A current sharing circuit for linear voltage regulators operating in parallel

Abstract

The application relates to the power supply technical field and discloses a current sharing circuit for parallel operation of linear voltage stabilizers, which mainly comprises a first linear voltage stabilizer U1, a second linear voltage stabilizer U2, a first current detection resistor R1, a second current detection resistor R2, an operational amplifier A and an adjusting resistor R3. The output ends of the U1 and the U2 are connected in parallel to a common output node and supply power to a load together. The R1 is connected in series between the input end of the U1 and a common input node, the R2 is connected in series between the input end of the U2 and the common input node, the inverting input end of the operational amplifier A is connected to a node between the R1 and the input node of the U1, and the non-inverting input end of the operational amplifier A is connected to a node between the R2 and the input node of the U2. The adjusting resistor R3 is connected between the output end of the operational amplifier A and the feedback end of the U1. The device realizes automatic balanced distribution of the load current in a high-precision range, prevents a single voltage stabilizer from being disabled due to overcurrent, and simultaneously maintains the inherent low-noise and high-precision output characteristics of the linear voltage stabilizer.

Description

Technical Field

[0001] This application relates to the field of power supply technology, and in particular to a current sharing circuit for parallel operation of linear regulators, which is suitable for electronic devices that require high precision, low noise, and large current output, such as radio frequency modules, audio amplifiers, ADC conversion circuits, etc. Background Technology

[0002] In electronic system power supply design, switching power supplies and linear regulators are two mainstream solutions. Switching power supplies are highly efficient and have a large output current, but their switching characteristics introduce high ripple noise and electromagnetic interference, making it difficult to meet the clean power supply requirements of sensitive circuits such as analog circuits, RF front-ends, high-precision ADCs, and audio codecs.

[0003] In contrast, linear regulators (especially low dropout linear regulators, or LDOs for short) have the advantages of extremely low ripple, low noise, fast response, and simple structure, making them the core components for high-precision, low-noise power supplies. However, their output current is limited, and their conversion efficiency is low, leading to severe heat generation. Typically, the single-channel output current does not exceed 1A, which limits their application range.

[0004] To increase the output current, multiple linear regulators can be connected in parallel to achieve current superposition. However, due to inherent differences in internal components such as reference voltage and error amplifiers, even regulators of the same model will exhibit slight differences in no-load output voltage when connected in parallel. This leads to a "load-grabbing" phenomenon, where the unit with the higher output voltage bears the majority of the current, resulting in uneven current distribution. This can trigger overcurrent or overheat protection, causing system failure.

[0005] Existing current sharing schemes, such as the "droop method," sacrifice voltage accuracy, while the "master-slave setting method" or "average current method" require dedicated control chips or complex circuits, which are costly and may introduce noise, thus violating the original design intention of linear regulators to be simple and low-noise.

[0006] Therefore, there is an urgent need in this field for a current sharing scheme specifically for parallel linear regulators that can achieve automatic current balancing without excessively increasing complexity and cost, thereby expanding the output current capability while maintaining the advantage of low noise.

[0007] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Utility Model Content

[0008] To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended as a general commentary, nor is it intended to identify key / important components or describe the scope of protection of these embodiments, but rather as a prelude to the detailed description that follows.

[0009] This disclosure provides a current sharing circuit for parallel operation of linear regulators, which solves the problem of how to effectively overcome the inherent slight differences in output voltage between parallel linear regulators caused by manufacturing tolerances without introducing complex circuits or dedicated control chips, thereby achieving automatic balanced distribution of load current within a high-precision range, preventing individual regulators from failing due to overcurrent, and simultaneously maintaining the inherent low-noise and high-precision output characteristics of linear regulators.

[0010] In some embodiments, the current sharing circuit for parallel operation of linear regulators includes: a first linear regulator U1, a second linear regulator U2, a first current sensing resistor R1, a second current sensing resistor R2, an operational amplifier A, and an adjustment resistor R3.

[0011] The outputs of U1 and U2 are connected in parallel to a common output node to supply power to the load. R1 is connected in series between the input of U1 and the common input node, and R2 is connected in series between the input of U2 and the common input node, used to detect the input current of U1 and U2 respectively.

