LLC resonant soft switching converter based on self-detection synchronous rectification and control method thereof

Abstract

The invention relates to an LLC resonant soft switching converter based on self-detection synchronous rectification and a control method thereof. The converter comprises an LLC resonance circuit, a secondary transformer with a center tap, a self-detection synchronous rectification circuit, an input filter circuit, an output filter circuit, an LLC resonance control circuit, a primary PFM drive circuit, an optocoupler isolation circuit, an output voltage sampling circuit and an operational amplifier compensation circuit. Switching tubes S1 and S2 in the primary PFM drive circuit adopt high-voltage MOS tubes, secondary synchronous rectifier tubes S3 and S4 adopt low-voltage MOS tubes, output voltage feedback control and secondary synchronous rectifier tube self-detection drive control are adopted, and the resonant soft switching converter with the 240V-300V input voltage range, the constant output of 28V / 300W and the full-load efficiency of 92% is realized. According to the invention, zero-voltage switching-on of the primary switch tube, zero-current switching-off of the secondary synchronous rectifier tube and accurate synchronous rectification control are realized, the loss of the rectifier circuit is reduced, the efficiency of the converter is improved, and the electromagnetic compatibility characteristic of the converter is optimized.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics and relates to an LLC resonant soft-switching converter based on self-detection synchronous rectification and a control method thereof. Background Art

[0002] The development trend of DC-DC converters is miniaturization and high efficiency. Increasing the switching frequency can effectively reduce the size of passive components, thereby reducing the size of the converter. However, the switching loss of traditional hard-switching converters is positively correlated with the switching frequency. The higher the switching frequency, the greater the switching loss and the lower the efficiency. Therefore, it is difficult to achieve both miniaturization and high efficiency with traditional hard-switching converters.

[0003] The LLC resonant soft-switching converter uses the LLC resonant circuit to achieve zero-voltage turn-on of the primary switching transistor and zero-current turn-off of the secondary synchronous rectifier, thereby reducing switching losses, facilitating higher switching frequencies, and reducing converter size. Compared to traditional diode rectifier circuits, the MOS transistor conduction voltage drop in the synchronous rectifier circuit is lower than the diode voltage drop, significantly reducing conduction losses and improving efficiency. However, because LLC resonant soft-switching converters use variable frequency control, traditional synchronous rectifier circuits are not ideal for use in LLC resonant soft-switching converters.

[0004] Therefore, it is necessary to realize an LLC resonant soft-switching converter based on self-detection synchronous rectification and a control method thereof. Summary of the Invention

[0005] To address the problems of large switching losses in traditional hard-switching DC-DC converters and the mismatch between traditional synchronous rectification circuits and LLC resonant soft-switching circuits, and to achieve miniaturization and high efficiency of DC-DC converters, the present invention proposes an LLC resonant soft-switching converter based on self-detecting synchronous rectification and a control method thereof. The converter has high switching frequency, small size, high power density, and high efficiency, taking into account the requirements of miniaturization and high efficiency of DC-DC converters.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An LLC resonant soft-switching converter based on self-detection synchronous rectification includes: an input filter circuit, an LLC resonant circuit, a transformer, a self-detection synchronous rectification circuit, an output filter circuit, an output voltage sampling circuit, an operational amplifier compensation circuit, an optocoupler isolation circuit, an LLC resonant control circuit, and a primary PFM drive circuit.

[0008] The input filter circuit filters the input voltage signal to obtain the input voltage DC component; the LLC resonant circuit converts the input voltage DC component into an AC square wave signal through a switch tube, and converts the AC square wave signal into a high-frequency resonant signal through an LLC resonant cavity; the transformer electrically isolates and transforms the amplitude of the high-frequency resonant signal; the self-detection synchronous rectifier circuit rectifies and outputs the high-frequency resonant signal after electrical isolation and amplitude transformation, and controls the rectifier tube to output a first output voltage signal containing an AC component through a synchronous rectifier controller; the output filter circuit filters the output voltage signal to obtain the output voltage DC component; the output The voltage sampling circuit divides and reduces the DC component of the output voltage to obtain a proportionally reduced second output voltage signal; the operational amplifier compensation circuit compares the second output voltage signal with a reference signal and outputs a voltage error feedback signal based on the comparison result; the optocoupler isolation circuit electrically isolates the voltage error feedback signal; the LLC resonant control circuit adjusts the PFM signal that drives the operating frequency of the switching tube based on the voltage error feedback signal and inputs the PFM signal into the primary PFM drive circuit; the primary PFM drive circuit conditions the PFM signal and uses the conditioned PFM signal to control the switching of the half-bridge switching tube in the LLC resonant circuit.

[0009] Furthermore, the transformer is a transformer with an intermediate tap on the secondary side; the transformer includes a primary winding, a first secondary winding and a second secondary winding; the opposite-name end of the first secondary winding is connected to the same-name end of the second secondary winding.

[0010] Furthermore, the LLC resonant circuit includes a resonant inductor Lr, an excitation inductor Lm and a resonant capacitor Cr; the first end of the resonant inductor Lr is connected to the middle node of the half-bridge switch tube in the LLC resonant circuit, the second end of the resonant inductor Lr is connected to the first end of the resonant capacitor Cr, the second end of the resonant capacitor Cr is connected to the same-name end of the excitation inductor Lm, and the opposite-name end of the excitation inductor Lm is connected to the input reference ground PGND; the same-name end of the excitation inductor Lm is connected to the same-name end of the primary winding of the transformer T, and the opposite-name end of the excitation inductor Lm is connected to the opposite-name end of the primary winding of the transformer T.

[0011] Furthermore, the LLC resonance control circuit includes an LLC resonance controller N1, a resistor RH, a resistor RL, a resistor Rss, a capacitor Css, a capacitor C FThe pin Line of the LLC resonant controller N1 is connected to the second end of the resistor RH and the first end of the resistor RL respectively. The first end of the resistor RH is connected to the input voltage Vin, and the second end of the resistor RL is connected to the input reference ground PGND. The pin Rfmin of the LLC resonant controller N1 is connected to the input reference ground PGND via the resistor Rss and the capacitor Css. The pin CSS of the LLC resonant controller N1 is connected to the node between the resistor Rss and the capacitor Css. The pin CF of the LLC resonant controller N1 is connected to the capacitor C F The first end is connected to the capacitor C F The second terminal is connected to the input reference ground PGND.

