Current equalization low-ripple voltage source based on equivalent resistance negative feedback

Abstract

The invention provides a current sharing low-ripple voltage source based on equivalent resistance negative feedback, which is characterized by comprising a common-mode filtering module, a direct-current converter module, a direct-current filtering module, a reference current module, a linear voltage regulator module based on equivalent resistance negative feedback regulation and the like. High-ripple direct-current voltage from 24V to 36V is input, and common-mode noise is suppressed through the common-mode filtering module; the direct-current converter module realizes primary voltage conversion and outputs 9V direct-current voltage; the direct current filtering module filters ripples in 9V direct current voltage; a linear voltage regulator in the reference current module provides reference; the linear voltage stabilizer module based on equivalent resistance negative feedback regulation reduces 9V direct current voltage to 5V direct current to be output, power supply current is improved through multi-path parallel connection and expansion, high ripple rejection ratio is achieved, and power output power is increased. The power density is high, output currents of the linear voltage stabilizer modules connected in parallel are balanced, the output power is large, the power supply rejection ratio is high, and the power supply is suitable for the field of precise instrument equipment power supply.

Description

Technical Field

[0001] A current-sharing low-ripple voltage source based on equivalent resistance negative feedback belongs to the field of electrical equipment / power supply design. Background Technique

[0002] DC power supplies are an indispensable part of electronic products and are used to supply power to electronic devices. With the rapid development of electronic technology, high-power devices are increasingly widely used, and there are higher and higher requirements for the output power, regulation time, ripple noise, and power conversion efficiency of high-power DC power supplies. In a measurement system with high precision, in addition to power supply ripple noise, requirements are also put forward for the power of the power supply. In addition, to ensure high-precision measurement and dynamic response, the power supply needs to have fast regulation ability and low-ripple characteristics. In some high-power application scenarios, such as certain industrial process control and environmental monitoring equipment, higher power output may be required to support the operation of the system. For example, some high-precision measurement devices may require power up to dozens of watts or even hundreds of watts, which requires the power supply to not only have high precision and low-ripple characteristics but also sufficient power output capacity. DC power supplies are mainly divided into DC-DC (Direct Current to Direct Current Switching Power Supply) and DC linear power supplies. Among them, DC linear power supplies are mainly based on low dropout voltage regulators (LDOs). DC-DC switching power supplies have high efficiency and small volume but large ripple; DC linear power supplies have high precision and small ripple but low efficiency and large heat generation.

[0003] The feedback regulation methods of DC power supplies are mainly divided into two categories: digital regulation and analog regulation. DC-DC switching power supplies usually use digital regulation, and DC linear power supplies usually use analog regulation. The basic principle of digital regulation is to convert the output voltage or current into a digital signal through an analog-to-digital converter, then compare it with a reference value, calculate the control signal through digital algorithms such as PID control, and then drive the power supply circuit through a digital-to-analog converter or pulse width modulation, etc.; analog regulation is mainly realized through analog circuits, and its core components usually include operational amplifiers, resistors, capacitors, etc. for forming a feedback loop; the basic principle of analog regulation is to form a feedback loop through devices such as operational amplifiers, resistors, and capacitors to monitor the output voltage or current, compare it with a reference signal, and adjust the control signal of the power supply according to the error signal to stabilize the output voltage or current.

[0004] DC switching power supplies are widely used due to their high power output and high conversion efficiency. A DC switching power supply is a type of switched-mode power supply. Its core principle is to convert the input DC voltage into a high-frequency pulsed voltage through the rapid switching action of switching elements (such as transistors), and then smooth the pulsed voltage into the required output DC voltage through a filter network composed of inductors and capacitors. Common pulse modulation modes include pulse width modulation, pulse frequency modulation, and hybrid modulation. This switching modulation method enables DC switching power supplies to achieve high power output and efficient power conversion under different input and output voltage conditions. In the paper "A Hybrid Modular DC-DC Converter for HVDC Applications" published by Binbin Li et al. in the IEEE Transactions on Power Electronics, Vol. 35, No. 4, pp. 3377-3389 in 2020, a new type of hybrid modular DC switching power supply for high-voltage direct current (HVDC) transmission applications was proposed. This DC converter can perform bidirectional power transmission of up to 4.5 kW between 500 V and 300 V, with a conversion efficiency of 99.31%. In the paper "Hybrid Modulated DC-DC Boost Converter for Wearable Devices" published by Tong Li et al. in Electronics, Vol. 11, No. 20, p. 3418 in 2022, a DC-DC boost converter chip for wearable devices was proposed using the BOOST boost debugging technique in the PCMC-PFM mode. The power density of this power chip is as high as 15.5 W / mm 2, the peak efficiency is 94.7%. Although the DC switching power supply achieves efficient power conversion through switching modulation, this switching action also introduces ripple. Ripple is the periodic fluctuation in the output voltage, mainly caused by the rapid switching action of the switching element. The existence of ripple may affect the performance of the circuit, especially in noise-sensitive applications such as analog signal processing, precision measurement, and communication systems. In the paper "A Switched-Capacitor DC-DC Converter with Unequal Duty Cycle for Ripple Reduction and Efficiency Improvement" published by Yulun Wu et al. in the 2019 IEEE International Conference on Integrated Circuits, Technology and Applications in 2019, the unequal duty cycle scheme regulation method is used and applied to the switched capacitor DC-DC. By adjusting the duty cycle, the energy transfer process becomes smoother and the output ripple is reduced. Through experimental comparison, it is found that in the equal duty cycle mode, the output ripple is as high as 92.3 mV, while in the unequal duty cycle mode, the output ripple is significantly reduced to 52.3 mV, a reduction of 43.6%. Although this reduction ratio is quite significant, the absolute value of the output ripple is still relatively high.

