Constant current circuit with positive terminal current sampling and electronic device

Abstract

This invention discloses a constant current circuit and electronic device for positive terminal current sampling. The constant current circuit is used to connect between an external power supply and a battery. The constant current circuit includes a sampling unit and a control unit. The sampling unit includes a sampling resistor and a first switching transistor. The input terminal of the control unit is connected to the external power supply, one end of the sampling resistor is connected to the output terminal of the control unit, and the other end is connected to the positive terminal of the battery. The input terminal of the first switching transistor is connected between the control unit and the sampling resistor, the control terminal of the first switching transistor is connected between the sampling resistor and the positive terminal of the battery, and the output terminal of the first switching transistor is connected to the detection terminal of the control unit. By placing the sampling unit at the positive terminal of the power supply, the problem of complex transformer windings caused by the need for an independent ground wire at the power supply terminal is solved. At the same time, the positive terminal current sampling can use low-power components, without having to withstand the large current of the sum of multiple circuits on the negative terminal, thus achieving high-precision and high-reliability current monitoring and control at low cost.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more particularly to a constant current circuit and electronic device for sampling positive terminal current. Background Technology

[0002] The current sensing circuit is a core component of the Battery Management System (BMS), primarily used to monitor the current during battery charging and discharging to achieve functions such as overcurrent protection and battery state estimation. Its core challenge lies in achieving high-precision, low-loss current measurement under high common-mode voltage while ensuring system safety and reliability. In existing constant-current circuits, the current sensing resistor is placed at the negative terminal, requiring a separate ground wire from the power supply. An independent ground wire complicates the transformer windings, increasing manufacturing time and material costs. Furthermore, current sensing at the negative terminal requires the sensing components to withstand the sum of multiple currents, necessitating the use of high-power components that are prone to damage, resulting in high production costs and poor circuit reliability. Summary of the Invention

[0003] To address the aforementioned issues, this invention provides a constant current circuit and electronic device for positive terminal current sampling. This device can sample the current at the positive terminal of the constant current circuit, resolving the problem of complex transformer windings caused by the need for an independent ground wire at the power supply end. Furthermore, the positive terminal current sampling can utilize low-power components, eliminating the need to withstand the large current of the sum of multiple circuits at the negative terminal, thus achieving high-precision and high-reliability current monitoring and control at low cost.

[0004] According to a first aspect of the present invention, a constant current circuit for sampling positive terminal current is provided, the constant current circuit being connected between an external power supply and a battery;

[0005] The constant current circuit includes a sampling unit and a control unit; the control unit is used to convert the external power supply into a charging current, and charge the battery through the sampling unit; the sampling unit includes a sampling resistor and a first switching transistor.

[0006] The input terminal of the control unit is connected to the external power supply; one end of the sampling resistor is connected to the output terminal of the control unit, and the other end is connected to the positive terminal of the battery; the input terminal of the first switching transistor is connected between the control unit and the sampling resistor; the control terminal of the first switching transistor is connected between the sampling resistor and the positive terminal of the battery; and the output terminal of the first switching transistor is connected to the detection terminal of the control unit.

[0007] The first switching transistor is used to amplify the voltage drop signal across the sampling resistor and then flow it into the detection terminal of the control unit. The control unit adjusts the charging current based on the voltage drop signal.

[0008] In one alternative embodiment, the sampling unit further includes a first resistor and a second resistor;

[0009] One end of the first resistor is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the control terminal of the first switching transistor.

[0010] One end of the second resistor is connected between the sampling resistor and the battery, and the other end is connected to the control terminal of the first switching transistor;

[0011] The first resistor and the second resistor are used to adjust the amplification factor of the first switching transistor.

[0012] In one alternative embodiment, the sampling unit further includes a first capacitor and a second capacitor;

[0013] One end of the first capacitor is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the output terminal of the first switching transistor.

[0014] One end of the second capacitor is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the control terminal of the first switching transistor;

[0015] The first capacitor is used to absorb the surge current when the constant current circuit starts up; the second capacitor is used to filter high-frequency noise in the charging current.

[0016] In one alternative embodiment, the control unit includes a control chip and a constant current inductor;

[0017] The input terminal of the control chip is connected to the external power supply, the detection terminal of the control chip is connected to the output terminal of the first switching transistor, and the constant current inductor is connected between the control chip and the sampling resistor.

[0018] The control chip is used to convert the current of the external power supply into the charging current, and adjust the magnitude of the charging current based on the voltage drop signal; the constant current inductor is used to keep the charging current constant, and the control chip adjusts the magnitude of the charging current based on the signal value.

[0019] In one alternative embodiment, the constant current circuit further includes a voltage feedback unit, and the control chip further includes a feedback terminal, wherein the voltage feedback unit is connected between the battery and the feedback terminal of the control chip;

[0020] The voltage feedback unit is used to collect the current voltage of the battery and send the current voltage to the control chip;

[0021] The control chip is used to adjust the charging current according to the current voltage of the battery in order to stabilize the charging voltage of the battery.