[0012] The inverting input of operational amplifier A is connected to the node between R1 and the input of U1, and its non-inverting input is connected to the node between R2 and the input of U2. Adjusting resistor R3 is connected between the output of operational amplifier A and the feedback terminal of U1.

[0013] The feedback terminal of U1 is connected to a first voltage divider resistor network consisting of a fourth resistor R4 and a fifth resistor R5 connected in series. The feedback terminal of U2 is connected to a second voltage divider resistor network consisting of a sixth resistor R6 and a seventh resistor R7 connected in series.

[0014] Preferably, the resistance values ​​of R4 and R6 are equal, the resistance values ​​of R5 and R7 are equal, and R4, R5, R6, and R7 are resistors with an accuracy of not less than 1% to ensure the symmetry and accuracy of the feedback voltage.

[0015] Preferably, R1 and R2 are precision power resistors with a resistance of no more than 30mΩ, which can provide accurate current detection signals while carrying large currents.

[0016] Preferably, operational amplifier A is a low input bias voltage operational amplifier, which can effectively respond to the small voltage difference across the sensing resistor.

[0017] Preferably, the resistance value of the regulating resistor R3 is configured such that the output voltage regulation range of U1 is limited to within ±4% of its nominal output voltage, thereby achieving stable and effective regulation.

[0018] Preferably, U1 and U2 are low-dropout linear regulators, which can reduce power consumption.

[0019] Preferably, U1 and U2 are placed on a shared heat dissipation structure, which can improve the system's heat dissipation capacity and thermal balance.

[0020] The current sharing circuit for parallel operation of linear regulators provided in this disclosure can achieve the following technical effects: This disclosure achieves significant benefits through its unique structural design. Its core lies in constructing a simple yet efficient self-balancing system. The circuit senses the load current state of the two branches in real time through current-sensing resistors connected in series in the input loops of each regulator, converting it into a small voltage signal. An operational amplifier, acting as a highly sensitive comparator and driver, continuously compares these two voltage signals. Once a current imbalance is detected, its output injects a correction signal into the feedback terminal of the regulator (U1) in the main control loop through adjusting a resistor.

[0021] This process essentially involves cleverly superimposing a dynamic, negative feedback "fine-tuning" mechanism onto the inherent voltage regulation feedback loop of the linear regulator. Instead of abrupt intervention, it precisely and continuously finely adjusts the output voltage of the regulator, guiding the output current values ​​of regulators (U1 and U2) to converge. This autonomous adjustment mechanism based on analog feedback enables the entire system to respond quickly to load changes or device parameter fluctuations, suppressing current imbalance to an extremely low level.

[0022] Specifically, this disclosure cleverly solves the problem of how to effectively overcome the inherent slight differences in output voltage between parallel linear regulators caused by manufacturing tolerances without introducing complex circuits or dedicated control chips, through an extremely simple analog feedback loop architecture of "sensing resistors (R1, R2) + operational amplifier (A) + regulating resistor (R3)". This achieves automatic balanced distribution of load current within a high-precision range, preventing individual regulators from failing due to overcurrent, while simultaneously maintaining the inherent low-noise, high-precision output characteristics of linear regulators. It utilizes general-purpose components to construct an autonomous, continuous, and high-precision analog control system, realizing: Real-time detection: Converts current differences into voltage signals by detecting resistors.

[0023] Precise comparison and drive: The difference signal is amplified by an operational amplifier.

[0024] Seamless closed-loop regulation: By adjusting the resistor, the correction signal is injected into the feedback node of the regulator (U1), and the linear regulator’s own regulation mechanism is used to fine-tune its output voltage, so that the current of the two tends to be consistent.

[0025] Therefore, this disclosure fundamentally resolves the contradiction between the four requirements of "simplicity, low cost, high precision, and low noise" in parallel current sharing applications, achieving a technological breakthrough.

[0026] The above general description and the description below are exemplary and illustrative only and are not intended to limit this application. Attached Figure Description

[0027] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations and drawings do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are shown as similar elements. The drawings are not to be scaled. And wherein: Figure 1 This is a schematic diagram of a parallel output circuit of a bilinear regulator without current sharing control in the existing technology.

[0028] Figure 2 This is a circuit diagram of an embodiment of the parallel current sharing circuit of the bilinear voltage regulator described in this utility model.