[0012] Furthermore, the primary PFM drive circuit includes a primary switch tube S1 and a primary switch tube S2; the source of the primary switch tube S1 is connected to the drain of the primary switch tube S2 and serves as an intermediate node of the half-bridge switch tube in the LLC resonant circuit, and the intermediate node is connected to the first end of the resonant inductor Lr; the drain of the primary switch tube S1 is connected to the input voltage Vin, and the gate of the primary switch tube S1 is connected to the first output end of the LLC resonant control circuit; the source of the primary switch tube S2 is connected to the input reference ground PGND, and the gate of the primary switch tube S2 is connected to the second output end of the LLC resonant control circuit; the source of the primary switch tube S1 is connected to A first parasitic diode is connected between the drains, the anode of the first parasitic diode is connected to the source of the primary switch tube S1, and the cathode of the first parasitic diode is connected to the drain of the primary switch tube S1; a second parasitic diode is connected between the source and drain of the primary switch tube S2, the anode of the second parasitic diode is connected to the source of the primary switch tube S2, and the cathode of the second parasitic diode is connected to the drain of the primary switch tube S2; the primary switch tubes S1 and S2 are high-voltage MOS tubes; the primary switch tubes S1 and S2 are high-voltage MOS tubes; the secondary synchronous rectifier tubes S3 and S4 are low-voltage MOS tubes.

[0013] Furthermore, the input filter circuit includes an input filter capacitor Cin; the input filter capacitor Cin is connected in parallel between the input voltage Vin and the input reference ground PGND; the output filter circuit includes an output filter capacitor Co; the output filter capacitor Co is connected in parallel between the output voltage Vo and the output reference ground SGND.

[0014] Furthermore, the output voltage sampling circuit includes a capacitor Co, a resistor RL, a resistor Rupper and a resistor Rflower; the first end of the capacitor Co is respectively connected to the opposite-name end of the first secondary winding and the same-name end of the second secondary winding of the transformer T, the second end of the capacitor Co is connected to the output reference ground SGND, and the resistor RL is connected in parallel to the two ends of the capacitor Co; the voltage of the first end of the capacitor Co is used as the output voltage Vo; the first end of the resistor Rupper is connected to the first end of the capacitor Co, the second end of the resistor Rupper is connected to the first end of the resistor Rflower, and the second end of the resistor Rflower is connected to the output reference ground SGND.

[0015] Furthermore, the self-detection synchronous rectification circuit includes a synchronous rectification controller N3, a secondary synchronous rectifier S3 and a secondary synchronous rectifier S4; the drain of the secondary synchronous rectifier S3 is connected to the same-name end of the first secondary winding of the transformer T1, the source of the secondary synchronous rectifier S3 is connected to the source of the secondary synchronous rectifier S4, and the gate of the secondary synchronous rectifier S3 is connected to the pin SR2 of the synchronous rectification controller N3; the gate of the secondary synchronous rectifier S4 is connected to the pin SR1 of the synchronous rectification controller N3, and the gate of the secondary synchronous rectifier S4 is connected to the opposite-name end of the second secondary winding of the transformer T1; the secondary synchronous rectifier S3 and the secondary synchronous rectifier S4 are both low-voltage MOS tubes, and are driven and controlled by self-detection of the secondary synchronous rectifier.

[0016] Furthermore, the optocoupler isolation circuit includes an optocoupler isolator N2, a resistor R1, a resistor R2, a resistor RFmin, a resistor RFmax1 and a resistor RFmax2; the optocoupler isolator N2 includes a phototransistor and a light-emitting diode; the anode of the light-emitting diode is connected to the output voltage Vo through the resistor R1, the first end of the resistor R2 is connected to the anode of the light-emitting diode, and the second end of the resistor R2 is connected to the output end of the op amp compensation circuit; the collector of the phototransistor is connected to the first end of the resistor RFmax2, and the second end of the resistor RFmax2 is connected to the pin STBY of the LLC resonant controller N1; the first end of the resistor RFmax1 is connected to the pin STBY of the LLC resonant controller N1, the second end of the resistor RFmax1 is respectively connected to the pin Rfmin of the LLC resonant controller N1, the first end of the resistor Rss, and the first end of the resistor RFmin, and the second end of the resistor RFmin is connected to the input reference ground PGND.

[0017] Furthermore, the operational amplifier compensation circuit includes an operational compensator N4, a capacitor C1, a capacitor C2 and a resistor R3; the non-inverting input terminal of the operational compensator N4 is connected to the reference voltage VREF, and the reverse input terminal is connected to the second output voltage signal; the first terminal of the capacitor C2 is connected to the reverse input terminal of the operational compensator N4, and the second terminal of the capacitor C2 is connected to the output terminal of the operational compensator N4; the first terminal of the capacitor C1 is connected to the reverse input terminal of the operational compensator N4, and the second terminal is connected to the output terminal of the operational compensator N4 via the resistor R3.

[0018] The present invention also includes a control method for the above-mentioned LLC resonant soft-switching converter based on self-detection synchronous rectification, the method comprising the following steps:

[0019] S1. The input filter circuit filters the input voltage signal to obtain the DC component of the input voltage.

[0020] The S2 and LLC resonant circuits process the DC component of the input voltage and convert the DC input voltage signal into an AC square wave signal through alternating switching of the primary switch tubes S1 and S2. The AC square wave signal is processed by the LLC resonant cavity composed of the resonant inductor Lr, the resonant inductor Lm and the resonant capacitor Cr to generate a high-frequency resonant signal.

[0021] S3. The transformer electrically isolates and transforms the amplitude of the high-frequency resonant signal.

[0022] S4 and the self-detection synchronous rectification circuit rectify and output the high-frequency resonant signal after electrical isolation and amplitude conversion, and control the secondary synchronous rectifier tubes S3 and S4 through the synchronous rectification controller N3 to output a first output voltage signal containing an AC component, and input the first output voltage signal into the output filter circuit.

[0023] S5. The output filter circuit filters the output voltage signal, attenuates the AC component on the output voltage bus through the filter capacitor Co, obtains the output voltage DC component Vo, and uses the output voltage DC component Vo as the input signal of the output voltage sampling circuit.

[0024] S6. The output voltage sampling circuit divides and reduces the DC component of the output voltage, and obtains a proportionally reduced second output voltage signal through the voltage divider resistors Rupper and Rlower as an input signal for the operational amplifier compensation circuit.

