Battery charging current adjustable control circuit and control method

Abstract

The invention discloses a battery charging current adjustable control circuit and a control method, and relates to the technical field of power supply control, the battery charging current adjustable control circuit comprises a charging circuit and a control circuit, the charging circuit comprises a BUCK power supply chip and a battery connected with the BUCK power supply chip, a feedback pin of the BUCK power supply chip is connected in series with a second resistor and then is connected with an output end of the charging circuit, and the control circuit is connected with the BUCK power supply chip. One end of the second resistor is connected in series with the first resistor and then grounded; the control circuit comprises a single chip microcomputer, the output end of the single chip microcomputer is connected with a fourth resistor and a third resistor in series and then is connected with a feedback pin of the BUCK power supply chip, one end of the third resistor is connected with a first capacitor in series and then is grounded, and a second capacitor is connected between the fourth resistor and the third resistor in series and then is grounded. Therefore, the charging voltage of the battery is adjustable, the charging current can be dynamically adjusted, the charging current is stabilized at a constant value, and the use safety is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply control, and in particular to a battery charging current adjustable control circuit and a control method. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] In the field of communication base station backup power, battery charging technology faces severe challenges. The backup power system usually needs to provide continuous and stable power support for long-term base station operation and maintenance, especially in the event of a city power outage or other power outage. In order to meet this high reliability requirement, the backup battery capacity of the communication base station is usually large and has high requirements for the battery charging current.

[0004] Many backup batteries have large capacities. Ordinary BUCK power chips can only set a fixed output voltage through resistor voltage division, and cannot achieve continuous adjustment. If the output voltage is too high and the battery voltage is too low, a very large current will be generated, bringing uncontrollable dangers and even causing loss of life and property. In addition, the reverse current problem is also one of the common faults in the battery charging process. Especially when the city power is out, the reverse current flowing into the battery may damage the battery and cause potential safety hazards. Summary of the invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a battery charging current adjustable control circuit and control method, so that the battery charging voltage can be adjusted, and then the charging current can be dynamically adjusted to stabilize the charging current at a constant value to ensure safe use.

[0006] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0007] In a first aspect, the present invention provides a battery charging current adjustable control circuit, comprising a charging circuit and a control circuit, wherein the charging circuit comprises a BUCK power chip and a battery connected to the BUCK power chip, wherein a feedback pin of the BUCK power chip is connected in series with a second resistor and then connected to an output end of the charging circuit, and one end of the second resistor is connected in series with a first resistor and then grounded; the control circuit comprises a single-chip microcomputer, wherein an output end of the single-chip microcomputer is connected in series with a fourth resistor and a third resistor and then connected to a feedback pin of the BUCK power chip, one end of the third resistor is connected in series with a first capacitor and then grounded, and a second capacitor is connected in series between the fourth resistor and the third resistor and then grounded.

[0008] A further technical solution is that the charging circuit includes a BUCK power chip, a first MOS tube, a second MOS tube, a first inductor, a third capacitor and a battery. The BUCK power chip is connected to the gates of the first MOS tube and the second MOS tube respectively, the source of the first MOS tube is connected in series with the first inductor and then connected to the positive connection point of the battery, and the source of the second MOS tube is connected in series with the third capacitor and then connected to the positive connection point of the battery.

[0009] According to a further technical solution, the charging circuit further includes a fifth resistor, a first end of the fifth resistor is connected to the source of the second MOS tube, and a second end of the fifth resistor is connected to the negative electrode connection point of the battery.

[0010] In a further technical solution, the first output pin of the BUCK power chip is connected to the gate of the first MOS tube, the drain of the first MOS tube is connected to the output end of the rectifier module, the source of the first MOS tube is connected to the first end of the first inductor, and the second end of the first inductor is connected to the positive connection point of the battery.

[0011] In a further technical solution, the second output pin of the BUCK power chip is connected to the gate of the second MOS tube, the drain of the second MOS tube is connected to the source of the first MOS tube, the source of the second MOS tube is connected to the second end of the third capacitor, and the first end of the third capacitor is connected to the positive electrode connection point of the battery.

[0012] A further technical solution is that the control circuit includes a single-chip microcomputer, the output end of the single-chip microcomputer is connected to the first end of the fourth resistor, the second end of the fourth resistor is respectively connected to the first end of the third resistor and the first end of the second capacitor, the second end of the second capacitor is grounded, the second end of the third resistor is respectively connected to the first end of the first resistor, the first end of the first capacitor, and the feedback pin of the BUCK power supply chip, and the second end of the first resistor, the second end of the first capacitor, and the second end of the first resistor R1 are all grounded.