[0005] In terms of the feedback regulation of DC power supplies, digital regulation usually uses a digital signal processor or a programmable microcontroller to achieve closed-loop feedback regulation. Although digital regulation has flexibility and programmability, the feedback regulation speed is slow, mainly due to ADC sampling delay, microcontroller processing delay, and PWM update delay. These delays increase the system's response time, and the common feedback regulation time is from 1 millisecond to over 100 milliseconds. The paper "Output Voltage Response Improvement and Ripple Reduction Control for Input-Parallel Output-Parallel High-Power DC Supply" published by Jianhui Meng et al. in the 9th issue of the 38th volume of the IEEE Transactions on Power Electronics (pages 1102-1112) in 2023 studied the problems of slow output voltage response speed and large ripple in DC-DC high-power applications and proposed an improved adaptive linear active disturbance rejection control method to improve the output voltage response speed. The study found that when using the traditional digital PI control method to handle load mutations, the response speed is slow. When switching from no load to heavy load, the time for the system to reach a stable state is about 150 milliseconds. During load mutations, the undershoot duration exceeds 1000 milliseconds. In contrast, for the proposed adaptive linear active disturbance rejection control method, when switching from no load to heavy load, the time for the system to reach a stable state is about 30 milliseconds, which is about 80% faster than PI control, and during load mutations, the undershoot duration is only 1-2 milliseconds. However, although the adaptive linear active disturbance rejection control method reduces the feedback regulation stabilization time, compared with the nanosecond and microsecond-level times of analog feedback regulation, the absolute value of the overall regulation time is still large. The paper "A Digitally Controlled Linear Power Supply for HALF Fast Orbit Correctors" published by Zhuoxia Shao et al. in Nuclear Instruments and Methods in Physics Research, A (Volume 1042, Page 167459) in 2022 proposed a digitally controlled linear power supply for fast orbit correctors. This power supply is based on the H-bridge topology and uses FPGA for full digital control, featuring fast response and high stability.Experiments show that for the proposed digital feedback control method, when switching from no load to heavy load, the time for the system to reach a stable state is approximately 3 milliseconds. When there is a sudden change in load, the overshoot duration is only 1 - 2 milliseconds. Although this digital method uses an FPGA as the core of feedback control, the system feedback time is still at the millisecond level. This indicates that although the relative improvement is significant, the feedback regulation speed of the DC power supply using digital regulation is still slow, especially in application scenarios that require extremely high response speeds.

[0006] The output ripple noise of a DC switching power supply is large, while the response speed of the digital regulation method is slow. To meet the requirements of low ripple and fast response of the power supply, DC linear power supplies have been widely used due to their advantages of low ripple and fast response. In 2024, the paper "A High Power Supply Rejection and Fast-transient LDO with Feed-forward Compensation using Current Sensing Technique" by Bongsu Kim et al. published in the Journal of Semiconductor Technology and Science, Volume 24, Issue 1, Pages 1598 - 1657, proposed a method for high power supply rejection ratio and stability of a low-dropout linear regulator. By using feed-forward compensation technology, a compensation signal proportional to the power supply noise is generated to adjust the output voltage, thus effectively improving the power supply rejection ratio of the DC linear power supply. Compared with traditional DC linear power supplies, the power supply rejection ratio has an improvement of -38 dB at 100 kHz. In 2024, the paper "A Novel Parallel Feed-Forward Current Ripple Rejection (PFFCRR) Technique for High Load Current High PSRR nMOS LDOs" by Yuhong Lu et al. published in the IEEE Journal of Solid-State Circuits, Volume 52, Issue 9, Pages 2463 - 2474, proposed a parallel feed-forward current ripple rejection technique aiming to solve the power supply rejection ratio problem of linear power supplies under high load current and low voltage. By sensing the current ripple caused by the power supply and canceling the original ripple through a current path parallel to the nMOS transfer FET, the power supply rejection ratio of the medium and high frequency linear power supply voltage is improved. Experiments show that under a 100 mV voltage difference and a 2.15 A load, the power supply rejection ratio is improved by 18 dB at 1 MHz and remains -35 dB at 10 MHz, which is especially suitable for load systems sensitive to power supply noise.

[0007] In addition to having a high power supply rejection ratio and extremely low power supply output ripple, the DC linear power supply also has fast dynamic response characteristics. In the paper "A Capacitorless Flipped Voltage Follower LDO with Fast Transient Using Dynamic Bias" published by Yange Lu et al. in Electronics, Volume 11, Issue 19, No. 3009 in 2022, a flipped voltage follower type capacitorless low dropout linear regulator with fast transient response was proposed. This DC linear power supply can quickly adjust the gate output of the power transistor. When the load changes from 0.1 mA to 20 mA and the conversion rate is 20 mA / ps, the recovery time is only 52 ns, and the response speed is very fast. In the paper "A Fast-Transient All-Digital LDO with Adaptive Clock Technique" published by Yu Yi et al. in Electronics, Volume 8, Issue 12, Page 1422 in 2019, aiming at the contradiction between transient response and current efficiency in traditional digital LDOs, an adaptive clock technique was proposed. A digital oscillator is used to generate a variable-frequency sampling clock. When an output voltage overshoot or undershoot is detected, the clock frequency and loop gain are automatically increased to shorten the transient response time. Experiments show that under the condition of a 40 mV input voltage overshoot, the response time is only 500 ns, and the response speed is extremely fast. In 2024, in the paper "Fully integrated LDO based on push-pull circuitry for enhanced power management in embedded systems" published by Hatim Ameziane et al. in the International Journal of Automation and Control, Volume 18, Issue 4, a fully integrated analog low dropout linear regulator with a slew rate enhancement circuit was proposed, which is implemented using push-pull current enhancement technology to ensure the fast response of the DC linear power supply.

