A synchronous rectification control circuit and a synchronous rectification power supply device

Abstract

The application relates to the technical field of power supply, and discloses a synchronous rectification control circuit and a synchronous rectification power supply device, which comprise a power conversion module, an output current sampling module and a PWM controller; the power conversion module comprises a freewheeling switch tube and is connected in parallel at two ends of a load; the output current sampling module is connected in series in a secondary winding loop, is used for collecting an output current flowing through the secondary winding loop, and generates an output current signal; the PWM controller is connected with the output current sampling module and is used for driving the freewheeling switch tube; the PWM controller is configured to compare the output current signal with a preset threshold value, generate a first group of PWM control signals when the output current signal is greater than or equal to the preset threshold value, and drive the freewheeling switch tube; and stop driving the freewheeling switch tube when the output current signal is less than the preset threshold value. The application can reduce no-load loss and adapt to the demand of electronic products for high power density and low loss.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power conversion, in particular to a synchronous rectification control circuit and a synchronous rectification power supply device. BACKGROUND

[0002] In the field of power conversion, synchronous rectification technology has become a core application technology for electronic products (especially small size, high power density devices) because it can significantly reduce conversion loss and improve power efficiency.

[0003] However, the existing synchronous rectification scheme has obvious limitations: when the load switches from full load to no load, the freewheeling switch tube remains on, forming an internal discharge circuit with the output inductor and energy storage capacitor, resulting in a large discharge current, which not only causes serious no-load loss, but also generates a high voltage spike at the switching-on and switching-off moments of the switch tube, which can easily cause the switch tube to overheat and even be damaged. In addition, there is a problem of unstable output voltage, which is difficult to meet the power supply requirements of precision electronic devices.

[0004] Therefore, there is an urgent need for a synchronous rectification control scheme that can adapt to load switching, reduce no-load loss, and ensure stable output. SUMMARY

[0005] To solve the above technical problems, the present application provides a synchronous rectification control circuit and a synchronous rectification power supply device.

[0006] In a first aspect, the present application provides a synchronous rectification control circuit, which adopts the following technical scheme:

[0007] A synchronous rectification control circuit, comprising: a power conversion module, the power conversion module comprising: a primary winding for connecting with a power supply to form a primary winding loop; a first switch tube arranged in the primary winding loop; a secondary winding for connecting with a load to form a secondary winding loop; a second switch tube arranged in the secondary winding loop; a freewheeling switch tube connected in parallel with the load; an output current sampling module arranged in the secondary winding loop, for collecting an output current flowing through the secondary winding loop and generating an output current signal; a PWM controller connected with the output current sampling module, connected with the first switch tube, the second switch tube and the freewheeling switch tube, for driving the first switch tube, the second switch tube and the freewheeling switch tube; wherein the PWM controller is configured to: compare the output current signal with a preset threshold value, when the output current signal is greater than or equal to the preset threshold value, generate and output a first group of PWM control signals to drive the first switch tube, the second switch tube and the freewheeling switch tube respectively at a preset timing; when the output current signal is less than the preset threshold value, generate and output a second group of PWM control signals to drive the first switch tube and the second switch tube respectively at a preset timing, and stop driving the freewheeling switch tube.

[0008] By adopting the technical scheme, in view of the problem that the freewheeling switch tube is still driven when the existing synchronous rectification power supply load is switched from full load to no load, resulting in large no-load loss and high voltage spike of the freewheeling switch tube, the circuit of the present application is constructed by current threshold adaptive control solution: on the one hand, the output current sampling module collects the output current in real time, and the PWM controller compares it with the preset threshold to dynamically switch the PWM control signal output mode; on the other hand, the freewheeling switch tube is stopped from being driven when the load is no load or light load (the output current is less than the threshold), preventing the formation of a large current loop after discharging the energy storage element, greatly reducing the no-load loss, and eliminating the voltage spike; when the load is full load (the output current is greater than or equal to the threshold), all switch tubes are normally driven, ensuring the power conversion efficiency, adapting to the demand of electronic products for high power density and low loss, and solving the pain point of large no-load loss and easy damage of switch tubes in traditional synchronous rectification circuit.

[0009] Optionally, the PWM controller comprises a conduction mode processing unit and a PWM generation control unit; the conduction mode processing unit receives the output current signal and compares it with the preset conduction threshold to generate a mode judgment signal; the PWM generation control unit receives the mode judgment signal, the input voltage signal and the output voltage signal, and generates and outputs the first group of PWM control signals or the second group of PWM control signals according to the state of the mode judgment signal.

[0010] By setting the conduction mode processing unit, the load mode is accurately judged, and the mode judgment signal is generated after comparing the output current with the conduction threshold; the PWM generation control unit combines the multi-channel sampling signal with the mode judgment signal to dynamically generate adaptive PWM control signal, ensuring that the power supply can work efficiently and stably under different load modes, and solving the problem that the traditional controller cannot adapt to the load mode.

[0011] Optionally, the PWM generation control unit comprises a PWM generator, a first accumulator, a second accumulator and a PI regulator; the first input end of the second accumulator is connected to the output voltage signal and the second input end is connected to the reference voltage, for performing accumulation operation on the deviation of the output voltage and the reference voltage, and the output end of the second accumulator is connected to the input end of the PI regulator; the PI regulator is used for performing integral regulation on the deviation accumulation value output by the second accumulator to eliminate static error, and the output end of the PI regulator is connected to the second input end of the first accumulator; the first input end of the first accumulator is connected to the input voltage signal output by the input voltage sampling module, for performing superposition calculation on the input voltage signal and the regulation signal output by the PI regulator, and the output end of the first accumulator is connected to the first input end of the PWM generator; the second input end of the PWM generator is connected to the output end of the on-off mode processing unit, for connecting the mode judgment signal, and the PWM generator generates and outputs the first group of PWM control signals or the second group of PWM control signals according to the superposition calculated signal and the mode judgment signal.

[0012] By adopting the above technical solution, the second accumulator and the PI regulator cooperate to eliminate the static error of the output voltage, and the first accumulator superposes the input voltage signal and the regulation signal to provide accurate basis for PWM generation; the PWM generator outputs adaptive control signals in combination with the mode judgment signal, realizes the combination of feedforward regulation and feedback regulation, takes into account the dynamic response speed and output stability of the power supply, and solves the problems of low regulation accuracy and slow response of the traditional control algorithm.