[0029] The illustration is explained below: U1 is the first linear regulator, U2 is the second linear regulator, R1 is the first current sensing resistor, R2 is the second current sensing resistor, A represents the operational amplifier, R3 represents the adjustment resistor, R4 is the fourth resistor, R5 is the fifth resistor, R6 is the sixth resistor, R7 is the seventh resistor, and R8 is the eighth resistor.

[0030] exist Figure 2 In the diagram, point a is the inverting input terminal of operational amplifier A, which is connected to the back end of R1.

[0031] exist Figure 2 In the diagram, point b is the non-inverting input of operational amplifier A, which is connected to the back end of R2.

[0032] exist Figure 2 In the diagram, point c is the connection point between the output terminal of operational amplifier A and the regulating resistor R3. Detailed Implementation

[0033] To provide a more detailed understanding of the features and technical content of the embodiments of this disclosure, the implementation of the embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of this disclosure. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be simplified in their depiction to simplify the drawings.

[0034] The terms "first," "second," etc., used in the embodiments of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this disclosure described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0035] In this disclosure, the terms "upper," "lower," "inner," "middle," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for better describing the embodiments of this disclosure and their implementations, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to require them to be constructed and operated in a specific orientation. Furthermore, some of the aforementioned terms may be used to indicate other meanings besides orientation or positional relationship; for example, the term "upper" may in some cases indicate a dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this disclosure according to the specific circumstances.

[0036] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this disclosure according to the specific circumstances.

[0037] Unless otherwise stated, the term "multiple" means two or more.

[0038] In this embodiment of the disclosure, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0039] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0040] It should be noted that, without conflict, the embodiments and features in this disclosure can be combined with each other.

[0041] Figure 1 As background technology, the problem of directly connecting two linear regulators in parallel is intuitively presented: due to the inherent differences between the devices, even if the same feedback network (R4 / R5, R6 / R7) is connected, the current (I1, I2) will be unevenly distributed, which provides a clear direction for improvement for this utility model.

[0042] Figure 2 This invention demonstrates a complete solution for automatic current sharing by detecting current deviation through operational amplifier A and dynamically adjusting the feedback voltage of U1 using R3.

[0043] Combination Figure 2 This disclosure provides a current sharing circuit for parallel operation of linear regulators, which mainly includes a first linear regulator U1, a second linear regulator U2, a first current sensing resistor R1, a second current sensing resistor R2, an operational amplifier A, and an adjustment resistor R3.

[0044] The outputs of U1 and U2 are connected in parallel to a common output node to supply power to the load. R1 is connected in series between the input of U1 and the common input node, and R2 is connected in series between the input of U2 and the common input node, used to detect the input current of U1 and U2 respectively.

[0045] The inverting input of operational amplifier A is connected to the node between R1 and the input of U1, and its non-inverting input is connected to the node between R2 and the input of U2. Adjusting resistor R3 is connected between the output of operational amplifier A and the feedback terminal of U1.

[0046] Operational amplifier A is used to compare the voltage drop across R1 and R2 to detect the difference in output current between U1 and U2. A compensation signal is introduced into the feedback loop of U1 by adjusting resistor R3, dynamically adjusting the output voltage of U1 to work in tandem with U2 and achieve current sharing. When there is a deviation in the parameters of U1 and U2, the system can automatically correct it, ensuring a more balanced current distribution and improving overall stability and load capacity. This current sharing circuit effectively solves the current unevenness problem caused by the dispersion of device parameters in traditional parallel methods, significantly improving the reliability and efficiency of the system. The introduction of an error detection and feedback adjustment mechanism using operational amplifiers achieves the design goal of achieving good current sharing without the need for precision matching components. In practical applications, this structure is suitable for high-reliability power supply systems, especially in scenarios requiring redundant design or high current output. This solution can also be extended to the parallel connection of multiple linear regulators, further improving its practicality and scalability. By reasonably setting the resistance values ​​of R1 and R2, high-precision current detection can be achieved without affecting overall efficiency, ensuring that operational amplifier A responds quickly to minute current differences. The value of the adjusting resistor R3 should balance the stability of the feedback loop and the current sharing response speed to avoid system oscillation caused by excessive phase delay. In actual layout, the detection path should be symmetrical to reduce measurement errors caused by parasitic parameters.