[0008] Although DC linear power supplies have low ripple and fast response speed, their efficiency is relatively low, usually only 40%-70%. Especially when the voltage difference between input and output is large, the efficiency will be even lower. In addition, their power is relatively low and they are generally suitable for small-current loads. In the paper "A Low-Power, Fast-Transient FVF-Based Output-Capacitorless LDO with Push-Pull Buffer and Adaptive Resistance Unit" published by Yuanzhe Li et al. in Electronics, Volume 12, Issue 6, Page 1285 in 2023, a push-pull buffer-based output-capacitorless low-dropout linear regulator was proposed. This study designed a push-pull buffer, which effectively improved the switching speed of the gate of the power transistor, could provide large charging and discharging currents, and thus improved the transient response and output power of the DC linear power supply. After testing, when powered by 1.8V, the output voltage of this power supply was regulated to 1.5V, the voltage difference was 300mV, the maximum voltage spike was 129mV, and the maximum output current was 50mA. Although the push-pull buffer was used, the output power was still limited. In the paper "A Fast-Transient 500-mA Digitally Assisted Analog LDO With 30-μV / mA Load Regulation and 0.0073-ps FoM in 65-nm CMOS" published by Feng Chen et al. in the IEEE Journal of Solid-State Circuits (JSSC), Volume 52, Issue 2, Pages 511-520 in 2021, aiming at the problems of slow transient response and high static power consumption of traditional LDOs in a wide load range, a digital-assisted analog hybrid architecture was proposed, with a maximum output current of 500mA and an output power of 0.6W, which was 208 times higher than the earlier 2.4mA design. Although the power has been greatly improved, the output power is still very low and is only suitable for low-power applications.In 2024, Changhong Lin et al. proposed a design method for a high power supply rejection ratio (PSR) capacitor-less low dropout regulator (LDO) in the paper "High PSR capacitor-less LDO with adaptive bulk-driven feedforward technique" published in the *International Journal of Circuit Theory and Applications*. This method can stably improve the PSR of a DC linear power supply under wide load conditions, with a PSR reaching -75 dB. However, the maximum output current of the power supply is only 100 mA, making it suitable for low-power applications. In 2019, Guigang Cai et al. proposed an adaptive current step size control architecture in the paper "A Fast-Transient-Response Fully-Integrated Digital LDO With Adaptive Current Step Size Control" published on pages 3610 - 3619 of Volume 66, Issue 9 of the *IEEE Transactions on Circuits and Systems I: Regular Papers*. By introducing an auxiliary MOS block and dynamically adjusting the switching strategy, this architecture eliminates the limit cycle oscillation under light load. With an output voltage of 0.6 V, the ripple voltage is reduced to 1.2 mV. The maximum output current of this linear power supply is 100 mA, and the full-load output power is 0.06 W, which is 41 times higher than the earlier 2.4 mA design. Although the voltage output ripple is reduced, the power output of the power supply is very low. In 2023, Mali Gao et al. proposed a fully integrated low dropout regulator in the paper "Fully Integrated 1.8V Output 300mA Load LDO with Fast Transient Response" published in *Electronics*, Volume 12, Issue 6, Article ID 1409. This regulator can quickly charge and discharge transient currents, accelerating the transient response without sacrificing circuit stability. When the load current jumps from 3 mA to 300 mA, the settling time of the DC linear power supply's steady-state output is only 400 ns. Although the regulation time is very fast, the maximum load current is 300 mA, and the theoretical maximum output power is only 0.54 W.Therefore, although DC linear power supplies perform excellently in terms of low ripple and fast response, they are limited in applications where high power and high efficiency are required.