[0013] Optionally, the power conversion module further comprises an output inductor and an energy storage capacitor, the output inductor is connected in series between the second switch tube and the load, and the energy storage capacitor is connected in parallel across the load.

[0014] By adopting the above technical solution, the output inductor plays a role in filtering and smoothing current, preventing current fluctuation from affecting the working stability of the load; the energy storage capacitor can store electrical energy to maintain the stability of the output voltage when the load changes, and at the same time, in cooperation with the control strategy of the freewheeling switch tube, reduces the loss caused by the discharge loop formed by the inductor and the energy storage capacitor in the no-load state, and further improves the output stability and efficiency of the power supply.

[0015] Optionally, the output current sampling module comprises: a shunt resistor connected in series in the secondary winding loop; a signal amplification unit, the input end of the signal amplification unit is electrically connected to the two ends of the shunt resistor, for amplifying the voltage signal at the two ends of the shunt resistor to generate an output current signal; and a third analog-to-digital conversion unit, the input end of the third analog-to-digital conversion unit is electrically connected to the output end of the signal amplification unit, for converting the output current signal into a digital signal and transmitting it to the PWM controller.

[0016] By adopting the technical scheme, the shunt resistor can accurately collect the secondary loop current, the weak voltage signal is amplified by the signal amplification unit, and accurate detection can be ensured in a small current scene; the third analog-digital conversion unit converts the analog signal into a digital signal, adapts to the digital control requirement of the PWM controller, and solves the problems of low current sampling precision and inability to adapt to a wide load range in the prior art.

[0017] Optionally, the synchronous rectification control circuit further comprises an input voltage sampling module connected between the input end of the primary winding and the input end of the PWM controller, configured to collect the input voltage of the power conversion module and generate an input voltage signal; wherein the PWM controller is further configured to feed forward adjust the PWM control signal according to the input voltage signal.

[0018] By adopting the technical scheme, the input voltage sampling module collects the input voltage change in real time, the PWM controller adjusts the PWM control signal in advance through feed forward adjustment, reduces the influence of input voltage fluctuation on the output voltage, improves the dynamic response speed of the power supply, and solves the voltage fluctuation problem caused by the lag of the traditional feedback adjustment.

[0019] Optionally, the input voltage sampling module comprises a first voltage dividing unit and a first analog-digital conversion unit, the first voltage dividing unit comprises a fourth resistor and a fifth resistor connected in series, a first end of the fourth resistor is connected to the power supply and the input end of the primary winding, a second end of the fifth resistor is grounded, an input end of the first analog-digital conversion unit is connected to a connection node of the fourth resistor and the fifth resistor, and an output end of the first analog-digital conversion unit is connected to the PWM controller.

[0020] By adopting the technical scheme, the first voltage dividing unit divides the input high voltage into a low voltage signal, which adapts to the sampling requirement of the first analog-digital conversion unit; the first analog-digital conversion unit converts the analog signal into a digital signal, provides accurate input voltage data for the feed forward adjustment of the PWM controller, ensures the adjustment precision, and solves the problems of difficult input voltage sampling and easy interference.

[0021] Optionally, the synchronous rectification control circuit further comprises an output voltage sampling module, an input end of the output voltage sampling module is connected to both ends of the load, and an output end of the output voltage sampling module is connected to an input end of the PWM controller, configured to collect the output voltage of the power conversion module and generate an output voltage signal; wherein the PWM controller is further configured to adjust the PWM control signal through a PI regulator according to the output voltage signal and a reference voltage, for correcting the deviation of the output voltage.

[0022] By adopting the technical scheme, the output voltage sampling module monitors the output voltage in real time, the PI regulator dynamically adjusts the duty cycle of the PWM control signal by comparing the deviation of the output voltage from the reference voltage, ensures the stability of the output voltage, prevents voltage deviation caused by load change or input voltage fluctuation, and solves the problem of poor output voltage stability of the synchronous rectification circuit.

[0023] Optionally, the output voltage sampling module comprises a second voltage dividing unit and a second analog-digital conversion unit, the second voltage dividing unit comprises a first resistor and a second resistor connected in series, the first end of the first resistor is connected to the positive electrode of the load, and the second end of the second resistor is connected to the negative electrode of the load; the input end of the second analog-digital conversion unit is connected to the connection node of the first resistor and the second resistor, and the output end is connected to the PWM controller, for converting the voltage signal after voltage division into a digital signal and transmitting the digital signal to the PWM controller.

[0024] By adopting the technical scheme, the second voltage dividing unit reduces the high output voltage to the sampling range suitable for the second analog-digital conversion unit, preventing damage to the second analog-digital conversion unit caused by excessively high voltage; the second analog-digital conversion unit converts the analog signal after voltage division into a digital signal, ensuring that the PWM controller accurately obtains the output voltage information and providing a reliable basis for voltage regulation, and solving the problem that the traditional voltage sampling cannot adapt to high-voltage scenarios.

[0025] In a second aspect, the application provides a synchronous rectification power supply device, which adopts the following technical scheme:

[0026] A synchronous rectification power supply device comprises the synchronous rectification control circuit according to any one of the first aspect.

[0027] By adopting the technical scheme, the synchronous rectification power supply device integrates the synchronous rectification control circuit with adaptive conduction mode control, compared with the traditional diode rectification or synchronous rectification power supply without conduction mode control, not only greatly reduces the conversion loss (such as the MOS tube rectification loss of only 1W, far lower than the 7W of diode rectification), but also solves the problem of large loss and voltage peak damage of the switching tube when the load is empty; at the same time, through multiple sampling and accurate regulation, the output voltage is stable when the input voltage fluctuates and the load switches, which adapts to the demand of electronic products for small size, high power density and high reliability, and is especially suitable for scenes with strict requirements for power supply efficiency and stability.

