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 u

Description

The present disclosure relates to the field of circuit design technologies, and in particular, to a current-limiting protection circuit for continuous lithium battery charging. BACKGROUND In recent years, with the implementation of low-carbon economies and the rapid development of the energy storage market, lithium batteries have been used more widely in the field of household energy storage. At present, with the increasing demand for electricity by families, it is often necessary to increase the capacity of lithium batteries. The capacity expansion of a lithium battery is generally achieved by increasing the number of battery cells connected in series in the lithium battery, or by using several or dozens of batteries in parallel. However, when the capacity of the lithium battery is increased by using battery cells connected in series, the presence of the internal resistance of the battery cells may lead to a higher internal resistance of the lithium battery and higher voltage consumed by the internal resistance as the number of battery cells connected in series increases and the number of uses increases. An excessive charging current of the lithium battery may result in a rapid rise in the temperature of the lithium battery, which will not only affect the capacity of the battery cells and the performance of the battery, but also reduce the number of cycles and shorten the service life of the lithium battery. In addition, when the capacity of the lithium battery is increased by using a number of batteries in parallel, at a high charging current of the lithium battery, the capacity variation among batteries may impose a higher charging current on batteries with a lower capacity, leading to a great impact on the lithium battery system and compromised stability of the lithium battery system. In summary, when the capacity of the lithium battery is increased by using battery cells connected in series, an excessive charging current of the lithium battery may cause problems of overheat, a short service life, and reduced performance of the battery; when the capacity of the lithium battery is increased by using a number of batteries in parallel, an excessive charging current of the lithium battery may lead to problems of great impact on the system and unstable operation. In the prior art, a current-limiting circuit with low control precision may be used to deal with a series of problems caused by high charging currents of the lithium battery, which, however, cannot completely avoid the above problems when the lithium battery is continuously charged for a long time. SUMMARY OF THE INVENTION To achieve the high-precision control and adjustment of a current in a charging process of a lithium battery, reduce the charging current, and avoid problems of overheat, short service lives, and reduced performance in the battery, as well as great impact on the system and unstable operation that are caused by long-term charging at a high current, the present application provides a current-limiting protection circuit for continuous lithium battery charging. The present application provides a current-limiting protection circuit for continuous lithium battery charging, which adopts the following technical solution: the currentlimiting protection circuit for continuous lithium battery charging includes a current sampling and determining unit, a PWM control unit, a current-limiting unit, a monitoring unit, and a PWM compensation unit. The current sampling and determining unit is configured to sample a battery charging current Lharge, and output a current-limiting control signal to the PWM control unit according to the determination of the magnitude of the battery charging current Icharge. The PWM control unit is configured to generate a first PWM control signal according to the current-limiting control signal and a voltage signal output by the PWM compensation unit, and output the first PWM control signal to the current-limiting unit. The current-limiting unit is configured to adjust the battery charging current Icharge according to the first PWM control signal, so as to reduce the battery charging current Icharge to a preset charging current-limiting protection value Imax. The monitoring unit is configured to acquire the battery charging current Icharge adjusted by the current-limiting unit, and output the adjusted battery charging current Icharge to the PWM compensation unit. The PWM compensation unit is configured to adjust the magnitude of the voltage signal output to the PWM control unit according to the adjusted battery charging current Icharge. The PWM control unit is further configured to change a duty cycle of the first PWM control signal according to the voltage signal after the magnitude adjustment, generate a second PWM control signal, and output the second PWM control signal to the currentlimiting unit. The current-limiting unit is further configured to further adjust the battery charging current Icharge according to the second PWM control signal, such that the battery charging current Icharge is reduced to the preset charging current-limiting protection value Im ax. By adopting the above technical solution: on one hand, by sampling the battery charging current and quickly switching to a current-limiting protection mode in response to the determination of a high battery charging current, the current-limiting unit performs primary current-limiting control and adjustment on the battery charging current in time, thereby reducing the charging current; on the other hand, due to an error in the circuit system, the primary adjustment of the charging current may be insufficient, so a secondary adjustment is performed, that is, the adjusted battery charging current is acquired in real time, and the PWM control signal for controlling the current-limiting unit is subjected to frequency compensation, thereby achieving high-precision control and adjustment of the battery charging current, avoiding the problems of overheat, short service lives, and reduced performance of the battery, as well as great impact on the system, and unstable operation that are caused by long-term charging at a high current, and ensuring the safety of continuous lithium battery charging. In addition, the currentlimiting protection circuit of the present application is achieved by means of hardware and possesses the advantages of a simple circuit structure, quick response, reliable action, and high control efficiency. In one specific embodiment, the current-limiting protection circuit for continuous lithium battery charging further includes a drive enhancement unit. The drive enhancement unit is separately connected to the PWM control unit and the currentlimiting unit. The drive enhancement unit is configured to receive the first PWM control signal output by the PWM control unit, enhance a drive capability of the first PWM control signal, and output the first PWM control signal with the enhanced drive capability to the current-limiting unit. The current-limiting unit is configured to adjust the battery charging current Icharge according to the first PWM control signal with the enhanced drive capability, so as to reduce the battery charging current Icharge to a preset charging current-limiting protection value Im ax. And / or, the drive enhancement unit is configured to receive the second PWM control signal output by the PWM control unit, enhance a drive capability of the second PWM control signal, and output the second PWM control signal with the enhanced drive capability to the current-limiting unit. The