[0009] To integrate the advantages of high-power output and high conversion efficiency of DC switching power supplies, as well as low ripple and fast response of DC linear power supplies, a hybrid design scheme of the two power supplies can be adopted. In the paper "A 92%-Efficiency Battery Powered Hybrid DC-DC Converter for IoT Applications" published by Elhebeary Mahmoud et al. in the 10th issue of the 67th volume of "IEEE Transactions on Circuits and Systems I" (pages 3342-3351) in 2020, a two-stage hybrid power management unit was designed. The first stage uses a switched-capacitor DC-DC voltage divider to achieve a buck function by selecting the switch size, and the efficiency is increased to more than 95% within the target load current range; the second stage uses a new type of high-efficiency low-dropout linear regulator with a voltage drop of less than 30mV to regulate the output voltage of the first stage; this hybrid architecture can regulate the 1.3V input voltage to 0.4V with a power efficiency greater than 80%; the overall efficiency reaches 92%. However, due to the form of single DC linear power supply, the maximum power of the overall power supply is limited by the maximum output power of the DC linear power supply, and it can only output a current of 1μA - 240μA, meeting the application requirements from sub-microwatts to hundreds of microwatts. In 2020, in the paper "Improved Bootstrap Methods for Powering Floating Gate Drivers of Flying Capacitor Multilevel Converters and Hybrid Switched-Capacitor Converters" published by Zichao Ye et al. in the 6th issue of the 35th volume of "IEEE Transactions on Power Electronics" (pages 5965-5977), a hybrid mode of DC switching power supply and DC linear power supply was used in the cascaded bootstrap method with a low-dropout linear regulator. This mode has a simple structure and high applicability, can supply power to a large number of series switches, reducing the size of the converter power stage by half and the cost to one-sixth, and the DC linear power supply can filter the voltage changes caused by AC operation, keeping the circuit stable in different working modes; in terms of power supply output efficiency, due to the small input-output voltage difference of the DC linear power supply, the hybrid design of DC switching power supply and DC linear power supply can provide higher efficiency compared with traditional DC converters.In the paper "An NMOS-LDO Regulated Switched-Capacitor DC–DC Converter With Fast-Response Adaptive-Phase Digital Control" published by Yan Lu et al. in the IEEE Transactions on Power Electronics, Volume 31, Issue 2, pages 1294-1303, a fully integrated buck-type multiphase switched-capacitor DC-DC converter using 65-nm CMOS technology is designed and regulated by NMOS-LDO. The DC-DC part has a small output ripple when operating at 90 MHz. After being regulated by a DC linear power supply with a 50-mV voltage difference, the output ripple is further attenuated, achieving an output ripple of less than 2 mV, which is better than most comparative designs. In 2021, the paper "A novel DC-DC converter and LDO cascaded circuit with improved dynamic response and loop stability" published by Hao Zhou et al. in IEICE Electronics Express, Volume 18, Issue 8, pages 1-5, proposed a novel DC-DC converter and DC linear power supply cascaded circuit. By quantifying the gate voltage of the P-channel field-effect transistor in the DC linear power supply and comparing it with the target value, an error value is formed to control the feedback coefficient of the DC-DC converter. The response time of the converter is shortened from 2.01 ms to 88 μs, and the response speed is increased by 22 times. However, limited by the power of a single DC linear power supply, the maximum output current of the system is 300 mA, which cannot meet the demand for greater power.

[0010] To solve the problems of excessive ripple in the above DC switching power supply, slow response time of system feedback regulation, and limitations of DC linear power supply in terms of efficiency and power, and to meet the requirements of low ripple and fast feedback response regulation at the same time, the present invention proposes a current-sharing low-ripple voltage source based on equivalent resistance negative feedback. In the parallel module of DC linear power supplies, multiple DC linear power supplies are paralleled by the current-sharing method based on equivalent resistance negative feedback, which can effectively share the load current, thereby greatly improving the output power of the power supply and enhancing the load-carrying capacity. This parallel structure enables the power supply to meet the requirements of high-power application scenarios and breaks through the limitation of the low power of traditional single DC linear power supplies. Secondly, the introduction of the current-sharing method based on equivalent resistance negative feedback realizes the balanced distribution of current and error correction. This feedback mechanism can monitor and adjust the current difference between parallel DC linear power supplies in real time to ensure the uniform distribution of current, further improving the stability and reliability of the power supply. At the same time, this design performs excellently in ripple control. Under an input voltage with 80 mV ripple noise, when the output voltage is 5 V and the full-load power output is 20 W, the measured ripple voltage is only 2.4 mV. Compared with a single DC switching power supply, the ripple is significantly reduced.

[0011] In terms of voltage conversion efficiency, its efficiency is between 70% and 90%, which is significantly higher than the efficiency of 40% - 70% of the single DC linear power supply scheme. This improvement in efficiency is mainly due to the optimization of the parallel structure and the feedback mechanism, enabling the power supply to maintain a high energy conversion efficiency under different load conditions. In addition, the feedback regulation time of this power supply is also greatly shortened, with the regulation time between 10 us and 100 us, and the regulation speed is 10 - 100 times faster than that of the DC switching power supply, which can quickly respond to load changes and achieve fast feedback regulation. This makes the power supply perform excellently in high-load and low-ripple applications, better adapt to rapidly changing load requirements, and improve the overall performance of the system. Summary of the Invention

[0012] The present invention aims to solve the problems of excessive ripple in a single switching power supply, low efficiency of a single linear voltage regulator and its inability to be paralleled. It not only effectively reduces the power supply ripple, improves the efficiency of the linear voltage regulator, but also realizes the parallel current-sharing output of multiple linear voltage regulators to meet the power supply requirements for low ripple, high power and fast feedback response regulation.

[0013] To achieve the above technical objectives, the technical solution adopted by the present invention is: combining a switching power supply and a linear voltage regulator, through a modular design, proposing a current-sharing method based on equivalent resistance negative feedback to ensure balanced output current after the linear power supplies are paralleled, designing a filter to filter out switching ripple noise, and improving the power supply rejection ratio. The present invention includes a common-mode filtering module, a DC converter module, a DC filtering module, a linear voltage regulator module based on equivalent resistance negative feedback regulation, etc.

[0014] In the common-mode filtering module, the common-mode filtering inductor filters the high-frequency common-mode noise of the power input current, and the RC low-pass filter filters the high-frequency noise components in the voltage; the cut-off frequency of the common-mode filter is shown in Equation (1):

[0015]

[0016] where N is the number of turns of the coil, μ is the magnetic permeability of the magnetic core, A c is the cross-sectional area of the magnetic core, l c is the magnetic path length, L is the inductance of the common-mode inductor, and C is the capacitance of the filtering capacitor.

