Synchronous rectification controlled flyback converter forced resonance soft control circuit and method

Abstract

The invention relates to the technical field of microelectronics, and discloses a forced resonance soft control circuit and method for a synchronous rectification controlled flyback converter, and a single-end flyback converter in the circuit comprises a power supply circuit and a main power transformer; the output end of a PWM (Pulse Width Modulation) controller in the forced resonance soft switching circuit is connected with the input end of a preceding-stage signal conversion unit; the output end of the preceding-stage signal conversion unit is arranged in a branch mode, and one branch is connected to a preceding-stage power tube at the synonym end of a primary winding of the main power transformer through a driver. The other branch is connected to a synchronous rectifier tube at the dotted terminal of the secondary winding of the main power transformer through a digital isolator, a post-stage signal change unit and a post-stage driver in sequence; and the output end of the power supply circuit is respectively connected with the PWM controller, the pre-stage signal conversion unit, the driver and the power input end of the digital isolator. According to the invention, accurate control of the synchronous rectifier tube at the dotted terminal of the secondary winding of the main power transformer is realized.

Description

Technical Field

[0001] The invention relates to the field of microelectronic technology, and in particular to a forced resonance soft control circuit and method of a synchronous rectification controlled flyback converter. Background Art

[0002] The single-ended flyback power conversion topology has a simple circuit structure, a small number of components, and mature technology. It is widely used in small power supply products (less than 300W). In recent years, based on the goal of miniaturization and high efficiency of power supplies, the switching frequency of power supplies has been continuously improved. In order to reduce switching losses, people have made improvements based on the single-ended flyback power topology. Before the main power tube of the previous stage is turned on, a narrow pulse signal is applied to force the drain-source voltage of the main power tube to be pulled up. After the narrow pulse ends, the main power tube of the previous stage generates a reverse current through natural resonance, thereby realizing zero voltage switching (ZVS) of the main power tube. This forced resonant soft switching power conversion technology for single-ended flyback converters usually includes two specific solutions: forced resonant soft switching through the auxiliary winding of the transformer and forced resonant soft switching through the injection of a drive signal on the synchronous rectifier side.

[0003] Among them, in the forced resonant soft switching circuit based on auxiliary winding control, the scheme includes input filter inductor and capacitor L1, Cin, power transformer T1, output rectifier diode D2, output filter capacitor Co, front-stage power switch MOS tube Q1, transformer T1 auxiliary winding (T1-5 / T1-6), resonant capacitor C2, resonant switch MOS tube Q2, the principle is as follows Figure 1 As shown. In the invention patent with application number 202210810563.1, named as the control circuit and conversion circuit of the forced resonant soft-switching flyback power converter, the disclosed implementation case uses an integrated controller to realize two-way signal control, such as Infineon's forced resonant flyback controller XDPS21071. This device is in peak current control mode, outputs two drive signals GD0 and GD1, has a switching frequency of 140kHz, and starts at 600V high voltage. The specific circuit principle is as follows Figure 2 As shown, the driving signal is Figure 3 As shown. Among them, the GD0 terminal outputs a PWM drive signal, and the duty cycle of the signal is adjusted with the MFIO terminal voltage loop control signal and the CS current loop control signal; the GD1 terminal outputs a resonant circuit drive narrow pulse signal, and the signal width tGD1on and the lead time tZVSdead can be set according to the corresponding parameters of the converter. This case has the following problems in the application: forced soft switching is required through the transformer auxiliary winding, resonant capacitor, and resonant switch. This increases the manufacturing cost of the transformer and the complexity of the control circuit. At the same time, the switching frequency of the existing integrated controller (XDPS21071) is only 140kHz, which cannot meet higher frequency applications.

