Switching converter and control method thereof

Abstract

The invention relates to the field of switching converter design, and discloses a control method of an asymmetric half-bridge flyback converter. A clock signal is arranged on the secondary side of the converter, a primary side excitation current signal is simulated in real time, a driving control signal of a primary side switch tube is generated on the secondary side according to the clock signal and the simulated excitation current signal, and the driving control signal is transmitted to the primary side through a high-reliability signal isolator. According to the asymmetric half-bridge flyback converter, on and off of a primary side switching tube are controlled, output voltage stabilization and primary side peak current control are achieved, the problems that an existing optocoupler feedback control scheme is low in reliability, and output protection is not timely and accurate enough are effectively solved, and the asymmetric half-bridge flyback converter has higher reliability, better output protection performance and smaller size; and the application occasions of high reliability, high performance and small size can be simultaneously met.

Description

Technical Field

[0001] The present invention relates to the field of switch converter design, and in particular to a switch converter and a control method thereof. Background Art

[0002] Switching converter, also known as switching power supply, is a power supply device that realizes power conversion and transmission by controlling the opening and closing of semiconductor switching devices. It has many advantages such as high efficiency, small size, light weight, etc., and is widely used in consumer electronics, new energy, industrial control, aerospace and other fields. Asymmetric half-bridge flyback converter has the characteristics of easy soft switching, transformer and resonant capacitor to transfer energy together, and can achieve higher efficiency and smaller size than conventional flyback converter, becoming a research hotspot for small and medium power applications.

[0003] Referring to FIG. 1(a) and FIG. 1(b), the existing asymmetric half-bridge flyback converter usually adopts the peak current control scheme shown in FIG. (b), which adopts an optocoupler and 431 as a feedback network, and transmits the error amplification signal COMP of the output voltage to the primary controller through optocoupler isolation. The primary controller has a built-in clock signal. When the clock signal comes, the main switch tube Q1 is turned on by delaying the dead time, and the excitation inductance Lm and the resonant capacitor Cr of the transformer T are used to store energy. When the primary excitation current peak signal CS increases to the error amplification signal COMP of the output voltage, the main switch tube Q1 is turned off, and the auxiliary switch tube Q2 is turned on after the dead time, the secondary rectifier diode D is turned on, and the energy stored in the excitation inductance Lm and the resonant capacitor Cr is transferred to the secondary side. When the clock signal comes, the auxiliary switch tube Q2 is turned off, thereby realizing cycle-by-cycle energy transmission and output voltage regulation.

[0004] The existing peak current control scheme has the advantages of fast response speed to input and output changes, easy compensation of the control loop, and easy implementation of peak current protection, but it has the following problems:

[0005] 1. It is necessary to use an optocoupler to isolate and transmit the output voltage error amplification signal. Since the reliability of the optocoupler will decrease with the aging of the device, temperature changes, and current transfer ratio changes, it cannot meet high-reliability applications;

[0006] 2. The optocoupler can only transmit the output voltage error amplification signal to the primary side, and it is difficult to quickly and accurately implement output protection functions such as overvoltage and short circuit. Summary of the invention

[0007] In view of this, the present invention proposes a control method for a switching converter, which can effectively solve the problem that the prior art cannot meet high reliability applications and is difficult to quickly and accurately implement output protection functions while retaining the advantages of the prior art.

[0008] The inventive concept of this application is:

[0009] The main controller of the switching converter is set on the secondary side. On the one hand, the primary side excitation current signal is constructed in real time on the secondary side, and the driving signal of the primary side switch tube is generated according to the clock signal and the excitation current signal of the secondary side. The switch tube driving signal is transmitted to the primary side through a high-reliability signal isolator to control the opening and closing of the primary side switch tube to achieve output voltage regulation and primary side peak current control. On the other hand, the output voltage and output current are directly detected on the secondary side to quickly and accurately achieve output protection.

[0010] In order to solve the above technical problems, the technical solutions provided by the present invention are as follows:

[0011] A control method for a switching converter is used for realizing a peak current control scheme and fast and accurate output protection on the secondary side of an asymmetric half-bridge flyback converter, the control method comprising:

[0012] A clock signal is set on the secondary side, and the excitation current signal on the primary side is simulated in real time to generate an excitation current simulation signal. A control signal of the primary switch tube is generated on the secondary side according to the clock signal and the excitation current simulation signal. The drive control signal is transmitted to the primary side through the signal isolator to control the opening and closing of the primary switch tube, thereby realizing output voltage regulation and primary peak current control.

[0013] Specifically, at the initial moment of each switching cycle, the initial value of the excitation current signal is judged by the secondary side main controller. If the initial value of the excitation current signal is less than the first preset value of the excitation current, the first control method is started to control the opening and closing of the switch tube on the primary side; if the initial value of the excitation current signal is equal to the second preset value of the excitation current, the second control method different from the first control method is started to control the opening and closing of the switch tube on the primary side; wherein the first preset value of the excitation current < the second preset value of the excitation current.

[0014] Preferably, the secondary side main controller determines the initial value of the excitation current signal by detecting the excitation voltage within a period of time at the beginning of each switching cycle; when the excitation voltage is less than the second voltage preset value and greater than the first voltage preset value, the controller determines that the initial value of the excitation current signal is equal to the second preset value of the excitation current; when the excitation voltage is greater than the third voltage preset value, the controller determines that the initial value of the excitation current signal is less than the first preset value of the excitation current, wherein the first voltage preset value < the second voltage preset value < the third voltage preset value.