[0017] In the DC converter module, a BUCK buck converter is used to achieve a first-stage bucking process. This bucking process can achieve a voltage conversion efficiency of more than 90% at a switching frequency of 500 KHz to improve the power output of the subsequent circuit. Given the ESR value R of the capacitor s , the filtering inductor value L and the switching frequency f of the BUCK converter sw , and the input and output voltage amplitudes V in and V o , the amplitude of the switching noise introduced by this process is shown in Equation (2):

[0018]

[0019] The DC filtering module uses a CLC-π filter to partially filter the switching noise output by the previous DC converter module. Given the noise frequency, the parameters of the filter are calculated as shown in Equation (3):

[0020]

[0021] where f c is the cut-off frequency of the filter, L is the inductance value of the filter, C is the capacitance value of the filter, and R load is the load impedance of the filter. Based on this, the parameters of the CLC-π filter can be adjusted according to the size of the load impedance R load to achieve the suppression of switching noise.

[0022] In the linear regulator module based on equivalent resistance negative feedback regulation, a current sharing method based on equivalent resistance negative feedback is adopted. This method constructs an equivalent resistance to feed back the current deviation output by the linear regulator to its voltage dividing resistor network, thereby improving the current sharing degree of each linear regulator. The overall power output of the power supply is provided by two or more parallel linear regulators. Through this method, parallel connection realizes a low-ripple and high-power voltage output. When constructing the equivalent resistance for negative feedback, the balanced output of the current of each linear regulator is realized through circuits such as a current sampler, a voltage differential amplifier, an equivalent resistance regulator, and a phase compensator. The current sampler collects the load trunk current of the linear regulator, inputs the current amplitude and the reference current amplitude into the voltage differential amplifier to obtain the current deviation, inputs the deviation into the equivalent resistance regulator, and then passes through the phase compensator, so as to adjust the impedance and phase compensation of the feedback resistor network of the linear regulator to optimize the output current sharing degree, thereby improving its dynamic response performance and reducing the fluctuation and imbalance of the output current. The specific steps of the equivalent resistance negative feedback regulation method are as follows:

[0023] Step 1: Install a current sampler at the load end of the linear regulator to obtain the reference current I ref , install a current sampler at the load end of the parallel linear regulators to obtain the current I k , calculate the current deviation ΔI = I k -I ref through a current differential amplifier, and convert the current deviation ΔI into a voltage deviation ΔV through a linear resistor;

[0024] Step 2: The equivalent resistance regulator uses a variable resistance regulator implemented by NMOS. Input the voltage deviation in Step 2 plus the bias voltage into the NMOS gate. The bias voltage ensures that the gate-source voltage V GS > V TH and the drain-source voltage V DS < V GS -V TH so that the NMOS operates in the linear region. At this time, the NMOS can be equivalent to a resistance, and this equivalent resistance is shown in Equation (4):

[0025]

[0026] where, μ n is the electron mobility, C ox is the gate oxide capacitance value per unit area, W and L are the width and length of the NMOS respectively, V GS is the gate-source voltage amplitude, V TH is the threshold voltage amplitude. For a specific NMOS, V GSThe value controls the equivalent impedance, which is connected in parallel to the feedback resistor network of the linear voltage regulator. By adjusting the parameters of the feedback resistor network, the amplitude of the output voltage of the linear voltage regulator is adjusted. The adjusted voltage amplitude is shown in Equation (5):

[0027]

[0028] Where, V ref is the amplitude of the reference voltage source inside the linear voltage regulator, I adj is the current value of the adjustment pin of the linear voltage regulator, R1 and R2 are the external voltage dividing resistor values of the linear voltage regulator. By comparing the voltage of the voltage dividing node with the reference voltage, the output signal of the error amplifier controls the power transistor inside the linear voltage regulator to adjust the output current of the linear voltage regulator and ensure the balanced output of each path of current;

[0029] Step 3: Install a phase compensator at the output of the equivalent resistance regulator. The compensation capacitor in the phase compensator increases the phase margin of the feedback circuit, avoids phase distortion and delay, and thus improves the stability of the system. The transfer function of the feedback system composed of the current differential amplifier and the equivalent resistance regulator is shown in Equation (6):

[0030]

[0031] Where, A dm is the common-mode gain of the current differential amplifier, g m is the transconductance of the NMOS, R L is the load impedance, C gs is the gate-source capacitance value, C gd is the gate-drain capacitance value, C is the compensation capacitance value. Therefore, the phase-frequency of this feedback system is shown in Equation (7):

[0032] ∠H(jw) = arctan(-wR L (C gs + C gd + C))(7)

[0033] It is necessary to satisfy that the compensation capacitance value C is numerically much larger than C gs and C gd , increase the phase margin of the system, and improve the system stability. At the same time, the compensation capacitor and the load resistor form a low-pass filter to suppress high-frequency noise. The cut-off frequency of the filter is shown in Equation (8):

[0034]

[0035] It is necessary to satisfy that the compensation capacitance value C is numerically much larger than C gs and C gd , and the cut-off frequency f cSignificantly reduced, and high-frequency noise will be significantly attenuated above the cut-off frequency. The diode in the phase compensator isolates the equivalent resistance regulator and the feedback resistance network of the linear regulator. According to the one-way conductivity of the diode, the regulated current flows unidirectionally through the equivalent resistance regulator and does not enter the feedback resistance network. In addition, this diode isolates the noise from the current sampler and the current differential amplifier, preventing the noise from entering the linear regulator through the feedback resistance network, thereby reducing the output voltage fluctuation of the linear regulator. Description of the Drawings