[0004] Among them, in the forced resonant soft switching circuit based on synchronous rectification control, the circuit includes input capacitor Ci, transformer T, power tubes Q1, Q2, and output filter capacitor Co. Among them, Lm is the excitation inductance, Lplk is the leakage inductance of the transformer winding, Q1 is the primary main power tube, Coss1 is the parasitic capacitance of the main switch tube Q1, S1 is the driving signal for driving the main switch tube Q1, Q2 is the secondary power tube, S2 is the driving signal for driving the secondary switch tube Q2, and Coss2 is the parasitic capacitance of the secondary switch tube Q2. The principle is as follows Figure 4 As shown, the key node waveform is as follows Figure 6 As shown. The key to implementing forced resonance through the secondary-side synchronous rectifier is: ① The forced drive narrow pulse signal must be ahead of the previous main power tube Q1, and leave a dead time. ② The single-ended flyback transformer must operate in discontinuous mode (DCM). ③ The output synchronous rectification control must support the precise shutdown of the transformer DCM current. However, the current technology cannot meet the above control drive technical solutions. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a forced resonant soft control circuit and method of a flyback converter with synchronous rectification control, so as to solve the technical problem of how to realize forced resonant soft switching of a flyback converter based on synchronous rectification control in the prior art.

[0006] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a forced resonance soft control circuit of a flyback converter controlled by synchronous rectification, comprising a single-ended flyback converter and a forced resonance soft switching circuit; The single-ended flyback converter includes a power supply circuit and a main power transformer; The forced resonant soft switching circuit includes a PWM controller U1, a front-stage signal conversion unit U2, a driver U3, a digital isolator U4, a rear-stage signal change unit U5 and a rear-stage driver U6; The output end of the PWM controller U1 is connected to the input end of the front-stage signal conversion unit U2; the output end of the front-stage signal conversion unit U2 is branched, one branch is connected to the front-stage power tube Q1 at the opposite end of the primary winding of the main power transformer through the driver U3, and the other branch is connected to the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer through the digital isolator U4, the rear-stage signal change unit U5 and the rear-stage driver U6 in sequence; The output end of the power supply circuit is respectively connected to the power input end of the PWM controller U1, the front-stage signal conversion unit U2, the driver U3 and the digital isolator U4.

[0007] Preferably, the PWM controller U1, the front-stage signal conversion unit U2, the first driver U3 and the digital isolator U4 are all provided with a one-end grounding setting.

[0008] Preferably, the model of the PWM controller U1 includes UC1843 or LM5020.

[0009] Preferably, the front-stage signal conversion unit U2 includes a Schmidt inverter U2_1, a Schmidt inverter U2_2, a Schmidt inverter U2_3, a high-speed AND gate U2_4, a diode D1, a resistor R1, a resonant capacitor C1, a diode D2, a resistor R2 and a resonant capacitor C2; The input end of the Schmidt inverter U2_1 is connected to the anode of the diode D1, one end of the resistor R1, and one end of the resonant capacitor C1, and the output end of the Schmidt inverter U2_1 is connected to the input end of the Schmidt inverter U2_2; The input end of the Schmidt inverter U2_3 is connected to the anode of the diode D2, one end of the resistor R2, and one end of the resonant capacitor C2, and the output end of the Schmidt inverter U2_3 is connected to the input end of the high-speed AND gate U2_4.

[0010] Furthermore, the resistor R1 and the resonant capacitor C1 as well as the resistor R2 and the resonant capacitor C2 respectively constitute a delayed opening circuit.

[0011] Preferably, the driver U3 and the post-stage driver U6 are single-output drivers, and the models of the driver U3 and the post-stage driver U6 include but are not limited to MIC4420.

[0012] Preferably, the digital isolator U4 is a bidirectional dual-channel capacitive isolation type digital isolator, and the model of the digital isolator U4 includes but is not limited to NSi8221N0.

[0013] Preferably, one end of the subsequent signal changing unit U5 is also connected to the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer.