[0028] In summary, the application has at least one of the following beneficial technical effects:

[0029] 1. The circuit of the present application is constructed with current threshold adaptive control solution: on the one hand, the output current sampling module collects output current in real time, and the PWM controller compares with the preset threshold to dynamically switch the PWM control signal output mode; on the other hand, the freewheeling switch tube is stopped driving when the load is light (the output current is less than the threshold), preventing the discharge of energy storage elements to form a large current loop after the switch tube is turned on, greatly reducing the no-load loss, and eliminating voltage spikes at the same time; when the load is full (the output current is greater than or equal to the threshold), all switch tubes are normally driven to ensure the power conversion efficiency, adapt to the demand of electronic products for high power density and low loss, and solve the core pain points of large no-load loss and easy damage of switch tubes in traditional synchronous rectification circuit;

[0030] 2. By setting the conduction mode processing unit, the load mode is accurately judged, and the mode judgment signal is generated after comparing the output current with the conduction threshold; the PWM generation control unit combines the multi-channel sampling signal and the mode judgment signal to dynamically generate the adaptive PWM control signal, ensuring that the power supply can work efficiently and stably under different load modes, and solving the problem that the traditional controller cannot adapt to the load mode;

[0031] 3. The second accumulator cooperates with the PI regulator to eliminate the static error of the output voltage, and the first accumulator superimposes the input voltage signal and the adjustment signal to provide accurate basis for PWM generation; the PWM generator outputs the adaptive control signal in combination with the mode judgment signal, realizes the combination of feedforward regulation and feedback regulation, and takes into account the dynamic response speed and output stability of the power supply, solving the problem of low regulation accuracy and slow response of the traditional control algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a circuit structure diagram of a synchronous rectification control circuit provided in the related art;

[0033] Figure 2 is a circuit block diagram of a synchronous rectification control circuit provided in the embodiment of the present application;

[0034] Figure 3 is a power supply PWM waveform diagram output by the synchronous rectification control circuit provided in the embodiment of the present application;

[0035] Figure 4 is a power supply PWM waveform diagram output by the synchronous rectification control circuit provided in the related art;

[0036] Figure 5 is a circuit structure diagram of a synchronous rectification control circuit provided in the embodiment of the present application.

[0037] Explanation of reference signs:

[0038] 10, power conversion module; 20, output current sampling module; 30, PWM controller; 40, input voltage sampling module; 50, output voltage sampling module. DETAILED DESCRIPTION

[0039] The accompanying drawings are incorporated in and constitute a part of this specification and will be understood together with the general description of the application and specific embodiments described below. Figures 1-5 The application is described in further detail below.

[0040] In modern electronic devices, switching mode power supply (SMPS) is widely used due to its high efficiency and high power density. In various topologies of switching mode power supply, for example, forward converter, energy is transferred from the primary side to the secondary side through a high-frequency transformer, and then supplied to the load after rectification and filtering. As shown in the figure, the circuit mainly includes a transformer T1, a forward rectifier diode D1 connected to the secondary winding of T1, a freewheeling diode D2, an output energy storage inductor L1, and an output filter capacitor C2. The working principle is as follows: in the energy transfer stage: when the switch Q1 on the primary side of the transformer T1 is turned on, the secondary winding generates an induced voltage. The voltage charges the inductor L1 and the capacitor C2 through the forward rectifier diode D2, and supplies power to the load RL. At this time, the freewheeling diode D1 is cut off due to the reverse bias; in the freewheeling stage: when the primary side switch Q1 is turned off, the secondary winding voltage disappears, and the forward rectifier diode D2 is cut off due to the loss of forward bias. Since the energy stored in the inductor L1 needs to maintain the continuous flow of current, the inductor L1 current will flow through the freewheeling diode D1 and the load RL to form a freewheeling circuit until the next switching period arrives. Figure 1 Although the circuit structure using diode rectification is simple, it can barely be used in low-power and low-efficiency scenarios such as traditional household appliance auxiliary power supply, but with the upgrading of the demand for high power density and low standby power consumption in consumer electronics, industrial control and other fields, its inherent defects are increasingly prominent, especially when the load is switched from heavy load to light load or no load. Since the diode is a non-controllable device, the control strategy cannot be adjusted according to the change of the load, and the reverse recovery off time of the diode will cause the current to flow back to the circuit from the output capacitor C2 through the inductor L1 and the freewheeling diode D1, causing a series of technical problems:

[0041] Excessive no-load and light-load power consumption: the reverse current needs to flow through the freewheeling diode D1 and the inductor L1, and the forward conduction voltage drop of the diode and the copper loss of the inductor are added, resulting in a high no-load power consumption ratio, a decrease in system efficiency, and a failure to meet the low standby power consumption requirements of modern devices;

[0042]

[0043] ​The risk of overvoltage breakdown of components: since the freewheeling diode D1 is uncontrollable, the cutoff of the reverse current depends on the natural decay of the inductor current, and when the current is suddenly cut off, the inductor L1 will generate a reverse induced voltage, which resonates with the parasitic parameters of the circuit to form a sharp peak, which is easy to break down the freewheeling diode D1 or the components on the output side;

[0044] In addition, there are limitations in the improvement scheme, and the prior art has tried to use a Schottky diode to reduce the on-voltage drop, or use a high-loss inductor to suppress the sharp peak, but none of them can solve the problem of fixed control strategy when the load is switched, and the technical scheme has obvious shortcomings.

[0045] To solve the above technical problems, as shown in Figure 2 The application provides a synchronous rectification control circuit, which comprises a power conversion module 10, and the power conversion module 10 comprises: a primary winding, which is connected with a power supply to form a primary winding loop; a first switch tube Q1 connected in series in the primary winding loop; a secondary winding having a first output end VOUT+ and a second output end VOUT GND, which is connected with a load to form a secondary winding loop; a second switch tube Q2 connected in series in the secondary winding loop formed by the secondary winding and the load; a freewheeling switch tube Q3, the input end and the output end of the freewheeling switch tube Q3 are connected to the first output end and the second output end of the secondary winding respectively, and the freewheeling switch tube Q3 is connected in parallel with the load; an output current sampling module 20 connected in series in the secondary winding loop, which is used to collect the output current flowing through the secondary winding loop and generate an output current signal; a PWM controller 30 connected with the output current sampling module 20 and used to drive the first switch tube Q1, the second switch tube Q2 and the freewheeling switch tube Q3, and the PWM controller 30 is configured to: compare the output current signal with a preset threshold value; when the output current signal is greater than or equal to the preset threshold value, generate and output a first group of PWM control signals to drive the first switch tube Q1, the second switch tube Q2 and the freewheeling switch tube Q3 respectively at a preset time sequence; when the output current signal is less than the preset threshold value, generate and output a second group of PWM control signals to drive the first switch tube Q1 and the second switch tube Q2 respectively at a preset time sequence, and stop driving the freewheeling switch tube Q3.