[0015] Preferably, the secondary side main controller judges the initial value of the excitation current signal through the working mode of the asymmetric half-bridge flyback converter. When the asymmetric half-bridge flyback converter works in the continuous mode, it is judged that the initial value of the excitation current signal is less than the first preset value of the excitation current; when the asymmetric half-bridge flyback converter works in the discontinuous mode, it is judged that the initial value of the excitation current signal is equal to the second preset value of the excitation current.

[0016] Preferably, the switch tube located on the primary side includes a main switch tube and an auxiliary switch tube. The first control method mainly operates in the following steps in a complete switching cycle:

[0017] Step 1: starting from the rising edge of the clock signal, after a first delay time, the secondary side main controller sends a control signal for controlling the main switch tube to be turned on, and transmits the control signal for controlling the main switch tube to be turned on to the primary side controller through the signal isolator;

[0018] Step 2: After receiving the control signal for controlling the main switch tube to turn on, the primary side controller controls the main switch tube to turn on;

[0019] Step 3: After the main switch tube is turned on, the primary side controller detects the zero-crossing moment of the excitation current signal on the primary side, and transmits the zero-crossing moment signal to the secondary side main controller through the signal isolator;

[0020] Step 4: After receiving the zero-crossing time signal, the secondary-side main controller turns on the secondary-side excitation current simulation circuit, and simulates the excitation current signal of the primary side of the asymmetric half-bridge flyback converter through the secondary-side excitation current simulation circuit to generate an excitation current simulation signal;

[0021] Step 5: When the excitation current analog signal reaches the set value, the secondary side main controller sends a control signal for controlling the main switch tube to be turned off, and transmits the control signal for controlling the main switch tube to be turned off to the primary side controller through the signal isolator;

[0022] Step 6: After receiving the control signal for controlling the main switch tube to turn off, the primary side controller controls the main switch tube to turn off;

[0023] Step 7: After the main switch tube is turned off, when the secondary side main controller detects that the excitation voltage is less than the second voltage preset value, the secondary side main controller turns off the secondary side excitation current analog circuit, and sends a control signal for controlling the auxiliary switch tube to turn on after a second delay time;

[0024] Step 8: After receiving the control signal for controlling the auxiliary switch tube to turn on, the primary side controller controls the auxiliary switch tube to turn on;

[0025] Step 9: The secondary-side main controller determines a control signal for controlling the auxiliary switch tube to be turned off, and transmits the signal for controlling the auxiliary switch tube to be turned off to the primary-side controller through a signal isolator;

[0026] Step 10: After receiving the signal for controlling the auxiliary switch tube to turn off, the primary side controller controls the auxiliary switch tube to turn off until the next clock signal arrives, and starts a new switching cycle.

[0027] Preferably, the switch tube located on the primary side includes a main switch tube and an auxiliary switch tube. The second control method mainly operates in the following steps in a complete switching cycle:

[0028] Step 1: starting from the rising edge of the clock signal, after a first delay time, the secondary side main controller sends a control signal for controlling the main switch tube to be turned on, and transmits the control signal for controlling the main switch tube to be turned on to the primary side controller through the signal isolator;

[0029] Step 2: After receiving the control signal for controlling the main switch tube to turn on, the primary side controller controls the main switch tube to turn on;

[0030] Step 3: After the main switch tube is turned on, when the secondary side main controller detects that the excitation voltage is greater than the second voltage preset value, the secondary side excitation current simulation circuit is turned on, and the excitation current signal of the primary side of the asymmetric half-bridge flyback converter is simulated by the secondary side excitation current simulation circuit to generate an excitation current simulation signal;

[0031] Step 4: When the excitation current analog signal reaches the set value, the secondary side main controller sends a control signal for controlling the main switch tube to be turned off, and transmits the control signal for controlling the main switch tube to be turned off to the primary side controller through the signal isolator;

[0032] Step 5: After receiving the control signal for controlling the main switch tube to turn off, the primary side controller controls the main switch tube to turn off;

[0033] Step 6: After the main switch tube is turned off, when the secondary side main controller detects that the excitation voltage is less than the second voltage preset value, the secondary side excitation current analog circuit is turned off, and a control signal for controlling the auxiliary switch tube to be turned on is issued after a second delay time;

[0034] Step 7: After receiving the control signal for controlling the auxiliary switch tube to turn on, the primary side controller controls the auxiliary switch tube to turn on;

[0035] Step 8: The secondary-side main controller determines a control signal for controlling the auxiliary switch tube to be turned off, and transmits the control signal for controlling the auxiliary switch tube to be turned off to the primary-side controller through a signal isolator;

[0036] Step 9: After receiving the control signal for controlling the auxiliary switch tube to turn off, the primary side controller controls the auxiliary switch tube to turn off until the next clock signal arrives, and starts a new switching cycle.

[0037] Preferably, the first preset value of the excitation current is a negative threshold, the second preset value of the excitation current is zero, and the set value is a preset value representing the peak value of the excitation current.

[0038] Preferably, the secondary side of the asymmetric half-bridge flyback converter includes: a primary side controller, a main switch tube, an auxiliary switch tube, a resonant capacitor and a primary winding of a transformer; the secondary side of the asymmetric half-bridge flyback converter includes: a secondary side excitation current simulation circuit, a secondary side main controller, an output rectifier tube, an output capacitor and a secondary winding of a transformer.

