Sustainable charging current-limiting protection circuit for lithium battery

Abstract

Disclosed in the present invention is a sustainable charging current-limiting protection circuit for a lithium battery. The circuit comprises a current sampling and determination unit, a PWM control unit, a current-limiting unit, a monitoring unit and a PWM compensation unit, wherein a charging current of a battery is sampled and determined by means of the current sampling and determination unit, so as to output a current-limiting control signal; the PWM control unit outputs a first PWM control signal according to the current-limiting control signal and a voltage signal that is output by the PWM compensation unit, such that the current-limiting unit adjusts the charging current of the battery; and the PWM compensation unit acquires the adjusted charging current of the battery by means of the monitoring unit, and adjusts the magnitude of the voltage signal, such that the PWM control unit outputs a second PWM control signal, and the current-limiting unit is controlled to further adjust the charging current of the battery to a charging current-limiting protection value. In the present application, when a charging current of a lithium battery is too high, primary adjustment and secondary adjustment steps are sequentially performed to implement the high-precision control and adjustment of the charging current of the battery, thereby reducing the charging current.

Description

A lithium battery continuous charging current limiting protection circuit Technical Field

[0001] The present invention relates to the technical field of circuit design, and in particular to a lithium battery sustainable charging current limiting protection circuit. Background Art

[0002] In recent years, with the implementation of a low-carbon and environmentally friendly economy and the rapid development of the energy storage market, lithium batteries have become more widely used in the field of household energy storage. At present, with the increasing demand for household electricity consumption, it is often necessary to increase the capacity of lithium batteries. The expansion of lithium batteries is generally achieved by increasing the number of series-connected cells in the lithium battery, or by connecting several or dozens of batteries in parallel.

[0003] However, when the capacity of the lithium battery is increased by connecting battery cells in series, due to the existence of the internal resistance of the battery cells, as the number of battery cells in series increases and the number of uses increases, the internal resistance of the lithium battery becomes larger, and the voltage consumed by the internal resistance also becomes higher and higher. If the charging current is large when charging the lithium battery, the temperature of the lithium battery will rise rapidly, which will not only affect the battery cell capacity and battery performance, but also reduce the number of uses and lifespan of the lithium battery.

[0004] In addition, when the capacity of the lithium battery is increased by using multiple batteries in parallel, due to the differences in capacity between the batteries, if the lithium battery charging current is large, the small-capacity battery will be subjected to a larger charging current than the large-capacity battery, which will have a great impact on the lithium battery system and affect the stability of the lithium battery system.

[0005] In summary, when increasing the capacity of a lithium battery by connecting cells in series, if the charging current is high, it can lead to problems such as battery heating, a shortened service life, and reduced performance. Furthermore, when increasing the capacity of a lithium battery by connecting multiple cells in parallel, if the charging current is high, it can lead to significant system impact and unstable operation. In the prior art, to address the series of problems caused by the high charging current of lithium batteries, the current limiting circuits used have low control accuracy, and even when the lithium battery is continuously charged for an extended period, these problems cannot be avoided.

[0006] Summary of the Invention

[0007] In order to achieve high-precision control and regulation of the current during the charging process of a lithium battery, reduce the charging current, and avoid long-term high-current charging that causes battery heating, short service life, performance degradation, large system impact, and unstable operation, the present application provides a lithium battery continuous charging current limiting protection circuit.

[0008] The present application provides a lithium battery sustainable charging current limiting protection circuit, which adopts the following technical solution: the lithium battery sustainable charging current limiting protection circuit includes a current sampling and judgment unit, a PWM control unit, a current limiting unit, a monitoring unit, and a PWM compensation unit;

[0009] Current sampling and judgment unit, used to sample the battery charging current I charge , and according to the battery charging current I charge The current limit control signal is output to the PWM control unit based on the current size.

[0010] a PWM control unit, configured to generate a first PWM control signal according to the current limiting control signal and the voltage signal output by the PWM compensation unit, and output the signal to the current limiting unit;

[0011] A current limiting unit is used to limit the battery charging current I according to the first PWM control signal charge Adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX ;

[0012] Monitoring unit, used to obtain the battery charging current I adjusted by the current limiting unit charge and the regulated battery charging current I charge Output to PWM compensation unit;

[0013] The PWM compensation unit is used to adjust the battery charging current I charge Adjust the magnitude of the voltage signal output to the PWM control unit;

[0014] a PWM control unit, further configured to change a duty cycle of the first PWM control signal according to the adjusted voltage signal, generate a second PWM control signal, and output the second PWM control signal to the current limiting unit;

[0015] The current limiting unit is further configured to control the battery charging current I according to the second PWM control signal. charge Further adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX .

[0016] By adopting the above technical solution, on the one hand, by sampling the battery charging current and quickly responding to the current limiting protection mode when it is judged that the battery charging current is too high, the battery charging current is promptly subjected to initial current limiting control and adjustment through the current limiting unit, thereby reducing the charging current; on the other hand, due to errors in the circuit system, the initial adjustment of the charging current may not be in place, so a secondary adjustment process is performed, that is, the adjusted battery charging current is obtained in real time, and the frequency compensation is performed on the PWM control signal used to control the current limiting unit, thereby achieving high-precision control and adjustment of the battery charging current, avoiding long-term high-current charging that causes battery heating, short service life, performance degradation, large system impact, and unstable operation, thereby ensuring the safety of lithium batteries for continuous long-term charging; in addition, the current limiting protection circuit of the present application is implemented by hardware functions, and also has the advantages of simple circuit structure, fast response speed, reliable operation, and high control efficiency.