[0013] In a further technical solution, the relationship between the voltage at the output terminal of the single chip microcomputer and the voltage at the output terminal of the charging circuit is expressed as:

[0014]

[0015] Among them, V fb Indicates the reference voltage of the feedback pin of the BUCK power chip, V pwm Represents the microcontroller output voltage, V out It represents the output voltage of the charging circuit, and R1, R2, R3, and R4 represent voltage-dividing resistors.

[0016] In a further technical solution, the control circuit first determines the resistance value of the second resistor, and then calculates the resistance values ​​of the third resistor, the fourth resistor and the first resistor according to a formula, which is expressed as:

[0017]

[0018]

[0019] Among them, V fb Indicates the reference voltage of the feedback pin of the BUCK power chip, V pwmmax Indicates the maximum voltage of the microcontroller output terminal, V outmax It indicates the maximum voltage at the output of the charging circuit. R1, R2, R3 and R4 indicate the voltage-dividing resistors.

[0020] A further technical solution is that the battery charging current adjustable control circuit also includes an anti-backflow circuit, including a third MOS tube, a fourth MOS tube, a first diode, a sixth resistor and a seventh resistor. The drain of the third MOS tube is connected to the positive connection point of the battery, the source of the third MOS tube is connected to the load, and the gate of the third MOS tube is connected in series with the first diode and the sixth resistor respectively and then connected to the load; the gate of the third MOS tube is also connected in series with the seventh resistor and then connected to the drain of the fourth MOS tube, and the gate of the fourth MOS tube is connected to the I / O terminal of the single-chip computer.

[0021] In a second aspect, the present invention provides a battery charging current adjustable control method, comprising:

[0022] The PWM wave output by the microcontroller is filtered by two stages of RC to obtain a smooth and controllable voltage which is then input into the charging circuit.

[0023] When the output voltage of the charging circuit is higher than the battery voltage, the battery is charged;

[0024] The single chip microcomputer samples the voltage across the fifth resistor to obtain a sampled voltage, and calculates the charging current according to the sampled voltage;

[0025] The measured value of the charging current is compared with the set value, and the PWM wave is adjusted so that the measured value of the charging current is equal to the set value.

[0026] One or more of the above technical solutions have the following beneficial effects:

[0027] In the field of communication base stations, the battery charging current is required to be high. Due to the large battery capacity, the large charging current may cause heating or explosion during the battery charging process, causing danger. The circuit provided by the present invention sets the BUCK output voltage and adjusts the output voltage to keep the voltage difference with the battery voltage small. The battery charging voltage will increase linearly, and the BUCK output voltage can also increase linearly to maintain a constant charging current value. The circuit greatly saves circuit costs and improves system reliability and working durability.

[0028] The circuit of the present invention controls the feedback pin of the BUCK power chip through the single-chip microcomputer output PWM, and further controls the output voltage of the charging circuit to limit the charging current, thereby greatly saving circuit costs and improving system reliability and working durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0030] Figure 1 is a circuit diagram of a battery charging current adjustable control circuit according to an embodiment of the present invention;

[0031] Figure 2 is a circuit diagram of a control circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0033] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0034] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0035] Embodiment 1

[0036] like Figure 1 , 2 As shown, this embodiment discloses a battery charging current adjustable control circuit, including: a charging circuit and a control circuit, the charging circuit includes a BUCK power chip and a battery connected to the BUCK power chip, a feedback pin of the BUCK power chip is connected in series with a second resistor and then connected to the output end of the charging circuit, one end of the second resistor is connected in series with a first resistor and then grounded; the control circuit includes a single-chip microcomputer, an output end of the single-chip microcomputer is connected in series with a fourth resistor and a third resistor and then connected to the feedback pin of the BUCK power chip, one end of the third resistor is connected in series with a first capacitor and then grounded, and a second capacitor is connected in series between the fourth resistor and the third resistor and then grounded.

[0037] In this embodiment, if Figure 1 As shown, the charging circuit includes a BUCK power chip, a first MOS tube Q1, a second MOS tube Q2, a first inductor L1, a third capacitor C3, a fifth resistor R5 and a battery (battery pack). The BUCK power chip is connected to the gates of the first MOS tube Q1 and the second MOS tube Q2 respectively. The source of the first MOS tube Q1 is connected in series with the first inductor L1 and then connected to the positive electrode connection point of the battery. The source of the second MOS tube Q2 is connected in series with the third capacitor C3 and then connected to the positive electrode connection point of the battery. The negative electrode connection point of the battery is connected in series with the fifth resistor R5 and then connected to the source of the second MOS tube Q2.