[0039] Preferably, the excitation current signal of the primary side of the asymmetric half-bridge flyback converter is simulated in real time on the secondary side, including: detecting the excitation voltage in real time through the secondary side excitation current simulation circuit, and converting the excitation voltage into current according to the proportion K, charging a capacitor of a certain capacitance through the current, simulating the excitation current signal of the primary side through the capacitor voltage, and the capacitor value satisfies the following relationship:

[0040]

[0041] Where K is the proportional coefficient of the excitation voltage converted to current, Lm is the excitation inductance, N is the transformer turns ratio, and Rcs is the excitation current sampling resistor.

[0042] Preferably, in the stage of simulating the excitation current signal, the simulation starts when the excitation current is zero and ends after the main switch is completely turned off, that is, when the excitation voltage drops to zero.

[0043] Preferably, the excitation voltage can be detected by placing the converter output rectifier at the lower end, with the rectifier anode connected to the secondary ground and the cathode connected to one end of the secondary winding of the transformer. The excitation voltage can be detected by detecting the voltage at the cathode end of the rectifier and the output voltage.

[0044] Preferably, the signal isolator is a capacitive isolator.

[0045] Preferably, the secondary side main controller samples the output voltage and sets overvoltage and short-circuit voltage comparison thresholds. When it is detected that the output voltage exceeds or is lower than the output voltage threshold, the main switch tube and auxiliary switch tube drive signals are quickly turned off to achieve accurate and rapid output protection.

[0046] The present invention also provides a switching converter, which includes: a secondary circuit, a signal isolator and a primary circuit;

[0047] The secondary circuit includes a clock generating circuit, a secondary excitation current simulation circuit and a secondary main controller. The clock generating circuit is used to generate a clock signal; the secondary excitation current simulation circuit is used to simulate the excitation current signal generated in the primary circuit in real time to obtain the excitation current simulation signal; the secondary main controller is used to generate a control signal according to the clock signal and the excitation current simulation signal;

[0048] The signal isolator is used to transfer the control signal to the primary circuit;

[0049] The primary circuit includes a primary controller and a switching circuit. The primary controller is used to receive a control signal and output a drive signal according to the control signal to control the opening and closing of the switch tube in the switching circuit to achieve output voltage regulation and peak current control on the primary side.

[0050] The working principle of the present invention will be analyzed in conjunction with specific embodiments, which will not be described in detail here. The beneficial effects of the present invention are as follows:

[0051] (1) The capacitor isolator is used for the isolation and transmission of the primary and secondary side signals. Compared with the optocoupler, it has the advantages of fast transmission speed, good temperature characteristics, strong anti-interference, and long life, which can meet the high reliability application occasions;

[0052] (2) The secondary side simulates the excitation current information of the primary side in real time, and the secondary side main controller realizes the primary side peak current control and output voltage regulation, making it easier to achieve accurate output and rapid protection;

[0053] (3) Compared with optocoupler isolators, capacitor isolators have a smaller size and are easier to integrate with primary and secondary side main controllers, thus enabling applications with ultra-small size and minimal peripherals. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1( a ) is a circuit diagram of a conventional asymmetric half-bridge flyback converter;

[0055] FIG1( b ) is a schematic diagram of peak current control of a conventional asymmetric half-bridge flyback converter;

[0056] Figure 2 The asymmetric half-bridge flyback converter circuit and the controller block diagram of the present invention;

[0057] Figure 3 It is a schematic diagram of the internal circuit of the asymmetric half-bridge flyback converter controller of the present invention;

[0058] Figure 4 It is a schematic diagram of the excitation current simulation circuit of the present invention;

[0059] Figure 5 This is a working waveform diagram of the present invention when the initial value of the excitation current is negative;

[0060] Figure 6This is a working waveform diagram of the present invention when the initial value of the excitation current is zero;

[0061] Figure 7 This is the working waveform diagram of the present invention when the initial value of the excitation current is positive. DETAILED DESCRIPTION

[0062] In order to make the present invention more clear and understandable, the technical solution of the present invention will be described more clearly and completely below in conjunction with the accompanying drawings and specific embodiments.

[0063] Please refer to Figure 2 , a switching converter, comprising: an asymmetric half-bridge flyback converter and a controller

[0064] The asymmetric half-bridge flyback converter includes an input voltage port Vin, a main switch tube Q1 and an auxiliary switch tube Q2, a resonant capacitor Cr, a transformer T, a rectifier switch D, an output filter capacitor Co, an output voltage port Vo, an excitation current sampling resistor Rcs, a primary side reference ground GND, and a secondary side reference ground SGND, wherein the leakage inductance of the transformer T is Lr, the excitation inductance is Lm, and the primary-to-secondary turns ratio is N. The switch tube circuit composed of the main switch tube Q1 and the auxiliary switch tube Q2, the resonant capacitor Cr, the primary winding of the transformer T, and the current sampling resistor Rcs form a primary circuit (i.e., the primary side); the secondary winding of the transformer T, the rectifier switch D, and the output filter capacitor Co form a secondary circuit (i.e., the secondary side).

[0065] The controller is used to stabilize the output voltage of the asymmetric half-bridge flyback converter within an expected value, and to protect the output load and the converter itself according to the output load working condition.

[0066] The secondary side of the controller is provided with an input terminal VO, an input terminal VM, and a reference ground SGND; the primary side of the controller is provided with an input terminal CS, an output terminal G1, an output terminal G2, and a reference ground GND.