[0017] In a specific embodiment, the lithium battery continuous charging current limiting protection circuit further includes a driving enhancement unit; the driving enhancement unit is connected to the PWM control unit and the current limiting unit respectively;

[0018] The driving enhancement unit is configured to receive the first PWM control signal output by the PWM control unit, enhance the driving capability of the first PWM control signal, and output the first PWM control signal with enhanced driving capability to the current limiting unit;

[0019] The current limiting unit is used to control the battery charging current I according to the first PWM control signal after the driving capability is enhanced. charge Adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX ;

[0020] and / or the driving enhancement unit is configured to receive a second PWM control signal output by the PWM control unit, enhance the driving capability of the second PWM control signal, and output the second PWM control signal with enhanced driving capability to the current limiting unit;

[0021] The current limiting unit is used to control the battery charging current I according to the second PWM control signal with enhanced driving capability. charge Further adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX .

[0022] By adopting the above technical solution, the driving enhancement unit is used to improve the driving capabilities of the first PWM control signal and the second PWM control signal, thereby improving the dynamic anti-interference capability and response speed of the system.

[0023] In a specific implementation scheme, the PWM control unit includes a comparator U1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R10, a capacitor C1, and a comparator U2;

[0024] The first end of the resistor R1 and the first end of the resistor R10 are respectively connected to the power supply voltage VCC1; the second end of the resistor R1 is respectively connected to the first end of the resistor R2, the non-inverting input end of the comparator U1, and the first end of the resistor R3; the second end of the resistor R2 is connected to the first end of the capacitor C1, and the second end of the resistor R2 and the first end of the capacitor C1 are both grounded; the second end of the capacitor C1 is respectively connected to the inverting input end of the comparator U1 and the first end of the resistor R4; the second end of the resistor R4 is respectively connected to the output end of the comparator U1, the second end of the resistor R3, the second end of the resistor R10, the non-inverting input end of the comparator U2, and the current sampling and judgment unit; the inverting input end of the comparator U2 is connected to the PWM compensation unit, and the output end of the comparator U2 is connected to the drive enhancement unit.

[0025] By adopting the above technical solution, in the PWM control unit, when the battery charging current I charge Greater than the charging current limit protection value I max When the charging current is reduced, the comparator U1 and related components generate a triangular wave signal, which is then combined with the voltage signal output by the PWM compensation unit to generate a corresponding PWM control signal through the comparator U2, so that the current limiting unit reduces the charging current.

[0026] In a specific implementation scheme, the current limiting protection circuit is connected to the positive electrode B+ of the lithium battery, the negative electrode B- of the lithium battery, the external positive input terminal, and the external negative input terminal, and the external positive input terminal and the external negative input terminal are used as charging input terminals for inputting electrical energy;

[0027] The current sampling and judgment unit includes a resistor R9, an operational amplifier U3, a comparator U4, and a transistor Q4; the first end of the resistor R9 is connected to the negative electrode B- of the lithium battery and the non-inverting input end of the operational amplifier U3; the second end of the resistor R9 is connected to the external negative input end and the inverting input end of the operational amplifier U3; the output end of the operational amplifier U3 is connected to the inverting input end of the comparator U4; the non-inverting input end of the comparator U4 is configured with a first reference voltage V REF1 The output end of the comparator U4 is connected to the base of the transistor Q4; the emitter of the transistor Q4 is grounded; and the collector of the transistor Q4 is connected to the PWM control unit.

[0028] By adopting the above technical solution, in the current sampling and judgment unit, the comparator U3 obtains the current size of the battery charging current at this time and outputs the corresponding comparison result. The comparator U4 then uses the comparison result output by the comparator U3 and the preset reference voltage to determine the battery charging current I charge Not greater than the charging current limit protection value I max When the battery charging current I charge Greater than the charging current limit protection value I max When , the transistor Q4 is controlled to be cut off, so that the PWM control unit starts to output the PWM control signal.

[0029] In a specific implementation scheme, the PWM compensation unit includes a resistor R5, a resistor R6, a resistor R7, a transistor Q1, and a capacitor C2;

[0030] The first end of the resistor R5 is connected to the power supply voltage VCC2; the second end of the resistor R5 is respectively connected to the inverting input end of the comparator U2, the first end of the capacitor C2, the first end of the resistor R6, and the collector of the transistor Q1; the second end of the capacitor C2 is respectively connected to the second end of the resistor R6 and the emitter of the transistor Q1, and the second end of the capacitor C2, the second end of the resistor R6, and the emitter of the transistor Q1 are all grounded; the base of the transistor Q1 is connected to the first end of the resistor R7; the second end of the resistor R7 is connected to the current limiting unit and the monitoring unit.

[0031] By adopting the above technical solution, in the PWM compensation unit, through the design of the resistor R7, when the adjusted battery charging current I charge Still greater than the charging current limit protection value I MAX When the transistor Q1 is turned on, combined with the design of resistor R5, resistor R6 and capacitor C2, the voltage value of the inverting input terminal of the comparator U2 can be adjusted to achieve fine adjustment of the PWM signal output by the comparator U2, even if the current limiting unit further finely adjusts the battery charging current I charge , so that the battery charging current I charge Reduce to the preset charging current limit protection value I MAX .

[0032] In a specific implementation scheme, the current limiting unit includes a MOS tube QC2, a diode D1, and an inductor L1;

[0033] The gate of the MOS transistor QC2 is connected to the drive enhancement unit; the source of the MOS transistor QC2 is respectively connected to the monitoring unit and the PWM compensation unit; the drain of the MOS transistor QC2 is connected to the first end of the inductor L1 and the positive electrode of the diode D1; the second end of the inductor L1 is respectively connected to the second end of the resistor R9 and the external negative input terminal; the cathode of the diode D1 is respectively connected to the positive electrode B+ of the battery and the external positive input terminal.