[0046] Specifically, the PWM controller 30 can be an MCU (micro control unit, such as STM32 series), a DSP (digital signal processor, such as TMS320 series), or a dedicated power management chip (such as UCC28950), which is internally provided with a continuous conduction mode (CCM) / discontinuous conduction mode (DCM) processing unit. A preset threshold is set based on the critical current value of CCM and DCM. When it is detected that the output current is greater than or equal to the threshold, the circuit works in the continuous conduction mode (CCM), and at this time, the energy transfer is continuous, the PWM controller 30 outputs a first group of PWM control signals, controls the first switch tube Q1 and the second switch tube Q2 to be turned on according to the preset time sequence, and drives the freewheeling switch tube Q3 to be turned on in the freewheeling stage, so as to reduce the freewheeling loss; when the output current is less than the threshold, the circuit enters the discontinuous conduction mode (DCM), and the energy transfer is interrupted, the PWM controller 30 switches to a second group of PWM control signals, and only drives the first switch tube Q1 and the second switch tube Q2 to act according to the conventional time sequence, while stopping driving the freewheeling switch tube Q3, so as to avoid the additional energy loss and voltage impact caused by the mis-opening of the freewheeling switch tube Q3 in the discontinuous stage.

[0047] Referring to Figure 3 and Figure 4 , respectively, the power supply PWM waveform diagram output by the synchronous rectification control circuit provided by the embodiment of the present application ( Figure 3 ) and the power supply PWM waveform diagram output by the synchronous rectification control circuit provided in the related art ( Figure 4 ) are shown, and from the waveform comparison, it can be seen that in the present application, when the output current value is lower than the CCM / DCM critical value (the critical value is the short horizontal line marked as CCM / DCM value in the figure), Figure 3 , the PWMA waveform for driving the first switch tube Q1 and the PWMA-SR waveform for driving the second switch tube Q2 are normally output, while the PWMA- / SR waveform for driving the freewheeling switch tube Q3 has no output, that is, the freewheeling switch tube Q3 remains off; in contrast, in the circuit of the related art ( Figure 4 ), no matter whether the output current is lower than the critical value, the PWMA waveform for driving the first switch tube, the PWMA-SR waveform for driving the second switch tube, and the PWMA- / SR waveform for driving the freewheeling switch tube are continuously output, and the freewheeling switch tube is always in the driving state. When the output current value is greater than or equal to the CCM / DCM critical value, in the circuit of the present application ( Figure 3 ), the PWMA waveform for driving the first switch tube Q1, the PWMA-SR waveform for driving the second switch tube Q2, and the PWMA- / SR waveform for driving the freewheeling switch tube Q3 are all normally output, which is consistent with the waveform output state of the related art ( Figure 4 ), and ensures the energy conversion efficiency at full load.

[0048] It can be understood that, for the existing synchronous rectification power supply without CCM (continuous conduction mode) / DCM (discontinuous conduction mode) control strategy, when the load switches from full load to no load, the freewheeling switch Q3 is still driven, resulting in large no-load loss and over-voltage spike of the freewheeling switch Q3 which is easy to break down and damage. The circuit of the present application solves the problem by using "current threshold adaptive control" solution: on the one hand, the output current sampling module 20 collects the output current in real time, and the PWM controller 30 compares it with the preset threshold to dynamically switch the PWM control signal output mode; on the other hand, the freewheeling switch Q3 is stopped from being driven when there is no load or light load (the output current is less than the threshold), preventing it from forming a large current loop after being turned on to discharge the energy storage element, greatly reducing the no-load loss and eliminating the voltage spike; when there is full load (the output current is greater than or equal to the threshold), the first switch Q1, the second switch Q2 and the freewheeling switch Q3 are normally driven, ensuring the power conversion efficiency, adapting to the demand of electronic products for high power density and low loss, and solving the pain points of large no-load loss and easy damage of the switch in the traditional synchronous rectification circuit.

[0049] It should be noted that in the embodiments of the present application, the switches of the power conversion module 10 are all three-terminal control devices, specifically including the first switch Q1 on the primary side, the second switch Q2 and the freewheeling switch Q3 on the secondary side. Such three-terminal devices can establish a driving connection with the control signal output by the PWM controller 30 through the third terminal (gate), realizing accurate on / off control. Preferably, MOS (Metal-Oxide Semiconductor Field Effect Transistor) is used. Compared with the traditional design of using diode rectification on the output side of the transformer, the present application uses MOS as the synchronous rectification switch, which has a significant advantage in the secondary winding circuit. When the traditional diode rectification is used, the loss calculation formula is PD=VF×IO, where the forward voltage drop VF of the diode is usually 0.7V. If the output current IO is 10A, the rectification loss PD=0.7V×10A=7W. When the MOS rectification is used, the on-voltage drop VDS=RDS(ON)×IO (RDS(ON) is the on-resistance of the MOS), if RDS(ON) is 10mΩ (i.e. 0.01Ω), and the output current IO is also 10A, the rectification loss Pm=RDS(ON)×IO²=0.01Ω×(10A)²=1W. By comparison, the synchronous rectification scheme using MOS greatly reduces the loss compared with diode rectification, which can effectively improve the conversion efficiency. At the same time, combined with the CCM / DCM adaptive control strategy, the performance in light load and no load scenarios is further optimized.

[0050] Referring to Figure 5In one embodiment, the PWM controller 30 includes a conduction mode processing unit (CCM / DCM module in the figure) and a PWM generation control unit. The conduction mode processing unit receives the output current signal and compares it with a preset conduction threshold (e.g., 5A, the specific value can be set according to the transformer T1 parameters and load characteristics) to generate a mode judgment signal (e.g., high level indicates CCM mode, low level indicates DCM mode). The PWM generation control unit receives the mode judgment signal, the input voltage signal Vin, and the output voltage signal Vout, and generates and outputs a first set of PWM control signals or a second set of PWM control signals according to the state of the mode judgment signal.