[0022] In one alternative embodiment, the constant current circuit further includes a system chip, the input of which is connected to the battery, and the output of which is connected to the detection terminal of the control unit. The system chip is used to detect the state of the battery, and when the battery is detected to be in an abnormal state, it controls the control unit to stop outputting the charging current.

[0023] In one alternative approach, the control chip adjusts the magnitude of the charging current by regulating the duty cycle of the output current.

[0024] In one alternative embodiment, the constant current circuit further includes a transformer connected between the external power supply and the control chip, the transformer being used to supply power to the control chip.

[0025] According to a second aspect of the present invention, an electronic device is provided, the electronic device including a battery and a constant current circuit as described in any implementation of the first aspect, the constant current circuit being connected between the external power supply and the battery.

[0026] The beneficial effects of this invention are as follows: By placing the sampling unit at the positive terminal of the power supply, this application solves the problem of complex transformer windings caused by the need for an independent ground wire at the power supply end, and optimizes the cross-regulation rate. Simultaneously, the positive terminal current sampling can use low-power components, eliminating the need to withstand the large current of the sum of multiple circuits on the negative terminal, thus achieving high-precision and high-reliability monitoring and control of the positive terminal current at low cost. Furthermore, this application introduces a voltage feedback unit, allowing the control chip to simultaneously combine the current sampling signal and the voltage feedback unit to achieve dual closed-loop control of "constant current + constant voltage," dynamically matching the battery state and solving the problem that a single mode cannot simultaneously address fast charging and safety. Finally, this application also uses a system chip to detect abnormal states of the circuit and the battery state, forming a dual protection measure of the control chip and the system chip, reducing the safety risks of the constant current circuit. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0028] Figure 1 This is a schematic diagram illustrating the connection between a constant current circuit and a battery and an external power supply, as provided in an embodiment of this application.

[0029] Figure 2 This is a schematic diagram of the topology of a constant current circuit provided in an embodiment of this application;

[0030] Figure 3 This is a schematic diagram showing the connection between another constant current circuit and a battery and an external power supply provided in an embodiment of this application. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of this application, the application will be described in detail below with reference to the accompanying drawings and specific embodiments. Although the accompanying drawings and specific embodiments describe exemplary embodiments of the present invention, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0032] The terms "first," "second," and similar words used in this application do not indicate any order, quantity, or importance, but are merely used for distinction. The terms "including," and similar words used in this application mean that the element preceding the word encompasses the elements listed after the word, and do not exclude the possibility of including other elements. The technical solutions of this application are not limited to the execution order described in the embodiments. The steps in the execution order can be combined, broken down, or their order can be changed, as long as the logical relationship of the execution content is not affected.

[0033] All terms used in this application (including technical or scientific terms) have the same meaning as understood by one of ordinary skill in the art to which this application pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein. Technologies and equipment known to one of ordinary skill in the art may not be discussed in detail, but where appropriate, such technologies and equipment should be considered part of the specification.

[0034] First, the relevant terms involved in the application embodiments will be explained.

[0035] A battery management system (BMS), also known as a battery nanny or battery steward, is mainly used for intelligent management and maintenance of each battery cell, monitoring the battery status, preventing overcharging and over-discharging, and thus extending the battery's lifespan.

[0036] The current sensing circuit is a core component of the battery management system (BMS). The basic principle of the current sensing circuit is to measure the current in the circuit and convert it into a processable electrical signal. In a circuit, a voltage drop occurs when current flows through a resistor or wire. This voltage drop is proportional to the current flowing through it; therefore, the magnitude of the current can be calculated by measuring this voltage drop.

[0037] Current sensing is a fundamental and crucial technology that provides essential information for system protection, control, monitoring, diagnosis, and metering by measuring the current in a circuit. Its beneficial effects include significantly improved safety, reliability, efficiency, and performance, enabling complex control strategies and precise energy management, making it an indispensable component of modern electronic and electrical systems. Various technologies exist for implementing current sensing, each with its own advantages and disadvantages.

[0038] In existing constant current limiting detection circuits, the resistor is typically placed on the negative terminal. This necessitates a separate ground wire from the power supply. A separate ground wire complicates the transformer windings, increasing manufacturing time and material costs. Current technology requires independent windings, which results in poor cross-regulation. To compensate for voltage fluctuations, a dummy load is needed, increasing power loss, requiring additional system operation, and reducing efficiency. Using conventional methods, the low-voltage winding wire and rectifier diodes must withstand the combined current from multiple sources, potentially damaging components. Furthermore, precise resistor weight matching is required, demanding higher component precision.

[0039] To address the aforementioned issues, this application provides a constant current circuit for positive terminal current sampling. This circuit samples the positive terminal current of the constant current circuit and converts the control signal to the control chip via the sampling circuit. This allows the negative output terminal to be shared, simplifying transformer design and fabrication, reducing leakage inductance, and optimizing the cross-regulation. Simultaneously, by utilizing the voltage drop across the sampling resistor and the constant conduction voltage of the switching transistor, current balance is achieved, resulting in a constant current effect.