[0034] By adopting the above technical solution, in the current limiting unit, the battery charging current is gradually reduced through the MOS tube QC2, the battery charging current is prevented from changing suddenly through the inductor L1, thereby improving the stability of the circuit, and the reverse flow of current is prevented through the diode D1, thereby further ensuring the stability of the circuit.

[0035] In a specific implementation scheme, the comparator U1 includes a high output threshold V1 and a low output threshold V2, V1 = VCC1*Rb / [Ra*Rc / (Ra+Rc)+Rb], V2 = VCC1*Rd / (Rd+Ra), wherein Ra is the resistance value of the resistor R1, Rb is the resistance value of the resistor R2, Rc is the sum of the resistance values ​​of the resistor R3 and the resistor R10, and Rd is the resistance value of the resistor R2 and the resistor R3 in parallel.

[0036] In a specific embodiment, when the transistor Q1 is in the off state, the voltage signal output by the PWM compensation unit is V REF2 , V REF2 =VCC2*Rf / (Re+Rf), where Re is the resistance value of the resistor R5, and Rf is the resistance value of the resistor R6.

[0037] In a specific implementation scheme, the frequencies of the first PWM control signal and the second PWM control signal output by the PWM control unit are adjusted by changing the sizes of the resistor R4 and the capacitor C1 in the PWM control unit.

[0038] In a specific implementation scheme, the size of the voltage signal output from the PWM compensation unit to the PWM control unit is changed by changing the sizes of the resistor R5 and the resistor R6 in the PWM compensation unit.

[0039] In summary, the technical solution of this application includes at least the following beneficial technical effects:

[0040] 1. On the one hand, by sampling the battery charging current and quickly responding to the current limiting protection mode when it is judged that the battery charging current is too high, the current limiting unit is used to promptly perform initial current limiting control and adjustment on the battery charging current, thereby reducing the charging current; on the other hand, due to errors in the circuit system, the initial adjustment of the charging current may not be in place. Therefore, through the secondary adjustment process, that is, the adjusted battery charging current is obtained in real time, the PWM control signal used to control the current limiting unit is frequency compensated to further reduce the charging current, thereby achieving high-precision control and adjustment of the battery charging current, avoiding long-term high-current charging that causes battery heating, short service life, performance degradation, large system impact, and unstable operation, thereby ensuring the safety of lithium batteries for continuous long-term charging; in addition, the current limiting protection circuit of the present application is implemented by hardware functions and also has the advantages of simple circuit structure, fast response speed, reliable operation, and high control efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG1 is a schematic structural diagram of a current limiting protection circuit in an embodiment of the present application;

[0042] FIG2 is a detailed circuit diagram of a current limiting protection circuit in an embodiment of the present application.

[0043] Explanation of the accompanying symbols: 1. Current sampling and judgment unit; 2. PWM control unit; 3. Current limiting unit; 4. Monitoring unit; 5. PWM compensation unit; 6. Drive enhancement unit; 7. Positive charging line; 8. Negative charging line. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0045] The present application discloses a lithium battery sustainable charging current limiting protection circuit. Referring to Figure 1, the current limiting protection circuit includes a current sampling and judgment unit 1, a PWM control unit 2, a current limiting unit 3, a monitoring unit 4, and a PWM compensation unit 5; the PWM control unit 2 is respectively connected to the current sampling and judgment unit 1 and the current limiting unit 3; the monitoring unit 4 is respectively connected to the current limiting unit 3 and the PWM compensation unit 5; the PWM compensation unit 5 is also connected to the PWM control unit 2.

[0046] Current sampling and judgment unit 1, used to sample the battery charging current I charge , and according to the battery charging current I charge The current limiting control signal is output to the PWM control unit 2;

[0047] a PWM control unit 2, configured to generate a first PWM control signal according to the current limiting control signal and the voltage signal output by the PWM compensation unit 5, and output the signal to the current limiting unit 3;

[0048] The current limiting unit 3 is used to control the battery charging current I according to the first PWM control signal. charge Adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX .

[0049] Monitoring unit 4, used to obtain the battery charging current I adjusted by current limiting unit 3 charge and the regulated battery charging current I charge Output to PWM compensation unit 5;

[0050] PWM compensation unit 5, used for adjusting the battery charging current I charge Adjust the magnitude of the voltage signal output to the PWM control unit 2;

[0051] The PWM control unit 2 is further configured to change the duty cycle of the first PWM control signal according to the adjusted voltage signal, generate a second PWM control signal, and output the second PWM control signal to the current limiting unit 3;

[0052] The current limiting unit 3 is further configured to control the battery charging current I charge Further adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX .

[0053] Therefore, the current limiting protection circuit of the present application, on the one hand, samples the battery charging current and, when it is judged that the battery charging current is too high, quickly responds to the current limiting protection mode, and promptly performs initial current limiting control and adjustment on the battery charging current through the current limiting unit, thereby reducing the charging current; on the other hand, due to errors in the circuit system, the initial adjustment of the charging current may not be in place, so through a secondary adjustment process, that is, the adjusted battery charging current is obtained in real time, the frequency compensation of the PWM control signal used to control the current limiting unit is performed, and the charging current is further reduced, thereby achieving high-precision control and adjustment of the battery charging current, avoiding long-term high-current charging causing battery heating, short service life, performance degradation, large system impact, and unstable operation, thereby ensuring the safety of lithium batteries for continuous long-term charging; in addition, the current limiting protection circuit of the present application is implemented by hardware functions, and also has the advantages of simple circuit structure, fast response speed, reliable operation, and high control efficiency.

[0054] Furthermore, referring to FIG. 1 , the current limiting protection circuit further includes a driving enhancement unit 6 , which is connected to the PWM control unit 2 and the current limiting unit 3 , respectively.