[0051] Specifically, the conduction mode processing unit can employ a comparator circuit with a built-in reference. Its function is to compare the output current signal (or convert it to a voltage signal) with an internally stored threshold current (or corresponding voltage signal, such as 0.05V for 5A). When the voltage corresponding to the current signal is greater than or equal to the threshold voltage, it is determined to be in CCM mode, and a high-level mode judgment signal is output; when the voltage corresponding to the current signal is less than the threshold voltage, it is determined to be in DCM mode, and a low-level mode judgment signal is output. The PWM generation and control unit can employ a dedicated power control chip (such as the UC3843), which integrates a PWM generator and PI regulator. The circuit includes a mode judgment signal, an input voltage signal, and an output voltage signal. When a high-level mode judgment signal is received, the PWM generator generates a first set of drive signals, including PWMA, PWMA-SR, and PWMA- / SR, according to a preset duty cycle (e.g., 50%), which drive the first switch Q1, the second switch Q2, and the freewheeling switch Q3, respectively. When a low-level mode judgment signal is received, the PWM generator cuts off the PWMA- / SR signal output, retaining only the second set of drive signals, PWMA and PWMA-SR, to control the turn-off of the freewheeling switch Q3.

[0052] Understandably, by setting up a conduction mode processing unit, the load mode can be accurately determined. The output current is compared with the conduction threshold to generate a mode judgment signal. The PWM generation control unit combines multiple sampling signals and the mode judgment signal to dynamically generate an appropriate PWM control signal, ensuring that the power supply can work efficiently and stably under different load modes, thus solving the problem that traditional controllers cannot adapt to load modes.

[0053] Continue to refer to Figure 5In an embodiment, the PWM generation control unit comprises a PWM generator (PWM module in the figure), a first accumulator, a second accumulator and a PI regulator; the first input end of the second accumulator is connected to the output voltage signal, and the second input end is connected to the reference voltage, for performing accumulation operation on the deviation of the output voltage and the reference voltage, and the output end of the second accumulator is connected to the input end of the PI regulator; the PI regulator is used for performing integral regulation on the deviation accumulation value output by the second accumulator to eliminate static error, the output end of the PI regulator is connected to the second input end of the first accumulator, the first input end of the first accumulator is connected to the input voltage signal output by the input voltage sampling module 40, for performing superposition calculation on the input voltage signal and the regulation signal output by the PI regulator, and the output end of the first accumulator is connected to the first input end of the PWM generator, the second input end of the PWM generator is connected to the output end of the conduction mode processing unit, for connecting the mode judgment signal, and the PWM generator generates and outputs the first group of PWM control signals or the second group of PWM control signals according to the superposition calculated signal and the mode judgment signal.

[0054] Specifically, the second accumulator captures the difference between the output voltage signal and the reference voltage (such as the preset 5V output target voltage) in real time, continuously accumulates the deviation, forms a deviation accumulation and outputs it to the PI regulator, to prevent regulation lag caused by single deviation; the PI regulator quickly responds to the deviation change through the proportional term (P) and gradually offsets the accumulated static error through the integral term (I), to ensure that the output voltage is finally stabilized near the reference voltage and reduce the influence of continuous deviation. The first accumulator linearly superimposes the input voltage signal (such as 12V-24V wide range input) and the regulation signal output by the PI regulator, which not only compensates the influence of input voltage fluctuation on the output (feedforward regulation), but also integrates the feedback regulation amount of voltage deviation, to generate an accurate PWM control reference signal. After receiving the reference signal, the PWM generator determines the duty cycle of the PWM control signal (such as dynamically adjusting to 30%-60% according to the superposition signal), and combines the mode judgment signal of the conduction mode processing unit: if it is high (CCM mode), three complete driving signals including PWMA, PWMA-SR and PWMA- / SR are generated to control the first switch Q1, the second switch Q2 and the freewheeling switch Q3 to be turned on in a preset time sequence; if it is low (DCM mode), the core parameters such as the duty cycle remain unchanged, and only the PWMA- / SR signal output is cut off, to ensure that the first two switches work normally while the freewheeling switch Q3 is turned off.

[0055] It can be understood that the second accumulator cooperates with the PI regulator to eliminate the output voltage static error, and the first accumulator superimposes the input voltage signal and the regulation signal to provide accurate basis for the PWM generator; the PWM generator outputs adaptive control signal in combination with the mode judgment signal to realize the combination of feedforward regulation and feedback regulation, and takes into account the dynamic response speed and output stability of the power supply, and solves the problems of low regulation accuracy and slow response of the traditional control algorithm.

[0056] With reference to the foregoing Figure 5 In an embodiment, the power conversion module 10 further comprises an output inductor L1 and an energy storage capacitor C2, the output inductor L1 is connected in series between the second switch tube Q2 and the load, and the energy storage capacitor C2 is connected in parallel across the load.

[0057] Specifically, the output inductor L1 is connected in series between the second switch tube Q2 and the load, when the second switch tube Q2 is turned on, the energy output by the secondary winding is supplied to the load through L1, and at the same time L1 stores electromagnetic energy; when the second switch tube Q2 is turned off, L1 generates a counter electromotive force through self-induction, at this time if the freewheeling switch tube Q3 is turned on (in CCM mode), L1 can form a freewheeling circuit through Q3 to release the stored energy to the load and the energy storage capacitor C2, preventing voltage spikes caused by sudden current changes, and smoothing the output current; the energy storage capacitor C2 is connected in parallel across the load, in the second switch tube Q2 conduction stage, in addition to supplying power to the load, the excess energy will be stored in C2; when Q2 is turned off or the load instantaneously increases, C2 releases the stored energy to supplement the power supply, maintains the output voltage stable, and reduces the voltage ripple. In DCM mode (freewheeling switch tube Q3 is turned off), the remaining energy of L1 only forms a circuit through the load and C2, and Q3 is turned off to avoid L1 and Q3, the secondary winding forming an additional discharge path, reducing the invalid energy loss of the energy storage element, especially when the load is empty, the energy storage of C2 can maintain the output voltage, and L1 does not need to continuously discharge, further reducing the standby power consumption.