[0014] Further, the subsequent signal changing unit U5 includes a single-ended flyback synchronous rectification controller U5_1 and a high-speed OR gate U5_2; The CS end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the drain of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer; the DIS end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the source of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer; the DRV end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the input end of the high-speed OR gate U5_2; the other input end of the high-speed OR gate U5_2 is connected to the output end of the digital isolator U4; the output end of the high-speed OR gate U5_2 is connected to the post-stage driver U6.

[0015] In a second aspect, the present invention further provides a forced resonance soft control method for a flyback converter controlled by synchronous rectification, based on the above-mentioned forced resonance soft control circuit for a flyback converter controlled by synchronous rectification, comprising the following process: The power supply circuit of the single-ended flyback converter supplies power to the PWM controller U1, the front-stage signal conversion unit U2, the driver U3 and the digital isolator U4 respectively; wherein the PWM signal output by the PWM controller U1 is fed into the front-stage signal conversion unit U2, and after being converted by the front-stage signal conversion unit U2, a PWM drive signal OUT1 and an advanced narrow pulse signal OUT2 are generated; wherein the PWM drive signal OUT1 controls the front-stage power tube Q1 at the opposite end of the primary winding of the main power transformer through the driver U3; the advanced narrow pulse signal OUT2 is input to the signal conversion unit U5 through the digital isolator U4, and at the same time, the signal conversion unit U5 converts the control signal generated by the synchronous rectifier tube Q2 at the same end of the secondary winding of the main power transformer detected, and synchronously inputs the control signal to the rear-stage driver U6 in combination with the input signal of the digital isolator U4, and drives the synchronous rectifier tube Q2 at the same end of the secondary winding of the main power transformer through the rear-stage driver U6.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides a forced resonance soft control circuit of a flyback converter controlled by synchronous rectification. By introducing a forced resonance soft switching circuit, the present invention can effectively reduce the loss in the switching process. In a traditional hard switching circuit, a switch device will generate a large voltage and current overlap when it is turned on and off, resulting in switching losses. The forced resonance soft switching circuit uses the resonance principle to switch the switch device under zero voltage or zero current conditions, thereby significantly reducing the switching loss and improving the energy efficiency of the entire flyback converter. The combination of the PWM controller U1 and the front-stage signal conversion unit U2 enables the control signal to be accurately adjusted according to the changes in the load and input voltage. This dynamic adjustment capability helps to maintain the stability of the output voltage and enhance the adaptability and stability of the circuit. In particular, in the case of sudden load changes or input voltage fluctuations, this control circuit can respond quickly and keep the output voltage constant. Through the connection of the digital isolator U4, the rear-stage signal change unit U5 and the rear-stage driver U6, the present invention realizes the precise control of the synchronous rectifier tube Q2 at the same-name end of the secondary winding of the main power transformer. Synchronous rectification technology can further improve the efficiency of the converter because it allows the use of low on-resistance MOSFETs as rectification devices on the secondary side instead of traditional diodes. In this way, the voltage drop and power consumption generated during the rectification process are greatly reduced.

[0017] Furthermore, the present invention forms a highly integrated control circuit by organically combining components such as a PWM controller, a signal conversion unit, a driver, a digital isolator, and a signal change unit. This integrated design not only reduces the volume and weight of the circuit, but also helps to improve the reliability and maintainability of the circuit. The use of the digital isolator also enhances the electrical isolation between circuits and improves the safety of the system.

[0018] Furthermore, the present invention not only realizes the drive timing generation of the primary and secondary side switches, but also realizes the soft switching control of the primary side switch by adding signal conversion units on the primary and secondary sides and cooperating with the common single-output PWM controller and single-ended flyback synchronous rectification controller. Compared with the prior art, there is no need for transformer auxiliary winding, resonant switch and resonant capacitor, and it is not limited by the switching frequency of the existing controller, and the application circuit is simple and the cost is low.