[0040] like Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram illustrating the connection between a constant current circuit and a battery and an external power supply, as provided in an embodiment of this application. Figure 2 This is a topological schematic diagram of a constant current circuit provided in an embodiment of this application. The constant current circuit includes a sampling unit and a control unit; the control unit is used to convert the external power supply into a charging current, which is then used to charge the battery through the sampling unit; the sampling unit includes a sampling resistor and a first switching transistor.

[0041] The input terminal of the control unit is connected to the external power supply. One end of the sampling resistor is connected to the output terminal of the control unit, and the other end is connected to the positive terminal BAT of the battery. The input terminal of the first switching transistor is connected between the control unit and the sampling resistor. The control terminal of the first switching transistor is connected between the sampling resistor and the positive terminal BAT of the battery. The output terminal of the first switching transistor is connected to the detection terminal of the control unit.

[0042] The first switching transistor is used to amplify the voltage drop signal across the sampling resistor and then flow it into the detection terminal of the control unit. The control unit adjusts the charging current based on the amplified voltage drop signal.

[0043] It should be noted that a battery can be a device that converts chemical energy into electrical energy through a chemical reaction. It consists of one or more electrochemical units (cells), each containing positive and negative electrodes, an electrolyte, and insulating materials, and can continuously provide current in a closed circuit. Its core function is to store and release electrical energy. The battery in this embodiment can be a lead-acid battery, lithium-ion battery, nickel-cadmium battery, alkaline battery, or other batteries used to provide stable direct current.

[0044] In some embodiments, the sampling resistor may be a single resistor or two resistors connected in parallel (e.g., ...). Figure 2 The embodiments of this application do not specifically limit the specific resistors to R187 and R181 shown, or three or more resistors connected in parallel.

[0045] In some embodiments, the switching transistor in this application may be a bipolar transistor or a metal-oxide-semiconductor field-effect transistor (MOS transistor). For example, in some embodiments, the first and second switching transistors in this application are PNP bipolar transistors.

[0046] It should be noted that the switching transistor in this embodiment operates in an amplification state in the circuit. The input, control, and output terminals of the first switching transistor can correspond to the emitter, base, and collector of a PNP transistor, respectively.

[0047] Specifically, after the constant current circuit provided in this embodiment is started, the current from the external power supply flows into the control unit through the input terminal. The control unit converts the current from the external power supply into the charging current required by the battery. The charging current flows sequentially through the sampling resistor and the battery to form a charging circuit. When the charging current flows through the sampling resistor, a voltage drop signal is generated across the sampling resistor. Since the first switching transistor is operating in an amplification state, the first switching transistor converts the voltage drop signal across the sampling resistor into a current signal, which is then amplified and flows into the detection terminal of the control unit. The control unit obtains this current signal through the detection terminal to achieve real-time current monitoring of the positive terminal of the power supply. At the same time, the control unit can also compare the current signal with an internally preset reference current signal. If the current signal is greater than the reference value, the control unit reduces the output charging current; if the current signal is less than the reference value, the control unit increases the output charging current. Through this closed-loop adjustment process, the charging current is eventually stabilized at a set constant value, achieving constant current charging of the battery. In addition, when the control unit detects an abnormal power supply current (e.g., an abnormal increase in current due to a short circuit), it can implement functions such as power supply overcurrent protection.

[0048] The constant current circuit for positive terminal current sampling provided in this application solves the problem of complex transformer windings caused by the need for an independent ground wire at the power supply terminal by placing the sampling unit at the positive terminal. Simultaneously, the positive terminal current sampling can use low-power components, eliminating the need to withstand the large current of the sum of multiple circuits on the negative terminal, thus achieving high-precision and high-reliability monitoring and control of the power supply positive terminal current at low cost. Furthermore, it eliminates the need to place the constant current limiting detection resistor at the negative terminal, simplifying the transformer winding setup and saving manufacturing time and material costs. At the same time, placing the detection component at the positive terminal avoids the need to withstand the large current of the sum of multiple currents, preventing damage to the components.

[0049] like Figure 2 As shown, in some embodiments, the sampling unit further includes a first resistor R182 and a second resistor R183; one end of the first resistor R182 is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the control terminal of the first switching transistor Q23; one end of the second resistor R183 is connected between the sampling resistor and the battery, and the other end is connected to the control terminal of the first switching transistor Q23; the first resistor R182 and the second resistor R183 are used to adjust the amplification factor of the first switching transistor.

[0050] Specifically, the first resistor R182 and the second resistor R183 form a voltage divider network, which together adjusts the base bias voltage of the first switching transistor Q23, thereby controlling its amplification factor. The base bias voltage refers to the critical DC voltage in a transistor amplifier circuit that puts the transistor in amplification mode. The amplification factor refers to the multiple by which the emitter current exceeds the base current, which is also the DC current amplification factor of the transistor.