[0067] The controller input terminal VO is electrically connected to the output voltage port Vo for sampling the output voltage of the switching converter; the controller input terminal VM is electrically connected to the cathode of the rectifier switch D and one end of the secondary winding of the transformer for sampling the excitation voltage of the transformer; the controller secondary reference ground SGND is electrically connected to the negative electrode of the output filter capacitor Co; the controller input terminal CS is electrically connected to one end of the excitation current sampling resistor Rcs, the source of the auxiliary switch tube Q2, and one end of the resonant capacitor Cr for sampling the excitation current signal; the controller output terminals G1 and G2 are electrically connected to the gates of the main switch tube Q1 and the auxiliary switch tube Q2, respectively, for realizing the switching control of the main switch tube Q1 and the auxiliary switch tube Q2.

[0068] Please refer to the internal diagram of the controller Figure 3The controller is divided into three parts: primary side controller, secondary side main controller and capacitor isolator. Figure 2 In addition to the existing ports, the primary side controller and the secondary side main controller interact with each other through the capacitor isolator to control the signal PWM1, the signal PWM2 and the zero-crossing time signal ZCD, wherein the control signal PWM1 and the control signal PWM2 are generated by the secondary side main controller, transmitted to the primary side controller through the capacitor isolator, and are used to generate the drive signals for controlling the main switch tube Q1 and the auxiliary switch tube Q2 respectively. The zero-crossing time signal ZCD is a signal obtained by the zero-crossing detection of the excitation current, generated by the primary side controller, transmitted to the secondary side main controller through the capacitor isolator, and is used by the secondary side main controller to determine the time to start the excitation current simulation circuit. The secondary side main controller is also provided with a port VC, and a capacitor C is connected between the VC port and the secondary side reference ground SGND, which is used to realize the excitation current signal simulation. Since the voltage of the port VC is the voltage of the capacitor C, the voltage of the capacitor C is labeled as VC below. In this embodiment, a clock generating circuit for generating a clock signal CLCOK is provided in the secondary side main controller.

[0069] Please refer to the schematic diagram of the secondary excitation current simulation circuit Figure 4 , the following combination Figure 2 Explain the working principle of the secondary excitation current simulation circuit. Figure 2 It can be seen that when the main switch tube Q1 is turned on, the rectifier switch D is in the off state, the transformer starts to be excited, and the voltage on the excitation current signal sampling resistor Rcs is:

[0070]

[0071] From formula (1), we can see that V CS According to the excitation voltage V LM , Excitation inductance L M , sampling resistor R CS The slope of the related circuit increases linearly with the on-time of the main switch Q1, so a capacitor C can be built on the secondary side to pass the constant current source I C Charge the capacitor C and use the voltage VC of the capacitor C to simulate the excitation current signal. Assume that the voltage VC of the capacitor C is:

[0072]

[0073] Comparing equations (1) and (2), if the constant current source I C For a voltage-controlled current source VCCS with a coefficient of K controlled by the excitation voltage reflected by the secondary side, then:

[0074]

[0075] Substituting equation (3) into equation (2) and making equation (2) equal to equation (1), we can obtain that the capacitance C satisfies the following relationship:

[0076]

[0077] That is, when the value of the capacitor C satisfies formula (4), the voltage VC of the capacitor C on the secondary side is consistent with the excitation current signal on the primary side, thereby realizing that the secondary side simulates the primary side excitation current signal.

[0078] It should be noted that in order to ensure the accuracy of the excitation current signal simulation, the secondary excitation current simulation circuit needs to be turned on when the excitation current signal passes through zero, such as Figure 4 As shown, the input of the voltage-controlled current source VCCS is the secondary side excitation voltage VM-VO (i.e., the voltage difference between the voltage of the cathode of the rectifier switch D and the output voltage V0), the coefficient of the voltage-controlled current source VCCS is K, the initial value of the capacitor voltage VC is zero, and when the excitation current signal is detected to pass through zero, the control switch S1 is closed, and the voltage VC of the capacitor C increases synchronously with the excitation current signal; when the simulation of the excitation current signal ends, the control switch S2 is closed to release the voltage VC of the capacitor C to zero.

[0079] Based on the simulation principle of the above-mentioned excitation current signal, the present invention proposes a control method for an asymmetric half-bridge flyback switching converter, including: setting a clock signal on the secondary side of the converter, and simulating the excitation current signal on the primary side in real time to generate an excitation current simulation signal, generating a control signal of the primary switch tube on the secondary side according to the clock signal and the excitation current simulation signal, transmitting the control signal to the primary side through a signal isolator, controlling the opening and closing of the primary side switch tube, and realizing output voltage stabilization and primary side peak current control.

[0080] Specifically, at the initial moment of each switching cycle, the secondary side main controller judges the initial value of the excitation current. If the initial value of the excitation current signal is less than the first preset value of the excitation current, the first control method is started; if the initial value of the excitation current signal is equal to the second preset value of the excitation current, the second control method is started; if the initial value of the excitation current signal is greater than the third preset value of the excitation current, the third control method is started.

[0081] Among them, the first preset value of excitation is a negative threshold, the third preset value of excitation current is a positive threshold, the second preset value of excitation current is a range value less than the third preset value of excitation current and greater than the first preset value of excitation current. In this embodiment, the second preset value of excitation current is zero.

[0082] The initial value of the excitation current signal is determined by the secondary side main controller at the initial moment of each switching cycle.