[0019] The present invention also provides a forced resonance soft control method for a flyback converter controlled by synchronous rectification, wherein an accurate PWM signal is outputted by a PWM controller U1, and after being transformed by a front-stage signal conversion unit U2, a PWM drive signal OUT1 and an advanced narrow pulse signal OUT2 are generated. This precise signal control can ensure that the front-stage power tube Q1 and the synchronous rectifier tube Q2 at the same-name end of the secondary winding of the main power transformer perform switching actions at the best time, thereby reducing switching losses and improving energy efficiency. The introduction of the advanced narrow pulse signal OUT2 enables the synchronous rectifier tube Q2 at the same-name end of the secondary winding of the main power transformer to pre-adjust the state before the front-stage power tube Q1 acts, ensuring a smooth transition of the current and further reducing energy losses. The precise control of the synchronous rectifier tube Q2 at the same-name end of the secondary winding of the main power transformer depends on the detection and transformation of the same-name end signal of the secondary winding by the signal conversion unit U5, and the isolated transmission of the digital isolator U4. This design makes the synchronous rectification process more efficient and reliable, and significantly improves the rectification efficiency. The post-stage driver U6 drives the synchronous rectifier Q2 according to the control signal of the same-name end of the secondary winding of the main power transformer, ensuring that it switches synchronously with the secondary winding current of the main power transformer, effectively reducing the voltage drop and power consumption during the rectification process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the principle of an auxiliary winding resonant soft switching circuit in the prior art; Figure 2 It is a schematic diagram of the application principle of XDPS21071 in the prior art; Figure 3 It is a schematic diagram of the driving waveform of XDPS21071 in the prior art; Figure 4 It is a block diagram of the principle of single-ended flyback driven by synchronous rectification side in the prior art; Figure 5 Schematic diagram of a forced resonant soft switching circuit of a flyback converter in an embodiment of the present invention; Figure 6 Schematic diagram of the circuit structure of the signal conversion unit U2 in an embodiment of the present invention; Figure 7 This is a waveform diagram of a soft switching pulse signal generating circuit in an embodiment of the present invention; Figure 8 Schematic diagram of the circuit structure of the signal conversion unit U5 in an embodiment of the present invention; Fig. 9 Schematic diagram of internal node waveforms of the signal conversion unit U5 in an embodiment of the present invention; Fig.10 Schematic diagram of the position and connection relationship in the flyback converter according to an embodiment of the present invention; Fig.11 Schematic diagram of a forced resonant soft switching circuit driven by a synchronous rectification side in an embodiment of the present invention; In the figure: 1. Single-ended flyback converter; 2. Forced resonant soft switching circuit. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0022] The object of the present invention is to provide a synchronous rectification controlled flyback converter forced resonant soft control circuit and method to solve the technical problem of how to realize the forced resonant soft switching of the flyback converter based on synchronous rectification control in the prior art.

[0023] The present invention is further described in detail below in conjunction with the accompanying drawings: Example 1 See also Figure 5In one embodiment of the present invention, a forced resonance soft control circuit of a flyback converter controlled by synchronous rectification is provided, comprising a single-ended flyback converter 1 and a forced resonance soft switching circuit 2; the single-ended flyback converter 1 comprises a power supply circuit and a main power transformer; the forced resonance soft switching circuit 2 comprises a PWM controller U1, a front-stage signal conversion unit U2, a driver U3, a digital isolator U4, a rear-stage signal change unit U5 and a rear-stage driver U6; the output end of the PWM controller U1 is connected to the input end of the front-stage signal conversion unit U2; the output end of the front-stage signal conversion unit U2 is branched, one branch is connected to the front-stage power tube Q1 at the opposite end of the primary winding of the main power transformer through the driver U3, and the other branch is connected to the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer through the digital isolator U4, the rear-stage signal change unit U5 and the rear-stage driver U6 in sequence; the output end of the power supply circuit is respectively connected to the power input end of the PWM controller U1, the front-stage signal conversion unit U2, the driver U3 and the digital isolator U4.

[0024] Specifically, the PWM controller U1 , the front-stage signal conversion unit U2 , the first driver U3 , and the digital isolator U4 are all provided with one end grounded.

