC3 pin, a capacitor C15 is connected between the VC3 pin and the VC2 pin, a capacitor C16 is connected between the VC2 pin and the VC1 pin, and the VC1 pin is grounded through the capacitor C17.

[0012] As a further preferred technical solution of the present utility model, the main control chip U1 is further connected with a secondary protection circuit. The secondary protection circuit includes an MOS transistor Q5. The MOS transistor Q5 is connected between the positive electrode of the lithium-ion battery pack and the ground. The control end of the MOS transistor Q5 is connected to the PUSE pin of the main control chip U1 through a resistor R17.

[0013] As a further preferred technical solution of the present utility model, the main control chip U1 is further connected with a temperature sampling circuit. The temperature sampling circuit includes a thermosensitive resistor RT2, a thermosensitive resistor RT3, a thermosensitive resistor RT4, and a thermosensitive resistor RT5 that are successively connected to the TS1 pin, the TS2 pin, the TS3 pin, and the TS4 pin of the main control chip U1. The thermosensitive resistors RT2, RT3, RT4, and RT5 are respectively arranged on four battery cells of the lithium-ion battery pack.

[0014] As a further preferred technical solution of the present utility model, the main control chip U1 is further connected with a power display circuit.

[0015] As a further preferred technical solution of the present utility model, the main control chip U1 is further connected with a host communication circuit.

[0016] For the automatic charging and power-off protection circuit of the lithium-ion battery pack of the present utility model, adopting the above technical solution, the following beneficial effects can be achieved:

[0017] 1) The automatic charging and power-off protection circuit of the lithium-ion battery pack of the present utility model is composed of the integrated circuit BQ40Z50 (main control unit, precise power algorithm) and its peripheral circuits, supports the use of 1 to 4 series of lithium battery cells, and includes voltage, current, temperature protection, power display, etc.; monitors each battery cell separately, and can quickly turn off when the charging / discharging voltage or charging / discharging current exceeds the protection threshold, with high control accuracy;

[0018] 2) The automatic charging and power-off protection circuit of the lithium-ion battery pack of the present utility model adopts the integrated circuit BQ40Z50, making the peripheral circuit design simple, with low cost, and is conducive to the miniaturization design of devices. Description of the Drawings

[0019] The following further describes the present utility model in detail with reference to the drawings and specific embodiments.

[0020] Figure 1 It is a structural schematic diagram of the automatic charging and power-off protection circuit for the lithium-ion battery pack.

[0021] Figure 2 It is a pin diagram of the main control chip U1;

[0022] Figure 3 It is a circuit diagram of the voltage acquisition circuit;

[0023] Figure 4 is the circuit diagram of the current acquisition circuit;

[0024] Figure 5 is the circuit diagram of the primary protection circuit;

[0025] Figure 6 is the circuit diagram of the secondary protection circuit;

[0026] Figure 7 is the circuit diagram of the temperature sampling circuit;

[0027] Figure 8 is the circuit diagram of the host communication circuit;

[0028] Figure 9 is the circuit diagram of the power display circuit;

[0029] Figure 10 is the overall circuit diagram of the automatic charging and power-off protection circuit for the lithium-ion battery pack.

[0030] The realization of the purpose, functional features and advantages of the present utility model will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific embodiments

[0031] The following will further describe the present utility model in conjunction with the accompanying drawings and specific embodiments. Terms such as "upper", "lower", "left", "right", "middle" and "one" cited in the preferred embodiments are only for the convenience of description and are not used to limit the scope of implementation of the present utility model. The change or adjustment of their relative relationships shall also be regarded as the scope of implementation of the present utility model without substantial change in the technical content.