[0036] Attached Figure 1 : System structure diagram of a current-sharing low-ripple voltage source based on equivalent resistance negative feedback

[0037] Attached Figure 2 : Voltage noise diagrams before and after passing through the common-mode filtering module

[0038] Attached Figure 3 : Voltage noise diagrams before and after passing through the DC filtering module

[0039] Attached Figure 4 (a): Test result diagram of direct parallel current sharing of linear regulators without adopting the solution of the present invention

[0040] Attached Figure 4 (b): Test result diagram of parallel current sharing of linear regulators by using the equivalent resistance negative feedback regulation method Detailed Embodiment

[0041] The technical solution of the present invention will be further described in conjunction with the accompanying drawings. The present invention proposes a current-sharing low-ripple voltage source based on equivalent resistance negative feedback, including a common-mode filtering module, a DC converter module, a DC filtering module, a reference current module, a linear regulator module based on equivalent resistance negative feedback regulation, etc.;

[0042] The common-mode filtering module includes a common-mode filtering inductor 101, an RC low-pass filter 102, etc. The common-mode filtering inductor 101 filters out the high-frequency common-mode noise of the power input current, and the RC low-pass filter 102 filters out the high-frequency noise components in the voltage. Measure the input voltage common-mode noise as shown in the attached Figure 2 figure. The peak value of the common-mode noise reaches 68.46 mV. A common-mode inductor with an inductance value of 10 μH and a DC resistance of 0.035 Ω is selected, and the coupling coefficient of the common-mode inductor is 0.99. Filter the input voltage common-mode noise, and the result is as shown in the attached Figure 2 figure. The peak value of the output noise is only 8.62 mV. After testing, the common-mode filtering module filters out the common-mode noise of the input voltage source well.

[0043] In the DC converter module 103, a BUCK step-down converter is used to achieve the first-level step-down of the input voltage. After testing, the switching frequency of this module is 500.05 KHz, the input voltage is 24.0 V, the average output voltage is 8.94 V, the output current is 5.58 A, and the voltage conversion efficiency is 93.7%. Calculate the capacitance and inductance values in the DC filter 104 according to the switching frequency. The capacitor bank in this part needs to use the form of ceramic capacitors in parallel with electrolytic capacitors. Electrolytic capacitors have the advantages of low cost and large capacitance, but the ESR is too large. It is necessary to connect ceramic capacitors in parallel to reduce the ESR value of the entire capacitor bank, as shown in the appendix Figure 3 , the peak value of the switching ripple output by the DC converter module is 72.66 mV. After filtering the switching ripple using the DC filter module, the peak value of the ripple is only 4.23 mV.

[0044] In the reference current module, the linear voltage regulator 105 is connected to the common voltage output port V of the voltage source out , set the voltage dividing resistors of the linear voltage regulator 105 to 120 Ω and 360 Ω to make the output voltage amplitude of the linear voltage regulator 5 V. Use the current sampler 106 to detect the output current of the linear voltage regulator 105 to provide a reference current for the linear voltage regulator module based on equivalent resistance negative feedback regulation;

[0045] In the linear voltage regulator module based on equivalent resistance negative feedback regulation, the current sharing method based on equivalent resistance negative feedback is adopted. By constructing an equivalent resistance, the current deviation output by the linear voltage regulator is negatively fed back to its voltage dividing resistor network, thereby improving the current sharing degree of each linear voltage regulator. The overall power output of the power supply is provided by two or more parallel linear voltage regulators. Through this method of parallel connection, a low-ripple and high-power voltage output is achieved; when constructing an equivalent resistance for negative feedback, circuits such as the current differential amplifier 109, the equivalent resistance regulator 110, and the phase compensator 111 are used to achieve the balanced output of the current of each linear voltage regulator. The current sampler 106 samples the main line current at the load end of the linear voltage regulator 105, obtains the current deviation through the current differential amplifier 109, and inputs the deviation into the equivalent resistance regulator 110, thereby adjusting the impedance and phase compensation of the feedback resistor network of the linear voltage regulator 107 to optimize the output current sharing degree, and then improving its dynamic response performance, reducing the fluctuations and imbalance of the output current. The specific steps of the equivalent resistance negative feedback regulation method are as follows:

[0046] Step 1: Install the current sampler 106 at the load end of the linear voltage regulator 105 to obtain the reference current I ref , install the current sampler 108 at the load end of the parallel linear voltage regulator 107 to obtain the current I k , calculate the current deviation ΔI = I k - I ref, and the current deviation ΔI is converted into a voltage deviation ΔV through a linear resistor. The linear resistor should be a sampling resistor with a small resistance value and a large power. Here, a surface-mount resistor with a resistance value of 20 mΩ and a power of 3 W is used;