[0025] Specifically, models of the PWM controller U1 include UC1843 or LM5020.

[0026] Specifically, according to Figure 6 As shown, the front-stage signal conversion unit U2 includes a Schmidt inverter U2_1, a Schmidt inverter U2_2, a Schmidt inverter U2_3, a high-speed AND gate U2_4, a diode D1, a resistor R1, a resonant capacitor C1, a diode D2, a resistor R2 and a resonant capacitor C2; the input end of the Schmidt inverter U2_1 is connected to the anode of the diode D1, one end of the resistor R1, and one end of the resonant capacitor C1, and the output end of the Schmidt inverter U2_1 is connected to the input end of the Schmidt inverter U2_2; the input end of the Schmidt inverter U2_3 is connected to the anode of the diode D2, one end of the resistor R2, and one end of the resonant capacitor C2, and the output end of the Schmidt inverter U2_3 is connected to the input end of the high-speed AND gate U2_4.

[0027] The resistor R1 and the resonant capacitor C1 as well as the resistor R2 and the resonant capacitor C2 respectively form a delayed opening circuit.

[0028] Specifically, the driver U3 and the subsequent driver U6 are single-output drivers, and the models of the driver U3 and the subsequent driver U6 include but are not limited to MIC4420.

[0029] Specifically, the digital isolator U4 is a bidirectional dual-channel capacitive isolation type digital isolator, and the model of the digital isolator U4 includes but is not limited to NSi8221N0.

[0030] In this embodiment, one end of the subsequent signal changing unit U5 is also connected to the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer.

[0031] Specifically, according to Figure 8 As shown, the post-stage signal changing unit U5 includes a single-ended flyback synchronous rectifier controller U5_1 and a high-speed OR gate U5_2; the CS end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the drain of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer; the DIS end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the source of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer; the DRV end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the input end of the high-speed OR gate U5_2; the other input end of the high-speed OR gate U5_2 is connected to the output end of the digital isolator U4; the output end of the high-speed OR gate U5_2 is connected to the post-stage driver U6.

[0032] In summary, the present embodiment provides a forced resonant soft control circuit for a flyback converter controlled by synchronous rectification. By introducing a forced resonant soft switching circuit, the present invention can effectively reduce the loss during the switching process. In a traditional hard switching circuit, a switch device will generate a large voltage and current overlap when it is turned on and off, resulting in switching losses. The forced resonant soft switching circuit uses the resonance principle to switch the switch device under zero voltage or zero current conditions, thereby significantly reducing the switching loss and improving the energy efficiency of the entire flyback converter. The combination of the PWM controller U1 and the front-stage signal conversion unit U2 enables the control signal to be accurately adjusted according to the changes in the load and input voltage. This dynamic adjustment capability helps to maintain the stability of the output voltage and enhance the adaptability and stability of the circuit. In particular, in the case of sudden load changes or input voltage fluctuations, this control circuit can respond quickly and keep the output voltage constant. Through the connection of the digital isolator U4, the rear-stage signal change unit U5 and the rear-stage driver U6, the present invention realizes the precise control of the synchronous rectifier Q2 at the opposite end of the secondary winding. Synchronous rectification technology can further improve the efficiency of the converter because it allows the use of low on-resistance MOSFETs as rectification devices on the secondary side instead of traditional diodes. In this way, the voltage drop and power consumption generated during the rectification process are greatly reduced.