[0032] As Figure 1 shown, the present utility model provides an automatic charging and power-off protection circuit for a lithium-ion battery pack. The lithium-ion battery pack is composed of four battery cells connected in series. The lithium-ion battery pack is connected to the charging and discharging interface through the charging and discharging main circuit. It is characterized in that it includes a main control chip U1 (model BQ40Z50, produced by Texas Instruments) (refer to Figure 2 shown) and a voltage acquisition circuit, a current acquisition circuit and a primary protection circuit connected to the main control chip U1;

[0033] The voltage acquisition circuit is used to monitor the voltage, send the parameters back to the main control chip U1, compare with the internal voltage comparison circuit, and control the action of the protection circuit in real time. Refer to Figure 3, the voltage acquisition circuit is connected to each battery cell of the lithium-ion battery pack to acquire the voltage of each battery cell; the voltage acquisition circuit includes a resistor R20, a resistor R21, a resistor R22, and a resistor R23. The VC4 pin of the main control chip U1 is connected to the fourth battery cell of the lithium-ion battery pack through the resistor R20, the VC3 pin of the main control chip U1 is connected to the third battery cell of the lithium-ion battery pack through the resistor R21, the VC2 pin of the main control chip U1 is connected to the second battery cell of the lithium-ion battery pack through the resistor R20, and the VC4 pin of the main control chip U1 is connected to the first battery cell of the lithium-ion battery pack through the resistor R23. A capacitor C14 is connected between the VC4 pin and the VC3 pin, a capacitor C15 is connected between the VC3 pin and the VC2 pin, a capacitor C16 is connected between the VC2 pin and the VC1 pin, and the VC1 pin is grounded through a capacitor C17.

[0034] The current acquisition circuit is used for current sampling, sending the parameters back to the main control chip U1, comparing with the internal voltage comparison circuit, and controlling the operation of the protection circuit in real time. Refer to Figure 4 , the current acquisition circuit is connected in series with the sampling resistor R19 in the negative bus of the charging and discharging main circuit of the lithium-ion battery pack to acquire the current of the lithium-ion battery pack during the charging and discharging processes. The SRP pin of the main control chip U1 is connected to one end of the sampling resistor R19 through the resistor R30, and the SRN pin of the main control chip U1 is connected to the other end of the sampling resistor R19 through the resistor R30.

[0035] Refer to Figure 5 , in the primary protection circuit, there are a MOS transistor Q1, a charging MOS transistor Q2, a discharging MOS transistor Q3, and a MOS transistor Q4. The charging MOS transistor Q2 and the discharging MOS transistor Q3 are connected in series in the positive bus of the charging and discharging main circuit of the lithium-ion battery pack. The BAT pin of the main control chip U1 is connected to the positive electrode of the lithium-ion battery pack. The MOS transistor Q1 is connected in parallel with the MOS transistor Q2 after being connected through a resistor R1. The MOS transistor Q4 is connected in parallel with the discharging MOS transistor Q3. One end of the charging MOS transistor Q2 connected to the positive electrode of the lithium-ion battery pack is connected to the control end of the charging MOS transistor Q2 through a resistor R2. One end of the discharging MOS transistor Q3 connected to the positive electrode of the charging and discharging interface is connected to the control end of the discharging MOS transistor Q3 through a resistor R3. The drain of the MOS transistor Q4 is grounded through a resistor R4. The equipotential point in series between the charging MOS transistor Q2 and the discharging MOS transistor Q3 is connected to the control end of the MOS transistor Q1 through a resistor R5;

[0036] The control terminal of the charging MOS transistor Q2 is connected to the CHG pin of the main control chip U1 through a resistor R7. The control terminal of the MOS transistor Q1 is connected to the PCHG pin of the main control chip U1 through a resistor R8. The control terminal of the discharging MOS transistor Q3 is connected to the VCC pin of the main control chip U1 through a resistor R9. The drain of the MOS transistor Q4 is connected to the DSG pin of the main control chip U1 through a resistor R10. The primary protection circuit further includes a capacitor C1 and a capacitor C2. The capacitor C1 and the capacitor C2 are connected in series and then form a parallel connection structure with the series-connected charging MOS transistor Q2 and discharging MOS transistor Q3.