[0083] Preferably, the secondary side main controller detects the excitation voltage on the secondary side within a period of time at the beginning of each switching cycle to determine the initial value of the excitation current. When the excitation voltage is less than the first voltage preset value, the secondary side main controller determines that the initial value of the excitation current signal is greater than the third excitation current preset value; when the excitation voltage is less than the second voltage preset value and greater than the first voltage preset value, the secondary side main controller determines that the initial value of the excitation current signal is equal to the second excitation current preset value; when the excitation voltage is greater than the third voltage preset value, the secondary side main controller determines that the initial value of the excitation current signal is less than the first excitation current preset value. Wherein, the first voltage preset value < the second voltage preset value < the third voltage preset value.

[0084] Optionally, the secondary side main controller performs an initial judgment on the excitation current through the working mode of the switching converter. When the switching converter works in the continuous mode, it is judged that the initial value of the excitation current signal is less than the first preset value of the excitation current; when the switching converter works in the discontinuous mode, it is judged that the initial value of the excitation current signal is equal to the second preset value of the excitation current; when switching from the discontinuous mode to the continuous mode, it is switched to the first switching cycle of the continuous mode, and it is judged that the initial value of the excitation current signal is greater than the third preset value of the excitation current; when switching from the continuous mode to the discontinuous mode, it is switched to the first switching cycle of the discontinuous mode, and it is judged that the initial value of the excitation current signal is less than the first preset value of the excitation current.

[0085] The working principles of the first control method, the second control method and the third control method are described below with reference to different initial value states of the excitation current signal and in combination with specific waveforms.

[0086] When the initial value of the excitation current signal is less than the first preset value of the excitation current, that is, when the initial value of the excitation current signal is a negative current, the first control method is adopted. For the waveform diagram of its working principle, please refer to Figure 5 , combined with Figure 3 , the main operating steps of a complete switching cycle are as follows:

[0087] Step 1, at the rising edge of the clock signal CLCOK, the secondary side main controller determines that the initial value of the excitation current signal is less than the first preset value of the excitation current, and takes the rising edge of the clock signal CLCOK as the starting point. After a first delay time, the secondary side main controller sends a rising edge of the control signal PWM1 for controlling the main switch tube Q1 to be turned on, and transmits the control signal PWM1 to the primary side controller through the signal isolator;

[0088] Step 2: After the primary side controller receives the rising edge of the control signal PWM1, it converts it into the rising edge of the drive signal GQ1 to control the main switch tube Q1 to turn on;

[0089] Step 3: After the main switch Q1 is turned on, the primary controller detects the zero-crossing moment of the excitation current signal ( Figure 5 The signal is transmitted to the secondary side main controller via the signal isolator.

[0090] Step 4: After receiving the excitation current zero-crossing time signal ZCD, the secondary side main controller turns on the secondary side excitation current simulation circuit, so that the capacitor C in the secondary side excitation current simulation circuit is charged, and the voltage VC of the capacitor C gradually increases. At this time, the voltage VC of the capacitor C is the excitation current simulation signal;

[0091] Step 5: When the excitation current analog signal reaches the set value COMP ( Figure 5 At time t3, the secondary side main controller sends a falling edge of a control signal PMW1 for controlling the shutdown of the main switch tube Q1, and transmits the control signal PMW1 to the primary side controller through a signal isolator; wherein the set value COMP is a preset value representing the peak value of the excitation current, which is determined by the output voltage error amplification signal.

[0092] Step 6: After the primary side controller receives the falling edge of the control signal PMW1, it converts it into the falling edge of the drive signal GQ1 to control the main switch tube Q1 to turn off;

[0093] Step 7, after the main switch tube Q1 is turned off, the voltage of the secondary winding of the transformer is reversed, and the anode voltage VM of the rectifier switch D decreases. When the secondary side main controller detects that the anode voltage VM of the rectifier switch D is less than the second voltage preset value, the secondary side excitation current analog circuit is turned off, and after a second delay time, a rising edge of the control signal PMW2 for controlling the auxiliary switch tube Q2 to be turned on is issued;

[0094] Step 8: After the primary side controller receives the rising edge of the control signal PWM2, it converts it into the rising edge of the drive signal GQ2 to control the auxiliary switch tube Q2 to turn on;

[0095] Step 9, the secondary side main controller determines the falling edge of the auxiliary switch tube Q2 turn-off signal PMW2 according to the corresponding control mode, and transmits the control signal PWM2 to the primary side controller through the signal isolator;

[0096] Step 10: After the primary side controller receives the falling edge of the control signal PWM2, it converts it into the falling edge of the drive signal GQ2, controls the auxiliary switch tube Q2 to turn off, until the next clock signal of the secondary side arrives, and starts a new switching cycle.

[0097] Preferably, a high transmission rate capacitor isolator is used, and its signal transmission delay is very small. It can be considered that the control signal PWM1 is synchronized with the drive signal GQ1 (the solid line signal in the figure), and the control signal PWM2 is synchronized with the drive signal GQ2 (the dotted line signal in the figure). The relevant delay is mainly the turn-on and turn-off delay of the switch tube. Figure 5In the embodiment, when the driving signal GQ1 of the main switch tube Q1 is turned off at time t3, the main switch tube Q1 is actually turned off at time t4 due to the influence of the turn-off delay. At this time, the peak value of the excitation current is slightly larger than the set value COMP. This phenomenon can be compensated by the voltage feedforward commonly used by those skilled in the art, and will not affect the control method, which will not be elaborated here.