current-limiting unit is configured to further adjust the battery charging current Icharge according to the second PWM control signal with the enhanced drive capability, so as to reduce the battery charging current Icharge to a preset charging current-limiting protection value Imax. By adopting the above technical solution, the use of the drive enhancement unit improves the drive capabilities of the first PWM control signal and the second PWM control signal, thereby improving the dynamic anti-interference capability and the response speed of the system. In one specific embodiment, the PWM control unit includes a comparator UI, a resistor RI, a resistor R2, a resistor R3, a resistor R4, a resistor RIO, a capacitor Cl, and a comparator U2. A first terminal of the resistor RI and a first terminal of the resistor RIO are separately connected to a power supply voltage VCC1. A second terminal of the resistor RI is separately connected to a first terminal of the resistor R2, a non-inverting input terminal of the comparator UI, and a first terminal of the resistor R3. A second terminal of the resistor R2 is connected to a first terminal of the capacitor Cl, and the second terminal of the resistor R2 and the first terminal of the capacitor C1 are both grounded. A second terminal of the capacitor Cl is separately connected to an inverting input terminal of the comparator UI and a first terminal of the resistor R4. A second terminal of the resistor R4 is separately connected to an output terminal of the comparator UI, a second terminal of the resistor R3, a second terminal of the resistor RIO, a non-inverting input terminal of the comparator U2, and the current sampling and determining unit. An inverting input terminal of the comparator U2 is connected to the PWM compensation unit, and an output terminal of the comparator U2 is connected to the drive enhancement unit. By adopting the above technical solution, in the PWM control unit, when the battery charging current Icharge is greater than the charging current-limiting protection value Imax, a triangular wave signal is generated by the comparator UI and related elements, and then a corresponding PWM control signal is generated by the comparator U2 in combination with the voltage signal output by the PWM compensation unit, such that the current-limiting unit reduces the charging current. In one specific embodiment, the current-limiting protection circuit is connected to a battery positive electrode B+ of the lithium battery, the battery negative electrode B- of the lithium battery, an external positive electrode input terminal, and the external negative electrode input terminal, and the external positive electrode input terminal and the external negative electrode input terminal are configured to input electricity as charging input terminals. The current sampling and determining unit includes a resistor R9, an operational amplifier U3, a comparator U4, and a triode Q4. A first terminal of the resistor R9 is separately connected to a battery negative electrode B- of the lithium battery and a noninverting input terminal of the operational amplifier U3. A second terminal of the resistor R9 is separately connected to an external negative electrode input terminal and an inverting input terminal of the operational amplifier U3. An output terminal of the operational amplifier U3 is connected to an inverting input terminal of the comparator U4. A non-inverting input terminal of the comparator U4 is configured with a first reference voltage Vrefi. An output terminal of the comparator U4 is connected to a base of the triode Q4. An emitter of the triode Q4 is grounded. A collector of the triode Q4 is connected to the PWM control unit. By adopting the above technical solution, in the current sampling and determining unit, the comparator U3 acquires the magnitude of the battery charging current at present and outputs a corresponding comparison result, and then the comparator U4 controls, according to the comparison result output by the comparator U3 and the preset reference voltage, the triode Q4 to be turned on and the PWM control unit not to output a PWM control signal when the battery charging current Icharge is not greater than the charging current-limiting protection value Imax, and controls the triode Q4 to be turned off when the battery charging current Icharge is greater than the charging current-limiting protection value Imax, such that the PWM control unit starts to output a PWM control signal. In one specific embodiment, the PWM compensation unit includes a resistor R5, a resistor R6, a resistor R7, a triode QI, and a capacitor C2. A first terminal of the resistor R5 is connected to a power supply voltage VCC2. A second terminal of the resistor R5 is separately connected to the inverting input terminal of the comparator U2, a first terminal of the capacitor C2, a first terminal of the resistor R6, and a collector of the triode QI. A second terminal of the capacitor C2 is separately connected to a second terminal of the resistor R6 and an emitter of the triode QI, and the second terminal of the capacitor C2, the second terminal of the resistor R6, and the emitter of the triode QI are all grounded. Abase of the triode QI is connected to a first terminal of the resistor R7. A second terminal of the resistor R7 is connected to the current-limiting unit and the monitoring unit. By adopting the above technical solution, in the PWM compensation unit, with the design of the resistor R7, when the adjusted battery charging current Icharge is still greater than the charging current-limiting protection value Imax, the triode QI is turned on, and further, in combination with the design of the resistor R5, the resistor R6, and the capacitor C2, the voltage value at the inverting input terminal of the comparator U2 can be adjusted to achieve fine adjustment of the PWM signal output by the comparator U2. That is, the current-limiting unit further performs fine adjustment on the battery charging current Lharge to reduce the battery charging current Lharge to the preset charging current-limiting protection value Imax. In one specific embodiment, the current-limiting unit includes an MOS transistor QC2, a diode DI, and an inductor LI. Agate of the MOS transistor QC2 is connected to the drive enhancement unit. A source of the MOS transistor QC2 is separately connected to the monitoring unit and the PWM compensation unit. A drain of the MOS transistor QC2 is connected to a first terminal of the inductor LI and a positive electrode of the diode DI. A second terminal of the inductor LI is separately connected to the second terminal of the resistor R9 and the external negative electrode input terminal. A negative electrode of the diode DI is separately connected to the battery positive electrode B+ and the external positive electrode input terminal. By adopting the above technical solution, in the current-limiting unit, the battery charging current is gradually reduced through the MOS transistor QC2, and a sudden change of the battery charging current is prevented through the inductor LI, thereby improving the stability of the circuit. A reverse flow of the current is prevented through the diode DI, thus further ensuring the stability of the circuit. In one specific embodiment, the comparator UI comprises a high output threshold VI and a low output threshold V2; VI = VCC1 x Rb / [Ra x Rc / (Ra + Rc) + Rb], and V2 = VCC1 x Rd / (Rd + Ra), where Ra is the resistance value of the resistor RI, Rb is the resistance value of the resistor R2, Rc is the sum of the resistance values of the resistor R3 and the resistor RIO, and Rd is the resistance value of the parallel combination of the resistor R2 and the resistor R3. In one specific embodiment, when the triode QI is in a cut-off state, the magnitude of the voltage signal output by the PWM compensation unit is Vref2, and Vref2 = VCC2 x Rf / (Re + Rf), where Re is the resistance value of the resistor R5, and Rf is the resistance value of the resistor R6. In one specific embodiment, 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 resistance of the resistor R4 and the capacitance of the capacitor Cl in the PWM control unit. In one specific embodiment, the magnitude of the voltage signal output by the PWM compensation unit to the PWM control unit is changed by changing the resistances of the resistor R5 and the resistor R6 in the PWM compensation unit. In summary, the technical solutions of the present application at least include the following beneficial technical effects. 