[0037] Refer to Figure 6 , the main control chip U1 is further connected with a secondary protection circuit for overvoltage monitoring and protection of the lithium-ion battery pack, and further independently monitors whether each battery cell has an overvoltage state. The secondary protection circuit includes a MOS transistor Q5. The MOS transistor Q5 is connected between the positive electrode of the lithium-ion battery pack and the ground. The control terminal of the MOS transistor Q5 is connected to the PUSE pin of the main control chip U1 through a resistor R17. The secondary protection circuit works synchronously with the primary protection circuit. If one path fails, there is at least one more path. The protection threshold of the secondary circuit can be set higher, making the protection performance better.

[0038] Refer to Figure 7 , the main control chip U1 is further connected with a temperature sampling circuit. The temperature sampling circuit is used to transmit parameters back to the main control chip U1 and compare them with the internal voltage comparison circuit to control the action of the protection circuit in real time. The temperature sampling circuit includes a thermosensitive resistor RT2, a thermosensitive resistor RT3, a thermistor RT4, and a thermistor RT5 connected to the TS1 pin, TS2 pin, TS3 pin, and TS4 pin of the main control chip U1 in sequence. The thermistor RT2, thermistor RT3, thermistor RT4, and thermistor RT5 are respectively arranged on the four battery cells of the lithium-ion battery pack.

[0039] Refer to Figure 8 , the main control chip U1 is further connected with a host communication circuit so that the main control chip U1 can perform information interaction with the host using the SMBus communication protocol.

[0040] Refer to Figure 9 , the main control chip U1 is further connected with a battery level display circuit for monitoring the battery level of the lithium-ion battery pack.

[0041] The overall circuit diagram of this embodiment is shown in Figure 10 As shown, the automatic charging and power-off protection circuit for the lithium-ion battery pack is used to monitor and protect the state of the lithium-ion battery cells. The specific principle is as follows:

[0042] ① Voltage detection and protection function

[0043] The main control chip U1 detects the voltages of the first to fourth battery cells of the battery pack through four pins, VC1, VC2, VC3, and VC4, respectively, so as to monitor the battery voltage. During the charging process, when the battery voltage exceeds the set battery voltage protection threshold, the charging MOS transistor Q2 is turned off, avoiding overcharging of the battery; similarly, during the discharging process, when the voltage detection pin detects that the battery voltage is lower than the set discharging voltage threshold, the discharging MOS transistor Q3 is turned off, avoiding over-discharging of the battery.

[0044] ② Overcurrent detection protection function

[0045] During the charging and discharging processes of the battery, the main control chip U1 determines whether the battery pack is in an overcurrent state by detecting the voltage across the sampling resistor R19. During the charging process, when it is detected that the charging current exceeds the set charging current protection threshold, the charging MOS transistor Q2 is turned off, avoiding overcurrent during overcharging of the battery; similarly, during the discharging process, when it is detected that the discharging current exceeds the set discharging current protection threshold, the discharging MOS transistor Q3 is turned off, avoiding overcurrent during battery discharging.

[0046] ③ Temperature detection protection function

[0047] The main control chip U1 monitors the temperatures of the MOS transistor and the battery cells in real time through the NTC negative temperature coefficient sensors, RT2 and RT3. When the temperature is too high or too low, the charging and discharging functions of the battery are prohibited, avoiding the risks brought by charging and discharging the battery at high and low temperatures.

[0048] Although the specific implementation manners of the present utility model have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to this implementation manner without departing from the principle and essence of the present utility model. The protection scope of the present utility model is only defined by the appended claims.