[0047] Step 2: The equivalent resistance regulator 110 uses an NMOS to implement a variable resistance regulator. The model of this NMOS transistor is NDS331N of ON Semiconductor, and the package is SOT-3. V TH The minimum is 0.5 V. After adding the bias voltage to the voltage deviation in Step 2, it is input to the NMOS gate. Adjust the bias voltage to ensure that the gate-source voltage V GS > V TH and the drain-source voltage V DS < V GS - V TH to make the NMOS work in the linear region. At this time, the NMOS can be equivalent to a resistor. This equivalent resistance is calculated according to Equation (4). For a specific NMOS, the equivalent impedance can be controlled by adjusting the V GS value. This impedance is connected in parallel to the feedback resistor network of the linear regulator. By adjusting the parameters of the feedback resistor network, the regulation of the output voltage amplitude of the linear regulator is realized. The selected model of the linear regulator is the LM317T-DG three-terminal regulator of STMicroelectronics. The internal reference voltage source V adj is 1.25 V. The maximum current I adj of the regulator adjustment pin is 100 μA, and the maximum continuous output current is 2.2 A. The TO-220 package is used to increase the heat dissipation area. The external voltage-dividing resistors R1 and R2 of the linear regulator are set to 120 Ω and 360 Ω respectively. The adjusted voltage amplitude is calculated according to Equation (5). Finally, the regulation of the output current of the linear regulator is realized to ensure the balanced output of each path of current. After testing, the situation of directly paralleling the output currents of the linear regulators without using equivalent resistance negative feedback is shown in Attachment Figure 4 (a). When the two paths of linear regulators are directly paralleled, the output current shows serious imbalance. In the initial stage, only one path of linear regulator bears all the loads, resulting in rapid heating of this path of regulator, an increase in internal resistance, and further increase in internal resistance and performance degradation as the temperature rises, and a rapid decrease in output current. Then the other path of linear regulator starts to work. This alternating working mode will lead to serious imbalance of the output current and an oscillation phenomenon. The current balance degree is 6.96%; when the two paths of linear regulators are paralleled using the equivalent resistance negative feedback method, the output current situation is shown in Attachment Figure 4 (b). The two paths of output currents are balanced, and the current balance degree is increased to 85.14%;

[0048] Step 3: Install a phase compensator 111 at the output end of the equivalent resistance regulator 110. The compensation capacitor in the phase compensator 111 improves the phase margin of the feedback circuit, avoids phase distortion and delay, and thus improves the stability of the system. Under the test conditions where VDS is equal to 10V, VGS is equal to 0V, and the excitation signal frequency is 1MHz, the gate-source capacitance C gs of this NMOS is 162pF, and the gate-drain capacitance C gs is 28pF. Set the compensation capacitor value to 10nF. The phase-frequency of the feedback system composed of the current differential amplifier 109, the equivalent resistance regulator 110, and the phase compensator 111 is calculated according to Equation (7). Since the compensation capacitor value C is much larger than C gs and C gd , the phase margin of the system is improved, avoiding phase distortion. At the same time, the compensation capacitor and the load resistor form a low-pass filter to suppress high-frequency noise. The cut-off frequency of the filter is calculated according to Equation (8). Since the compensation capacitor value C is much larger than C gs and C gd , the cut-off frequency f c is significantly reduced, and high-frequency noise will be significantly attenuated above the cut-off frequency. The diode in the phase compensator 111 decouples the equivalent resistance regulator 110 and the feedback resistor network of the linear regulator. This diode is a Schottky diode, which has a lower forward conduction voltage drop, a fast switching speed, and good high-frequency characteristics. According to the unidirectional conductivity of the Schottky diode, the regulated current flows unidirectionally through the equivalent resistance regulator 110 and will not enter the feedback resistor network. In addition, this diode isolates the noise from the current sampler 108 and the current differential amplifier 109, avoiding the noise from entering the linear regulator 107 through the feedback resistor network, thereby reducing the output voltage fluctuation.

Claims

1. A current-sharing low-ripple voltage source based on equivalent resistance negative feedback, characterized in that: Including common mode filter module, DC converter module, DC filter module, reference current module, linear regulator module based on equivalent resistance negative feedback regulation, etc.; The common mode filter module includes a common mode filter inductor 101, an RC low-pass filter 102, etc.; the DC converter module includes a BUCK step-down converter 103, etc.; the DC filter module includes a CLC-π filter 104, etc.; the reference current module includes a linear regulator 105, a current sampler 106, etc.; the linear regulator module based on equivalent resistance negative feedback regulation includes a linear regulator 107, a current sampler 108, a current differential amplifier 109, an equivalent resistance regulator 110, a phase compensator 111, etc.; In the common-mode filter module, the DC voltage input port is connected to the common-mode filter inductor 101, and the DC voltage input range is 24V-36V. The high-frequency common-mode noise of the DC voltage is filtered out by the common-mode filter inductor 101, and the RC low-pass filter 102 filters out the high-frequency noise components in the DC voltage; In the DC converter module, a BUCK step-down converter 103 is used to implement a first-stage step-down process. The step-down process can achieve a voltage conversion efficiency of more than 90% at a switching frequency of 500KHz to improve the power output of subsequent circuits. The switching noise introduced by this process is based on Calculation, R s is the equivalent series resistance of the capacitor, f sw is the switching frequency of the BUCK converter, V o is the output voltage amplitude, V in is the input voltage amplitude, L is the filter inductance value of the BUCK converter; In the DC filter module, a CLC-π filter 104 is used to partially filter out the switching noise output by the DC converter module. The known noise frequency can be obtained according to Calculate the filter parameters, f c is the filter cutoff frequency, L is the filter inductance, C is the filter capacitance, R load is the filter load impedance, which can be calculated based on the load impedance R load The size of the CLC-π filter is adjusted to suppress the switching noise. In the reference current module, the linear regulator 105 is connected to the common voltage output port V out , setting the output voltage amplitude of the voltage source through the voltage divider resistor of the linear regulator 105, using the current sampler 106 to detect the output current of the linear regulator 105, and providing a reference current for the linear regulator module based on equivalent resistance negative feedback regulation; In the linear regulator module based on equivalent resistance negative feedback regulation, a current balancing method based on equivalent resistance negative feedback is adopted. This method constructs an equivalent resistor to negatively feedback the current deviation output by the linear regulator to its voltage-dividing resistor network, thereby improving the current balancing degree of each linear regulator. The overall power output of the power supply is provided by two or more linear regulators in parallel, and low-ripple and high-power voltage output is achieved through current balancing parallel connection. When constructing an equivalent resistor for negative feedback, the balanced output of the current of each linear regulator is achieved through circuits such as a current sampler 108, a voltage differential amplifier 109, an equivalent resistance regulator 110, and a phase compensator 111. The current sampler 108 collects the load trunk current of the linear regulator 107, inputs the current amplitude and the reference current amplitude into the voltage differential amplifier 109 to obtain the current deviation, and inputs the deviation into the equivalent resistance regulator 110, and then passes through the phase compensator 111, thereby performing impedance adjustment and phase compensation on the feedback resistance network of the linear regulator 107.