[0033] Example 2 This embodiment 2 provides a synchronous rectification controlled flyback converter forced resonance soft control method, based on the above-mentioned synchronous rectification controlled flyback converter forced resonance soft control circuit, including the following process: The power supply circuit of the single-ended flyback converter 1 supplies power to the PWM controller U1, the front-stage signal conversion unit U2, the driver U3 and the digital isolator U4 respectively; wherein the PWM signal output by the PWM controller U1 is fed into the front-stage signal conversion unit U2, and after being converted by the front-stage signal conversion unit U2, a PWM drive signal OUT1 and an advanced narrow pulse signal OUT2 are generated; wherein the PWM drive signal OUT1 controls the front-stage power tube Q1 at the opposite end of the primary winding of the main power transformer through the driver U3; the advanced narrow pulse signal OUT2 is input to the signal conversion unit U5 through the digital isolator U4, and at the same time, the signal conversion unit U5 converts the control signal generated by the synchronous rectifier tube Q2 at the same end of the secondary winding of the main power transformer detected, and synchronously inputs the control signal to the rear-stage driver U6 in combination with the input signal of the digital isolator U4, and drives the synchronous rectifier tube Q2 at the same end of the secondary winding of the main power transformer through the rear-stage driver U6.

[0034] Specifically, the signal conversion unit U2 converts the single output PWM signal generated by the PWM controller U1 to generate two drive signals, namely, the PWM signal OUT1 with the same duty cycle and the leading narrow pulse drive signal OUT2. The node waveforms of the signal conversion circuit U2 are as follows: Figure 7 Shown Among them, the leading narrow pulse signal OUT2: at t0, V PWM From low to high, the voltage is charged to capacitor C2 through resistor R2, and the voltage of C2 (voltage at point C) rises slowly. Between t0 and t1, the voltage at point C is lower than the threshold voltage V of the Schmitt inverter. TH , point D outputs a high level. At this time, the voltage at point D and Vpwm pass through the high-speed AND gate U2_4 and then output a high level. At t1, the voltage at point C is higher than the Schmitt inverter threshold voltage V TH , the level at point D is flipped to a low level, and the level at point D and Vpwm are turned to a low level after passing through the high-speed AND gate U2_4. Between t1-t3, the level at point C is high, and the level at point D is low. After passing through the high-speed AND gate U2_4, the output of the advanced narrow pulse signal OUT2 is a low level. Between t3-t4, Vpwm is a low level, and point D is a high level. After passing through the high-speed AND gate U2_4, the output of the advanced narrow pulse signal OUT2 is a low level. The width of the advanced narrow pulse signal OUT2 is determined by the charging time of the resistor R2 and the capacitor C2.

[0035] PWM drive signal OUT1: At t0, V PWM It flips from low to high and charges capacitor C1 through resistor R1. The voltage of C1 (voltage at point A) rises slowly. Between t0 and t2, the voltage at point A is lower than the threshold voltage V of the Schmitt inverter. TH, point B outputs high level, OUT1 outputs low level. At t2, the voltage at point A is higher than the Schmitt inverter threshold voltage V TH , point B flips to low level, and PWM drive signal OUT1 flips to high level. Between t2 and t3, Vpwm is high level, point B is low level, and PWM drive signal OUT1 outputs high level. At t3, Vpwm flips to low level, capacitor C1 discharges quickly through diode D1, the voltage at point A drops to low level, point B flips to high level, and PWM drive signal OUT1 outputs low level. The delay time between PWM drive signal OUT1 and Vpwm is determined by the charging time of resistor R1 and capacitor C1.

[0036] Delay time T t0-t2 T delay1 , narrow pulse width T t0-t1 T delay2 The delay time between the narrow pulse and the PWM drive signal OUT1 is T delay1 -T delay2 .

[0037]

[0038]

[0039] The node waveform of the subsequent signal changing unit U5 in this embodiment is as follows: Fig. 9 shown.

[0040] Among them, the PWM drive signal OUT1 is the drive signal of the front-stage power MOS tube, and DRV is the output signal of the secondary synchronous rectifier driver. This signal is generated by the synchronous rectifier U5_3 by detecting the drain-source voltage of the synchronous rectifier tube Q2 at the same end of the secondary winding of the main power transformer. The output signal of the digital isolator U4 is the front-stage narrow pulse signal transmitted to the secondary side through the digital isolator. This signal is synthesized with the DRV signal through the OR gate to form the output signal of the high-speed OR gate U5_2.