Claims

1. A lithium-ion battery pack automatic charging power-off protection circuit, the lithium-ion battery pack is composed of four cells, the lithium-ion battery pack is connected to the charging and discharging interface through the charging and discharging main circuit, characterized in that: It includes a main control chip U1 of model BQ40Z50 and a voltage collection circuit, a current collection circuit and a primary protection circuit connected to the main control chip U1; The voltage collection circuit is connected to each battery cell of the lithium-ion battery pack to collect the voltage of each battery cell; The current collection circuit is connected in series to the negative busbar of the lithium-ion battery pack charging and discharging main circuit through the sampling resistor R19 to collect the current of the lithium-ion battery pack during the charging and discharging process; The primary protection circuit is provided with a MOS tube Q1, a charging MOS tube Q2, a discharging MOS tube Q3 and a MOS tube Q4. The charging MOS tube Q2 and the discharging MOS tube Q3 are connected in series to the positive busbar of the main charging and discharging circuit of the lithium-ion battery pack. The BAT pin of the main control chip U1 is connected to the positive electrode of the lithium-ion battery pack. The MOS tube Q1 is connected in parallel with the MOS tube Q2 after being connected to the resistor R1. The MOS tube Q4 is connected in parallel with the discharging MOS tube Q3. The end of the charging MOS tube Q2 connected to the positive electrode of the lithium-ion battery pack is connected to the control end of the charging MOS tube Q2 through the resistor R2. The end of the discharging MOS tube Q3 connected to the positive electrode of the charging and discharging interface is connected to the control end of the discharging MOS tube Q3 through the resistor R3. The control end of the MOS tube Q4 is grounded through the resistor R4. The equipotential point in series between the charging MOS tube Q2 and the discharging MOS tube Q3 is connected to the control end of the MOS tube Q1 through the resistor R5. The control end of the charging MOS tube Q2 is connected to the CHG pin of the main control chip U1 through the resistor R7, the control end of the MOS tube Q1 is connected to the PCHG pin of the main control chip U1 through the resistor R8, the control end of the discharging MOS tube Q3 is connected to the VCC pin of the main control chip U1 through the resistor R9, and the drain of the MOS tube Q4 is connected to the DSG pin of the main control chip U1 through the resistor R10.

2. The automatic charging power-off protection circuit for a lithium-ion battery pack according to claim 1, characterized in that: The primary protection circuit further includes a capacitor C1 and a capacitor C2. The capacitor C1 and the capacitor C2 are connected in series and then form a parallel connection structure with the charging MOS tube Q2 and the discharging MOS tube Q3 connected in series.

3. The automatic charging power-off protection circuit for a lithium-ion battery pack according to claim 1, characterized in that: The voltage acquisition circuit includes resistors R20, R21, R22, and R23. The VC4 pin of the main control chip U1 is connected to the fourth battery cell of the lithium-ion battery pack through the resistor R20, the VC3 pin of the main control chip U1 is connected to the third battery cell of the lithium-ion battery pack through the resistor R21, the VC2 pin of the main control chip U1 is connected to the second battery cell of the lithium-ion battery pack through the resistor R20, and the VC4 pin of the main control chip U1 is connected to the first battery cell of the lithium-ion battery pack through the resistor R23.

4. The automatic charging power-off protection circuit for a lithium-ion battery pack according to claim 3, characterized in that: A capacitor C14 is connected between the VC4 pin and the VC3 pin, a capacitor C15 is connected between the VC3 pin and the VC2 pin, a capacitor C16 is connected between the VC2 pin and the VC1 pin, and the VC1 pin is grounded via a capacitor C17.

5. The lithium-ion battery pack automatic charging power-off protection circuit according to claim 1, characterized in that: The main control chip U1 is also connected to a secondary protection circuit, which includes a MOS tube Q5. The MOS tube Q5 is connected between the positive electrode of the lithium-ion battery pack and the ground. The control end of the MOS tube Q5 is connected to the PUSE pin of the main control chip U1 through a resistor R17.

6. The automatic charging power-off protection circuit for a lithium-ion battery pack according to any one of claims 1 to 5, characterized in that: The main control chip U1 is also connected to a temperature sampling circuit, which includes a thermistor RT2, a thermistor RT3, a thermistor RT4, and a thermistor RT5 which are sequentially connected to the TS1 pin, the TS2 pin, the TS3 pin, and the TS4 pin of the main control chip U1. The thermistor RT2, the thermistor RT3, the thermistor RT4, and the thermistor RT5 are respectively arranged on the four cells of the lithium-ion battery pack.

7. The automatic charging power-off protection circuit for a lithium-ion battery pack according to any one of claims 1 to 5, characterized in that: The main control chip U1 is also connected to a power display circuit.

8. The automatic charging power-off protection circuit for a lithium-ion battery pack according to any one of claims 1 to 5, characterized in that: The main control chip U1 is also connected to a host communication circuit.

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