1. On one hand, by sampling the battery charging current and quickly switching to a current-limiting protection mode in response to the determination of a high battery charging current, the current-limiting unit performs primary current-limiting control and adjustment on the battery charging current in time, thereby reducing the charging current; on the other hand, due to an error in the circuit system, the primary adjustment of the charging current may be insufficient, so a secondary adjustment is performed, that is, the adjusted battery charging current is acquired in real time, and the PWM control signal for controlling the current-limiting unit is subjected to frequency compensation to further reduce the charging current, thereby achieving high-precision control and adjustment of the battery charging current, avoiding the problems of overheat, short service lives, and reduced performance of the battery, as well as great impact on the system, and unstable operation that are caused by long-term charging at a high current, and ensuring the safety of continuous lithium battery charging. In addition, the current-limiting protection circuit of the present application is achieved by means of hardware and possesses the advantages of a simple circuit structure, quick response, reliable action, and high control efficiency. BRIEF DESCRIPTION OF THE DRAWINGS FIG. lisa structural schematic of a current-limiting protection circuit according to one example of the present application; and FIG. 2 is a detailed circuit diagram of a current-limiting protection circuit according to one example of the present application. Description of reference numerals: 1, current sampling and determining unit; 2, PWM control unit; 3, current-limiting unit; 4, monitoring unit; 5, PWM compensation unit; 6, drive enhancement unit; 7, positive electrode charging line; 8, negative electrode charging line. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To make the objectives, technical solutions, and advantages of the present application clearer, embodiments of the present application will be described in further detail with reference to the drawings. The present application discloses a current-limiting protection circuit for continuous lithium battery charging. Referring to FIG. 1, the current-limiting protection circuit includes a current sampling and determining unit 1, a PWM control unit 2, a currentlimiting unit 3, a monitoring unit 4, and a PWM compensation unit 5. The PWM control unit 2 is separately connected to the current sampling and determining unit 1 and the current-limiting unit 3. The monitoring unit 4 is separately connected to the currentlimiting unit 3 and the PWM compensation unit 5. The PWM compensation unit 5 is further connected to the PWM control unit 2. The current sampling and determining unit 1 is configured to sample a battery charging current Lharge, and output a current-limiting control signal to the PWM control unit 2 according to the determination of the magnitude of the battery charging current Icharge. The PWM control unit 2 is configured to generate a first PWM control signal according to the current-limiting control signal and a voltage signal output by the PWM compensation unit 5, and output the first PWM control signal to the current-limiting unit 3. The current-limiting unit 3 is configured to adjust the battery charging current Icharge according to the first PWM control signal, so as to reduce the battery charging current Icharge to a preset charging current-limiting protection value Imax. The monitoring unit 4 is configured to acquire the battery charging current Icharge adjusted by the current-limiting unit 3, and output the adjusted battery charging current Icharge to the PWM compensation unit 5. The PWM compensation unit 5 is configured to adjust the magnitude of the voltage signal output to the PWM control unit 2 according to the adjusted battery charging current Lharge. The PWM control unit 2 is further configured to change a duty cycle of the first PWM control signal according to the voltage signal after the magnitude adjustment, generate a second PWM control signal, and output the second PWM control signal to the currentlimiting unit 3. The current-limiting unit 3 is further configured to further adjust the battery charging current Lharge according to the second PWM control signal, such that the battery charging current Lharge is reduced to the preset charging current-limiting protection value Imax. Therefore, according to the current-limiting protection circuit of the present application, on one hand, by sampling the battery charging current and quickly switching to a current-limiting protection mode in response to the determination of a high battery charging current, the current-limiting unit performs primary current-limiting control and adjustment on the battery charging current in time, thereby reducing the charging current; on the other hand, due to an error in the circuit system, the primary adjustment of the charging current may be insufficient, so a secondary adjustment is performed, that is, the adjusted battery charging current is acquired in real time, and the PWM control signal for controlling the current-limiting unit is subjected to frequency compensation to further reduce the charging current, thereby achieving high-precision control and adjustment of the battery charging current, avoiding the problems of overheat, short service lives, and reduced performance of the battery, as well as great impact on the system, and unstable operation that are caused by long-term charging at a high current, and ensuring the safety of continuous lithium battery charging. In addition, the current-limiting protection circuit of the present application is achieved by means of hardware and possesses the advantages of a simple circuit structure, quick response, reliable action, and high control efficiency. Furthermore, still referring to FIG. 1, the current-limiting protection circuit further includes a drive enhancement unit 6. The drive enhancement unit 6 is separately connected to the PWM control unit 2 and the current-limiting unit 3. The drive enhancement unit 6 is configured to receive the first PWM control signal output by the PWM control unit 2, enhance a drive capability of the first PWM control signal, and output the first PWM control signal with the enhanced drive capability to the current-limiting unit 3. The current-limiting unit 3 is configured to adjust the battery charging current Lharge according to the first PWM control signal with the enhanced drive capability, so as to reduce the battery charging current Icharge to a preset charging current-limiting protection value Imax. And / or, the drive enhancement unit 6 is further configured to receive the second PWM control signal output by the PWM control unit 2, enhance a drive capability of the second PWM control signal, and output the second PWM control signal with the enhanced drive capability to the current-limiting unit 3. The current-limiting unit 3 is further configured to further adjust the battery charging current Icharge according to the second PWM control signal with the enhanced drive capability, so as to reduce the battery charging current Icharge to a preset charging current-limiting protection value Imax. The drive enhancement unit 6 may amplify the first PWM control signal to enhance the drive capability of the first PWM control signal, or may amplify the second PWM control signal to enhance the drive capability of the second PWM control signal. Therefore, the drive enhancement unit improves the drive capabilities of the first PWM control signal and the second PWM control signal output by the PWM control unit, thereby improving the dynamic anti-interference capability and the response speed of the system. Furthermore, the drive enhancement unit may adopt a push-pull drive circuit. FIG. 2 is an implementation of a current-limiting protection circuit for continuous lithium battery charging according to the present application, which is described in detail below with reference to FIG. 2. Referring to FIG. 2, shown is an implementation of a current-limiting protection circuit for continuous lithium battery charging. The current-limiting protection circuit is separately connected to the lithium battery and an external access terminal. The lithium battery includes a battery positive electrode B+ of the lithium battery and a battery negative electrode B- of the lithium battery. The external access terminal includes an external positive electrode input terminal P+ / C+ and an external negative electrode input terminal P- / C-. Specifically, the current-limiting protection circuit is connected to the battery positive electrode B+ of the lithium battery, the battery negative electrode B- of the lithium battery, the external positive electrode input terminal P+ / C+, and the external negative electrode input terminal P- / C-. The battery positive electrode B+ is connected to the external positive electrode input terminal P+ / C+ via a positive electrode charging line 7, and the battery negative electrode B- is connected to the external negative electrode input terminal P- / C- via a negative electrode charging line 8. An MOS transistor QC1 and an MOS transistor QD1 are connected in series between the battery negative electrode B- and the external negative electrode input terminal P- / C-. The MOS transistor QC1 is a charging MOS transistor, the MOS transistor QD1 is a discharging MOS transistor, and the MOS transistor QC1 and the MOS transistor QD1 are configured to control the charging and discharging of the lithium battery. The external positive electrode input terminal P+ / C+ and the external negative electrode input terminal P- / C- may be connected to a load, or may serve as charging input terminals for electricity input. When the lithium battery is in a discharging state, the external positive electrode input terminal P+ / C+ and the external negative electrode input terminal P- / C- are connected to the load, and in this case, a current is output from the battery positive electrode B+ of the lithium battery to the load through the positive electrode charging line 7 and the external positive electrode input terminal P+ / C+, and is then returned to the battery negative electrode B- of the lithium battery from the external negative electrode input terminal P- / C- through the negative electrode charging line 8, such that the lithium battery supplies power to the load. When the lithium battery is in a charging state, the external positive electrode input terminal P+ / C+ and the external negative electrode input terminal P- / C- can be connected to a charger, and in this case, a current is output to the lithium battery through the charger, the external positive electrode input terminal P+ / C+, the positive electrode charging line 7, and the battery positive electrode B+ of the lithium battery in sequence, and is then returned to the charger from the battery negative electrode B- of the lithium battery through the negative electrode charging line 8 and the external negative electrode input terminal P- / C-. Specifically, referring to FIG. 2, the current sampling and determining unit 1 includes a resistor R9, an operational amplifier U3, a comparator U4, and a triode Q4. The elements are connected in the following manner: The resistor R9 is connected in series in the negative electrode charging line 8. A first terminal of the resistor R9 is separately connected to a battery negative electrode B- of the lithium battery and a non-inverting input terminal of the operational amplifier U3, and a second terminal of the resistor R9 is separately connected to an external negative electrode input terminal and an inverting input terminal of the operational amplifier U3. An output terminal of the operational amplifier U3 is connected to an inverting input terminal of the comparator U4. A non-inverting input terminal of the comparator U4 is configured with a first reference voltage Vrefi. An output terminal of the comparator U4 is connected to a base of the triode Q4. An emitter of the triode Q4 is grounded. A collector of the triode Q4 is connected to the PWM control unit 2. Furthermore, the current sampling and determining unit 1 may further include a filter circuit consisting of a resistor RI 1, a resistor RI2, and a capacitor C3. The first terminal of the resistor R9 is separately connected to the battery negative electrode B- of the lithium battery and a first terminal of the resistor Rll, and the second terminal of the resistor R9 is separately connected to the external negative electrode input terminal P- / C- and a first terminal of the resistor R12. A second terminal of the resistor Rll is separately connected to a first terminal of the capacitor C3 and the non-inverting input terminal of the operational amplifier U3. A second terminal of the resistor R12 is separately connected to a second terminal of the capacitor C3 and the inverting input terminal of the operational amplifier U3. Still referring to FIG. 2, the PWM control unit 2 includes a comparator U1, a resistor RI, a resistor R2, a resistor R3, a resistor R4, a resistor RIO, a capacitor Cl, and a comparator U2. The elements are connected in the following manner: A first terminal of the resistor RI and a first terminal of the resistor RIO are separately connected to a power supply voltage VCC1. A second terminal of the resistor RI is separately connected to a first terminal of the resistor R2, a non-inverting input terminal of the comparator UI, and a first terminal of the resistor R3. A second terminal of the resistor R2 is connected to a first terminal of the capacitor Cl, and the second terminal of the resistor R2 and the first terminal of the capacitor C1 are both grounded. A second terminal of the capacitor Cl is separately connected to an inverting input terminal of the comparator UI and a first terminal of the resistor R4. A second terminal of the resistor R4 is separately connected to an output terminal of the comparator UI, a second terminal of the resistor R3, a second terminal of the resistor RIO, a non-inverting input terminal of the comparator U2, and the current sampling and determining unit 1. Specifically, the second terminal of the resistor R4 is connected to the