[0025] S7. The operational amplifier compensation circuit compares the second output voltage signal with the reference signal, and uses the output voltage error feedback signal Ve as the input signal on the diode side of the optocoupler isolation circuit through the compensation circuit composed of the operational amplifier compensator N4, the resistor R3, the capacitor C1 and the capacitor C2.

[0026] S8. The optocoupler isolation circuit electrically isolates the voltage error feedback signal Ve, and inputs the electrically isolated voltage error feedback signal into the STBY pin of the LLC resonant controller N1 in the LLC resonant control circuit.

[0027] S9, LLC resonant control circuit adjusts the PFM signal that drives the operating frequency of the switch tube, transmits the input voltage error feedback signal to the LLC resonant control controller, and inputs the PFM signal that adjusts the operating frequency of the switch tube into the primary PFM drive circuit.

[0028] S10, the primary PFM drive circuit conditions the PFM signal and controls the operation of the half-bridge switches S1 and S2 in the LLC resonant circuit, thereby forming a feedback closed-loop control of the output voltage Vo.

[0029] Compared with the prior art, the advantages of the present invention are:

[0030] The present invention proposes an LLC resonant soft-switching converter with a constant voltage output and variable frequency control using a self-detecting synchronous rectification circuit. The LLC resonant soft-switching converter based on self-detecting synchronous rectification and its control method are converters with a constant voltage output and variable frequency control using a self-detecting synchronous rectification circuit. The LLC resonant soft-switching converter based on self-detecting synchronous rectification can achieve zero-voltage and zero-current switching of the switch tube and precise synchronous rectification control, while reducing the switching loss of the switch tube and the conduction loss of the secondary rectifier tube, increasing the switching frequency, reducing the converter size, and effectively suppressing the increase in loss, thereby improving the efficiency of the DC-DC converter and meeting the requirements of both miniaturization and high efficiency of the DC-DC converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a circuit diagram of an LLC resonant soft-switching converter based on self-detection synchronous rectification in the present invention;

[0032] Figure 2 is a functional block diagram of synchronous rectification controller N3;

[0033] Figure 3 This is the functional block diagram of LLC resonant controller N1;

[0034] Figure 4 This is a prototype diagram of the LLC resonant soft-switching converter based on self-detection synchronous rectification in the present invention;

[0035] Figure 5 It is the efficiency curve of the test prototype;

[0036] Figure 6 This is the test waveform of the test prototype Figure 1 ;

[0037] Figure 7 This is the test waveform of the test prototype Figure 2 . DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings:

[0039] Precise synchronous rectification control and light-load optimization control of the LLC resonant converter are one of the technical difficulties in the rectification control of the LLC resonant converter. Although the traditional Schottky rectification method can avoid the problem of malfunction of the synchronous rectifier tube when the operating frequency changes or when the load is light, the conduction loss is large and it cannot achieve the purpose of optimizing efficiency. The conventional main control chip synchronous rectification drive and transformer auxiliary winding synchronous rectification drive are both unable to effectively achieve precise synchronous rectification control and light-load optimization control, which can easily cause the synchronous rectifier tube to malfunction, increase losses, and even damage the synchronous rectifier tube. The LLC resonant soft-switching converter based on self-detection synchronous rectification proposed in the present invention effectively solves the technical difficulties of precise synchronous rectification control and light-load optimization control of the LLC resonant converter, improves the robustness of the synchronous rectification circuit, and at the same time reduces the switching loss of the switch tube and the conduction loss of the secondary rectifier tube, achieving the technical effect of further improving the efficiency of the LLC resonant converter, and taking into account the miniaturization and high efficiency requirements of the DC-DC converter.

[0040] like Figure 1 The LLC resonant soft-switching converter based on self-detection synchronous rectification is shown in the figure. The converter includes an input filter circuit, an LLC resonant circuit, a transformer, a self-detection synchronous rectification circuit, an output filter circuit, an output voltage sampling circuit, an op amp compensation circuit, an optocoupler isolation circuit, an LLC resonant control circuit, and a primary PFM drive circuit. The prototype of the LLC resonant soft-switching converter based on self-detection synchronous rectification is shown in the figure. Figure 4 As shown. The transformer is a transformer with an intermediate tap on the secondary side. The self-detecting synchronous rectification circuit can implement synchronous rectification according to the characteristics of the rectification circuit, is not affected by the frequency conversion control, and is suitable for LLC resonant soft-switching converters. The LLC resonant soft-switching converter based on self-detecting synchronous rectification described in the present invention achieves zero-voltage turn-on of the primary switching tube and zero-current turn-off of the secondary synchronous rectifier tube, reducing the loss of the rectification circuit, improving the converter efficiency, and optimizing the converter's electromagnetic compatibility characteristics.

[0041] Specifically, the input filter circuit is used to filter the input voltage signal to effectively attenuate the AC component on the input voltage busbar and use the resulting DC component of the input voltage as the input signal for the LLC resonant circuit. The LLC resonant circuit processes the DC component of the input voltage by converting it into an AC square wave signal through a switching transistor. This AC square wave signal then generates a high-frequency resonant signal through the LLC resonant cavity. Within the resonant cavity, the AC square wave signal interacts with the resonant element to generate a high-frequency resonant signal, providing a suitable input signal for subsequent transformer isolation and voltage conversion steps, thereby achieving the power conversion and transmission functions of the entire power supply system. The transformer is used to electrically isolate and amplitude-convert the high-frequency resonant signal, and the resulting electrical signal is input into a self-detecting synchronous rectifier circuit. The self-detecting synchronous rectifier circuit rectifies and outputs the high-frequency resonant signal after electrical isolation and amplitude conversion by the transformer. The output voltage signal, which contains the AC component, is input into the output filter circuit through adaptive control of the rectifier transistors by the synchronous rectifier controller N3. The output filter circuit is configured to filter the output voltage signal to effectively attenuate the AC component on the output voltage bus, and to use the resulting DC component of the output voltage as the input signal to the output voltage sampling circuit. The output voltage sampling circuit is configured to divide and reduce the DC component of the output voltage, and to use the resulting proportionally scaled output voltage signal as the input signal to the op amp compensation circuit. The op amp compensation circuit is configured to compare the proportionally scaled output voltage signal with a reference signal, and to use the output voltage error feedback signal as the diode-side input signal in the optocoupler isolation circuit. The optocoupler isolation circuit is configured to electrically isolate the voltage error feedback signal and input the electrically isolated voltage error feedback signal into the LLC resonant control circuit. The LLC resonant control circuit is configured to adjust the PFM signal that drives the operating frequency of the switching tube, transmit the input voltage error feedback signal to the internal control logic unit of the controller, and input the PFM signal that adjusts the operating frequency of the switching tube into the primary PFM drive circuit. The primary PFM drive circuit is used to condition the PFM signal to enhance the drive current and control the switching of the half-bridge switch tube in the LLC resonant circuit so that the LLC resonant circuit converts the input voltage DC signal into an AC square wave signal.