2. The current-sharing low-ripple voltage source based on equivalent resistance negative feedback according to claim 1, characterized in that: A current balancing method based on equivalent resistance negative feedback is proposed to achieve output current balancing after multiple linear regulators are connected in parallel. The current balancing method based on equivalent resistance negative feedback samples the trunk current of the parallel linear regulators, inputs the current and the reference current into the current differential amplifier, and the output of the current differential amplifier acts on the resistor feedback network of the parallel linear regulators to adjust the output voltage of the parallel linear regulators, and finally adjust the output trunk current of the linear regulators. The specific steps of the regulation method based on equivalent resistance negative feedback are as follows: Step 1: Install a current sampler and a current differential amplifier at the load end of the linear regulator to realize current deviation detection; A current sampler 106 is installed at the load end of the linear regulator 105 to obtain a reference current I ref , a current sampler 108 is installed at the load end of the parallel linear regulator 107 to obtain the current I k , the current deviation ΔI=I is calculated by the current differential amplifier 109 k -I ref , and convert the current deviation ΔI into a voltage deviation ΔV through a linear resistor; Step 2: Convert the current deviation into an equivalent resistance through an N-channel Metal-Oxide-Semiconductor Field-Effect Transistor (NMOS), and adjust the feedback resistor network of the linear regulator to achieve output current regulation of the linear regulator; The equivalent resistance regulator 110 uses NMOS to implement a variable resistance regulator. The voltage deviation ΔV is added to the bias voltage and then input into the NMOS gate. The bias voltage ensures that the gate-source voltage V GS >V TH And the drain-source voltage V DS <V GS -V TH Make NMOS work in the linear region. At this time, NMOS can be equivalent to a resistor. The equivalent resistor is based on Calculate μ n is the electron mobility, C ox is the gate oxide capacitance per unit area, W and L are the width and length of NMOS, respectively, V GS is the gate-source voltage amplitude, V TH is the threshold voltage amplitude, which can be adjusted by V GS The impedance of the equivalent resistor is controlled by the value, and the equivalent resistor is connected in parallel to the feedback resistor network of the linear regulator 107. The output voltage amplitude of the linear regulator 107 is adjusted by adjusting the parameters of the feedback resistor network. The adjusted voltage amplitude is based on Calculate, V ref is the reference voltage source amplitude inside the linear regulator 107, I adj is the current value of the adjustment pin of the linear regulator 107, R1 and R2 are the external voltage-dividing resistor values ​​of the linear regulator 107, and the error signal generated by comparing the voltage at the voltage-dividing node with the reference voltage inside the linear regulator 107 is used to control the conduction degree of the power transistor inside the linear regulator 107, and finally realize the regulation of the output current of the linear regulator 107 to ensure the current balanced output. Step 3: Suppress high-frequency noise and improve the stability of the equivalent resistance negative feedback system through phase compensation and noise isolation design; A phase compensator 111 is installed at the output end of the equivalent resistance regulator 110. The phase compensator 111 mainly includes a compensation capacitor and a diode. The transfer function of the feedback system composed of the current differential amplifier 109, the equivalent resistance regulator 110 and the phase compensator 111 is calculated according to Calculation, A dm is the common mode gain of the current differential amplifier 109, g m is the transconductance of NMOS, R L is the load impedance, C gs is the gate-source capacitance, C gd is the gate-drain capacitance value, C is the compensation capacitance value, therefore, the phase frequency of the feedback system is calculated according to ∠H(jω)=arctan(-ωR L (V gs +C gd +C)) calculation, when selecting the compensation capacitor, it is necessary to ensure that the capacitance C is much larger than C gs and C gd , to improve the phase margin of the feedback circuit; At the same time, the compensation capacitor and the load resistor form a low-pass filter to suppress high-frequency noise. The filter cutoff frequency is based on Calculate and select compensation capacitors to ensure that the capacitance C is much larger than C gs and C gd , so that the cut-off frequency f c Significantly reduce and suppress high-frequency noise; A diode is installed in the phase compensator 111 so that the regulating current flows unidirectionally through the equivalent resistance regulator 110 without entering the feedback resistance network, thereby avoiding mutual interference between the equivalent resistance regulator 110 and the linear regulator 107, and isolating the noise of the current sampler 108 and the current differential amplifier 109, thereby reducing the output voltage fluctuation of the linear regulator 107.

Images