[0051] In this embodiment, the base of the first switching transistor Q23 is connected to the high-potential end of the sampling resistor (near the output end of the control unit) through a first resistor R182, and simultaneously connected to the low-potential end of the sampling resistor (near the battery) through a second resistor R183. Further, one end of the first resistor R182 is connected to the common node (high-potential side of the main circuit) between the output end of the control unit and the sampling unit, and the other end is connected to the base of the first switching transistor Q23, providing an upper bias voltage to the base of the first switching transistor Q23. One end of the second resistor R183 is connected to the base of the first switching transistor Q23, and the other end is connected to the common node (low-potential side of the main circuit, near the battery) between the sampling resistor and the positive terminal of the battery, providing a lower bias voltage to the base of the first switching transistor Q23.

[0052] It should be noted that the voltage divider network composed of the first resistor R182 and the second resistor R183 can change the conduction threshold of the first switch Q23 by adjusting the resistance ratio of the two resistors, thereby adjusting the base potential of the first switch Q23, and thus changing the amplification factor of the first switch Q23. Finally, the adjustment is fed back to the control unit to achieve fine adjustment of the charging current reference.

[0053] By setting the resistance values ​​of the first resistor R182 and the second resistor R183, the charging current of the constant current circuit can be flexibly adjusted to adapt to the charging needs of different batteries and expand the applicable scenarios of the constant current circuit.

[0054] In some embodiments, the sampling unit further includes a first capacitor C46 and a second capacitor C45. One end of the first capacitor C46 is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the output terminal of the first switching transistor Q23. One end of the second capacitor C45 is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the control terminal of the first switching transistor Q23. The first capacitor is used to absorb the surge current when the constant current circuit starts up. The second capacitor C45 is used to filter high-frequency noise in the charging current. The first capacitor can prevent the constant current capacitor from being mistakenly started at the moment of power-on.

[0055] In this embodiment, one end of the first capacitor C46 is connected to the common node (high potential side of the main circuit) between the output terminal of the control unit and the sampling unit, and the other end is connected to the collector of the first switching transistor Q23. During power-on, the capacitor's charging characteristic is used to delay the operation of the first switching transistor Q23, suppressing false feedback caused by power-on surge current. Simultaneously, it filters out high-frequency interference from the collector, resulting in a cleaner signal fed back to the control unit. The second capacitor C45 is connected in parallel across the first resistor R182 to filter out high-frequency noise in the sampling signal, such as ripple interference from the switching power supply, making the base voltage of the first switching transistor Q23 more stable and preventing false triggering.

[0056] It should be noted that at the moment the circuit is powered on, the external power supply voltage surges. To prevent false feedback caused by the inrush current, the first capacitor C46 slowly builds up voltage during the charging process. The first switching transistor Q23 will briefly stop working, thereby temporarily stopping the sampling unit and delaying the control unit's adjustment of the charging current, thus avoiding false feedback due to the inrush current. Inrush current refers to the peak current flowing into the power supply device at the moment the power is turned on.

[0057] The function of the second capacitor C45 is to filter high-frequency noise. The high-frequency noise generated by the high-frequency operation of the first switch Q23 in the charging current will be coupled to the base of the first switch Q23 through the sampling resistor; by absorbing the high-frequency noise, the second capacitor C45 ensures that the signal received by the base only contains the real charging current information, thus avoiding malfunction of the first switch Q23.

[0058] The stability of the constant current circuit is improved by addressing the surge current generated at the moment of circuit startup and the high-frequency noise interference in the charging current.

[0059] In some implementations, such as Figure 2 As shown, the control unit includes a control chip U1 and a constant current inductor L4. The input terminal of the control chip U1 is connected to the external power supply POWER SUPPLY, and the detection terminal of the control chip U1 is connected to the output terminal of the first switching transistor Q23. The constant current inductor L4 is connected between the control chip U1 and the sampling resistor. The control chip U1 is used to convert the current of the external power supply POWER SUPPLY into the charging current and adjust the magnitude of the charging current based on the voltage drop signal. The constant current inductor L4 is used to keep the charging current constant.

[0060] Specifically, the control chip U1, as the core controller of the circuit, converts the voltage and current of the external power supply into charging voltage and current adapted to the battery. This is achieved, for example, through various topologies (such as BUCK circuits and LDO circuits), to achieve voltage reduction or boost. It also receives sampling signals through the detection terminal and adjusts the output current in real time (e.g., by changing the PWM duty cycle of the output pin). The control chip U1 can be a synchronous rectification buck converter, such as the MP2307 and MP2315; classic asynchronous buck chips, such as the LM2596 and TPS5430; or a buck-boost integrated converter, such as the XL6009.

[0061] By utilizing the characteristic of constant current inductor L4 that "inductor current cannot change abruptly," energy is stored or released when control chip U1 switches, thus smoothing fluctuations in the charging current. For example, when the output of control chip U1 is turned off, the inductor releases energy to maintain continuous current, ensuring stable charging current and avoiding current spikes or drops caused by switching actions.