[0042] As a further improvement to the above technical solution, the transformer is a transformer with a center-tapped secondary. The transformer includes a primary winding, a first secondary winding, and a second secondary winding; the opposite-name terminals of the first secondary winding are connected to the same-name terminals of the second secondary winding. The transformer used in this embodiment is a PCB-level transformer.

[0043] As a further improvement to the above technical solution, the LLC resonant circuit includes a resonant inductor Lr, an excitation inductor Lm, and a resonant capacitor Cr. The first end of the resonant inductor Lr is connected to the middle node of the half-bridge switching transistor in the LLC resonant circuit, the second end of the resonant inductor Lr is connected to the first end of the resonant capacitor Cr, the second end of the resonant capacitor Cr is connected to the same-name terminal of the excitation inductor Lm, and the opposite-name terminal of the excitation inductor Lm is connected to the input reference ground PGND. The same-name terminal of the excitation inductor Lm is connected to the same-name terminal of the primary winding of the transformer T, and the opposite-name terminal of the excitation inductor Lm is connected to the opposite-name terminal of the primary winding of the transformer T. The resonant inductor Lr, the resonant capacitor Cr, and the excitation inductor Lm resonate, thereby achieving soft switching conversion. The current in the resonant inductor Lr flows bidirectionally, and its magnetic core operates in the first and third quadrants. The resonant inductor Lr in the present invention uses an XECMWSA1005S-4R7M inductor with an inductance of 4.7uH and a saturation current of 15A. The resonant capacitor Cr is a CC41-1210-CG-630V-223-J type ceramic capacitor with a capacitance of 22nF, six of which are connected in parallel. The magnetizing inductor Lm is 50μH. These components interact to produce resonance, achieving soft switching conversion, with an operating frequency of 100kHz to 300kHz.

[0044] As a further improvement of the above technical solution, the primary PFM drive circuit includes a primary switch tube S1 and a primary switch tube S2; the source of the primary switch tube S1 is connected to the drain of the primary switch tube S2 and serves as an intermediate node of the half-bridge switch tube in the LLC resonant circuit, and the intermediate node is connected to the first end of the resonant inductor Lr; the drain of the primary switch tube S1 is connected to the input voltage Vin, and the gate of the primary switch tube S1 is connected to the first output terminal ( Figure 1 The source of the primary switch tube S2 is connected to the input reference ground PGND, and the gate of the primary switch tube S2 is connected to the second output terminal ( Figure 1 The primary switching transistor S1 is connected to the LLC resonant controller N1 pin LVG. A first parasitic diode is connected between the source and drain of the primary switching transistor S1, with the anode of the first parasitic diode connected to the source of the primary switching transistor S1 and the cathode of the first parasitic diode connected to the drain of the primary switching transistor S1. A second parasitic diode is connected between the source and drain of the primary switching transistor S2, with the anode of the second parasitic diode connected to the source of the primary switching transistor S2 and the cathode of the second parasitic diode connected to the drain of the primary switching transistor S2. Preferably, the primary switching transistors S1 and S2 are high-voltage MOS transistors.

[0045] The primary PFM driver circuit amplifies and shapes the PFM signal to enhance its drive capability and ensure reliable operation of the switches in the LLC resonant circuit. By adjusting the on- and off-frequency of the switches, the LLC resonant circuit is controlled, ultimately achieving a stable output voltage. The LLC resonant control circuit precisely adjusts the PFM signal through a series of detection, judgment, and adjustment steps, transmitting it to the primary PFM driver circuit for feedback control of the entire power system's output voltage. Primary switches S1 and S2 utilize high-voltage MOSFETs, while secondary synchronous rectifiers S3 and S4 utilize low-voltage MOSFETs. Utilizing output voltage feedback control and a secondary synchronous rectifier self-detection drive circuit, this resonant soft-switching converter achieves a constant output of 28V / 300W over a 240V to 300V input voltage range, with a full-load efficiency of 92%.

[0046] As a further improvement of the above technical solution, the input filter circuit includes an input filter capacitor Cin; the input filter capacitor Cin is connected in parallel between the input voltage Vin and the input reference ground PGND.

[0047] As a further improvement of the above technical solution, the output filter circuit includes an output filter capacitor Co; the output filter capacitor Co is connected in parallel between the output voltage Vo and the output reference ground SGND.

[0048] As a further improvement to the above technical solution, the output voltage sampling circuit is connected in parallel to the output end of the main circuit. The output voltage sampling signal is connected to the LLC resonant controller N1 via the op amp compensator N4 and the optocoupler isolator N2. The LLC resonant controller N1 provides drive signals HVG and LVG to the primary switching tubes S1 and S2, and the synchronous rectifier controller N3 is used to provide drive signals SR2 and SR1 to the secondary synchronous rectifier tubes S3 and S4. The output voltage sampling circuit includes a capacitor Co, a resistor RL, a resistor Rupper, and a resistor Rflower. The first end of the capacitor Co is respectively connected to the opposite-name terminal of the first secondary winding and the same-name terminal of the second secondary winding of the transformer T, the second end of the capacitor Co is connected to the output reference ground SGND, and the resistor RL is connected in parallel to both ends of the capacitor Co. The voltage at the first end of the capacitor Co is used as the output voltage Vo. The first end of the resistor Rupper is connected to the first end of the capacitor Co, the second end of the resistor Rupper is connected to the first end of the resistor Rflower, and the second end of the resistor Rflower is connected to the output reference ground SGND.