[0047] Preferably, the feedback terminal of U1 is connected to a first voltage divider resistor network consisting of R4 and R5 connected in series. The feedback terminal of U2 is connected to a second voltage divider resistor network consisting of R6 and R7 connected in series. The first end of R4 is connected to the output terminal of U1, and the second end of R4 is connected to the first end of R5 to form the feedback node of U1, with the second end of R5 grounded. The first end of R6 is connected to the output terminal of U2, and the second end of R6 is connected to the first end of R7 to form the feedback node of U2, with the second end of R7 grounded.

[0048] Understandably, by independently setting the voltage divider feedback networks of U1 and U2, the output voltage reference of each regulator can be adjusted separately, thereby achieving soft start or gradual current sharing control in the initial stage of system power-on. The resistance values ​​of R4 to R7 should be selected with low temperature drift and high precision to ensure stability under long-term operation. When there is a deviation between the two output currents, op-amp A detects the voltage difference change across R1 and R2 and dynamically adjusts the feedback voltage of U1 through R3, causing its output current to converge towards U2, ultimately achieving static balance. This structure achieves bidirectional automatic adjustment without master-slave configuration, enhancing the system's symmetry and fault tolerance. In multi-board parallel or hot-swappable scenarios, this design effectively suppresses circulating current surges and improves system reliability. Simultaneously, a low-pass filter circuit should be configured at the input of op-amp A to suppress high-frequency interference and avoid false triggering of adjustment actions. R1 and R2 should preferably be milliohm-level precision sampling resistors, and their layout should be close to the output terminals of the corresponding regulators to reduce the impact of trace inductance.

[0049] When the output currents of U1 and U2 are inconsistent, a voltage difference is generated across R1 and R2. Operational amplifier A detects this difference and outputs a corresponding level. By adjusting R3, the feedback voltage of U1 is changed, thereby adjusting its output current to approach the output current of U2. Through this negative feedback mechanism, the system achieves dynamic current sharing, effectively suppressing current imbalance caused by device parameter deviations. This structure requires no precision matching components, has good compatibility, and is suitable for various parallel linear regulator scenarios. It can significantly improve current sharing accuracy and system reliability while ensuring stability. Furthermore, the high-gain characteristic of operational amplifier A ensures that even a small current difference triggers a significant adjustment, thereby greatly improving the sensitivity and dynamic adjustment accuracy of the current sharing response. This allows the system to maintain good current sharing performance under dynamic conditions such as sudden load changes or temperature rise variations. Simultaneously, the introduction of adjusting resistor R3 effectively isolates the direct coupling between the op-amp output and the U1 feedback network, avoiding control loop oscillation and further enhancing system stability and reliability. This solution has a simple structure, requires no additional digital control unit, and can achieve fully analog automatic current sharing, making it suitable for high-precision power management applications.

[0050] As an example, the feedback terminal of U2 is connected to the second voltage divider resistor network, fixing its output voltage reference and acting as the master regulator. The feedback terminal of U1 is connected to the first voltage divider resistor network, acting as the slave regulator, whose output voltage is dynamically adjusted by the output of operational amplifier A. In this case, operational amplifier A injects compensation current into the feedback node of U1 through R3, changing its voltage division ratio, thereby adjusting the output voltage of U1 and achieving dynamic balance of the output current. This master-slave structure maintains stable output voltage while achieving automatic current balancing, ensuring high current sharing accuracy even under dynamic load changes or ambient temperature fluctuations. By appropriately setting the voltage divider resistor values ​​and operational amplifier gain, the trade-off between adjustment speed and stability can be further optimized. Furthermore, capacitors can be introduced into the compensation network to improve phase margin and suppress the risk of high-frequency oscillations. The entire current sharing mechanism requires no complex communication protocols or digital processor intervention, offering advantages such as rapid response, high reliability, and low cost, making it suitable for applications with stringent redundancy and efficiency requirements, such as industrial power supplies, LED drivers, and battery charging.

[0051] Preferably, the resistance values ​​of R4 and R6 are equal, the resistance values ​​of R5 and R7 are equal, and R4, R5, R6, and R7 are resistors with an accuracy of not less than 1% to ensure the symmetry and accuracy of the feedback voltage. With this configuration, the feedback voltage division ratios of U1 and U2 remain highly consistent, effectively eliminating the reference offset introduced by resistor mismatch and ensuring the static accuracy of current sharing control. Operational amplifier A only responds to minute voltage deviations caused by differences in output current, avoiding misadjustment and improving the system's anti-interference capability.