[0058] It can be understood that the output inductor L1 functions to filter and smooth the current, preventing current fluctuations from affecting the stability of the load; the energy storage capacitor C2 can store energy to maintain the output voltage stable when the load changes, and at the same time cooperate with the control strategy of the freewheeling switch tube to reduce the loss caused by the discharge circuit formed by L1 and C2 when the load is empty, further improving the output stability and efficiency of the power supply.

[0059] With reference to the foregoing Figure 5In an embodiment, the output current sampling module 20 comprises: a shunt resistor R3 connected in series in the secondary winding loop, one end connected with the second switch tube Q2, and the other end connected with the second output end VOUGND of the secondary winding; a signal amplification unit, the input end of the signal amplification unit being electrically connected with the two ends of the shunt resistor R3, for amplifying the voltage signal at the two ends of the shunt resistor to generate an output current signal; and a third analog-to-digital conversion unit ADC3, the input end of the third analog-to-digital conversion unit ADC3 being electrically connected with the output end of the signal amplification unit, for converting the output current signal into a digital signal and transmitting the digital signal to the PWM controller 30.

[0060] Specifically, the shunt resistor R3 is selected as a low-resistance high-precision resistor (such as 0.01Ω, 1% precision), which is connected in series in the output loop of the secondary winding (for example, between the second output end of the secondary winding and the ground). When the current flows through the secondary loop, a weak voltage signal proportional to the current is generated at the two ends of R3 (according to Ohm's law U=IR, for example, 5A current corresponds to 0.05V voltage). The signal amplification unit adopts a dedicated current amplifier (such as INA282), the two input ends of which are directly connected across the two ends of R3. By using the high sensitivity characteristic of the current amplifier to the small differential voltage, the voltage signal at the two ends of R3 is converted into an amplified current signal proportional to the current, and then the corresponding voltage signal is output through the internal conversion circuit (for example, when the gain is set to 100 times, 0.05V input corresponds to 5V output, and 0.001V input corresponds to 0.1V output), ensuring that the signal can still be linearly amplified to a range suitable for subsequent processing in the light load small current (such as 0.1A corresponding to 0.001V original signal) scenario. The third analog-to-digital conversion unit ADC3 preferably adopts a 12-bit or higher precision ADC chip to convert the analog signal IOCY output by the current amplifier into a digital signal (such as 0-4095 digital quantity), and transmit the digital signal to the PWM controller 30 through a data interface (such as SPI or parallel interface) for on-off mode processing unit, to provide accurate digital quantity basis for current threshold comparison.

[0061] It can be understood that the shunt resistor R3 can accurately collect the secondary loop current, the signal amplification unit amplifies the weak voltage signal to ensure accurate detection in the small current scenario, and the ADC3 converts the analog signal into a digital signal to adapt to the digital control requirements of the PWM controller 30, solving the problem of low precision of traditional current sampling and inability to adapt to a wide load range.

[0062] Continuing to refer to Figure 5In an embodiment, the synchronous rectification control circuit further comprises an input voltage sampling module 40 connected between the input end of the primary winding and the input end of the PWM controller 30, configured to collect the input voltage of the power conversion module 10 and generate an input voltage signal; wherein the PWM controller 30 is further configured to feed forward adjust the first group or the second group of PWM control signals according to the input voltage signal.

[0063] Specifically, the input voltage sampling module 40 can be composed of a voltage dividing resistor network (such as resistors R4 and R5 in series), wherein one end of R4 is connected to the input end of the primary winding (connected to the input voltage Vin), and the other end is connected to R5 in series and then grounded, and through the voltage dividing principle, the high input voltage (such as 310V DC after AC 220V rectification or DC 12-24V) is converted into a low voltage signal (such as 0-3.3V) that the PWM controller 30 can withstand. The low voltage signal is transmitted to the first accumulator of the PWM controller 30 after being converted into a digital signal by the first analog-to-digital conversion unit ADC1 as the input voltage signal.

[0064] After receiving the input voltage signal, the PWM controller 30 processes it through the built-in feed forward algorithm, and when the input voltage rises, the duty cycle of the PWM control signal is reduced in advance (for example, when the input voltage rises from 24V to 30V, the duty cycle is pre-adjusted from 50% to 40%), to prevent the output voltage from rising due to excess input energy; when the input voltage decreases, the duty cycle is increased in advance (for example, when the input voltage decreases from 24V to 18V, the duty cycle is pre-adjusted from 50% to 65%), to compensate for insufficient input energy and prevent the output voltage from falling. This adjustment does not need to wait for the output voltage to deviate, but directly adjusts the PWM parameters in real time according to the input changes, complementing the feedback adjustment.

[0065] It can be understood that the input voltage sampling module 40 collects the input voltage changes in real time, and the PWM controller 30 adjusts the PWM control signal in advance through feed forward adjustment to reduce the impact of input voltage fluctuations on the output voltage, improve the dynamic response speed of the power supply, and solve the problem of voltage fluctuations caused by the lag of traditional feedback adjustment.

[0066] Continuing to refer to Figure 5 In an embodiment, the input voltage sampling module 40 comprises a first voltage dividing unit and a first analog-to-digital conversion unit ADC1, the first voltage dividing unit comprises a fourth resistor R4 and a fifth resistor R5 connected in series, a first end of the fourth resistor R4 is connected to the input end of the primary winding and a power supply, a second end of the fifth resistor R5 is grounded, an input end of the first analog-to-digital conversion unit ADC1 is connected to a connection node of the fourth resistor R4 and the fifth resistor R5, and an output end of the first analog-to-digital conversion unit ADC1 is connected to the PWM controller 30.

[0067] Specifically, in the first voltage dividing unit, the fourth resistor R4 is selected as a high-voltage resistor (such as 1 MΩ, 0.25 W), and the fifth resistor R5 is selected as a precision resistor (such as 10 kΩ, 1% precision). After the two are connected in series, a voltage dividing circuit is formed. When the power voltage (such as 310V DC after AC220V rectification or DC 48V) is connected to the input end of the primary winding, the voltage is divided by R4 and R5, and a low-voltage signal proportional to the input voltage is generated at the connection node of the two. According to the voltage dividing formula U=Vin×R5 / (R4+R5), for example, when the input voltage is 310V, the voltage after voltage division is about 3V. The low-voltage signal is further connected to the sampling end of the first analog-to-digital conversion unit ADC1 through the isolator. The ADC1 preferably uses a chip with 8-bit or higher precision (such as a single-chip microcomputer module with a built-in ADC) to convert the analog voltage dividing signal into a digital quantity (such as 3V corresponding to a digital value of 240), and transmit it to the first accumulator of the PWM controller 30 through the data bus as the original data for feedforward regulation.