[0062] In this embodiment, the control chip U1 can be an XL4501E1. The XL4501E1 is a high-efficiency step-down DC-DC converter chip with integrated MOSFETs. Its pin functions can include a power input pin (VIN), a current sensing pin (CS), a power switch pin (SW), and a ground pin (GND).

[0063] In this embodiment, as Figure 2 As shown. The control chip U1 serves as the control core, and the specific connection method can be as follows:

[0064] The GND pin is directly connected to the SGND terminal, which is ground in the diagram.

[0065] The VIN pin is connected to the input power supply POWER SUPPLY, and a filter capacitor C40 is connected in parallel between the VIN pin and the external power supply POWER SUPPLY to ground to eliminate noise.

[0066] A third resistor R180 is connected to the CS pin to limit current and protect the chip pin. This current then flows to the collector of the first switching transistor Q23 to receive the current signal from the sampling unit. The CS pin is also connected to a filter capacitor C42 and a voltage regulator resistor R76. These two capacitors are connected in parallel and grounded, providing amplitude limiting protection. The resulting RC low-pass filter also filters high-frequency noise.

[0067] A constant current inductor L4 is connected to the SW pin. Through the high-frequency switching of the internal switch of the control chip U1, the energy storage (when the internal switch of the control chip U1 is on, the charging current flows through the constant current inductor L4 to the sampling unit, and then to the battery) and energy release (when the internal switch of the control chip U1 is off, the constant current inductor L4 maintains the charging current through freewheeling, flowing through the sampling unit to the battery) of the constant current inductor L4 are controlled, thus achieving constant current control. By utilizing the energy conversion and constant current storage and release characteristics of the control chip U1, the charging efficiency and current stability are improved, reducing the damage to the battery caused by current fluctuations.

[0068] In some implementations, a second diode D40 can be connected in series between the sampling unit and the battery. The cathode of the second diode D40 is connected to the positive terminal BAT of the battery, and the anode of the second diode D40 is connected to the sampling unit. By setting the second diode D40, the backflow of battery current can be effectively prevented from damaging the constant current circuit.

[0069] In some implementations, a third diode D39 may be provided between the SW pin and VIN pin of the control chip U1. The cathode of the third diode D39 is connected to the VIN pin, and the anode of the third diode D39 is connected to the SW pin. By providing the third diode D39, damage to the control chip U1 caused by the input voltage of the VIN pin being less than the output voltage of the SW pin can be effectively prevented.

[0070] In some implementations, a fourth diode D23 can be provided between the SW pin and the ground terminal SGND. The cathode of the fourth diode D23 is connected to the SW pin, and the anode of the fourth diode D23 is connected to the ground terminal SGND. The fourth diode D23 effectively clamps the voltage. If the voltage at the SW pin is less than -0.7V (the forward voltage drop of the diode), the fourth diode D23 conducts, clamping the voltage at the SW pin at -0.7V. This limits voltage spikes at the SW pin, protects the internal switching transistor (MOSFET) of U1 from overvoltage damage and auxiliary inductor freewheeling, and optimizes energy conversion.

[0071] In some implementations, such as Figure 2 As shown, a polarized capacitor C41 and a bleeder resistor R206 can be connected in parallel between the constant current inductor L4 and the ground terminal SGND. When the internal switch of the control chip U1 switches from on to off, the constant current inductor L4 will generate a high back electromotive force because "current cannot change abruptly". The polarized capacitor C41 can quickly absorb this energy, clamping the back electromotive force at a low level, protecting the switch and inductor from high voltage surges. The charge stored in the polarized capacitor C41 needs to be slowly discharged to ground through the bleeder resistor R206. Through the above settings, the cooperation of the inductor, polarized capacitor C41, and bleeder resistor R206 smooths the fluctuation of the charging current, and with the PWM control of the control chip U1, a stable constant current is output.

[0072] In some embodiments, the constant current circuit further includes a voltage feedback unit, and the control chip U1 further includes a feedback terminal. The voltage feedback unit is connected between the battery and the feedback terminal of the control chip U1. The voltage feedback unit is used to collect the current voltage of the battery and send the current voltage to the control chip U1. The control chip U1 is used to adjust the charging current according to the current voltage of the battery to stabilize the charging voltage of the battery.

[0073] It should be noted that voltage feedback is a closed-loop control mechanism that monitors the output voltage of the circuit in real time, compares the sampled signal with a preset reference voltage, and uses the error signal to adjust the system output. Specifically, the voltage feedback unit collects the current charging voltage of the battery in real time and transmits the voltage signal to the feedback terminal of the control chip U1. The voltage feedback unit includes a sampling stage (which can obtain the voltage value through a voltage divider resistor or a dedicated sensor), a comparison stage (which compares the voltage value with a reference source to generate an error signal), and an adjustment stage (the error signal drives the device to adjust the output to achieve voltage regulation).