[0049] As a further improvement to the above technical solution, the self-detecting synchronous rectification circuit uses a synchronous rectification controller N3 to implement a self-detecting synchronous rectification function. The self-detecting synchronous rectification circuit includes a synchronous rectification controller N3, a secondary synchronous rectifier S3, and a secondary synchronous rectifier S4. The drain of the secondary synchronous rectifier S3 is connected to the same-name terminal of the first secondary winding of the transformer T, the source of the secondary synchronous rectifier S3 is connected to the source of the secondary synchronous rectifier S4, and the gate of the secondary synchronous rectifier S3 is connected to the pin SR2 of the synchronous rectification controller N3; the gate of the secondary synchronous rectifier S4 is connected to the pin SR1 of the synchronous rectification controller N3, and the gate of the secondary synchronous rectifier S4 is connected to the opposite-name terminal of the second secondary winding of the transformer T. Both the secondary synchronous rectifier S3 and the secondary synchronous rectifier S4 are low-voltage MOS transistors and are driven and controlled by the self-detecting secondary synchronous rectifiers.

[0050] like Figure 2 As shown, the synchronous rectifier controller N3 has a total of 8 pins. The SYNC pin is the gate turn-off synchronization terminal. When this pin receives a falling edge, its function is to immediately reduce the gate voltage and turn off the synchronous rectifier. The EN / OFF pin is the enable / off time control terminal, which is used to adjust the minimum off time of the synchronous rectifier. The TON pin is the on-time control terminal, which is used to adjust the minimum on time. The VCC pin is the power supply terminal, which is used to power the integrated circuit within the controller. The GATE pin is the gate drive terminal, which is used to control the switching operation of the synchronous rectifier. The GND pin is the power ground terminal, which is used as the reference ground for the integrated circuit within the controller. The VS pin is the source detection terminal, which is used to detect the source voltage of the synchronous rectifier. The VD pin is the drain detection terminal, which is used to detect the drain voltage of the synchronous rectifier.

[0051] As a further improvement of the above technical solution, the LLC resonant control circuit includes an LLC resonant controller N1, a resistor RH, a resistor RL, a resistor Rss, a capacitor Css, a capacitor C F The pin Line of the LLC resonant controller N1 is connected to the second end of the resistor RH and the first end of the resistor RL respectively. The first end of the resistor RH is connected to the input voltage Vin, and the second end of the resistor RL is connected to the input reference ground PGND. The pin Rfmin of the LLC resonant controller N1 is connected to the input reference ground PGND via the resistor Rss and the capacitor Css; the pin CSS of the LLC resonant controller N1 is connected to the node between the resistor Rss and the capacitor Css, and the pin CF of the LLC resonant controller N1 is connected to the capacitor C F The first end is connected to the capacitor C F The second terminal is connected to the input reference ground PGND.

[0052] As a further improvement to the above technical solution, the optocoupler isolation circuit includes an optocoupler isolator N2, a resistor R1, a resistor R2, a resistor RFmin, a resistor RFmax1, and a resistor RFmax2. The optocoupler isolator N2 includes a phototransistor and a light-emitting diode; the anode of the light-emitting diode is connected to the output voltage Vo via the resistor R1, the first end of the resistor R2 is connected to the anode of the light-emitting diode, and the second end of the resistor R2 is connected to the output end of the operational amplifier compensation circuit; the collector of the phototransistor is connected to the first end of the resistor RFmax2, and the second end of the resistor RFmax2 is connected to the pin STBY of the LLC resonant controller N1; the first end of the resistor RFmax1 is connected to the pin STBY of the LLC resonant controller N1, the second end of the resistor RFmax1 is respectively connected to the pin Rfmin of the LLC resonant controller N1, the first end of the resistor Rss, and the first end of the resistor RFmin, and the second end of the resistor RFmin is connected to the input reference ground PGND.

[0053] As a further improvement of the above technical solution, the operational amplifier compensation circuit includes an operational compensator N4, a capacitor C1, a capacitor C2 and a resistor R3; the non-inverting input terminal of the operational compensator N4 is connected to the reference voltage VREF, and the reverse input terminal is connected to the second output voltage signal; the first terminal of the capacitor C2 is connected to the reverse input terminal of the operational compensator N4, and the second terminal of the capacitor C2 is connected to the output terminal of the operational compensator N4; the first terminal of the capacitor C1 is connected to the reverse input terminal of the operational compensator N4, and the second terminal is connected to the output terminal of the operational compensator N4 via the resistor R3.

[0054] As a further improvement to the above technical solution, the LLC resonant controller N1, model CSV65099, is a two-terminal control chip for resonant topology architectures. It offers a 50% duty cycle, with the high-side and low-side switches operating 180° out of phase at the same time. A fixed dead time is inserted between the high-side and low-side switches to achieve soft switching and high-frequency operation. Output voltage modulation is achieved through variable frequency operation, and the converter's switching frequency range can be set by selecting external components. During startup, to prevent inrush current, the switching frequency is gradually reduced from a programmable startup limit frequency until the control loop reaches stability. The startup frequency variation is nonlinear, minimizing output voltage overshoot, and the startup time can also be set externally. Under light load conditions, the controller enters an intermittent pulse mode to reduce the converter's input power consumption. Other features include non-latching line voltage protection and primary overcurrent protection, latching secondary overcurrent protection, and latching overtemperature and overvoltage protection. The output voltage is compared with the reference voltage of the operational amplifier circuit by the sampling and conditioning circuit, and then fed back to the LLC resonant controller through the optocoupler isolation circuit. The controller controls the converter based on the output voltage feedback control method.

[0055] like Figure 3As shown, the LLC resonant controller N1 has a total of 15 pins. Pin Css is the soft-start pin, which controls the startup process to a soft start. The capacitor Css connected to this pin and the resistor Rss connected to the RFmin pin jointly determine the maximum operating frequency during soft start. Pin DELAY is the overcurrent delay shutdown pin, which sets the maximum duration of the overload current. Pin CF is the oscillation frequency setting capacitor pin, which serves as a timing capacitor. The capacitor CF connected to this pin and the resistor connected to the RFmin pin jointly determine the oscillator switching frequency. Pin RFmin is the minimum oscillation frequency setting pin, which connects to the RFmin resistor to set the minimum oscillation frequency. Pin STBY is the burst mode threshold pin, which regulates the controller into burst mode under light load conditions. Pin ISEN is the current sense pin, which detects the current flowing through the main circuit. Pin LINE is the input voltage sense pin, which detects the input voltage of the main circuit. Pin DIS is the enable pin, which shuts down the controller when the voltage on this pin exceeds 1.85V. Pin PFC-STOP is the PFC controller interface terminal, which controls the PFC controller to stop operation. Pin GND is the controller ground terminal, which serves as the reference ground for the controller's internal integrated circuits. Pin LVG is the low-side driver output terminal, which drives the low-side switch of the half-bridge circuit. Pin VCC is the power supply terminal, which powers the controller's internal integrated circuits. Pin OUT is the high-side driver ground terminal, which provides a current return path for the high-side gate drive current of the half-bridge circuit. Pin HVG is the high-side driver output terminal, which drives the high-side switch of the half-bridge circuit. Pin VBOOT is the high-side bootstrap power supply terminal, which powers the high-side bootstrap capacitor.