[0041] The specific principle and structure of this embodiment Fig.10 As shown, the dotted box in the figure is a forced resonant soft switching circuit 2 based on synchronous rectification control. The rest is a common single-ended flyback converter 1 and part of its control circuit, including a power conversion circuit, an error sampling and amplification circuit, an optical coupler, etc.

[0042] Specific process Fig.11As shown, the PWM controller U1 generates a pulse width drive signal OUT according to the feedback signal FB, and the signal is passed through the front-stage signal conversion unit U2 to generate an advanced narrow pulse signal OUT2 and a delayed PWM pulse width signal OUT1. The advanced narrow pulse signal OUT2 is transmitted to the secondary side through the digital isolator U4, and is synthesized into a control signal with the pulse width signal DRV generated by the synchronous rectification controller through the high-speed OR gate U5_2. The signal is amplified by the rear-stage driver U6 to generate a gate drive signal of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer. The signal contains two parts of information. The narrow pulse signal comes from the front stage and is the leading front-stage main power tube drive signal. The synchronous rectification control signal comes from the single-ended flyback synchronous rectification controller U5_1. The controller adopts NCP4306, and controls the on and off of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer in real time by detecting the voltage of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer.

[0043] In summary, the present embodiment provides a forced resonance soft control method for a flyback converter with synchronous rectification control, which outputs an accurate PWM signal through the PWM controller U1, and after the conversion of the front-stage signal conversion unit U2, generates a PWM drive signal OUT1 and an advanced narrow pulse signal OUT2. This precise signal control can ensure that the front-stage power tube Q1 and the synchronous rectifier tube Q2 at the same-name end of the secondary winding of the main power transformer perform switching actions at the best time, thereby reducing switching losses and improving energy efficiency. The introduction of the advanced narrow pulse signal OUT2 enables the synchronous rectifier tube Q2 at the same-name end of the secondary winding of the main power transformer to pre-adjust the state before the front-stage power tube Q1 acts, ensuring a smooth transition of the current and further reducing energy losses. The precise control of the synchronous rectifier tube Q2 at the same-name end of the secondary winding of the main power transformer depends on the detection and conversion of the same-name end signal of the secondary winding by the signal conversion unit U5, and the isolated transmission of the digital isolator U4. This design makes the synchronous rectification process more efficient and reliable, and significantly improves the rectification efficiency. The post-stage driver U6 drives the synchronous rectifier Q2 according to the control signal of the same-name end of the secondary winding of the main power transformer, ensuring that it switches synchronously with the secondary winding current of the main power transformer, effectively reducing the voltage drop and power consumption during the rectification process.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A forced resonance soft control circuit of a flyback converter controlled by synchronous rectification, characterized in that: It includes a single-ended flyback converter (1) and a forced resonant soft switching circuit (2); The single-ended flyback converter (1) comprises a power supply circuit and a main power transformer; The forced resonant soft switching circuit (2) comprises a PWM controller U1, a front-stage signal conversion unit U2, a driver U3, a digital isolator U4, a rear-stage signal change unit U5 and a rear-stage driver U6; The output end of the PWM controller U1 is connected to the input end of the front-stage signal conversion unit U2; the output end of the front-stage signal conversion unit U2 is branched, one branch is connected to the front-stage power tube Q1 at the opposite end of the primary winding of the main power transformer through the driver U3, and the other branch is connected to the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer through the digital isolator U4, the rear-stage signal change unit U5 and the rear-stage driver U6 in sequence; The output end of the power supply circuit is respectively connected to the power input end of the PWM controller U1, the front-stage signal conversion unit U2, the driver U3 and the digital isolator U4.

2. The forced resonance soft control circuit of a flyback converter controlled by synchronous rectification according to claim 1, characterized in that: The PWM controller U1, the front-stage signal conversion unit U2, the first driver U3 and the digital isolator U4 are all provided with one end grounded.