collector of the triode Q4 in the current sampling and determining unit 1. An inverting input terminal of the comparator U2 is connected to the PWM compensation unit 5, and an output terminal of the comparator U2 is connected to the drive enhancement unit 6. Still referring to FIG. 2, the drive enhancement unit 6 includes a triode Q2 and a triode Q3. The elements are connected in the following manner: A collector of the triode Q2 is connected to a power supply voltage VDD. Abase of the triode Q2 is separately connected to a base of the triode Q3 and the output terminal of the comparator U2. An emitter of the triode Q2 is separately connected to an emitter of the triode Q3 and the current-limiting unit 3. A collector of the triode Q3 is separately connected to the monitoring unit 4, a source of the MOS transistor QC1, and a source of the MOS transistor QD1. Still referring to FIG. 2, the current-limiting unit 3 includes a MOS transistor QC2, a diode DI, and an inductor LI. The elements are connected in the following manner: A gate of the MOS transistor QC2 is connected to the drive enhancement unit 6. Specifically, the gate of the MOS transistor QC2 is separately connected to the emitter of the triode Q2 and the emitter of the triode Q3. A source of the MOS transistor QC2 is separately connected to the monitoring unit 4 and the PWM compensation unit 5. A drain of the MOS transistor QC2 is connected to a first terminal of the inductor LI and a positive electrode of the diode DI. A second terminal of the inductor LI is separately connected to the second terminal of the resistor R9 and the external negative electrode input terminal P- / C-. Specifically, the second terminal of the inductor LI is connected to the external negative electrode input terminal P- / C- through the MOS transistor QC1 and the MOS transistor QD1. A negative electrode of the diode DI is separately connected to the battery positive electrode B+ and the external positive electrode input terminal P+ / C-. Still referring to FIG. 2, the monitoring unit 4 includes a resistor R8. A first terminal of the resistor R8 is separately connected to the source of the MOS transistor QC2 and the PWM compensation unit 5, and a second terminal of the resistor R8 is separately connected to the collector of the triode Q3, the source of the MOS transistor QC1, and the source of the MOS transistor QD1. Still referring to FIG. 2, the PWM compensation unit 5 includes a resistor R5, a resistor R6, a resistor R7, a triode QI, and a capacitor C2. The elements are connected in the following manner: A first terminal of the resistor R5 is connected to a power supply voltage VCC2. A second terminal of the resistor R5 is separately connected to the inverting input terminal of the comparator U2, a first terminal of the capacitor C2, a first terminal of the resistor R6, and a collector of the triode QI. A second terminal of the capacitor C2 is separately connected to a second terminal of the resistor R6 and an emitter of the triode QI, and the second terminal of the capacitor C2, the second terminal of the resistor R6, and the emitter of the triode QI are all grounded. Abase of the triode QI is connected to a first terminal of the resistor R7. A second terminal of the resistor R7 is connected to the current-limiting unit 3 and the monitoring unit 4. Specifically, the second terminal of the resistor R7 is connected to the source of the MOS transistor QC2 and the first terminal of the resistor R8. Still referring to FIG. 2, a drain of the MOS transistor QC1 is separately connected to the second terminal of the inductor LI and the second terminal of the resistor R9. The source of the MOS transistor QC1 is separately connected to the second terminal of the resistor R8, the collector of the triode Q3, and the source of the MOS transistor QD1. A gate of the MOS transistor QC1 may be connected to a control chip, and the control chip controls the ON / OFF state of the MOS transistor QC1. A drain of the MOS transistor QD1 is connected to the external negative electrode input terminal P- / C-. A gate of the MOS transistor QD1 may be connected to a control chip, and the control chip controls the ON / OFF state of the MOS transistor QD1. With reference to FIG. 2, a control process of the current-limiting protection circuit for continuous lithium battery charging is described in detail below. The resistor R9 is a current detection resistor. The operational amplifier U3 acquires the battery charging current Lharge by detecting the current flowing through the resistor R9 and reflects the battery charging current Lharge in the form of a voltage. The resistor RI 1, the resistor RI2, and the capacitor C3 form a filter circuit, which is configured to filter signals that are input to the non-inverting input terminal and the inverting input terminal of the operational amplifier U3. Therefore, the operational amplifier U3 generates a corresponding voltage value according to the current flowing through the resistor R9, and outputs the voltage value to the inverting input terminal of the comparator U4. The charging current-limiting protection value Imax may be preset by those skilled in the art according to actual situations, and the first reference voltage Vrefi configured at the non-inverting input terminal of the comparator U4 may be set according to the preset charging current-limiting protection value Imax, such that when the battery charging current kharge is less than the charging current-limiting protection value Imax, the voltage value at the inverting input terminal of the comparator U4 is less than the voltage value at the non-inverting input terminal of the comparator U4, and the comparator U4 outputs a high level. In this case, the triode Q4 is turned on, such that the voltage value at the non-inverting input terminal of the comparator U2 in the PWM control unit 2 is less than the voltage value at the inverting input terminal of the comparator U2, and the comparator U2 outputs a low level, that is, the PWM control unit 2 outputs a low level, such that the MOS transistor QC2 remains turned off, and in this case, the current-limiting unit 3 does not perform the current-limiting control operation. When the battery charging current Lharge is equal to the charging currentlimiting protection value Imax, 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 transistor QC2 still remains turned off, and the currentlimiting unit 3 does not perform the current-limiting control operation. When the battery charging current Uharge is greater than the charging current-limiting protection value Imax, the voltage value at the inverting input terminal of the comparator U4 is greater than the voltage value at the non-inverting input terminal of the comparator U4, and the comparator U4 outputs a low level. In this case, the triode Q4 is turned off, and the voltage value at the non-inverting input terminal of the comparator U2 in the PWM control unit 2 is determined by the output terminal of the comparator UI. The process of the PWM control unit 2 generating and outputting the first PWM control signal is described in detail below. In the PWM control unit 2, by designing the resistance values of the resistor RI, the resistor R2, the resistor R3, and the resistor RIO, a high output threshold VI and a low output threshold V2 of the comparator UI can be obtained according to two states of the high level and the low level output by the comparator UI; that is, when the comparator UI outputs the high level, the voltage value at the non-inverting input terminal of the comparator UI is VI, and when the comparator U1 outputs