[0056] As a further improvement to the above technical solution, the primary switching tubes (S1 and S2) and secondary synchronous rectifiers (S3 and S4) in the LLC resonant circuit can calculate the maximum voltage and peak current that the switching tubes (S1 and S2) can withstand during operation based on the circuit operating state, and then select switching tubes that meet the voltage and current requirements based on the derating factor. The main power switching tubes (S1 and S2) in the present invention withstand a maximum voltage of approximately 300V and a peak current of approximately 5A. Therefore, JR60N074F MOS tubes with a voltage withstand of 600V and a current flow of 33A are selected. The secondary synchronous rectifiers (S3 and S4) withstand a maximum voltage of approximately 60V and a peak current of approximately 20A. Therefore, two JCR10N004H MOS tubes with a voltage withstand of 100V and a current flow of 60A are selected and used in parallel.

[0057] As a further improvement of the above technical solution, the core of the high-frequency conversion circuit is the design of a planar power transformer. According to the basic design parameters of the circuit, such as input voltage range, output voltage, output power, output current, estimated efficiency, estimated input current, etc., the number of turns and size of each winding of the transformer in the present invention can be preliminarily set. Based on the AP method commonly used in engineering design, the magnetic core is preliminarily selected, and the core area and window area are iteratively designed with the number of winding turns and size to determine the optimal magnetic core, number of winding turns and size. The transformer in the present invention uses an ER28 / 10 / 20A core made of TPG33B magnetic material, and the primary and secondary turns are 10:2:2.

[0058] As a further improvement to the above technical solution, the primary switches S1 and S2 in the LLC resonant circuit are directly driven by the resonant controller N1, sourcing 0.3A and sinking 0.8A. A peripheral bootstrap circuit generates the high-side bias voltage, making it suitable for bridge circuit driving. Self-sensing synchronous rectification is a key technology for improving efficiency in LLC resonant converters at high output currents. The synchronous rectifier controller N3, model XS9211, is a high-performance controller suitable for LLC resonant converters, sourcing up to 1A and sinking up to 2A. Synchronous rectifier controller N3 detects the drain-source voltage of MOSFETs S3 and S4 to drive the gates, achieving synchronous rectification on the low-voltage secondary side. Synchronous rectifier controller N3 provides a programmable false trigger filter and a programmable timer to automatically switch to light-load mode. Its protection features prevent uncontrolled on-time due to open-circuit or short-circuit fault conditions.

[0059] The LLC resonant soft-switching converter based on self-detection synchronous rectification described in the present invention adopts a primary half-bridge LLC resonant conversion + secondary synchronous rectification structure in its main circuit. The control method of the LLC resonant soft-switching converter based on self-detection synchronous rectification includes the following steps:

[0060] The DC input voltage Vin is converted into a high-frequency resonant signal through the LLC resonant circuit. After isolation and voltage transformation by a transformer, rectification by a self-sensing synchronous rectification circuit on the secondary side, and filtering by an output capacitor, the DC output voltage Vo is obtained. The output voltage Vo signal passes through a sampling feedback circuit and an optocoupler isolator, transmitting the voltage error feedback signal to the LLC resonant control circuit. This signal is then controlled by the primary PFM drive circuit to switch the half-bridge switches in the LLC resonant circuit, thereby forming a closed-loop feedback control loop for the output voltage Vo.

[0061] The following describes in detail the control method of the LLC resonant soft-switching converter based on self-detection synchronous rectification, in combination with the circuit topology of the LLC resonant soft-switching converter based on self-detection synchronous rectification. The method includes the following steps:

[0062] S1. The input filter circuit filters the input voltage signal, effectively attenuates the AC component on the input voltage bus through the filter capacitor Cin, and uses the processed DC component of the input voltage as the input signal of the LLC resonant circuit.

[0063] The S2 and LLC resonant circuits process the DC component of the input voltage and convert the DC input voltage signal into an AC square wave signal by alternately switching the switching tubes S1 and S2. The AC square wave generates a high-frequency resonant signal through the LLC resonant cavity composed of the resonant inductors Lr, Lm and the resonant capacitor Cr.

[0064] S3. The transformer electrically isolates and transforms the high-frequency resonant signal, and then inputs the signal into the self-detecting synchronous rectification circuit. In this embodiment, the transformer uses an ER28 / 10 / 20A core made of TPG33B magnetic material, with a primary-to-secondary turns ratio of 10:2:2.

[0065] S4 and the self-detection synchronous rectification circuit rectify and output the high-frequency resonant signal, and adaptively control the rectifier tubes S3 and S4 through the synchronous rectification controller N3 to achieve low-impedance conduction, and input the output voltage signal containing the AC component into the output filter circuit.