[0098] When the initial value of the excitation current signal is equal to the second preset value of the excitation current, that is, when the initial value of the excitation current signal is zero current, the second control method is adopted. For the waveform diagram of its working principle, please refer to Figure 6 , combined with Figure 3 , the main operating steps of a complete switching cycle are as follows:

[0099] Step 1, at the rising edge of the clock signal CLOCK, the secondary side main controller determines that the initial value of the excitation current signal is equal to the second preset value of the excitation current, and takes the rising edge of the clock signal CLCOK as the starting point. After a first delay time, the secondary side main controller sends a rising edge of the control signal PWM1 for controlling the main switch tube Q1 to turn on, and transmits the control signal PWM1 to the primary side controller through the signal isolator;

[0100] Step 2: After the primary side controller receives the rising edge of the control signal PWM1, it converts it into the rising edge of the drive signal GQ1 to control the main switch tube Q1 to turn on;

[0101] Step 3: After the main switch tube Q1 is turned on, the voltage of the secondary winding of the transformer is reversed, and the anode voltage VM of the rectifier switch D rises. When the secondary main controller detects that the anode voltage VM of the rectifier switch D is greater than the second voltage preset value, the secondary excitation current simulation circuit is turned on to generate an excitation current simulation signal;

[0102] Step 4: When the excitation current analog signal reaches the set value COMP ( Figure 6 At time t3), the secondary side main controller sends a falling edge of a control signal PMW1 for controlling the main switch tube Q1 to turn off, and transmits the control signal PMW1 to the primary side controller through the control signal isolator;

[0103] Step 5: After the primary side controller receives the falling edge of the control signal PMW1, it converts it into the falling edge of the drive signal GQ1 to control the main switch tube Q1 to turn off;

[0104] Step 6: After the main switch tube Q1 is turned off, the voltage of the secondary winding of the transformer is reversed, and the anode voltage VM of the rectifier switch D decreases. When the secondary side main controller detects that the anode voltage VM of the rectifier switch D is less than the second voltage preset value, the secondary side excitation current analog circuit is turned off, and after a delay of the second delay time, a rising edge of the control signal PMW2 for controlling the auxiliary switch tube Q2 to be turned on is issued;

[0105] Step 7: After the primary side controller receives the rising edge of the control signal PWM2, it converts it into the rising edge of the drive signal GQ2 to control the auxiliary switch tube Q2 to turn on;

[0106] Step 8, the secondary side main controller determines the falling edge of the control signal PMW2 used to control the auxiliary switch tube Q2 to turn off according to the corresponding control mode, and transmits the control signal PMW2 to the primary side controller through the signal isolator;

[0107] Step 9: After the primary side controller receives the falling edge of the control signal PWM2, it converts it into the falling edge of the drive signal GQ2, controls the auxiliary switch tube Q2 to turn off, until the next clock signal of the secondary side arrives, and starts a new switching cycle.

[0108] When the initial value of the excitation current signal is greater than the third preset value of the excitation current, that is, when the initial value of the excitation current signal is a positive current, the third control method is adopted. For the waveform diagram of its working principle, please refer to Figure 7 , combined with Figure 3 The main operating steps of a complete switching cycle are as follows:

[0109] Step 1, at the rising edge of the clock signal CLCOK, the secondary side main controller determines that the initial value of the excitation current is greater than the third preset value of the excitation current, and takes the rising edge of the clock signal CLCOK as the starting point. After a first delay time, the secondary side main controller sends a rising edge of the control signal PWM2 for controlling the auxiliary switch tube Q2 to be turned on, and transmits the control signal PWM2 to the primary side controller through the signal isolator;

[0110] Step 2: After the primary side controller receives the rising edge of the control signal PWM2, it converts it into the rising edge of the drive signal GQ2 to control the auxiliary switch tube Q2 to turn on;

[0111] Step 3: After the auxiliary switch tube Q2 is turned on for the set time, the secondary side main controller sends a falling edge of the control signal PWM2 for controlling the auxiliary switch tube Q2 to be turned off, and transmits the control signal PWM2 to the primary side controller through the signal isolator;

[0112] Step 4: After the primary side controller receives the falling edge of the control signal PWM2, it converts it into the falling edge of the drive signal GQ2 to control the auxiliary switch tube Q2 to turn off;

[0113] Step 5: After the secondary-side main controller detects that the auxiliary switch Q2 is turned off, it triggers the next clock pulse after a second delay time to start a new switching cycle.

[0114] Preferably, the secondary side main controller samples the output voltage and sets comparison thresholds for output overvoltage protection and output short-circuit protection respectively, using a high-speed comparator to achieve accurate and fast protection within several switching cycles when the output voltage is higher than the overvoltage protection threshold or the output voltage is lower than the short-circuit protection threshold.

[0115] It should be pointed out that the control method of the asymmetric half-bridge flyback converter described in the embodiment of the present invention is still within the protection scope of the present invention by changing the position of the resonant capacitor, the main switch tube and the auxiliary switch tube of the asymmetric half-bridge flyback converter.

[0116] The signal isolation transmission of the present invention can have different forms, including but not limited to the following two ways:

[0117] (1) A capacitor isolator is used to transmit the control signal for controlling the main switch tube Q1 and the auxiliary switch tube Q2 from the secondary side to the primary side, and to transmit the excitation current zero-crossing signal from the primary side to the secondary side;

[0118] (2) A magnetic isolator is used to transmit the control signal for controlling the main switch tube Q1 and the auxiliary switch tube Q2 from the secondary side to the primary side in a unidirectional manner, and to transmit the excitation current zero-crossing signal from the primary side to the secondary side.