the low level, the voltage value at the non-inverting input terminal of the comparator UI is V2. In particular, the high output threshold VI of the non-inverting input terminal of the comparator UI satisfies that VI = VCC1 x Rb / [Ra x Rc / (Ra + Rc) + Rb], and the low output threshold V2 of the non-inverting input terminal of the comparator UI satisfies that V2 = VCC1 x Rd / (Rd + Ra), where Ra is the resistance value of the resistor RI, Rb is the resistance value of the resistor R2, Rc is the sum of the resistance values of the resistor R3 and the resistor RIO, and Rd is the resistance value of the parallel combination of the resistor R2 and the resistor R3. Specifically, according to the circuit design in the PWM control unit 2, the output terminal of the comparator U1 may output a triangular wave. The specific process is as follows: When the comparator UI outputs a high level, the voltage value at the non-inverting input terminal of the comparator UI is VI, and at the same time, the power supply voltage VCC1 charges the capacitor Cl through the resistor RIO and the resistor R4, such that the voltage value at the inverting input terminal of the comparator UI continuously increases from 0 V, and when the voltage value at the inverting input terminal of the comparator UI increases to a voltage greater than the voltage value VI at the non-inverting input terminal, the comparator UI outputs a low level. When the comparator U1 outputs a low level, the voltage value at the non-inverting input terminal of the comparator UI is V2, and the capacitor Cl discharges to the ground through the resistor R4, and when the voltage on the capacitor Cl drops from VI to a voltage lower than V2, the comparator outputs a high level again. According to the above process, the continuous charging and discharging process of the capacitor Cl allows the output terminal of the comparator UI to output a triangular wave. Therefore, a voltage waveform at the non-inverting input terminal of the comparator U2 is a voltage waveform at the output terminal of the comparator UI. In this case, the inverting input terminal of the comparator U2 is connected to the PWM compensation unit 5. Initially, when QC2 is in a cut-off state, the triode QI is not turned on, the triode QI is in a cut-off state, and the voltage value at the output terminal of the PWM compensation unit 5 is Vref2; that is, the magnitude of the voltage signal output by the PWM compensation unit 5 to the PWM control unit 2 is Vref2, and the voltage value at the inverting input terminal of the comparator U2 is also Vref2, and Vref2 = VCC2 X Rf / (Re + Rf), where Re is the resistance value of the resistor R5, and Rf is the resistance value of the resistor R6. Therefore, when the voltage value at the noninverting input terminal of the comparator U2 is higher than the voltage value Vref2 at the inverting input terminal of the comparator U2, the comparator U2 outputs a high level; when the voltage value at the non-inverting input terminal of the comparator U2 is lower than the voltage value Vref2 at the inverting input terminal of the comparator U2, 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 drive enhancement unit 6 enhances the drive capability of the first PWM control signal, the first PWM control signal is output to the current-limiting unit 3, such that the battery charging current Icharge is adjusted by turning on and off the MOS transistor QC2 in the current-limiting unit 3, and the battery charging current Icharge is reduced to the preset charging current-limiting protection value Imax. Furthermore, the first PWM control signal is a square wave signal. Therefore, it can be learned that, in the current sampling and determining unit 1, the comparator U3 acquires the magnitude of the battery charging current at present and outputs a corresponding comparison result, and then the comparator U4 controls, according to the comparison result output by the comparator U3 and the preset reference voltage, the triode Q4 to be turned on and the PWM control unit 2 not to output a PWM control signal when the battery charging current Icharge is not greater than the charging current-limiting protection value Imax, and controls the triode Q4 to be turned off when the battery charging current Icharge is greater than the charging currentlimiting protection value Imax, such that the PWM control unit 2 starts to output a PWM control signal. In the PWM control unit 2, when the battery charging current Icharge is greater than the charging current-limiting protection value Imax, a triangular wave signal is generated by the comparator U1 and related elements, and then a corresponding PWM control signal is generated by the comparator U2 in combination with the voltage signal output by the PWM compensation unit 5, such that the current-limiting unit 3 reduces the charging current. That the drive enhancement unit 6 enhances the drive capability of the first PWM control signal is described in detail below: When the first PWM control signal is at a high level, the triode Q2 is turned on, and the triode Q3 is turned off, and in this case, a current is output from the VDD, and a high current is injected into the current-limiting unit 3 through the triode Q2. When the first PWM control signal is at a low level, the triode Q2 is turned off, and the triode Q3 is turned on, and in this case, a high current is drawn from the current-limiting unit 3 through the triode Q3. As such, in one complete period of the first PWM control signal, the triode Q2 and the triode Q3 work alternately, thereby enhancing the drive capability of the first PWM control signal. The process of the current-limiting unit 3 adjusting the battery charging current Icharge to reduce the battery charging current Lharge is described in detail below: When the MOS transistor QC2 is in a turned-on state, a current is output to the lithium battery from the charger, the external positive electrode input terminal P+ / C+, the positive electrode charging line 7, and the battery positive electrode B+ of the lithium battery, and is then returned to the charger from the battery negative electrode B- of the lithium battery through the resistor R9, the inductor LI, the MOS transistor QC2, the resistor R8, the MOS transistor QD1, and the external negative electrode input terminal P- / C-, such that the battery charging current Icharge is gradually reduced. Furthermore, when the MOS transistor QC2 is in a cut-off state, the inductor LI can also transmit the stored energy to the battery positive electrode B+ through the diode DI to charge the lithium battery, thereby improving the operating efficiency of the system. Therefore, it can be learned that, in the current-limiting unit 3, the battery charging current is gradually reduced through the MOS transistor QC2, and a sudden change of the battery charging current is prevented through the inductor LI, thereby improving the stability of the circuit. A reverse flow of the current is prevented through the diode DI, thus further ensuring the stability of the circuit. That the monitoring unit 4 acquires the adjusted battery charging current Lharge and the PWM compensation unit 5 adjusts the magnitude of the voltage signal output to the PWM control unit 2 according to the adjusted battery charging current Lharge is described in detail below: When the current-limiting MOS transistor QC2 is in a tumed-on state, a current flows through the resistor R8 in the monitoring unit 4, and the value of the current flowing through the resistor R8 is the value of the battery charging current Lharge at present. Therefore, the PWM