[0074] Furthermore, the feedback terminal of the control chip U1 can be the FB pin of the control chip U1.

[0075] In this embodiment, as Figure 3 As shown, Figure 3 This is a schematic diagram illustrating the connection between another constant current circuit provided in this application and the battery and external power supply. The voltage feedback unit can be connected to the output terminal of the sampling unit and the FB pin of the control chip U1, feeding back the output voltage to the control chip U1. The control chip U1 compares the voltage value with the reference voltage, generates an error signal, and adjusts the output of the SW pin to achieve voltage regulation. For example, when the battery voltage is low, constant current fast charging is prioritized; when the voltage approaches the full charge threshold, the chip switches to constant voltage mode to reduce the current and avoid overvoltage.

[0076] By combining the voltage feedback unit described above, the control chip U1 can simultaneously utilize the current sampling signal and the voltage feedback unit to achieve "constant current + constant voltage" dual closed-loop control. When the battery voltage is lower than the set value, it charges with a constant current; when the voltage is higher than the set value and close to the battery voltage cutoff value, the charging current is reduced to avoid overvoltage, ultimately stabilizing at the set voltage and protecting battery life. This dual closed-loop control dynamically matches the battery state, solving the problem that a single mode cannot simultaneously achieve fast charging and safety.

[0077] In some embodiments, the voltage feedback unit further includes a feedback resistor, one end of which is connected to the positive terminal BAT of the battery, and the other end is connected to the feedback terminal of the control chip U1; the control chip U1 adjusts the charging current to stabilize the charging voltage of the battery by acquiring the voltage signal of the feedback resistor.

[0078] In this embodiment, as Figure 2As shown, the feedback resistor can be a series connection of a first feedback resistor R78 and a second feedback resistor R79. The first feedback resistor R78 is a pull-up resistor for the voltage divider network, with one end connected to the positive terminal of the high-potential battery in the main circuit, and the other end connected to the second feedback resistor R79 and the FB pin of the control chip U1. The second feedback resistor R79 is a pull-down resistor for the voltage divider network, with one end connected to the second feedback resistor R79 and the FB pin of the control chip U1, and the other end grounded. The control chip U1 obtains the feedback voltage signal through the FB pin and proportionally steps down the output high voltage (battery charging voltage) to a low voltage (1.25V reference value) recognizable by the FB pin of the control chip U1, allowing the control chip U1 to accurately monitor the output voltage of the constant current circuit.

[0079] For example, under the condition that the constant current circuit is 1A and the battery's full charge voltage is 4.2V, when the battery is charging close to full charge (4.2V), after the voltage is divided by the first feedback resistor R78 (100kΩ) and the second feedback resistor R79 (42kΩ), the voltage at pin FB rises to... ≈1.25V. When the control chip U1 detects that the FB pin has reached the reference value, it switches from constant current mode to constant voltage mode; the current gradually decreases as the battery voltage increases (e.g., drops to 0.1A) until it is fully charged.

[0080] Specifically, a high-precision resistor can be used in the feedback resistor to ensure accurate voltage division ratio, enabling the control chip U1 to accurately identify the battery voltage and avoid overvoltage or undercharge caused by voltage acquisition errors. By dividing the high battery voltage into a low voltage that the control chip U1 can recognize through the feedback resistor, a current detection circuit with high precision and high reliability for current monitoring and control can be achieved at low cost.

[0081] In some implementations, the filter capacitor C43 can be connected in parallel between the FB pin and the ground terminal SGND. The voltage regulator R80 is connected in parallel with the filter capacitor C43. The filter capacitor C43 and the resistor R80 form an RC filter to stabilize the voltage signal fed back to the FB pin and avoid high-frequency noise causing the control chip U1 to misjudge the output voltage.

[0082] In some embodiments, the constant current circuit described above further includes a system chip, the input terminal of which is connected to the battery, and the output terminal SoC of which is connected to the detection terminal of the control unit. The system chip is used to detect the state of the battery, and when the battery is detected to be in an abnormal state, it controls the control unit to stop outputting the charging current.

[0083] It should be noted that the system chip in the embodiments of this application can be a microcontroller unit (MCU), microprocessor unit (MPU), system on chip (System on Chip), digital signal processor (DSP), graphics processing unit (GPU), or other integrated circuits used to execute program instructions, process data, and control system operation.

[0084] The protection function of a single control chip U1 may fail to detect dangerous situations such as overcurrent and overtemperature due to its own failure. Adding an independent detection circuit for the system chip can prevent further damage to the circuit when an abnormality occurs. When the circuit is abnormal, the control chip U1 stops outputting.

[0085] In this embodiment, the system chip can operate independently of the control chip U1. It can detect abnormal states of the detection circuit and the battery state through additional sensors and analog-to-digital converters. When an abnormality is detected, the system chip can directly cut off the CS pin of the control chip U1, forcing it to stop outputting charging current. This forms a dual protection measure of the control chip U1 and the system chip, reducing the safety risks of the constant current circuit.