[0119] The above are only preferred embodiments of the present invention. It should be pointed out that the above preferred embodiments should not be regarded as limitations of the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. The embodiments will not be repeated here. The protection scope of the present invention should be based on the scope defined by the claims.

Claims

1. A control method for a switching converter, which is used for controlling an asymmetric half-bridge flyback converter, characterized in that: Control methods include: Setting a clock signal on the secondary side of the asymmetric half-bridge flyback converter, and simulating the excitation current signal on the primary side of the asymmetric half-bridge flyback converter in real time on the secondary side to generate an excitation current simulation signal; Generating, on the secondary side, a control signal for controlling a switch tube located on the primary side according to the clock signal and the excitation current analog signal; The control signal is transmitted to the primary side through a signal isolator to control the on and off of the switch tube on the primary side, so as to achieve output voltage regulation on the secondary side and peak current control on the primary side.

2. The control method of the switching converter according to claim 1, characterized in that: Also includes: At the initial moment of each switching cycle, the secondary side main controller determines the initial value of the excitation current signal. If the initial value of the excitation current signal is less than the first preset value of the excitation current, the following steps are performed: a1: starting from the rising edge of the clock signal, after a first delay time, the secondary-side main controller sends the control signal for controlling the main switch tube in the switch tube to turn on, and transmits the control signal for controlling the main switch tube in the switch tube to turn on to the primary-side controller through the signal isolator; a2: after receiving the control signal for controlling the main switch tube among the switch tubes to turn on, the primary side controller controls the main switch tube to turn on; a3: After the main switch tube is turned on, the primary side controller detects the zero-crossing moment of the excitation current signal on the primary side, and transmits the zero-crossing moment signal to the secondary side main controller through the signal isolator; a4: After receiving the zero-crossing time signal, the secondary-side main controller turns on the secondary-side excitation current simulation circuit to simulate the excitation current signal of the primary side of the asymmetric half-bridge flyback converter through the secondary-side excitation current simulation circuit.

3. The control method of the switching converter according to claim 1, characterized in that: Also includes: At the initial moment of each switching cycle, the secondary side main controller determines the initial value of the excitation current signal. If the initial value of the excitation current signal is equal to the second preset value of the excitation current, the following steps are performed: b1: starting from the rising edge of the clock signal, after a first delay time, the secondary-side main controller sends the control signal for controlling the main switch tube in the switch tube to turn on, and transmits the control signal for controlling the main switch tube in the switch tube to turn on to the primary-side controller through the signal isolator; b2: after receiving the control signal for controlling the main switch tube among the switch tubes to turn on, the primary side controller controls the main switch tube to turn on; b3: After the main switch tube is turned on, when the secondary side main controller detects that the excitation voltage is greater than the second voltage preset value, the secondary side excitation current simulation circuit is turned on to simulate the excitation current signal of the primary side of the asymmetric half-bridge flyback converter through the secondary side excitation current simulation circuit.

4. The control method of the switching converter according to claim 1, characterized in that: Also includes: At the initial moment of each switching cycle, the initial value of the excitation current signal is judged by the secondary side main controller, and if the initial value of the excitation current signal is less than the first preset value of the excitation current, the first control method is started to control the opening and closing of the switch tube located at the primary side; If the initial value of the excitation current signal is equal to the second preset value of the excitation current, a second control method different from the first control method is started to control the opening and closing of the switch tube located on the primary side; wherein the first preset value of the excitation current is less than the second preset value of the excitation current.

5. The control method of the switching converter according to claim 4, characterized in that: The secondary side main controller determines the initial value of the excitation current signal by detecting the excitation voltage within a period of time at the beginning of each switching cycle. When the excitation voltage is less than the second voltage preset value and greater than the first voltage preset value, the controller determines that the initial value of the excitation current signal is equal to the second preset value of the excitation current; when the excitation voltage is greater than the third voltage preset value, the controller determines that the initial value of the excitation current signal is less than the first preset value of the excitation current, wherein the first voltage preset value < the second voltage preset value < the third voltage preset value.

6. The control method of the switching converter according to claim 4, wherein: The secondary side main controller determines the initial value of the excitation current signal according to the working mode of the asymmetric half-bridge flyback converter, and when the asymmetric half-bridge flyback converter works in the continuous mode, determines that the initial value of the excitation current signal is less than the first preset value of the excitation current; When the asymmetric half-bridge flyback converter operates in the discontinuous mode, it is determined that the initial value of the excitation current signal is equal to the second preset value of the excitation current.