[0038] Specifically, the first output pin HO of the BUCK power chip is connected to the gate of the first MOS tube Q1, the drain of the first MOS tube Q1 is connected to the output end of the AC-DC rectifier module, the source of the first MOS tube Q1 is connected to the first end of the first inductor L1, and the second end of the first inductor L1 is connected to the positive electrode connection point of the battery (also referred to as the output end Vout of the charging circuit). The first output pin HO is used to output the high-end MOS tube Q1 to turn off, and the BUCK power chip generates a PWM wave to control Q1 and Q2 to turn on and off, so as to control the energy storage and release of the inductor L1 and achieve voltage reduction.

[0039] It should be noted that the PWM wave generated by the BUCK power chip is different from that generated by the microcontroller. The PWM wave generated by the BUCK power chip is used to control the MOS tube switch.

[0040] The output voltage at the output end of the AC-DC rectifier module is VRC, which can supply power to the battery and the load VL at the same time. It should be noted that the AC-DC rectifier module, also known as the AC-DC rectifier module, is a power conversion device that converts alternating current (AC) into direct current (DC). Its function is to obtain electrical energy from an AC power source (such as mains electricity, generator, etc.) in a battery charging system and convert it into a DC voltage to supply power to the battery or load. This embodiment is implemented by sampling an existing rectifier module, and the specific structure and working principle of the module will not be repeated here.

[0041] Specifically, the second output pin LO of the BUCK power chip is connected to the gate of the second MOS tube Q2, the drain of the second MOS tube Q2 is connected to the source of the first MOS tube Q1, the source of the second MOS tube Q2 is connected to the second end of the third capacitor C3, and the first end of the third capacitor C3 is connected to the positive electrode connection point of the battery (also known as the output end Vout of the charging circuit). The second output pin LO is used to output the low-end MOS tube Q2 off, and the third capacitor C3 is used to

[0042] In the charging circuit, the second MOS tube Q2 and the third capacitor C3 are used to filter the output voltage, so that the BUCK power chip outputs a relatively stable direct current to charge the battery.

[0043] Specifically, the source of the second MOS tube Q2 is also connected to the first end of the fifth resistor R5 and grounded, and the second end of the fifth resistor R5 is connected to the negative electrode connection point of the battery. The fifth resistor R5 is a sampling resistor, which is in the milliohm level. After being amplified 100 times by operation, it is connected to the single-chip microcomputer through RC filtering. The single-chip microcomputer collects the VBAT+ and VBAT- voltages at both ends of the fifth resistor R5 through ADC, and calculates the charging current through the VBAT+ and VBAT- voltages.

[0044] In this embodiment, if Figure 2 As shown, the control circuit includes a single-chip microcomputer, the output end of the single-chip microcomputer is connected to the first end of the fourth resistor R4, the second end of the fourth resistor R4 is respectively connected to the first end of the third resistor R3 and the first end of the second capacitor C2, the second end of the second capacitor C2 is grounded, the second end of the third resistor R3 is respectively connected to the first end of the first resistor R1, the first end of the first capacitor C1, and the feedback pin FB of the BUCK power chip, the second end of the first resistor R1 is grounded, the second end of the first capacitor C1 is grounded, and the second end of the first resistor R1 is grounded.

[0045] Furthermore, the feedback pin FB of the BUCK power chip is respectively connected to the first end of the first resistor R1, the second end of the third resistor R3, and the second end of the second resistor R2, and the first end of the second resistor R2 is connected to the output end of the charging circuit.

[0046] The microcontroller outputs PWM to control the feedback pin FB of the BUCK power chip, thereby controlling the output voltage V at the output end of the charging circuit. out To limit the charging current, stabilize the charging current at a constant value and ensure safe use.

[0047] like Figure 2 As shown, in the circuit V out is the output voltage of the charging circuit, V pwm It is the PWM wave voltage output by the microcontroller. The voltage connected to the feedback pin FB of the BUCK power chip consists of two parts. One part is V out The first part is generated by the voltage division of the second resistor R2 and the first resistor R1. The other part is the voltage of the microcontroller PWM wave after two-stage RC filtering. R4 and C2 form the first stage of filtering, and R3 and C1 form the second stage of filtering. These two parts of voltage jointly determine the input voltage of the feedback pin FB of the BUCK power chip.