[0052] Preferably, R1 and R2 are high-power precision resistors with a resistance of no more than 30mΩ, which can provide accurate current sensing signals in high-power applications. Their low temperature coefficient and high stability ensure that the current sampling accuracy is not affected over a wide temperature range, thereby guaranteeing the consistency and reliability of current sharing control under different operating conditions. The voltage signals across R1 and R2 are filtered and then input to operational amplifier A to further suppress high-frequency noise interference and improve the detection signal-to-noise ratio. The entire circuit layout should adopt a star grounding and short-path routing strategy to reduce common-mode interference and the influence of parasitic parameters. By selecting low-temperature drift, high-stability components and optimizing the PCB thermal design, the current imbalance caused by temperature gradients can be effectively reduced, ensuring long-term operational stability.

[0053] Preferably, operational amplifier A features low input bias current characteristics, ensuring accurate response to small voltage differences across the sense resistor. Its typical input offset voltage should be less than 1mV to avoid static regulation errors at zero current difference. Simultaneously, op-amp A's common-mode rejection ratio (CMRR) should be higher than 80dB to effectively suppress common-mode interference introduced by power supply fluctuations, ensuring accurate extraction of the current differential signal even in complex electromagnetic environments. Op-amp A's gain bandwidth should be no less than 1MHz to ensure sufficient response speed and loop stability under dynamic load changes. Combined with appropriate phase compensation, oscillations can be effectively avoided and system transient performance improved. The overall design balances accuracy, response, and reliability, making it suitable for parallel current sharing control of high-density power modules.

[0054] Preferably, the resistance value of the regulating resistor R3 is configured such that the output voltage adjustment range of U1 is limited to within ±4% of its nominal output voltage, thereby achieving stable and effective regulation. This limiting design prevents excessive deviation of the U1 output voltage due to over-adjustment of R3, avoiding adverse effects on other parts of the system, while ensuring that current sharing regulation is performed within a safe range. The resistance adjustment accuracy of R3 should be no less than 5%. It is recommended to use a multi-turn potentiometer or laser-trimmed resistor to achieve fine adjustment and long-term stability. During the adjustment process, dynamic calibration should be performed in conjunction with actual load conditions to ensure that the current sharing error is always less than 5% under different output currents. The mechanical durability and welding thermal stability of R3 should meet the requirements of industrial applications to avoid resistance drift due to vibration or temperature cycling. The entire current sharing circuit should be aged under full load conditions to screen for potential failure components and verify long-term operational reliability. By performing multi-point calibration within the typical operating temperature range, the influence of temperature drift can be further corrected, improving the overall accuracy of the system.

[0055] Preferably, both U1 and U2 are low-dropout linear regulators to reduce power consumption. Their typical dropout voltage is below 300mV, enabling stable output even with small input-output voltage differences, thus improving system efficiency. The load regulation of U1 and U2 should be better than ±0.5% to ensure minimal output voltage fluctuations under different load currents and maintain the accuracy of the current sharing control loop. Both should have a quiescent current below 5mA to reduce no-load power consumption, making them suitable for energy-efficient high-density power supply systems. To enhance thermal matching characteristics, U1 and U2 should preferably use the same package and be symmetrically laid out to reduce parameter mismatch caused by temperature differences. They integrate over-temperature protection and current limiting circuits, which can automatically cut off the output under abnormal operating conditions, improving system safety.

[0056] Preferably, U1 and U2 should be mounted on a shared heat dissipation structure to improve the system's heat dissipation capacity and thermal balance.

[0057] It is understandable that a shared heat dissipation structure can effectively reduce the temperature difference between the two components, thereby minimizing the output characteristic deviation caused by temperature differences and ensuring that U1 and U2 maintain consistent thermal response characteristics under load changes and ambient temperature fluctuations. This heat dissipation structure should have low thermal resistance; materials with a thermal conductivity of not less than 15 W / (m·K), such as aluminum or copper alloys, are recommended, along with thermal grease or phase change materials to enhance interfacial thermal conductivity. The heat dissipation structure design should ensure a smooth surface and uniform installation pressure to avoid localized poor contact leading to increased thermal resistance. The heat dissipation structure should be installed using a symmetrical fastening method to ensure uniform force on U1 and U2, avoiding package deformation or increased thermal resistance due to uneven mechanical stress. The surface of the heat dissipation structure should undergo anti-oxidation treatment to maintain long-term thermal stability. In high-temperature and high-humidity environments, the risk of leakage caused by condensation must be prevented. The entire current sharing system should be validated for thermal stability under complete thermal cycling conditions to ensure reliable operation within the range of -40°C to +85°C. During testing, the case temperature changes of U1 and U2 should be monitored to ensure that the temperature difference between them does not exceed 5°C.