[0086] For example, the system chip could be an STM32 series chip. The original charging current is 1A. When the control chip U1 malfunctions, the external power supply directly supplies power to the battery through the constant current inductor L4, causing the charging current to surge to 5A. The system chip detects the surge in charging current, disconnects the charging circuit through a relay, and issues a fault signal (such as a buzzer sounding and an indicator light flashing) to prevent the battery from exploding due to overcurrent.

[0087] By adding a system chip to detect the status of the circuit, the safety of the constant current circuit is enhanced, preventing battery damage when the control chip U1 fails to protect against short circuits and overheating.

[0088] In some implementations, the control chip U1 adjusts the magnitude of the charging current by adjusting the duty cycle of the output current.

[0089] In this embodiment, the formulas for the output voltage and the input voltage are as follows: Where D is the PWM duty cycle (on-time ratio), by adjusting the duty cycle, the control chip U1 can convert the high voltage into a charging voltage suitable for the battery. Duty cycle D = on-time / (on + off-time), directly determining the output energy P: when the current is too high, decrease the duty cycle (reduce output energy); when it is too low, increase the duty cycle (increase output energy). The PWM adjustment frequency of the control chip U1 can reach several hundred kHz, with a response time of only tens of microseconds, quickly suppressing current fluctuations and maintaining a constant charging current output.

[0090] For example, input voltage (External power supply), target output voltage (Charging the battery), for a buck converter, the duty cycle D is related to the input voltage and the output voltage as follows:

[0091]

[0092] The duty cycle calculated using the above formula is 41.7%, meaning that the control chip U1 controls the internal MOSFET to conduct for 41.7% of the total cycle via the PWM signal. After the control chip U1 starts up, it generates a fixed PWM signal through its internal oscillator, with an initial duty cycle of 0.417. If the output current... If the voltage suddenly increases from 1A to 1.2A, the sampling voltage will rise from 0.1V to 0.12V. The voltage at pin CS of control chip U1 increases, causing control chip U1 to decrease its duty cycle. A lower duty cycle results in lower output energy and a decrease in output current. Gradually return to 1A.

[0093] When the input voltage The voltage suddenly increased from 12V to 15V. The voltage will be increased to 15V multiplied by 0.417, which is approximately 6.25V, exceeding the target of 5V. The control chip U1 detects this via its FB pin. Increase the duty cycle, decrease it, and reduce it to 33.3%. Return to the target voltage value.

[0094] By adjusting the duty cycle of the output current through the control chip U1, the system can quickly respond to changes in current and ensure that the charging current stabilizes more quickly, thereby achieving a high-precision and highly stable constant current.

[0095] In some embodiments, the constant current circuit further includes a transformer connected between the external power supply POWER SUPPLY and the control chip U1, the transformer being used to supply power to the control chip U1.

[0096] It should be noted that the transformer in this embodiment is a device that converts electrical energy (voltage / current) based on the law of electromagnetic induction. Its core consists of a primary winding (input side), a secondary winding (output side), and an iron core (magnetic circuit). The output voltage is adjusted by the turns ratio.

[0097] In some implementations, the transformer may be a flyback transformer, a power frequency transformer, or an integrated isolated power supply module, etc.

[0098] The external power supply can be a high-voltage power source, such as 220V or 310V. The control chip U1 typically operates at 5V to 12V. Directly powering the control chip U1 would burn it out, and high-voltage noise could couple to the battery through the power supply. Adding a transformer connects the external power supply and the control chip U1. The transformer uses electromagnetic induction to convert the external high voltage to the low voltage required by the control chip U1, such as 3.3V or 5V, achieving electrical isolation between the primary (high voltage) and secondary (low voltage) sides, preventing high-voltage leakage or noise coupling to the control chip U1 and the battery. After isolation, even if the external power supply experiences a surge, such as a sudden change from 220V to 300V, the secondary voltage remains stable, protecting the control chip U1 and other circuit components.

[0099] The transformer described in this application not only achieves electrical isolation and low-voltage power supply, but also improves the transformer's cross-regulation rate. By setting a current sampling unit at the positive terminal of the power supply, the transformer windings are not complicated due to the need to run an independent ground wire from the power supply terminal, which would result in poor cross-regulation rate. At the same time, the increased power loss caused by adding a dummy load to compensate for voltage fluctuations is avoided, thus improving the overall efficiency of the constant current circuit described in this application.

[0100] This application also provides an electronic device, which includes a battery and a constant current circuit as described in any of the above embodiments and methods, wherein the constant current circuit is connected between the external power supply and the battery.

[0101] The constant current circuit of the electronic device may include a control unit and a sampling unit. The sampling unit includes a sampling resistor and a first switching transistor Q23. The control unit converts the external power supply into a stable charging current. The sampling resistor sends the signal value of the positive terminal charging current to the detection terminal of the control unit through the first switching transistor Q23. The control unit adjusts the charging current based on the signal value. By placing the sampling resistor at the positive terminal of the power supply, the design and fabrication of the transformer are simplified, avoiding the need for a separate ground wire and optimizing the transformer's cross-regulation. Furthermore, detecting the charging current at the positive terminal avoids the need for various detection components to withstand the large current sum of multiple currents when detecting current at the negative terminal (requiring the use of high-power components), thus achieving high-precision and high-reliability current monitoring and control at low cost.