[0055] The driving enhancement unit 6 is configured to receive the first PWM control signal output by the PWM control unit 2, enhance the driving capability of the first PWM control signal, and output the first PWM control signal with enhanced driving capability to the current limiting unit 3;

[0056] The current limiting unit 3 is used to control the battery charging current I according to the first PWM control signal after the driving capability is enhanced. charge Adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX ;

[0057] And / or, the driving enhancement unit 6 is further configured to receive the second PWM control signal output by the PWM control unit 2, enhance the driving capability of the second PWM control signal, and output the second PWM control signal with enhanced driving capability to the current limiting unit 3;

[0058] The current limiting unit 3 is further configured to control the battery charging current I according to the second PWM control signal with enhanced driving capability. charge Further adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX .

[0059] The drive enhancement unit 6 can amplify the first PWM control signal to enhance its driving capability, and can also amplify the second PWM control signal to enhance its driving capability. Thus, the drive enhancement unit improves the driving capability of the first and second PWM control signals output by the PWM control unit, thereby improving the system's dynamic anti-interference capability and response speed. Furthermore, the drive enhancement unit can employ a push-pull drive circuit.

[0060] FIG2 is an implementation of the current limiting protection circuit for continuous charging of a lithium battery of the present application, which is described in detail below with reference to FIG2 :

[0061] Referring to Figure 2, a current limiting protection circuit for continuous charging of a lithium battery is implemented. The current limiting protection circuit is connected to the lithium battery and an external access terminal, respectively. The lithium battery includes a positive electrode B+ and a negative electrode B- of the lithium battery. The external access terminal includes an external positive input terminal P+ / C+ and an external negative input terminal P- / C-. Specifically, the current limiting protection circuit is connected to the positive electrode B+ and the negative electrode B- of the lithium battery, the external positive input terminal P+ / C+, and the external negative input terminal P- / C-. A positive charging line 7 is connected between the positive electrode B+ and the external positive input terminal P+ / C+, and a negative charging line 8 is connected between the negative electrode B- and the external negative input terminal P- / C-. MOS transistors QC1 and QD1 are connected in series between the negative electrode B- and the external negative input terminal P- / C-. Among them, the MOS tube QC1 is a charging MOS tube, and the MOS tube QD1 is a discharging MOS tube. The MOS tube QC1 and the MOS tube QD1 are used to control the charging and discharging of the lithium battery.

[0062] The external positive input terminal P+ / C+ and the external negative input terminal P- / C- can be connected to a load, or can be used as charging input terminals for inputting electrical energy. When the lithium battery is in a discharging state, the external positive input terminal P+ / C+ and the external negative input terminal P- / C- are connected to the load. At this time, the current is output from the positive electrode B+ of the lithium battery, passes through the positive charging line 7 and the external positive input terminal P+ / C+ to the load, and then returns from the external negative input terminal P- / C- through the negative charging line 8 to the negative electrode B- of the lithium battery, thereby realizing the lithium battery supplying power to the load; when the lithium battery is in a charging state, the external positive input terminal P+ / C+ and the external negative input terminal P- / C- can be connected to a charger. At this time, the current passes through the charger, the external positive input terminal P+ / C+, the positive charging line 7, the positive electrode B+ of the lithium battery to the lithium battery, and then returns from the negative electrode B- of the lithium battery through the negative charging line 8 and the external negative input terminal P- / C- to the charger.

[0063] Specifically, referring to FIG2 , the current sampling and judging unit 1 includes a resistor R9, an operational amplifier U3, a comparator U4, and a transistor Q4. The connection of the components is as follows:

[0064] The resistor R9 is connected in series on the negative charging line 8. The first end of the resistor R9 is connected to the negative electrode B- of the lithium battery and the non-inverting input of the operational amplifier U3 respectively. The second end of the resistor R9 is connected to the external negative input and the inverting input of the operational amplifier U3 respectively. The output of the operational amplifier U3 is connected to the inverting input of the comparator U4. The non-inverting input of the comparator U4 is configured with a first reference voltage V REF1 The output end of the comparator U4 is connected to the base of the transistor Q4; the emitter of the transistor Q4 is grounded; the collector of the transistor Q4 is connected to the PWM control unit 2.

[0065] Furthermore, the current sampling and judgment unit 1 may further include a filtering circuit consisting of a resistor R11, a resistor R12, and a capacitor C3, wherein the first end of the resistor R9 is respectively connected to the battery negative electrode B- of the lithium battery and the first end of the resistor R11, and the second end of the resistor R9 is respectively connected to the external negative input terminal P- / C- and the first end of the resistor R12; the second end of the resistor R11 is respectively connected to the first end of the capacitor C3 and the non-inverting input terminal of the operational amplifier U3; the second end of the resistor R12 is respectively connected to the second end of the capacitor C3 and the inverting input terminal of the operational amplifier U3;

[0066] Continuing with FIG2 , the PWM control unit 2 includes a comparator U1 , a resistor R1 , a resistor R2 , a resistor R3 , a resistor R4 , a resistor R10 , a capacitor C1 , and a comparator U2 . The connections of the components are as follows:

[0067] The first end of the resistor R1 and the first end of the resistor R10 are respectively connected to the power supply voltage VCC1; the second end of the resistor R1 is respectively connected to the first end of the resistor R2, the non-inverting input end of the comparator U1, and the first end of the resistor R3; the second end of the resistor R2 is connected to the first end of the capacitor C1, and the second end of the resistor R2 and the first end of the capacitor C1 are both grounded; the second end of the capacitor C1 is respectively connected to the inverting input end of the comparator U1 and the first end of the resistor R4; the second end of the resistor R4 is respectively connected to the output end of the comparator U1, the second end of the resistor R3, the second end of the resistor R10, the non-inverting input end of the comparator U2, and the current sampling and judgment unit 1. Specifically, the second end of the resistor R4 is connected to the collector of the transistor Q4 in the current sampling and judgment unit 1; the inverting input end of the comparator U2 is connected to the PWM compensation unit 5, and the output end of the comparator U2 is connected to the drive enhancement unit 6.