[0058] In summary, this disclosure provides a current sharing circuit for parallel operation of linear regulators. It consists of an operational amplifier and two sensing resistors forming a current sharing control loop. The sensing resistors detect the deviation of the load current of each linear regulator and send the deviation voltage to the input terminal of the operational amplifier. By utilizing the linear output characteristics of the operational amplifier within the bias voltage range, the feedback input of the linear regulator is dynamically adjusted, thereby regulating the output voltage and achieving load current balance among the parallel linear regulators.

[0059] It should be noted that when using linear regulators in parallel, simply connecting two linear regulators in parallel is not advisable. Although two linear regulators may be of the exact same model, their internal components (such as error amplifiers and MOSFETs) will still have slight differences. These differences can only be minimized, not completely eliminated. For example... Figure 1 As shown, although the two parallel linear regulators are connected to the same feedback circuit, their inherent characteristics still result in slightly different output voltages. The linear regulator with the higher output voltage will dominate, sharing more current and causing load imbalance, which may lead to current limit protection or thermal shutdown.

[0060] To achieve an even distribution of the operating current between the two linear regulators, a control loop needs to be added, such as... Figure 2The current sharing control loop in the circuit mainly consists of operational amplifier A and sensing resistors R1 and R2. During operation, the load currents of the two linear regulators flow through sensing resistors R1 and R2 respectively. If the load currents of the two linear regulators are different, a voltage difference will form between points a and b on the back end of the sensing resistors. This voltage difference is fed into the operational amplifier, driving a change in the output voltage of the operational amplifier, which in turn changes the feedback voltage of U1, adjusting the output of U1 and thus reducing the current distribution deviation between the two linear regulators. In this design, U2 acts as the primary linear regulator with a fixed output voltage, while U1 acts as the secondary linear regulator, whose output voltage is subject to real-time control and dynamic adjustment.

[0061] The dynamic adjustment process of this circuit is as follows: 1) When the output voltage of U1 is slightly higher than that of U2 and the load current is larger, the current flowing through R1 is larger and the voltage at point a is lower than that at point b. At this time, the voltage at the positive terminal of the op-amp is higher than that at the negative terminal, the output voltage increases, and the voltage at point c increases. The internal regulation mechanism of U1 will reduce the output voltage in response to the increase of the FB signal, thereby reducing its load current. 2) When the output voltage of U1 is lower than that of U2 and the load current is smaller, the current flowing through R1 is smaller and the voltage at point a is higher than that at point b. At this time, the voltage at the negative terminal of the op-amp is higher than that at the positive terminal, the output voltage decreases, and the voltage at point c is driven to decrease. At this time, the internal regulation mechanism of U1 will increase the output voltage and the load current of U1 will increase. 3) Under load balance, the output voltages of the two linear regulators are very similar, and the load currents are almost the same. At this time, the current sharing control loop remains stable.

[0062] Since the purpose of this design is to enable the linear regulator to output a larger current, according to the power dissipation formula of the linear regulator: , for output current To ensure that power consumption does not exceed the limit in cases of large voltage fluctuations, linear regulators that allow for lower input-output voltage differences should be selected whenever possible.

[0063] Regarding the feedback resistors R4, R5, R6, and R7, the resistance values ​​of the two feedback circuits should be exactly the same, i.e., R4 equals R6, and R5 equals R7. Considering the inherent error of the resistors, high-precision resistors with an accuracy of 1% should be selected.

[0064] Regarding the sensing resistors R1 and R2, since they will carry a large current, power resistors should be selected. To ensure control accuracy, precision resistors with an accuracy of 1% or higher should be chosen. The resistance value should not be too large, generally 30mΩ or less is preferable.