[0048] When the BUCK power chip is working normally and stably, the average voltage of the FB pin is the reference voltage at the chip feedback pin, as shown in the following formula: V fb (This is a fixed value, the reference voltage of different chips is different), V fb It consists of two parts, so V out The voltage generated by the voltage divider of two resistors R2 and R1 and the voltage generated by the microcontroller PWM wave after two-stage RC filtering are regarded as two independent voltage sources, and the following formula is used to calculate V pwm and V out The relationship between them is expressed as:

[0049]

[0050] Among them, V fb Indicates the reference voltage of the feedback pin of the BUCK power chip, V pwm Indicates the voltage after the microcontroller timer peripheral generates PWM (microcontroller output voltage), V out It represents the output voltage of the charging circuit, and R1, R2, R3, and R4 represent voltage-dividing resistors.

[0051] The left side of the plus sign in formula (1) is V pwm The voltage of the feedback pin FB of the BUCK power chip when it acts alone. The voltage on the right side of the plus sign is V out When the BUCK power chip acts alone, the voltage of the feedback pin FB can be simplified into the following linear function form:

[0052] V out =-K*V pwm +B(2)

[0053] in, In the formula, R1, R2, R3, R4 and V fb are all fixed values. Given a single chip V pwm The corresponding V out The FB output voltage can be controlled in real time, thereby controlling the output current.

[0054] In the design of the control circuit, it is necessary to determine the resistance of each resistor. First, determine the resistance of the second resistor R2. The resistance of R2 can usually be selected between 1K and 100K. Then confirm the resistance of the third resistor R3 and the fourth resistor R4. According to formula (2), when V pwm When the output is 0, the output voltage reaches the maximum output value V outmax (This value is the maximum output voltage fixed value) as shown in formula (3); when V pwm Output is the highest level V of the microcontroller pwmmaxWhen , the output voltage is 0, as shown in formula (4).

[0055]

[0056]

[0057] Among them, V fb Indicates the reference voltage of the feedback pin of the BUCK power chip, V pwmmax Indicates the maximum voltage of the microcontroller output terminal, V outmax It indicates the maximum voltage at the output of the charging circuit. R1, R2, R3 and R4 indicate the voltage-dividing resistors.

[0058] By combining formula (3) and formula (4) and eliminating R1, we can get the values ​​of R3 and R4. Then, by substituting the values ​​of R3 and R4 into formula (3) or formula (4), we can get the value of R1.

[0059] In the control circuit design, the single-chip AD is used to sample the current value of the charging circuit to charge the battery. According to the sampled current value, the single-chip V pwm Output, and then adjust the output voltage V in real time out , and as the battery voltage increases, the output voltage V out It also increases linearly and can maintain a fixed current value for charging.

[0060] Through the above work flow, the PWM wave generated by the single-chip microcomputer is used to generate V after two-stage RC filtering by R4 and C2, R3 and C1. pwm and V out The voltage is divided by two resistors R2 and R1 and connected to the feedback pin FB of the BUCK power chip. This method ensures the accuracy of the battery charging current while improving the real-time performance of the battery charging control and the system reliability.

[0061] In this embodiment, if Figure 1 As shown, the battery charging current adjustable control circuit also includes an anti-backflow circuit, which is added to the positive output end of the battery, including a third MOS tube Q3, a fourth MOS tube Q4, a first diode D1, a sixth resistor R6 and a seventh resistor R7. The drain of the third MOS tube Q3 is connected to the positive connection point of the battery, the source of the third MOS tube Q3 is connected to the load VL, and the gate of the third MOS tube Q3 is connected in series with the first diode D1 and the sixth resistor R6 respectively, and then connected to the load VL; the gate of the third MOS tube Q3 is also connected in series with the seventh resistor R7 and then connected to the drain of the fourth MOS tube Q4, the source of the fourth MOS tube Q4 is grounded, and the gate of the fourth MOS tube Q4 is connected to the I / O terminal Vcon of the single-chip computer.

[0062] Furthermore, Vcon is the I / O terminal of the microcontroller, and the microcontroller outputs high and low levels to control Q4 to be turned off, and Q4 turns off to control Q3 to be turned off. The function is to control Q3 to generate less heat when it is turned on.