[0068] 2 , the driving enhancement unit 6 includes a transistor Q2 and a transistor Q3 , and the connection method of each component is as follows:

[0069] The collector of the transistor Q2 is connected to the power supply voltage VDD; the base of the transistor Q2 is respectively connected to the base of the transistor Q3 and the output end of the comparator U2; the emitter of the transistor Q2 is respectively connected to the emitter of the transistor Q3 and the current limiting unit 3; the collector of the transistor Q3 is respectively connected to the monitoring unit 4, the source of the MOS transistor QC1, and the source of the MOS transistor QD1.

[0070] Continuing with FIG2 , the current limiting unit 3 includes a MOS tube QC2, a diode D1, and an inductor L1. The connection method of each component is as follows:

[0071] The gate of the MOS transistor QC2 is connected to the drive enhancement unit 6. Specifically, the gate of the MOS transistor QC2 is connected to the emitter of the transistor Q2 and the emitter of the transistor Q3 respectively; the source of the MOS transistor QC2 is connected to the monitoring unit 4 and the PWM compensation unit 5 respectively; the drain of the MOS transistor QC2 is connected to the first end of the inductor L1 and the positive electrode of the diode D1; the second end of the inductor L1 is connected to the second end of the resistor R9 and the external negative input terminal P- / C- respectively. Specifically, the second end of the inductor L1 is connected to the external negative input terminal P- / C- through the MOS transistors QC1 and QD1; the cathode of the diode D1 is connected to the battery positive electrode B+ and the external positive input terminal P+ / C- respectively.

[0072] 2 , the monitoring unit 4 includes a resistor R8 , a first end of which is connected to the source of the MOS transistor QC2 and the PWM compensation unit 5 , and a second end of which is connected to the collector of the transistor Q3 , the source of the MOS transistor QC1 , and the source of the MOS transistor QD1 .

[0073] Continuing to refer to FIG2 , the PWM compensation unit 5 includes a resistor R5 , a resistor R6 , a resistor R7 , a transistor Q1 , and a capacitor C2 . The connection method of each component is as follows:

[0074] A first end of resistor R5 is connected to power supply voltage VCC2; a second end of resistor R5 is respectively connected to the inverting input end of comparator U2, the first end of capacitor C2, the first end of resistor R6, and the collector of transistor Q1; a second end of capacitor C2 is respectively connected to the second end of resistor R6 and the emitter of transistor Q1, and the second end of capacitor C2, the second end of resistor R6, and the emitter of transistor Q1 are all grounded; a base of transistor Q1 is connected to a first end of resistor R7; a second end of resistor R7 is connected to current limiting unit 3 and monitoring unit 4. Specifically, the second end of resistor R7 is connected to the source of MOS transistor QC2 and the first end of resistor R8.

[0075] Continuing with Figure 2 , the drain of MOS transistor QC1 is connected to the second end of inductor L1 and the second end of resistor R9, respectively. The source of MOS transistor QC1 is connected to the second end of resistor R8, the collector of transistor Q3, and the source of MOS transistor QD1, respectively. The gate of MOS transistor QC1 can be connected to a control chip, which controls the on / off state of MOS transistor QC1. The drain of MOS transistor QD1 is connected to the external negative input terminal P- / C-. The gate of MOS transistor QD1 can be connected to a control chip, which controls the on / off state of MOS transistor QD1.

[0076] The control process of the lithium battery continuous charging current limiting protection circuit is described in detail below with reference to FIG2:

[0077] Resistor R9 is a current detection resistor. The operational amplifier U3 detects the current flowing through resistor R9 to obtain the battery charging current I charge and the battery charging current I charge Resistors R11, R12, and C3 form a filter circuit that filters the signals input to the non-inverting and inverting inputs of operational amplifier U3. Therefore, operational amplifier U3 generates a voltage value corresponding to the current flowing through resistor R9 and outputs it to the inverting input of comparator U4.

[0078] Charging current limit protection value I max The setting of the first reference voltage V configured at the non-inverting input terminal of the comparator U4 can be preset by those skilled in the art according to the actual situation. REF1 Can be charged according to the preset current limiting protection value I max Set it so that when the battery charging current I charge Less than the charging current limit protection value I max When the voltage value of the inverting input terminal of the comparator U4 is less than the voltage value of the non-inverting input terminal of the comparator U4, the comparator U4 outputs a high level. At this time, the transistor Q4 is turned on, so that the voltage value of the non-inverting input terminal of the comparator U2 in the PWM control unit 2 is less than the voltage value of the inverting input terminal of the comparator U2. The comparator U2 outputs a low level, that is, the PWM control unit 2 outputs a low level, so that the MOS tube QC2 remains cut off. At this time, the current limiting unit 3 does not perform the current limiting control operation; and when the battery charging current I charge Equal to the charging current limit protection value I max , the output of the comparator U4 remains in the original state, that is, the comparator U4 still outputs a high level, the PWM control unit 2 still outputs a low level, the MOS tube QC2 still remains cut off, and the current limiting unit 3 does not perform the current limiting control operation.