7. The control method of the switching converter according to claim 5, characterized in that: The switch tube located at the primary side includes a main switch tube and an auxiliary switch tube. The first control method mainly operates in the following steps in a complete switching cycle: Step 1: starting from the rising edge of the clock signal, after a first delay time, the secondary-side main controller sends the control signal for controlling the main switch tube to be turned on, and transmits the control signal for controlling the main switch tube to be turned on to the primary-side controller through the signal isolator; Step 2: After receiving the control signal for controlling the main switch tube to be turned on, the primary side controller controls the main switch tube to be turned on; Step 3: After the main switch tube is turned on, the primary side controller detects the zero-crossing moment of the excitation current signal on the primary side, and transmits the zero-crossing moment signal to the secondary side main controller through the signal isolator; Step 4: After receiving the zero-crossing time signal, the secondary-side main controller turns on the secondary-side excitation current simulation circuit, and simulates the excitation current signal of the primary side of the asymmetric half-bridge flyback converter through the secondary-side excitation current simulation circuit to generate the excitation current simulation signal; Step 5: When the excitation current analog signal reaches a set value, the secondary side main controller sends the control signal for controlling the main switch tube to be turned off, and transmits the control signal for controlling the main switch tube to be turned off to the primary side controller through the signal isolator; Step 6: After receiving the control signal for controlling the main switch tube to turn off, the primary side controller controls the main switch tube to turn off; Step 7: After the main switch tube is turned off, when the secondary side main controller detects that the excitation voltage is less than the second voltage preset value, the secondary side main controller turns off the secondary side excitation current simulation circuit, and sends the control signal for controlling the auxiliary switch tube to turn on after a second delay time; Step 8: After receiving the control signal for controlling the auxiliary switch tube to be turned on, the primary side controller controls the auxiliary switch tube to be turned on; Step 9: the secondary-side main controller determines the control signal for controlling the auxiliary switch tube to be turned off, and transmits the signal for controlling the auxiliary switch tube to be turned off to the primary-side controller through the signal isolator; Step 10: After receiving the signal for controlling the auxiliary switch tube to turn off, the primary-side controller controls the auxiliary switch tube to turn off until the next clock signal arrives, thereby starting a new switching cycle.

8. The control method of the switching converter according to claim 5, wherein: The switch tube located at the primary side includes a main switch tube and an auxiliary switch tube. The second control method mainly operates in the following steps in a complete switching cycle: Step 1: starting from the rising edge of the clock signal, after a first delay time, the secondary-side main controller sends the control signal for controlling the main switch tube to be turned on, and transmits the control signal for controlling the main switch tube to be turned on to the primary-side controller through the signal isolator; Step 2: After receiving the control signal for controlling the main switch tube to be turned on, the primary side controller controls the main switch tube to be turned on; Step 3: After the main switch tube is turned on, when the secondary side main controller detects that the excitation voltage is greater than the second voltage preset value, the secondary side excitation current simulation circuit is turned on, and the excitation current signal of the primary side of the asymmetric half-bridge flyback converter is simulated by the secondary side excitation current simulation circuit to generate the excitation current simulation signal; Step 4: When the excitation current analog signal reaches a set value, the secondary side main controller sends the control signal for controlling the main switch tube to be turned off, and transmits the control signal for controlling the main switch tube to be turned off to the primary side controller through the signal isolator; Step 5: After receiving the control signal for controlling the main switch tube to turn off, the primary side controller controls the main switch tube to turn off; Step 6: After the main switch tube is turned off, when the secondary side main controller detects that the excitation voltage is less than the second voltage preset value, the secondary side excitation current analog circuit is turned off, and after a second delay time, the control signal for controlling the auxiliary switch tube to be turned on is issued; Step 7: After receiving the control signal for controlling the auxiliary switch tube to turn on, the primary side controller controls the auxiliary switch tube to turn on; Step 8: The secondary-side main controller determines the control signal for controlling the auxiliary switch tube to be turned off, and transmits the control signal for controlling the auxiliary switch tube to be turned off to the primary-side controller through a signal isolator; Step 9: After receiving the control signal for controlling the auxiliary switch tube to turn off, the primary-side controller controls the auxiliary switch tube to turn off until the next clock signal arrives, thereby starting a new switching cycle.

9. The control method of a switching converter according to any one of claims 7 and 8, characterized in that: The first preset value of the excitation current is a negative threshold, the second preset value of the excitation current is zero, and the set value is a preset value that represents the peak value of the excitation current.

10. The control method of the switching converter according to claim 1, wherein: The excitation current signal of the primary side of the asymmetric half-bridge flyback converter is simulated in real time on the secondary side, including: detecting the excitation voltage in real time through the secondary side excitation current simulation circuit, and converting the excitation voltage into current according to a proportion K, charging a capacitor with a certain capacitance through the current, simulating the excitation current signal of the primary side through the capacitor voltage, and the capacitor value satisfies the following relationship: Wherein K is the proportional coefficient of the excitation voltage converted to current, Lm is the excitation inductance, N is the transformer turns ratio, and Rcs is the excitation current sampling resistor.

11. The control method of the switching converter according to claim 1, characterized in that: The secondary side of the asymmetric half-bridge flyback converter includes: a primary side controller, a main switch tube, an auxiliary switch tube, a resonant capacitor and a primary winding of a transformer; the secondary side of the asymmetric half-bridge flyback converter includes: a secondary side excitation current simulation circuit, a secondary side main controller, an output rectifier tube, an output capacitor and a secondary winding of a transformer.

12. A switching converter, characterized in that: include: Secondary circuit, signal isolator and primary circuit; The secondary circuit includes a clock generating circuit, a secondary excitation current simulation circuit and a secondary main controller, wherein the clock generating circuit is used to generate a clock signal; the secondary excitation current simulation circuit is used to simulate the excitation current signal generated in the primary circuit in real time to obtain an excitation current simulation signal; the secondary main controller is used to generate a control signal according to the clock signal and the excitation current simulation signal; The signal isolator is used to transmit the control signal to the primary circuit; The primary circuit includes a primary controller and a switching circuit. The primary controller is used to receive the control signal and output a drive signal according to the control signal to control the opening and closing of the switch tube in the switching circuit to achieve output voltage stabilization and peak current control on the primary side.

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