3. The forced resonance soft control circuit of a flyback converter with synchronous rectification control according to claim 1, characterized in that: Models of the PWM controller U1 include UC1843 or LM5020.

4. The forced resonance soft control circuit of a flyback converter with synchronous rectification control according to claim 1, characterized in that: The front-stage signal conversion unit U2 includes a Schmidt inverter U2_1, a Schmidt inverter U2_2, a Schmidt inverter U2_3, a high-speed AND gate U2_4, a diode D1, a resistor R1, a resonant capacitor C1, a diode D2, a resistor R2 and a resonant capacitor C2; The input end of the Schmidt inverter U2_1 is connected to the anode of the diode D1, one end of the resistor R1, and one end of the resonant capacitor C1, and the output end of the Schmidt inverter U2_1 is connected to the input end of the Schmidt inverter U2_2; The input end of the Schmidt inverter U2_3 is connected to the anode of the diode D2, one end of the resistor R2, and one end of the resonant capacitor C2, and the output end of the Schmidt inverter U2_3 is connected to the input end of the high-speed AND gate U2_4.

5. The forced resonance soft control circuit of a flyback converter with synchronous rectification control according to claim 4, characterized in that: The resistor R1 and the resonant capacitor C1 as well as the resistor R2 and the resonant capacitor C2 respectively constitute a delayed opening circuit.

6. The forced resonance soft control circuit of a flyback converter with synchronous rectification control according to claim 1, characterized in that: The driver U3 and the subsequent driver U6 are single-output drivers, and the models of the driver U3 and the subsequent driver U6 include but are not limited to MIC4420.

7. The forced resonance soft control circuit of a flyback converter with synchronous rectification control according to claim 1, characterized in that: The digital isolator U4 is a bidirectional dual-channel capacitive isolation type digital isolator, and the model of the digital isolator U4 includes but is not limited to NSi8221N0.

8. The forced resonance soft control circuit of a flyback converter with synchronous rectification control according to claim 1, characterized in that: One end of the post-stage signal changing unit U5 is also connected to the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer.

9. The forced resonance soft control circuit of a flyback converter with synchronous rectification control according to claim 8, characterized in that: The post-stage signal changing unit U5 includes a single-ended flyback synchronous rectification controller U5_1 and a high-speed OR gate U5_2; The CS end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the drain of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer; the DIS end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the source of the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer; the DRV end of the single-ended flyback synchronous rectifier controller U5_1 is connected to the input end of the high-speed OR gate U5_2; the other input end of the high-speed OR gate U5_2 is connected to the output end of the digital isolator U4; the output end of the high-speed OR gate U5_2 is connected to the post-stage driver U6.

10. A forced resonance soft control method for a synchronous rectifier controlled flyback converter, based on a forced resonance soft control circuit for a synchronous rectifier controlled flyback converter according to any one of claims 1 to 9, characterized in that: The process includes the following: The power supply circuit of the single-ended flyback converter (1) supplies power to the PWM controller U1, the front-stage signal conversion unit U2, the driver U3 and the digital isolator U4 respectively; wherein the PWM signal output by the PWM controller U1 is input to the front-stage signal conversion unit U2, and after being converted by the front-stage signal conversion unit U2, a PWM drive signal OUT1 and an advanced narrow pulse signal OUT2 are generated; wherein the PWM drive signal OUT1 controls the front-stage power tube Q1 at the opposite end of the primary winding of the main power transformer through the driver U3; the advanced narrow pulse signal OUT2 is input to the signal conversion unit U5 through the digital isolator U4, and at the same time, the signal conversion unit U5 converts the control signal generated by the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer detected by combining the control signal generated by the signal conversion and the input signal of the digital isolator U4 to the rear-stage driver U6, and drives the synchronous rectifier Q2 at the same end of the secondary winding of the main power transformer through the rear-stage driver U6.

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