[0079] When the battery charging current I charge Greater than the charging current limit protection value I max When the voltage value of the inverting input terminal of the comparator U4 is greater than the voltage value of the non-inverting input terminal of the comparator U4, the comparator U4 outputs a low level. At this time, the transistor Q4 is turned off, and the voltage value of the non-inverting input terminal of the comparator U2 in the PWM control unit 2 is determined by the output terminal of the comparator U1. The process of the PWM control unit 2 generating and outputting the first PWM control signal is specifically described below:

[0080] In the PWM control unit 2, by designing the resistance values ​​of resistors R1, R2, R3, and R10, a high output threshold V1 and a low output threshold V2 of comparator U1 can be obtained based on the high and low output states of comparator U1. That is, when comparator U1 outputs a high level, the voltage value at the non-inverting input terminal of comparator U1 is V1; when comparator U1 outputs a low level, the voltage value at the non-inverting input terminal of comparator U1 is V2. Specifically, the high output threshold V1 of the non-inverting input terminal of comparator U1 = VCC1*Rb / [Ra*Rc / (Ra+Rc)+Rb], and the low output threshold V2 of the non-inverting input terminal of comparator U1 = VCC1*Rd / (Rd+Ra), where Ra is the resistance value of resistor R1, Rb is the resistance value of resistor R2, Rc is the sum of the resistance values ​​of resistors R3 and R10, and Rd is the resistance value of the parallel connection of resistors R2 and R3.

[0081] Specifically, according to the circuit design in the PWM control unit 2, the output terminal of the comparator U1 can output a triangular wave. The specific process is as follows:

[0082] When the comparator U1 outputs a high level, the voltage value at the non-inverting input terminal of the comparator U1 is V1. At the same time, the power supply voltage VCC1 charges the capacitor C1 through the resistor R10 and the resistor R4. Then the voltage value at the inverting input terminal of the comparator U1 starts to rise from 0V. When it rises to a value greater than the voltage value V1 at the non-inverting input terminal, the comparator U1 outputs a low level.

[0083] When the comparator U1 outputs a low level, the voltage value of the non-inverting input terminal of the comparator U1 is V2. At the same time, the capacitor C1 is discharged to the ground through the resistor R4. When the voltage on the capacitor C1 drops from V1 to lower than V2, the comparator outputs a high level again.

[0084] According to the above process, the output terminal of the comparator U1 can output a triangular wave through the continuous charging and discharging process of the capacitor C1.

[0085] Therefore, the voltage waveform at the non-inverting input of comparator U2 is the voltage waveform at the output of comparator U1. At the same time, the inverting input of comparator U2 is connected to the PWM compensation unit 5. Initially, QC2 is in the cut-off state, so the transistor Q1 is not conducting. The transistor Q1 is in the cut-off state, and the voltage value at the output of the PWM compensation unit 5 is V REF2 , that is, the voltage signal output by the PWM compensation unit 5 to the PWM control unit 2 is V REF2 , then the voltage value of the inverting input terminal of comparator U2 is also V REF2 , and V REF2=VCC2*Rf / (Re+Rf), where Re is the resistance of resistor R5 and Rf is the resistance of resistor R6. Therefore, when the voltage at the non-inverting input of comparator U2 is higher than the voltage V at the inverting input of comparator U2, REF2 When the voltage value of the comparator U2 non-inverting input terminal is lower than the voltage value V REF2 When , the comparator U2 outputs a low level. Therefore, through the above process, the PWM control unit 2 generates and outputs the first PWM control signal, and after the driving capability of the first PWM control signal is enhanced by the driving enhancement unit 6, it is output to the current limiting unit 3, so that the battery charging current I is controlled by the on-off of the MOS tube QC2 in the current limiting unit 3. charge Adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX Furthermore, the first PWM control signal is a square wave signal.

[0086] Therefore, it can be obtained that in the current sampling and judging unit 1, the comparator U3 obtains the battery charging current at this time and outputs the corresponding comparison result. The comparator U4 then uses the comparison result output by the comparator U3 and the preset reference voltage to determine the battery charging current I charge Not greater than the charging current limit protection value I max When the battery charging current I charge Greater than the charging current limit protection value I max When , the transistor Q4 is controlled to be turned off, so that the PWM control unit 2 starts to output the PWM control signal.

[0087] In the PWM control unit 2, when the battery charging current I charge Greater than the charging current limit protection value I max When the charging current is reduced, the comparator U1 and related components generate a triangular wave signal, and then combine the voltage signal output by the PWM compensation unit 5 to generate a corresponding PWM control signal through the comparator U2, so that the current limiting unit 3 reduces the charging current.

[0088] The following describes in detail how the drive enhancement unit 6 enhances the driving capability of the first PWM control signal: When the first PWM control signal is at a high level, transistor Q2 is turned on and transistor Q3 is turned off. Current is then output from VDD and fed into the current limiting unit 3 through transistor Q2. When the first PWM control signal is at a low level, transistor Q2 is turned off and transistor Q3 is turned on. A high current is then drawn from the current limiting unit 3 through transistor Q3. Thus, within a complete cycle of the first PWM control signal, transistors Q2 and Q3 operate alternately, enhancing the driving capability of the first PWM control signal.

[0089] Next, the current limiting unit 3 is used to control the battery charging current I charge Adjust the battery charging current I charge The reduction process is described in detail:

[0090] When the MOS tube QC2 is in the on state, the current is output from the charger, the external positive input terminal P+ / C+, the positive charging line 7, the positive electrode B+ of the lithium battery to the lithium battery, and then from the negative electrode B- of the lithium battery through the resistor R9, the inductor L1, the MOS tube QC2, the resistor R8, the MOS tube QD1, the external negative input terminal P- / C- back to the charger, thereby making the battery charging current I charge Gradually decrease.

[0091] Furthermore, when the MOS tube QC2 is in the cut-off state, the inductor L1 can also transfer the stored energy to the battery positive electrode B+ through the diode D1 to charge the lithium battery and improve the system operation efficiency.

[0092] Therefore, it can be obtained that in the current limiting unit 3, the battery charging current is gradually reduced by the MOS tube QC2, the battery charging current is prevented from changing suddenly by the inductor L1, thereby improving the stability of the circuit, and the reverse flow of current is prevented by the diode D1, thereby further ensuring the stability of the circuit.