[0063] Specifically, the drain of the third MOS tube Q3 is connected to the positive electrode connection point of the battery, the gate of the third MOS tube Q3 is respectively connected to the positive electrode of the first diode D1, the first end of the sixth resistor R6, and the first end of the seventh resistor R7, the cathode of the first diode D1 is respectively connected to the source of the third MOS tube Q3 and the load VL, the second end of the sixth resistor R6 is respectively connected to the cathode of the first diode D1, the source of the third MOS tube Q3, and the load VL; the second end of the seventh resistor R7 is connected to the drain of the fourth MOS tube Q4, the source of the fourth MOS tube Q4 is grounded, and the gate of the fourth MOS tube Q4 is connected to Vcon.

[0064] The above-mentioned anti-backflow circuit is a new method. Compared with the ordinary diode anti-backflow circuit, the circuit generates less heat. Assuming that the same current of 60A passes through, the diode voltage drop is 0.7V, the heat generation is 30W, and the PMOS conduction internal resistance of the circuit of the present invention is 2mR. At this time, the heat generation is 7.2W, which is greatly reduced.

[0065] The working principle of the anti-backflow circuit is that when the output voltage VRC of the AC-DC rectifier module exists, VRC charges the battery and supplies power to the load VL at the same time, and Q3 is turned off. Due to the action of the body diode of Q3, the current of the rectifier module is prevented from backflowing to the battery. When the mains power is cut off, the rectifier module does not output. At this time, the battery is powered by the body diode of Q3 (PMOS) to prevent the short-term power failure when the main and standby power of the base station equipment is switched. At this time, the Vcon of the microcontroller controls Q4 (NMOS) to turn on. After Q4 is turned on, the D1 voltage regulator diode clamps the GS of Q3 at -15V, turning on Q3. The internal resistance of the current passing through Q3 is low, and the heat is small; when the mains power is detected, Q4 is turned off by Vcon, and then Q3 is controlled to turn off.

[0066] Embodiment 2

[0067] This embodiment discloses a battery charging current adjustable control method, including:

[0068] The PWM wave output by the microcontroller is filtered by two stages of RC to obtain a smooth and controllable voltage which is then input into the charging circuit.

[0069] When the output voltage of the charging circuit is higher than the battery voltage, the battery is charged;

[0070] The single chip microcomputer samples the voltage across the fifth resistor to obtain a sampled voltage, and calculates the charging current according to the sampled voltage;

[0071] The measured value of the charging current is compared with the set value, and the PWM wave is adjusted so that the measured value of the charging current is equal to the set value.

[0072] In this embodiment, according to the above formula (2), K and B are fixed values, and the PWM wave voltage V output by the single chip microcomputer is adjusted. pwm The output voltage V of the charging circuit can be controlled out , and then control the charging current. The microcontroller timer peripheral is set to 1K frequency to output PWM wave, which is filtered by two stages of RC to become a smooth and controllable voltage. out When the voltage is higher than the battery voltage, the battery will be charged. At this time, there will be a voltage across the sampling resistor R5. The charging current is calculated based on the sampled voltage. The voltage V is calculated based on the comparison between the measured value of the battery charging current and the set value. pwm Adjust so that the measured value of charging current is equal to the set value.

[0073] The PWM generated by the microcontroller first decreases the output linearly from 3.3V to V out Will rise slowly, when V out When the voltage is higher than the battery voltage, the battery will be charged. Specifically, when the charging circuit is working, the initial duty cycle is 100% and the output voltage V pwm The highest, at this time the output voltage V out The minimum, can not reach the battery voltage, slowly reduce the duty cycle, V out Slowly increase until V out The output voltage is higher than the battery voltage and charges the battery.

[0074] During the battery charging process, the MCU samples the voltage at both ends of R5 after amplifying it 100 times, and then samples the voltage 1000 times to get the average value to ensure that the collected voltage will not jump due to noise. The collected voltage is converted into the battery charging current, and the collected current value is compared with the set current value. The output voltage V is adjusted by controlling the PWM generated by the MCU. out , and then revise the current value to achieve current control.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0076] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A battery charging current adjustable control circuit, characterized in that: The invention comprises a charging circuit and a control circuit, wherein the charging circuit comprises a BUCK power chip and a battery connected to the BUCK power chip, a feedback pin of the BUCK power chip is connected in series with a second resistor and then connected to an output end of the charging circuit, one end of the second resistor is connected in series with a first resistor and then grounded; the control circuit comprises a single-chip computer, an output end of the single-chip computer is connected in series with a fourth resistor and a third resistor and then connected to a feedback pin of the BUCK power chip, one end of the third resistor is connected in series with a first capacitor and then grounded, and a second capacitor is connected in series between the fourth resistor and the third resistor and then grounded.