[0066] Pins VS and VD of synchronous rectifier controller N3 are used to detect the source and drain voltages of rectifiers S3 and S4, respectively. During circuit operation, these pins collect voltage data in real time to determine the switching status of rectifiers S3 and S4. When the high-frequency resonant signal on the transformer secondary is in the positive half-cycle, the source and drain voltages of rectifiers S3 and S4 exhibit specific trends. Synchronous rectifier controller N3 monitors these voltage changes to determine when to turn on the rectifiers. The logic circuitry within synchronous rectifier controller N3 analyzes and determines when to turn on the rectifiers based on the detected voltage information. When the turn-on condition is determined to be met, the voltage difference between the drain and source reaches a certain threshold, indicating that it is time to turn on rectifiers S3 and S4. This achieves low-impedance conduction and effectively reduces conduction losses. Under light load conditions, due to the low secondary current, detecting the turn-on timing of synchronous rectifier N3 becomes difficult, which can easily cause malfunction of the synchronous rectifiers. However, synchronous rectifier controller N3 can adaptively adjust its judgment logic based on the detected low current state to avoid turning on the rectifier at inappropriate times. Once the turn-on conditions are determined to be met, synchronous rectifier controller N3 outputs a drive signal through its GATE pin. Pin SR2 is connected to the gate of rectifier S3, and pin SR1 is connected to the gate of rectifier S4. The drive signal is transmitted through these pins to the gate of the rectifier, turning on either rectifier S3 or S4. The voltage amplitude and waveform characteristics of the drive signal are optimized to ensure that the rectifier enters the low-impedance conduction state quickly and reliably. When synchronous rectifier controller N3 determines that rectifier S3 meets the turn-on conditions, its pin SR2 outputs a high-level drive signal, increasing the gate voltage of rectifier S3, turning on rectifier S3 and allowing current to flow from the transformer's secondary winding through rectifier S3 to the downstream circuit. During the rectifier conduction period, synchronous rectifier controller N3 continuously monitors the drain-source voltage of rectifiers S3 and S4. When a voltage change is detected indicating a rectifier needs to be shut down, such as when the drain-source voltage reverses and reaches a certain level, synchronous rectifier controller N3 outputs a shutdown signal through pin SYNC, lowering the gate voltage and quickly shutting off the rectifier to avoid additional losses caused by reverse current. Throughout the entire operating process, synchronous rectifier controller N3 continuously repeats the above detection, judgment, and control steps, adaptively controlling the on and off of rectifiers S3 and S4 based on the real-time circuit status, maintaining a low-impedance on-state at all times and improving rectification efficiency.

[0067] S5. The output filter circuit filters the output voltage signal, effectively attenuates the AC component on the output voltage bus through the filter capacitor Co, and uses the processed output voltage DC component Vo as the input signal of the output voltage sampling circuit.

[0068] S6. The output voltage sampling circuit divides and reduces the DC component of the output voltage, and the proportionally reduced output voltage signal obtained through the voltage dividing resistors Rupper and Rlower is used as the input signal of the operational amplifier compensation circuit.

[0069] S7. The operational amplifier compensation circuit compares the proportionally scaled output voltage signal with the reference signal. The output voltage error feedback signal Ve is used as the input signal on the diode side of the optocoupler isolation circuit through the compensation circuit composed of the operational amplifier compensator N4, resistor R3, capacitor C1 and capacitor C2.

[0070] S8. The optocoupler isolation circuit electrically isolates the voltage error feedback signal Ve, and inputs the electrically isolated voltage error feedback signal into the STBY pin of the LLC resonant controller N1.

[0071] S9, LLC resonant control circuit adjusts the PFM signal that drives the operating frequency of the switch tube, transmits the input voltage error feedback signal to the internal control logic unit of the controller, and inputs the PFM signal that adjusts the operating frequency of the switch tube into the primary PFM drive circuit.

[0072] After sampling and comparison, the output voltage generates a voltage error feedback signal. The Line pins of LLC resonant controller N1 are connected to resistors RH and RL, respectively. The first terminal of resistor RH is connected to the input voltage Vin, and the second terminal of resistor RL is connected to the input reference ground PGND. These two resistors form a voltage divider circuit, and pin Line detects the divided value of the input voltage Vin. Controller N1 internally uses this divided value to determine the input voltage, which serves as a key basis for the internal control logic. Pin Rfmin is connected to the input reference ground PGND via resistor Rss and capacitor Css, while pin CSS is connected to the node between resistor Rss and capacitor Css. The RC circuit formed by resistor Rss and capacitor Css determines the minimum operating frequency of the LLC resonant controller N1's internal oscillator. This set value affects the frequency adjustment range of the PFM signal within controller N1's internal control logic. When the voltage error feedback signal is transmitted to the internal control logic, it combines the input voltage detection value with the minimum frequency set value to make a comprehensive judgment on the current switching state of the power supply system. The internal control logic of LLC resonant controller N1 adjusts the frequency of the PFM signal based on the received voltage error feedback signal and other detection information. If the voltage error feedback signal indicates that the output voltage is higher than expected, the internal control logic increases the frequency of the PFM signal. In the LLC resonant circuit, increasing the operating frequency of the switching transistor changes the circuit's resonant state, reducing the transformer's energy transfer efficiency and thus lowering the output voltage. If the voltage error feedback signal indicates that the output voltage is lower than expected, the internal control logic of LLC resonant controller N1 decreases the frequency of the PFM signal. The lower switching frequency changes the resonant state of the LLC resonant circuit, improving the transformer's energy transfer efficiency and thereby increasing the output voltage. LLC resonant controller N1 generates the adjusted PFM signal internally and outputs it to the primary PFM driver circuit.

[0073] S10, the primary PFM drive circuit conditions the PFM signal to enhance the drive current and control the operation of the half-bridge switches S1 and S2 in the LLC resonant circuit, so that the LLC resonant circuit converts the input voltage DC signal Vin into an AC square wave signal and transmits it to the LLC resonant cavity.

[0074] The primary PFM driver circuit receives the PFM signal from the LLC resonant control circuit. Although this signal carries information for controlling the operating frequency of the switches, its driving capability is typically weak and cannot directly and effectively drive the half-bridge switches S1 and S2. Therefore, the primary PFM driver circuit's primary task is to condition the PFM signal, primarily by increasing its drive current to meet the switching requirements.

[0075] The conditioned PFM signal output by the primary PFM driver circuit controls the on / off switching of switches S1 and S2, respectively. When a portion of the PFM signal causes the gate voltage of S1 to reach its on-threshold, switch S1 turns on. At this point, current flows from the input voltage Vin through switch S1 and into components such as the resonant inductor Lr of the LLC resonant circuit. When another portion of the PFM signal causes the gate voltage of switch S2 to reach its on-threshold, switch S2 turns on, while switch S1 turns off. This changes the current path, flowing from components such as the resonant inductor Lr through switch S2 back to the input reference ground PGND. By alternating on and off, switches S1 and S2 chop the input DC voltage signal. This alternating on / off switching of switches S1 and S2 generates a voltage waveform at the junction of switches S1 and S2 (i.e., the point connected to the resonant inductor Lr). When the switch S1 is on, the voltage at this point is close to the input voltage Vin; when the switch S2 is on, the voltage at this point is close to the potential of the input reference ground PGND. In this way, the input DC voltage signal Vin is converted into an AC square wave signal.