compensation unit 5 can acquire the value of the adjusted battery charging current Lharge according to the magnitude of the current flowing through the resistor R8, and when the value of the adjusted battery charging current Lharge is greater than the charging current-limiting protection value Imax, adjust the magnitude of the voltage value Vref2 output to the inverting input terminal of the comparator U2 to change a duty cycle of the first PWM control signal output by the comparator U2, i.e., to change the duty cycle of the first PWM control signal output by the PWM control unit 2, such that the PWM control unit 2 generates the second PWM control signal and outputs the second PWM control signal to the current-limiting unit 3 after the drive enhancement unit 6 enhances the drive capability of the second PWM control signal, thereby allowing the current-limiting unit 3 to further adjust the battery charging current Icharge and reducing the battery charging current Icharge to the preset charging current-limiting protection value Imax. For the process of the drive enhancement unit 6 enhancing the drive capability of the second PWM control signal, reference is made to the related descriptions of the process of the drive enhancement unit 6 enhancing the drive capability of the first PWM control signal, which will not be recited herein. When the value of the adjusted battery charging current Icharge is greater than the charging current-limiting protection value Imax, the PWM compensation unit 5 adjusts the magnitude of the voltage value Vref2 output to the inverting input terminal of the comparator U2, i.e., adjusts the magnitude of the voltage signal output to the PWM control unit 2, which is specifically as follows: When the adjusted battery charging current Icharge is greater than the charging currentlimiting protection value Imax, the voltage across the resistor R8 may cause the triode QI to be turned on and work in an amplification region, and in this case, the capacitor C2 slowly discharges, such that the voltage value Vref2 at the inverting input terminal of the comparator U2 is reduced, and the duty cycle of the first PWM control signal output by the comparator U2 is reduced, thereby driving the MOS transistor QC2 to be turned on or off, further reducing the battery charging current Icharge, and stabilizing the battery charging current Icharge to be within the charging current-limiting protection value Imax. Therefore, it can be learned that, in the PWM compensation unit 5, with the design of the resistor R7, when the adjusted battery charging current Icharge is still greater than the charging current-limiting protection value Imax, the triode QI is turned on, and further, in combination with the design of the resistor R5, the resistor R6, and the capacitor C2, the voltage value at the inverting input terminal of the comparator U2 can be adjusted to achieve fine adjustment of the PWM signal output by the comparator U2. That is, the current-limiting unit 3 further performs fine adjustment on the battery charging current Icharge to reduce the battery charging current Icharge to the preset charging currentlimiting protection value Imax. In particular, in the PWM control unit 2, the charging and discharging time of the capacitor C1 can also be changed by changing the resistance of the resistor R4 and the capacitance of the capacitor Cl, and then the frequencies of the first PWM control signal and the second PWM control signal output by the PWM control unit 2 can be adjusted. Therefore, those skilled in the art can adjust the frequency of the first PWM control signal and the frequency of the second PWM control signal by changing the resistances or capacitances of the relevant resistors and capacitors in the PWM control unit 2 according to actual needs, such that the control of the battery charging current Icharge by the current-limiting unit 3 is more accurate. In particular, in the PWM compensation unit 5, the magnitude of the voltage value Vref2 at the output terminal of the PWM compensation unit 5 may also be changed by changing the resistances of the resistor R5 and the resistor R6, thereby adjusting the magnitude of the voltage signal output by the PWM compensation unit 5 to the PWM control unit 2. Therefore, those skilled in the art can 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 resistances of the relevant resistors in the PWM compensation unit 5, such that the control of the battery charging current Icharge by the current-limiting unit 3 is more accurate. The above are only preferred examples of the present application, and are not intended to limit the protection scope of the present application. Therefore, any equivalent variation made on the basis of the structures, shapes, and principles of the present application shall fall within the protection scope of the present application.

Claims

1. A current-limiting protection circuit for continuous lithium battery charging, comprising a current sampling and determining unit (1), a PWM control unit (2), a current-limiting unit (3), a monitoring unit (4), and a PWM compensation unit (5), whereinthe current sampling and determining unit (1) is configured to sample a battery charging current Lharge, and output a current-limiting control signal to the PWM control unit (2) according to the determination of the magnitude of the battery charging current Lharge Jthe PWM control unit (2) is configured to generate a first PWM control signal according to the current-limiting control signal and a voltage signal output by the PWM compensation unit (5), and output the first PWM control signal to the current-limiting unit (3);the current-limiting unit (3) is configured to adjust the battery charging current Lharge according to the first PWM control signal, to reduce the battery charging current Lharge to a preset charging current-limiting protection value Imax;the monitoring unit (4) is configured to acquire the battery charging current Lharge adjusted by the current-limiting unit (3), and output the adjusted battery charging current Lharge to the PWM compensation unit (5);the PWM compensation unit (5) is configured to adjust the magnitude of the voltage signal output to the PWM control unit (2) according to the adjusted battery charging current Icharge,the PWM control unit (2) is further configured to change a duty cycle of the first PWM control signal according to the voltage signal after the magnitude 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 configured to further adjust the battery charging current Lharge according to the second PWM control signal, such that the battery charging current Lharge is reduced to the preset charging current-limiting protection value Imax;the current sampling and determining unit (1) comprises a resistor R9, an operational amplifier U3, a comparator U4, and a triode Q4; a first terminal of the resistor R9 is separately connected to a battery negative electrode B- of the lithium battery and a non-inverting input terminal of the operational amplifier U3; a second terminal of the resistor R9 is separately connected to an external negative electrode input terminal and an inverting input terminal of the operational amplifier U3; an output terminal of the operational amplifier U3 is connected to an inverting input terminal of the comparator U4; a non-inverting input terminal of the comparator U4 is configured with a first reference voltage Vrefi; an output terminal of the comparator U4 is connected to a base of the triode Q4; an emitter of the triode Q4 is grounded; a collector of the triode Q4 is connected to the PWM control unit (2).