[0102] The electronic devices in this embodiment may be, for example, portable electronic devices, medical electronic devices, emergency electronic devices, energy storage network devices, sensor network devices, and other electronic devices.

[0103] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. Similarly, for the sake of brevity and to aid in understanding one or more aspects of the invention, in the description of exemplary embodiments of the invention above, various features of the embodiments are sometimes grouped together in a single embodiment, figure, or description thereof. The claims, which follow the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0104] Those skilled in the art will understand that the modules in the apparatus of the embodiments can be adaptively modified and placed in one or more apparatuses different from those of the embodiments. Modules, units, or components in the embodiments can be combined into a single module, unit, or component, and further, they can be divided into multiple sub-modules, sub-units, or sub-components, except that at least some of such features and / or processes or units are mutually exclusive.

[0105] It should be noted that the above embodiments are illustrative of the invention and not restrictive, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses should not be construed as limiting the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several different elements and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means can be embodied by the same item of hardware.

Claims

1. A constant current circuit for sampling the positive terminal current, characterized in that, The constant current circuit is connected between the external power supply and the battery; The constant current circuit includes a sampling unit and a control unit; the control unit is used to convert the external power supply into a charging current, and charge the battery through the sampling unit; the sampling unit includes a sampling resistor and a first switching transistor. The input terminal of the control unit is connected to the external power supply; one end of the sampling resistor is connected to the output terminal of the control unit, and the other end is connected to the positive terminal of the battery; the input terminal of the first switching transistor is connected between the control unit and the sampling resistor; the control terminal of the first switching transistor is connected between the sampling resistor and the positive terminal of the battery; and the output terminal of the first switching transistor is connected to the detection terminal of the control unit. The first switching transistor is used to amplify the voltage drop signal across the sampling resistor and then flow it into the detection terminal of the control unit. The control unit adjusts the charging current based on the amplified voltage drop signal. The control unit includes a control chip and a constant current inductor; The input terminal of the control chip is connected to the external power supply, the detection terminal of the control chip is connected to the output terminal of the first switching transistor, and the constant current inductor is connected between the control chip and the sampling resistor. The control chip is used to convert the current of the external power supply into the charging current, and adjust the magnitude of the charging current based on the voltage drop signal; the constant current inductor is used to keep the charging current constant. A fourth diode is provided between the SW pin and the ground terminal of the control chip. The cathode of the fourth diode is connected to the SW pin, and the anode of the fourth diode is connected to the ground terminal. A polarized capacitor and a bleeder resistor are connected in parallel between the constant current inductor and the ground terminal.

2. The constant current circuit according to claim 1, characterized in that, The sampling unit further includes a first resistor and a second resistor; One end of the first resistor is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the control terminal of the first switching transistor. One end of the second resistor is connected between the sampling resistor and the battery, and the other end is connected to the control terminal of the first switching transistor; The first resistor and the second resistor are used to adjust the amplification factor of the first switching transistor.

3. The constant current circuit according to claim 2, characterized in that, The sampling unit also includes a first capacitor and a second capacitor; One end of the first capacitor is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the output terminal of the first switching transistor. One end of the second capacitor is connected between the output terminal of the control unit and the sampling resistor, and the other end is connected to the control terminal of the first switching transistor; The first capacitor is used to absorb the surge current when the constant current circuit starts up; the second capacitor is used to filter high-frequency noise in the charging current.

4. The constant current circuit according to claim 1, characterized in that, The constant current circuit further includes a voltage feedback unit, and the control chip further includes a feedback terminal. The voltage feedback unit is connected between the battery and the feedback terminal of the control chip. The voltage feedback unit is used to collect the current voltage of the battery and send the current voltage to the control chip; The control chip is used to adjust the charging current according to the current voltage of the battery in order to stabilize the charging voltage of the battery.

5. The constant current circuit according to any one of claims 1-4, characterized in that, The constant current circuit also includes a system chip. The input terminal of the system chip is connected to the battery, and the output terminal of the system chip is connected to the detection terminal of the control unit. The system chip is used to detect the state of the battery. When the battery is detected to be in an abnormal state, it controls the control unit to stop outputting the charging current.

6. The constant current circuit according to claim 5, characterized in that, The control chip adjusts the magnitude of the charging current by regulating the duty cycle of the output current.

7. The constant current circuit according to claim 6, characterized in that, The constant current circuit also includes a transformer, which is connected between the external power supply and the control chip, and is used to supply power to the control chip.

8. An electronic device, characterized in that, The electronic device includes a battery and a constant current circuit according to any one of claims 1-7, the constant current circuit being connected between the external power source and the battery.

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