[0065] Regarding operational amplifier A, its input bias voltage should be as small as possible to accurately respond to minute voltage differences at the sense resistor. Typically, both the sense resistor and the load current are small, and the voltage deviation at the op-amp input is also small. If the op-amp bias voltage is too large, it will be unable to respond to minute voltage differences, thus failing to provide regulation.

[0066] Regarding the adjusting resistor R3, it connects the op-amp output terminal and the U1 feedback terminal, determining the adjustment amplitude of the feedback voltage, which in turn affects the variation range of the U1 output voltage. Therefore, its resistance value needs careful design. If the resistance of R3 is too small, the adjustment effect will be too strong, leading to an excessively large variation range of the U2 output voltage, potentially causing output instability. If the resistance of R3 is too large, the adjustment effect will be weakened, and the U2 output voltage cannot be effectively controlled. Generally, the value of R3 is around 15KΩ, which can ensure that the accuracy of the U1 and U2 output voltages is controlled within ±1.5%, thereby achieving a better adjustment effect.

[0067] As an example, this circuit includes two identical low-dropout linear regulators (LDOs), namely the first linear regulator U1 and the second linear regulator U2. The input terminals of U1 and U2 are connected to the DC input voltage Vin through the first current sensing resistor R1 and the second current sensing resistor R2, respectively, and their output terminals are connected in parallel to a common output node Vout, which together power the load.

[0068] The second linear regulator U2 is equipped with a fixed feedback resistor network, which consists of a sixth resistor R6 and a seventh resistor R7 connected in series. This network is used to compare the voltage with a reference voltage generated internally by the chip, thereby achieving closed-loop control of the output voltage. R6 is connected between the output terminal and the feedback terminal (FB) of U2, and R7 is connected between the feedback terminal and ground (GND). By setting the resistance ratio of R6 and R7, the output voltage of U2 is fixed at its rated value. In this embodiment, U2 is used as the main regulator.

[0069] The first linear regulator U1 is equipped with a symmetrical feedback resistor network, which consists of a fourth resistor R4 and a fifth resistor R5 connected in series. R4 is connected between the output terminal and the feedback terminal of U1, and R5 is connected between the feedback terminal and ground. To achieve initial voltage matching, the resistance value of R4 is equal to that of R6, and the resistance value of R5 is equal to that of R7. R4, R5, R6, and R7 are all precision metal film resistors with a tolerance of ±1% to reduce initial deviation.

[0070] The inverting input terminal (+) of operational amplifier A is connected to node a between the first current sensing resistor R1 and the input end of U1. The non-inverting input terminal (-) of operational amplifier A is connected to node b between the second current sensing resistor R2 and the input end of U2. Operational amplifier A needs to select a model with low input offset voltage to ensure that the tiny voltage difference between node a and node b can be effectively detected and responded to. The positive and negative power supply pins of operational amplifier A are respectively connected to a stable positive and negative power supply (not shown in the figure) or a suitable single-power supply circuit.

[0071] The adjustment resistor R3 is connected between the output end (node c) of operational amplifier A and the feedback end of the first linear regulator U1.

[0072] Working principle and process: When the circuit is in operation, the load currents I1 and I2 flowing through U1 and U2 generate corresponding voltage drops on the first current sensing resistor R1 and the second current sensing resistor R2 respectively. In the current balance state, I1≈I2, and since R1 = R2, the voltage difference between node a and node b is close to zero, the output of operational amplifier A remains unchanged, and the circuit is in a stable state.

[0073] When the load changes or device parameters drift leading to current imbalance, for example, I1>I2, the potential of node b will be higher than the potential of node a. After operational amplifier A detects this positive voltage difference, its output voltage (potential of node c) will rise. This voltage change acts on the feedback end of U1 through the adjustment resistor R3, causing the feedback voltage of U1 to rise. The error amplifier responds to the input change, drives the regulating transistor by amplifying the error signal, and then reduces the output voltage of U1. This process aims to reduce the current I1 flowing through U1, so that it gradually reaches a balanced state with the current I2.

[0074] Conversely, if I1<I2, the potential of node b is lower than that of node a, the output voltage of operational amplifier A decreases, the feedback voltage of U1 is reduced through R3, which in turn causes the output voltage of U1 to rise, the current I1 increases, and it also tends to balance.