2. The current-limiting protection circuit for continuous lithium battery charging according to claim 1, further comprising a drive enhancement unit (6), wherein the drive enhancement unit (6) is separately connected to the PWM control unit (2) and the current-limiting unit (3);the drive enhancement unit (6) is configured to receive the first PWM control signal output by the PWM control unit (2), enhance a drive capability of the first PWM control signal, and output the first PWM control signal with the enhanced drive capability to the current-limiting unit (3);the current-limiting unit (3) is configured to adjust the battery charging current Icharge according to the first PWM control signal with the enhanced drive capability, to reduce the battery charging current Icharge to a preset charging current-limiting protection value Imax;and / or, the drive enhancement unit (6) is configured to receive the second PWM control signal output by the PWM control unit (2), enhance a drive capability of the second PWM control signal, and output the second PWM control signal with the enhanced drive capability to the current-limiting unit (3);the current-limiting unit (3) is configured to further adjust the battery charging current Icharge according to the second PWM control signal with the enhanced drive capability, to reduce the battery charging current Icharge to a preset charging currentlimiting protection value Imax.

3. The current-limiting protection circuit for continuous lithium battery charging according to claim 2, wherein the PWM control unit (2) comprises a comparator UI, a resistor RI, a resistor R2, a resistor R3, a resistor R4, a resistor RIO, a capacitor Cl, and a comparator U2;a first terminal of the resistor RI and a first terminal of the resistor RIO are separately connected to a power supply voltage VCC1; a second terminal of the resistor RI is separately connected to a first terminal of the resistor R2, a non-inverting input terminal of the comparator UI, and a first terminal of the resistor R3; a second terminal of the resistor R2 is connected to a first terminal of the capacitor Cl, and the second terminal of the resistor R2 and the first terminal of the capacitor C1 are both grounded; a second terminal of the capacitor Cl is separately connected to an inverting input terminal of the comparator UI and a first terminal of the resistor R4; a second terminal of the resistor R4 is separately connected to an output terminal of the comparator UI, a second terminal of the resistor R3, a second terminal of the resistor RIO, a noninverting input terminal of the comparator U2, and the current sampling and determining unit (1); an inverting input terminal of the comparator U2 is connected to the PWM compensation unit (5), and an output terminal of the comparator U2 is connected to the drive enhancement unit (6).

4. The current-limiting protection circuit for continuous lithium battery charging according to claim 1, wherein the current-limiting protection circuit is connected to a battery positive electrode B+ of the lithium battery, the battery negative electrode B- of the lithium battery, an external positive electrode input terminal, and the external negative electrode input terminal; the external positive electrode input terminal and the external negative electrode input terminal are configured to input electricity as charging input terminals.

5. The current-limiting protection circuit for continuous lithium battery charging according to claim 3, wherein the PWM compensation unit (5) comprises a resistor R5, a resistor R6, a resistor R7, a triode QI, and a capacitor C2;a first terminal of the resistor R5 is connected to a power supply voltage VCC2; asecond terminal of the resistor R5 is separately connected to the inverting input terminal of the comparator U2, a first terminal of the capacitor C2, a first terminal of the resistor R6, and a collector of the triode QI; a second terminal of the capacitor C2 is separately connected to a second terminal of the resistor R6 and an emitter of the triode QI, and the second terminal of the capacitor C2, the second terminal of the resistor R6, and the emitter of the triode QI are all grounded; a base of the triode QI is connected to a first terminal of the resistor R7; and a second terminal of the resistor R7 is connected to the current-limiting unit (3) and the monitoring unit (4).

6. The current-limiting protection circuit for continuous lithium battery charging according to claim 3, wherein the current-limiting unit (3) comprises an MOS transistor QC2, a diode DI, and an inductor LI;a gate of the MOS transistor QC2 is connected to the drive enhancement unit (6); a source of the MOS transistor QC2 is separately connected to the monitoring unit (4) and the PWM compensation unit (5); a drain of the MOS transistor QC2 is connected to a first terminal of the inductor LI and a positive electrode of the diode DI; a second terminal of the inductor LI is separately connected to the second terminal of the resistor R9 and the external negative electrode input terminal; a negative electrode of the diode DI is separately connected to the battery positive electrode B+ and the external positive electrode input terminal.

7. The current-limiting protection circuit for continuous lithium battery charging according to claim 6, wherein the comparator UI comprises a high output threshold VI and a low output threshold V2; VI = VCC1 x Rb / [Ra x Rc / (Ra + Rc) + Rb], and V2 = VCC1 x Rd / (Rd + Ra), wherein Ra is a resistance value of the resistor RI, Rb is a resistance value of the resistor R2, Rc is a sum of the resistance values of the resistor R3 and the resistor RIO, and Rd is a resistance value of parallel combination of the resistor R2 and the resistor R3.

8. The current-limiting protection circuit for continuous lithium battery charging according to claim 5, wherein when the triode QI is in a cut-off state, the magnitude of the voltage signal output by the PWM compensation unit (5) is Vref2, and Vref2 = VCC2 x Rf / (Re + Rf), wherein Re is a resistance value of the resistor R5, and Rf is aresistance value of the resistor R6.

9. The current-limiting protection circuit for continuous lithium battery charging according to claim 3, wherein the frequencies of the first PWM control signal and the second PWM control signal output by the PWM control unit (2) are adjusted by changing a resistance of the resistor R4 and the capacitance of the capacitor Cl in the PWM control unit (2).

10. The current-limiting protection circuit for continuous lithium battery charging according to claim 5, wherein the magnitude of the voltage signal output by the PWM compensation unit (5) to the PWM control unit (2) is adjusted by changing the resistances of the resistor R5 and the resistor R6 in the PWM compensation unit (5).

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