[0093] Next, the monitoring unit 4 obtains the adjusted battery charging current I charge , and the PWM compensation unit 5 is based on the adjusted battery charging current I charge Adjust the magnitude of the voltage signal output to the PWM control unit 2, as detailed below:

[0094] When the current limiting MOS tube QC2 is in the on state, the current flows through the resistor R8 in the monitoring unit 4. The current value flowing through the resistor R8 is the current battery charging current I charge Therefore, the PWM compensation unit 5 can obtain the adjusted battery charging current I according to the current flowing through the resistor R8. charge value, and when the regulated battery charging current I chargeThe value is greater than the charging current limit protection value I MAX When the voltage V output to the inverting input terminal of the comparator U2 is adjusted REF2 The size of the first PWM control signal output by the comparator U2 is changed, that is, the duty cycle of the first PWM control signal output by the PWM control unit 2 is changed, so that the PWM control unit 2 generates a second PWM control signal, and after the driving capability of the second PWM control signal is enhanced by the driving enhancement unit 6, it is output to the current limiting unit 3, so that the current limiting unit 3 can control the battery charging current I charge Further adjustment is made so that the battery charging current I charge Reduce to the preset charging current limit protection value I MAX The process of the driving enhancement unit 6 enhancing the driving capability of the second PWM control signal can be referred to the related description of the process of the driving enhancement unit 6 enhancing the driving capability of the first PWM control signal, which will not be repeated here.

[0095] When the above-mentioned adjusted battery charging current I charge The value is greater than the charging current limit protection value I MAX When , the PWM compensation unit 5 adjusts the voltage value V output to the inverting input terminal of the comparator U2 REF2 The size of the voltage signal output to the PWM control unit 2 is adjusted, specifically:

[0096] When the regulated battery charging current I charge Greater than the charging current limit protection value I MAX When the voltage across the resistor R8 turns on the transistor Q1 and operates in the amplification region, the capacitor C2 discharges slowly, causing the voltage value V REF2 The duty cycle of the first PWM control signal output by the comparator U2 is reduced, thereby driving the on-off of the MOS tube QC2 and further reducing the battery charging current I charge , so that the battery charging current I charge Stable to the charging current limit protection value I MAX Within.

[0097] Therefore, it can be obtained that, in the PWM compensation unit 5, by designing the resistor R7, when the adjusted battery charging current I charge Still greater than the charging current limit protection value I MAX When the transistor Q1 is turned on, combined with the design of the resistor R5, the resistor R6 and the capacitor C2, the voltage value of the inverting input terminal of the comparator U2 can be adjusted to achieve fine adjustment of the PWM signal output by the comparator U2, even if the current limiting unit 3 further finely adjusts the battery charging current I charge , so that the battery charging current I charge Reduce to the preset charging current limit protection value IMAX .

[0098] In particular, in the PWM control unit 2, the charge and discharge time of the capacitor C1 can be changed by changing the size of the resistor R4 and the capacitor C1, thereby adjusting the frequency of the first PWM control signal and the second PWM control signal output by the PWM control unit 2. Therefore, those skilled in the art can adjust the frequency of the first PWM control signal and the second PWM control signal by changing the size of the relevant resistors and capacitors in the PWM control unit 2 according to actual needs, so that the current limiting unit 3 can adjust the battery charging current I charge The control is more accurate.

[0099] In particular, in the PWM compensation unit 5, the voltage value V at the output terminal of the PWM compensation unit 5 can be changed by changing the values ​​of the resistors R5 and R6. REF2 The size of the voltage signal output by the PWM compensation unit 5 to the PWM control unit 2 can be adjusted. Therefore, those skilled in the art set the current limiting protection condition according to actual needs, and adjust the duty cycle of the first PWM control signal output by the PWM control unit 2 by changing the size of the relevant resistor in the PWM compensation unit 5, so that the current limiting unit 3 can control the battery charging current I charge The control is more accurate.

[0100] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A lithium battery continuous charging current limiting protection circuit, characterized in that: It comprises a current sampling and judging unit (1), a PWM control unit (2), a current limiting unit (3), a monitoring unit (4), and a PWM compensation unit (5); The current sampling and judgment unit (1) is used to sample the battery charging current I charge , and according to the battery charging current I charge The magnitude is judged, and a current limiting control signal is output to a PWM control unit (2); A PWM control unit (2) is used to generate a first PWM control signal according to the current limiting control signal and the voltage signal output by the PWM compensation unit (5), and output the signal to the current limiting unit (3); A current limiting unit (3) is used to limit the battery charging current I according to the first PWM control signal. charge The battery charging current I charge Reduce to the preset charging current limit protection value I MAX ; A monitoring unit (4) is used to obtain the battery charging current I adjusted by the current limiting unit (3) charge and the regulated battery charging current I charge Output to the PWM compensation unit (5); A PWM compensation unit (5) is used to adjust the battery charging current I charge Adjusting the magnitude of the voltage signal output to the PWM control unit (2); The PWM control unit (2) is further configured to change the duty cycle of the first PWM control signal according to the voltage signal after the adjustment, generate a second PWM control signal, and output the second PWM control signal to the current limiting unit (3); The current limiting unit (3) is further used to control the battery charging current I according to the second PWM control signal. charge Further adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX ; The current sampling and judging unit (1) comprises a resistor R9, an operational amplifier U3, a comparator U4, and a transistor Q4; the first end of the resistor R9 is respectively connected to the negative electrode B- of the lithium battery and the in-phase input end of the operational amplifier U3; the second end of the resistor R9 is respectively connected to the external negative electrode input end and the inverting input end of the operational amplifier U3; the output end of the operational amplifier U3 is connected to the inverting input end of the comparator U4; the in-phase input end of the comparator U4 is configured with a first reference voltage V REF1 The output end of the comparator U4 is connected to the base of the transistor Q4; the emitter of the transistor Q4 is grounded; the collector of the transistor Q4 is connected to the PWM control unit (2).