[0075] Through this closed-loop control, the present utility model realizes high-precision automatic equalization of the output currents of the two parallel linear regulators.

[0076] In a feasible non-limiting example of the present utility model, each component can adopt the following parameters: Current sensing resistors R1, R2: precision sampling resistors with a resistance value of 30mΩ, an accuracy of ±1%, and a power that meets the maximum current requirement.

[0077] Adjustment resistor R3: the resistance value is about 15kΩ.

[0078] Feedback resistors R4, R5, R6, and R7: Selected based on the required output voltage. For example, to make the output voltage 5V, R4=R6=10kΩ and R5=R7=3.3kΩ can be selected.

[0079] Operational amplifier A: A precision op-amp with low input offset voltage (maximum 150μV) can be selected, such as OP400AY / 883.

[0080] Those skilled in the art can make adaptive adjustments to the model and parameters of the above-mentioned components based on the specific current capacity, voltage regulator model and control response speed requirements, without departing from the core concept of this utility model.

[0081] The foregoing description and accompanying drawings fully illustrate embodiments of the present disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included or substituted for parts and features of other embodiments. Embodiments of the present disclosure are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A current sharing circuit for parallel operation of linear voltage regulators, characterized in that, include: The outputs of the first linear regulator (U1) and the second linear regulator (U2) are connected in parallel to a common output node; The first current sensing resistor (R1) is connected in series between the input terminal of the first linear regulator (U1) and the common input node; The second current sensing resistor (R2) is connected in series between the input terminal of the second linear regulator (U2) and the common input node; An operational amplifier (A) has its inverting input connected to the node between the first current sensing resistor (R1) and the input of U1, and its non-inverting input connected to the node between the second current sensing resistor (R2) and the input of U2; An adjustment resistor (R3) is connected between the output of the operational amplifier (A) and the feedback terminal of the first linear regulator (U1).

2. The current sharing circuit according to claim 1, characterized in that, The feedback terminal of the first linear regulator (U1) is connected to a first voltage divider resistor network, and the feedback terminal of the second linear regulator (U2) is connected to a second voltage divider resistor network.

3. The current sharing circuit according to claim 2, characterized in that, The first voltage divider resistor network is composed of a fourth resistor (R4) and a fifth resistor (R5) connected in series. The first end of the fourth resistor (R4) is connected to the output terminal of the first linear regulator (U1), and the second end of the fourth resistor (R4) is connected to the first end of the fifth resistor (R5) and forms the feedback node of the first linear regulator (U1). The second end of the fifth resistor (R5) is grounded. The second voltage divider resistor network is composed of a sixth resistor (R6) and a seventh resistor (R7) connected in series. The first end of the sixth resistor (R6) is connected to the output terminal of the second linear regulator (U2), and the second end of the sixth resistor (R6) is connected to the first end of the seventh resistor (R7) and forms the feedback node of the second linear regulator (U2). The second end of the seventh resistor (R7) is grounded.

4. The current sharing circuit according to claim 3, characterized in that, The resistance value of the fourth resistor (R4) is equal to the resistance value of the sixth resistor (R6), and the resistance value of the fifth resistor (R5) is equal to the resistance value of the seventh resistor (R7).

5. The current sharing circuit according to claim 3, characterized in that, The fourth resistor (R4), the fifth resistor (R5), the sixth resistor (R6), and the seventh resistor (R7) are resistors with an accuracy of not less than one percent.

6. The current sharing circuit according to claim 1, characterized in that, The first current sensing resistor (R1) and the second current sensing resistor (R2) are precision power resistors with a resistance value of no more than 30 milliohms.

7. The current sharing circuit according to claim 1, characterized in that, The operational amplifier (A) is a low input bias voltage operational amplifier.

8. The current sharing circuit according to claim 3, characterized in that, The resistance value of the regulating resistor (R3) is configured such that the output voltage regulation range of the first linear regulator (U1) is limited to within ±4% of its nominal output voltage.

9. The current sharing circuit according to any one of claims 1 to 8, characterized in that, Both the first linear regulator (U1) and the second linear regulator (U2) are low-dropout linear regulators.

10. The current sharing circuit according to any one of claims 1 to 8, characterized in that, The first linear regulator (U1) and the second linear regulator (U2) are mounted on a common heat dissipation structure.

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