[0068] The selection of the voltage dividing resistor needs to consider both the voltage resistance and the precision. The high resistance value of R4 can reduce the loop current (such as 300μA when the input voltage is 310V), preventing excessive power consumption. The high precision of R5 ensures the stability of the voltage dividing ratio and reduces the sampling error. At the same time, the isolator can filter out high-frequency interference in the input voltage, making the signal collected by ADC1 more stable.

[0069] It can be understood that the first voltage dividing unit (R4, R5) divides the input high voltage into a low-voltage signal to adapt to the sampling needs of ADC1; ADC1 converts the analog signal into a digital signal to provide accurate input voltage data for the feedforward regulation of the PWM controller 30, ensuring the regulation accuracy and solving the problems of difficult input voltage sampling and susceptibility to interference.

[0070] Continuing to refer to Figure 5In an embodiment, the synchronous rectification control circuit further comprises an output voltage sampling module 50, an input end of the output voltage sampling module 50 being connected to both ends of the load, and an output end being connected to an input end of the PWM controller 30, for collecting an output voltage of the power conversion module 10 and generating an output voltage signal; wherein the PWM controller 30 is further configured to adjust the PWM control signal through a PI regulator according to the output voltage signal FB and a reference voltage (VREF), for correcting the deviation of the output voltage; the output voltage sampling module 50 comprises a second voltage dividing unit (R1, R2) and a second analog-digital conversion unit, the second voltage dividing unit (R1, R2) being used for voltage dividing the output voltage, comprising a first resistor R1 and a second resistor R2 connected in series, a first end of the first resistor R1 being connected to a positive pole of the load, and a second end of the second resistor R2 being connected to a negative pole of the load; an input end of the second analog-digital conversion unit ADC2 being connected to a connection node of the first resistor R1 and the second resistor R2, and an output end being connected to the PWM controller 30, for converting the voltage signal after voltage dividing into a digital signal and transmitting to the PWM controller 30.

[0071] Specifically, in the second voltage dividing unit, the first resistor R1 and the second resistor R2 are both selected from high-precision metal film resistors (such as 0.1% precision), wherein R1 can be selected from 10kΩ, and R2 can be selected from 1kΩ, and the two are connected in series and then connected in parallel between both ends of the load (such as between the positive and negative poles of the load with an output voltage of 12V). According to the voltage dividing principle, after the output voltage is divided by R1 and R2, a low-voltage sampling signal (for example, when the output voltage is 12V, the voltage after voltage dividing is 12V x R2 / (R1+R2)=1.09V) is generated at the connection node of the two, which is suitable for the input range of the second analog-digital conversion unit ADC2 (usually 0-3.3V or 0-5V).

[0072] The second analog-digital conversion unit ADC2 adopts a chip with a precision of 12 bits or above (such as an independent ADC chip ADS1115), converts the analog voltage signal after voltage dividing into a digital signal (for example, 1.09V corresponds to a digital value of about 1340, based on the conversion of 12-bit ADC full scale 3.3V corresponding to 4095), and transmits to the second accumulator of the PWM controller 30 through an I2C or SPI interface. Since the output voltage directly affects the working state of the load, the temperature drift characteristic of the voltage dividing resistor needs to be strictly controlled (such as selecting a resistor with a temperature drift of ±25ppm / °C or below), and at the same time, a 10nF ceramic capacitor can be connected in parallel at both ends of R2 to filter out the ripple interference in the output voltage, so as to ensure that the signal collected by ADC2 is stable and reliable.

[0073] After receiving the digital signal output by ADC2, the PWM controller 30 compares it with the internally stored reference voltage digital quantity (such as 12V corresponding to the digital value 1340). If the output voltage is too high (the digital quantity is greater than the reference value), the PI regulator reduces the duty cycle of the PWM control signal through integral operation to reduce energy output; if the output voltage is too low (the digital quantity is less than the reference value), the duty cycle is increased to supplement the energy output, so that the output voltage is finally stabilized around the reference value.

[0074] It can be understood that the output voltage sampling module 50 monitors the output voltage in real time, and the PI regulator dynamically adjusts the duty cycle of the PWM control signal by comparing the deviation of the output voltage from the reference voltage, so as to ensure the stability of the output voltage and prevent voltage deviation caused by load changes or input voltage fluctuations, thereby solving the problem of poor output voltage stability of the synchronous rectification circuit; the second voltage dividing unit (R1, R2) reduces the high output voltage to the sampling range suitable for ADC2, preventing damage to ADC2 caused by excessive voltage; ADC2 converts the analog signal after voltage division into a digital signal, ensuring that the PWM controller 30 accurately obtains the output voltage information and provides a reliable basis for voltage regulation, thereby solving the problem that traditional voltage sampling cannot adapt to high-voltage scenarios.

[0075] In an embodiment, the application also provides a synchronous rectification power supply device, which comprises the synchronous rectification control circuit in any of the above embodiments.

[0076] Specifically, the synchronous rectification power supply device comprises a housing, a built-in transformer (including a primary winding and a secondary winding), the above-mentioned synchronous rectification control circuit (including a PWM controller 30, an output current sampling module 20, an input voltage sampling module 40, an output voltage sampling module 50, etc.), and an input interface and an output interface. The input interface is used to connect an external power supply (such as AC 220V or DC 48V) to input energy through the primary winding; the output interface is used to connect a load (such as a server, communication equipment, etc.) to output stable voltage (such as DC 12V, 5V) through the secondary winding.

[0077] The modules are integrated by a PCB inside the device: the transformer uses a high-frequency magnetic core (such as a ferrite magnetic core) to reduce the size, the synchronous switch tube (Q1, Q2, Q3) is preferably a NMOS tube (such as a conduction resistor 10mΩ) with low conduction resistance to reduce conduction loss, and the PWM controller 30 uses a dedicated power management chip (such as a chip with an integrated conduction mode processing unit) to realize compact design. The housing is made of aluminum alloy material, which has heat dissipation and protection functions, ensuring stable operation of the device in a wide temperature environment of-40℃ to 85℃.