2. The lithium battery continuous charging current limiting protection circuit according to claim 1, characterized in that: It also includes a driving enhancement unit (6), wherein the driving enhancement unit (6) is connected to the PWM control unit (2) and the current limiting unit (3) respectively; The driving enhancement unit (6) is used to receive the first PWM control signal output by the PWM control unit (2), enhance the driving capability of the first PWM control signal, and output the first PWM control signal with enhanced driving capability to the current limiting unit (3); The current limiting unit (3) is used to control the battery charging current I according to the first PWM control signal after the driving capability is enhanced. charge The battery charging current I charge Reduce to the preset charging current limit protection value I MAX ; And / or, the driving enhancement unit (6) is used to receive the second PWM control signal output by the PWM control unit (2), enhance the driving capability of the second PWM control signal, and output the second PWM control signal with enhanced driving capability to the current limiting unit (3); The current limiting unit (3) is used to control the battery charging current I according to the second PWM control signal with enhanced driving capability. charge Further adjust the battery charging current I charge Reduce to the preset charging current limit protection value I MAX .

3. The lithium battery continuous charging current limiting protection circuit according to claim 2, characterized in that: The PWM control unit (2) comprises a comparator U1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R10, a capacitor C1, and a comparator U2; The first end of the resistor R1 and the first end of the resistor R10 are respectively connected to the power supply voltage VCC1; the second end of the resistor R1 is respectively connected to the first end of the resistor R2, the non-inverting input end of the comparator U1, and the first end of the resistor R3; the second end of the resistor R2 is connected to the first end of the capacitor C1, and the second end of the resistor R2 and the first end of the capacitor C1 are both grounded; the second end of the capacitor C1 is respectively connected to the inverting input end of the comparator U1 and the first end of the resistor R4; the second end of the resistor R4 is respectively connected to the output end of the comparator U1, the second end of the resistor R3, the second end of the resistor R10, the non-inverting input end of the comparator U2, and the current sampling and judgment unit (1); the inverting input end of the comparator U2 is connected to the PWM compensation unit (5), and the output end of the comparator U2 is connected to the drive enhancement unit (6).

4. The lithium battery continuous charging current limiting protection circuit according to claim 1, characterized in that: The current limiting protection circuit is connected to the positive electrode B+ of the lithium battery, the negative electrode B- of the lithium battery, the external positive input terminal, and the external negative input terminal. The external positive input terminal and the external negative input terminal are used as charging input terminals for inputting electric energy.

5. The lithium battery continuous charging current limiting protection circuit according to claim 3, characterized in that: The PWM compensation unit (5) comprises a resistor R5, a resistor R6, a resistor R7, a transistor Q1, and a capacitor C2; The first end of the resistor R5 is connected to the power supply voltage VCC2; the second end of the resistor R5 is respectively connected to the inverting input end of the comparator U2, the first end of the capacitor C2, the first end of the resistor R6, and the collector of the transistor Q1; the second end of the capacitor C2 is respectively connected to the second end of the resistor R6 and the emitter of the transistor Q1, and the second end of the capacitor C2, the second end of the resistor R6, and the emitter of the transistor Q1 are all grounded; the base of the transistor Q1 is connected to the first end of the resistor R7; and the second end of the resistor R7 is connected to the current limiting unit (3) and the monitoring unit (4).

6. The lithium battery continuous charging current limiting protection circuit according to claim 3, characterized in that: The current limiting unit (3) comprises a MOS tube QC2, a diode D1, and an inductor L1; The gate of the MOS tube QC2 is connected to the driving enhancement unit (6); the source of the MOS tube QC2 is respectively connected to the monitoring unit (4) and the PWM compensation unit (5); the drain of the MOS tube QC2 is connected to the first end of the inductor L1 and the diode D1 The second end of the inductor L1 is connected to the second end of the resistor R9 and the external negative input terminal respectively; the cathode of the diode D1 is connected to the positive electrode B+ of the battery and the external positive input terminal respectively.

7. The lithium battery continuous charging current limiting protection circuit according to claim 6, characterized in that: The comparator U1 includes a high output threshold V1 and a low output threshold V2; V1=VCC1*Rb / [Ra*Rc / (Ra+Rc)+Rb], V2=VCC1*Rd / (Rd+Ra), wherein Ra is the resistance value of the resistor R1, Rb is the resistance value of the resistor R2, Rc is the sum of the resistance values ​​of the resistor R3 and the resistor R10, and Rd is the resistance value of the resistor R2 and the resistor R3 in parallel.

8. The lithium battery continuous charging current limiting protection circuit according to claim 5, characterized in that: When the transistor Q1 is in the cut-off state, the voltage signal output by the PWM compensation unit (5) is V REF2 , V REF2 =VCC2*Rf / (Re+Rf), wherein Re is the resistance value of the resistor R5, and Rf is the resistance value of the resistor R6.

9. The lithium battery continuous charging current limiting protection circuit according to claim 3, characterized in that: By changing the sizes of the resistor R4 and the capacitor C1 in the PWM control unit (2), the frequencies of the first PWM control signal and the second PWM control signal output by the PWM control unit (2) are adjusted.

10. The lithium battery continuous charging current limiting protection circuit according to claim 5, characterized in that: By changing the sizes of the resistor R5 and the resistor R6 in the PWM compensation unit (5), the size of the voltage signal output by the PWM compensation unit (5) to the PWM control unit (2) is adjusted.

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