2. A battery charging current adjustable control circuit as claimed in claim 1, characterized in that: The charging circuit includes a BUCK power chip, a first MOS tube, a second MOS tube, a first inductor, a third capacitor and a battery. The BUCK power chip is connected to the gates of the first MOS tube and the second MOS tube respectively. The source of the first MOS tube is connected in series with the first inductor and then connected to the positive connection point of the battery. The source of the second MOS tube is connected in series with the third capacitor and then connected to the positive connection point of the battery.

3. A battery charging current adjustable control circuit as claimed in claim 2, characterized in that: The charging circuit also includes a fifth resistor, a first end of the fifth resistor is connected to the source of the second MOS tube, and a second end of the fifth resistor is connected to the negative electrode connection point of the battery.

4. A battery charging current adjustable control circuit as claimed in claim 2, characterized in that: The first output pin of the BUCK power chip is connected to the gate of the first MOS tube, the drain of the first MOS tube is connected to the output end of the rectifier module, the source of the first MOS tube is connected to the first end of the first inductor, and the second end of the first inductor is connected to the positive electrode connection point of the battery.

5. A battery charging current adjustable control circuit as claimed in claim 2, characterized in that: The second output pin of the BUCK power chip is connected to the gate of the second MOS tube, the drain of the second MOS tube is connected to the source of the first MOS tube, the source of the second MOS tube is connected to the second end of the third capacitor, and the first end of the third capacitor is connected to the positive electrode connection point of the battery.

6. A battery charging current adjustable control circuit as claimed in claim 1, characterized in that: The control circuit includes a single-chip microcomputer, an output end of the single-chip microcomputer is connected to the first end of the fourth resistor, the second end of the fourth resistor is respectively connected to the first end of the third resistor and the first end of the second capacitor, the second end of the second capacitor is grounded, the second end of the third resistor is respectively connected to the first end of the first resistor, the first end of the first capacitor, and a feedback pin of the BUCK power supply chip, and the second end of the first resistor, the second end of the first capacitor, and the second end of the first resistor R1 are all grounded.

7. A battery charging current adjustable control circuit as claimed in claim 6, characterized in that: The relationship between the voltage at the output terminal of the single chip microcomputer and the voltage at the output terminal of the charging circuit is expressed as: Among them, V fb Indicates the reference voltage of the feedback pin of the BUCK power chip, V pwm Represents the output voltage of the microcontroller, V out It represents the output voltage of the charging circuit, and R1, R2, R3, and R4 represent voltage-dividing resistors.

8. A battery charging current adjustable control circuit as claimed in claim 6, characterized in that: In the control circuit, the resistance value of the second resistor is first determined, and then the resistance values ​​of the third resistor, the fourth resistor and the first resistor are calculated according to the formula, which is expressed as: Among them, V fb Indicates the reference voltage of the feedback pin of the BUCK power chip, V pwmmax Indicates the maximum voltage of the microcontroller output terminal, V outmax It indicates the maximum voltage at the output of the charging circuit. R1, R2, R3 and R4 indicate the voltage-dividing resistors.

9. A battery charging current adjustable control circuit as claimed in claim 1, characterized in that: The battery charging current adjustable control circuit also includes an anti-backflow circuit, including a third MOS tube, a fourth MOS tube, a first diode, a sixth resistor and a seventh resistor. The drain of the third MOS tube is connected to the positive connection point of the battery, the source of the third MOS tube is connected to the load, and the gate of the third MOS tube is connected in series with the first diode and the sixth resistor respectively and then connected to the load; the gate of the third MOS tube is also connected in series with the seventh resistor and then connected to the drain of the fourth MOS tube, and the gate of the fourth MOS tube is connected to the I / O terminal of the single-chip computer.

10. A battery charging current adjustable control method, characterized in that: include: The PWM wave output by the microcontroller is filtered by two stages of RC to obtain a smooth and controllable voltage which is then input into the charging circuit. When the output voltage of the charging circuit is higher than the battery voltage, the battery is charged; The single chip microcomputer samples the voltage across the fifth resistor to obtain a sampled voltage, and calculates the charging current according to the sampled voltage; The measured value of the charging current is compared with the set value, and the PWM wave is adjusted so that the measured value of the charging current is equal to the set value.

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