[0078] It can be understood that the synchronous rectification power supply device integrates the adaptive CCM / DCM control synchronous rectification control circuit, compared with the traditional diode rectification or the synchronous rectification power supply without the CCM / DCM control, the conversion loss is greatly reduced (such as the MOS tube rectification loss is only 1W, far lower than 7W of the diode rectification), and the problem of large loss and switch tube voltage peak damage at no load is solved; at the same time, through multiple sampling and accurate adjustment, the output voltage is stable when the input voltage fluctuates and the load switches, the demand of electronic products for small size, high power density and high reliability is adapted, and it is especially suitable for scenes with strict requirements for power supply efficiency and stability.

[0079] The above are preferred embodiments of the present application, not to limit the protection scope of the present application, therefore: any equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A synchronous rectification control circuit, characterized in that, include: The power conversion module (10) includes: a primary winding for connecting to a power source to form a primary winding circuit; a first switching transistor disposed in the primary winding circuit; a secondary winding for connecting to a load to form a secondary winding circuit; a second switching transistor disposed in the secondary winding circuit; and a freewheeling switching transistor connected in parallel with the load. An output current sampling module (20) is set in the secondary winding circuit to collect the output current flowing through the secondary winding circuit and generate an output current signal; A PWM controller (30) is connected to the output current sampling module (20) and to the first switch, the second switch, and the freewheeling switch, for driving the first switch, the second switch, and the freewheeling switch; wherein, the PWM controller (30) is configured to: compare the output current signal with a preset threshold; when the output current signal is greater than or equal to the preset threshold, generate and output a first set of PWM control signals to drive the first switch, the second switch, and the freewheeling switch respectively under a preset timing sequence; when the output current signal is less than the preset threshold, generate and output a second set of PWM control signals to drive the first switch and the second switch respectively under a preset timing sequence, and stop driving the freewheeling switch; the PWM controller (30) includes a conduction mode processing unit and a PWM generation control unit; The conduction mode processing unit receives the output current signal and compares it with a preset conduction threshold to generate a mode judgment signal; the PWM generation control unit receives the mode judgment signal and generates and outputs a first set of PWM control signals or a second set of PWM control signals according to the state of the mode judgment signal. The PWM generation and control unit includes a PWM generator, a first accumulator, a second accumulator, and a PI regulator; The first input terminal of the second accumulator is connected to the output voltage signal, and the second input terminal is connected to the reference voltage. It is used to accumulate the deviation between the output voltage and the reference voltage. The output terminal of the second accumulator is connected to the input terminal of the PI regulator. The PI controller is used to integrally adjust the accumulated deviation value output by the second accumulator to eliminate static error. The output terminal of the PI controller is connected to the second input terminal of the first accumulator. The first input terminal of the first accumulator is connected to the input voltage signal, which is used to superimpose the input voltage signal and the adjustment signal output by the PI regulator for calculation. The output terminal of the first accumulator is connected to the first input terminal of the PWM generator. The second input terminal of the PWM generator is connected to the output terminal of the conduction mode processing unit and is used to receive the mode judgment signal. The PWM generator generates and outputs a first set of PWM control signals or a second set of PWM control signals based on the superimposed calculated signal and the mode judgment signal.

2. The synchronous rectification control circuit according to claim 1, characterized in that, The power conversion module (10) further includes an output inductor and an energy storage capacitor. The output inductor is connected in series between the second switching transistor and the load, and the energy storage capacitor is connected in parallel across the load.

3. The synchronous rectification control circuit according to claim 1, characterized in that, The output current sampling module (20) includes: a shunt resistor, a signal amplification unit and a third analog-to-digital converter. The shunt resistor is connected in series in the secondary winding circuit. The input terminal of the signal amplification unit is electrically connected to the two ends of the shunt resistor to amplify the output current signal. The input terminal of the third analog-to-digital converter is electrically connected to the output terminal of the signal amplification unit to convert the output current signal into a digital signal and transmit it to the PWM controller (30).

4. The synchronous rectification control circuit according to claim 1, characterized in that, It also includes: an input voltage sampling module (40), connected between the input terminal of the primary winding and the input terminal of the PWM controller (30), for acquiring the input voltage of the power conversion module (10) and generating an input voltage signal; The PWM controller (30) is further configured to perform feedforward adjustment of the PWM control signal based on the input voltage signal.

5. The synchronous rectification control circuit according to claim 4, characterized in that, The input voltage sampling module (40) includes a first voltage divider unit and a first analog-to-digital converter unit. The first voltage divider unit includes a fourth resistor and a fifth resistor connected in series. The first end of the fourth resistor is connected to the power supply and the input end of the primary winding. The second end of the fifth resistor is grounded. The input end of the first analog-to-digital converter unit is connected to the connection node of the fourth resistor and the fifth resistor. The output end of the first analog-to-digital converter unit is connected to the PWM controller (30).

6. The synchronous rectification control circuit according to claim 1, characterized in that, It also includes: an output voltage sampling module (50), whose input end is connected to both ends of the load and whose output end is connected to the input end of the PWM controller (30), used to collect the output voltage of the power conversion module (10) and generate an output voltage signal; The PWM controller (30) is further configured to adjust the PWM control signal through a PI regulator based on the output voltage signal and the reference voltage to correct the deviation of the output voltage.

7. The synchronous rectification control circuit according to claim 6, characterized in that, The output voltage sampling module (50) includes: a second voltage divider unit and a second analog-to-digital converter unit. The second voltage divider unit includes a first resistor and a second resistor connected in series. The first end of the first resistor is connected to the positive terminal of the load, and the second end of the second resistor is connected to the negative terminal of the load. The input end of the second analog-to-digital converter unit is connected to the connection node of the first resistor and the second resistor, and the output end is connected to the PWM controller (30). It is used to convert the voltage signal after voltage division into a digital signal and transmit it to the PWM controller (30).

8. A synchronous rectifier power supply device, characterized in that, Includes the synchronous rectification control circuit as described in any one of claims 1-7.

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