[0076] The LLC resonant soft-switching converter based on self-detection synchronous rectification and the control method thereof described in the present invention have the following innovations:

[0077] (1) The present invention solves the problem of precise control of synchronous rectification in LLC resonant converters, effectively avoids the risk of misoperation of synchronous rectification drive signals when the frequency changes, and achieves the technical effect of accurately synchronizing the drive signal of the LLC converter when the input voltage and output current change. Specifically, the LLC main topology circuit in the present invention is frequency-controlled, and the frequency of the drive signal of the primary switch tube will change with the input voltage and output current. Therefore, it is necessary to ensure that the drive signal of the secondary synchronous rectifier tube is accurately synchronized with the drive signal of the primary switch tube, otherwise the synchronous rectifier tube will be mistakenly turned on or off, increasing the conduction loss and reverse recovery loss. Conventional synchronous rectification methods are not easy to accurately synchronize the drive signal when the switching frequency changes, which can easily cause the synchronous rectifier tube to misoperate. The self-detection synchronous rectification circuit proposed in the present invention can adaptively realize the synchronous rectification function according to the characteristics of the secondary rectifier circuit, and is not affected by the frequency conversion control of the main circuit, which is conducive to the LLC resonant converter to achieve precise synchronous rectification.

[0078] (2) The present invention solves the problem of synchronous rectification control under light load conditions in the LLC resonant converter, effectively avoids the risk of malfunction of the synchronous rectification drive signal under light load, and achieves the technical effect of prohibiting the LLC converter from driving the synchronous rectification under light load and improving the light load efficiency. Specifically, under light load conditions, due to the small secondary current, it becomes difficult to detect the turn-on moment of the synchronous rectifier tube, which can easily cause the synchronous rectifier tube to malfunction and reduce the light load efficiency of the LLC resonant converter. The self-detection synchronous rectification circuit proposed in the present invention can effectively prohibit the synchronous rectification drive under light load, so that the LLC resonant converter performs rectification based on the synchronous rectifier tube body diode under light load, avoiding light load malfunction and improving light load efficiency.

[0079] (3) The present invention solves the technical problem of effectively suppressing the increase in loss of the LLC resonant converter while increasing the switching frequency and reducing the converter volume, and simultaneously reduces the switching loss of the switch tube and the conduction loss of the secondary rectifier tube, thereby achieving the technical effect of further improving the efficiency of the LLC resonant converter. Specifically, the LLC resonant soft-switching converter based on self-detection synchronous rectification described in the present invention can simultaneously reduce the switching loss of the switch tube and the conduction loss of the secondary rectifier tube, effectively suppress the increase in loss while increasing the switching frequency and reducing the converter volume, further improving the efficiency of the LLC resonant converter, and taking into account the requirements of miniaturization and high efficiency of the DC-DC converter.

[0080] This invention combines an LLC resonant soft-switching converter with a self-detecting synchronous rectification circuit, employing output voltage feedback control and optocoupler isolation to achieve a high-efficiency, high-power soft-switching DC-DC converter. Based on the LLC resonant soft-switching converter circuit, this invention improves the DC-DC converter's switching frequency and power density, achieving both miniaturization and high efficiency. Circuit parameters are: input voltage: 240V to 300V; output voltage: 28V; output power: 300W; conversion efficiency: no less than 92% at full load; operating frequency: 100kHz to 300kHz. Figure 4 This is a physical diagram of a prototype of the LLC resonant soft-switching converter based on self-detection synchronous rectification in the present invention. The test data of the prototype is shown in Table 1.

[0081] Table 1: Prototype test data

[0082]

[0083]

[0084] The efficiency curve of the above test prototype is as follows: Figure 5 As shown, the circuit key node test waveform is as follows Figure 6 and Figure 7 As shown. Figure 5It can be seen from the efficiency curve of the experimental prototype that the full-load efficiency of the prototype implemented based on the solution described in the present invention is as high as 92%, which is about 2% higher than the traditional hard-switching circuit or the LLC resonant soft-switching circuit that does not use synchronous rectification, proving that the solution described in the present invention can effectively improve efficiency. Figure 6 The green and yellow waveforms are the primary half-bridge switch drive waveforms and the primary resonant current waveforms. The red waveform is the primary resonant current waveform. Figure 6 It can be seen that the two half-bridge drive waveforms are alternately turned on. According to the red primary resonant current waveform, the circuit operating frequency is between the series-parallel resonant frequency and the series resonant frequency. At this time, the switch tube achieves zero voltage turn-on, which proves that the solution described in the present invention can effectively achieve zero voltage turn-on of the switch tube and reduce switching losses. Figure 7 The following is the waveform of the secondary synchronous rectifier and the secondary resonant current. The green and orange are the secondary synchronous rectifier drive waveforms, respectively. The blue is the secondary synchronous rectifier drain-source voltage waveform, and the red waveform is the secondary resonant current waveform. Figure 7 As can be seen, the secondary resonant current can resonate back to zero current, indicating that the circuit described in the present invention achieves zero-current shutdown of the secondary rectifier. The orange secondary synchronous rectifier drive waveform and the blue secondary synchronous rectifier drain-source voltage waveform are essentially consistent in timing, indicating that the present invention achieves precise synchronous rectification control. This proves that the scheme described in the present invention can effectively achieve zero-current shutdown of the switch and precise synchronous rectification control, reducing the switch turn-off loss and synchronous rectifier conduction loss.

[0085] In summary, the present invention combines an LLC resonant soft-switching converter with a self-detecting synchronous rectification circuit, employing output voltage feedback control and an optocoupler isolation circuit to achieve a resonant soft-switching converter with a 240V to 300V input voltage range, a constant output of 28V / 300W, and a full-load efficiency of 92%. The LLC resonant soft-switching converter based on self-detecting synchronous rectification described in the present invention improves the switching frequency and power density of the DC-DC converter, achieving both miniaturization and high efficiency. The primary circuit utilizes an LLC resonant soft-switching conversion circuit. The LLC resonant soft-switching converter utilizes zero-voltage, zero-current soft-switching technology, which reduces switching losses compared to traditional hard-switching technology, allows for higher switching frequencies, and reduces the size of passive components, thereby reducing the converter's size. Therefore, the LLC resonant soft-switching converter based on self-detecting synchronous rectification offers certain advantages in terms of high efficiency and miniaturization. The secondary circuit utilizes a self-detecting synchronous rectification circuit. In applications where switching power supplies require high current output, traditional diode rectifier circuits suffer from high losses. To reduce losses in the secondary rectifier circuit and accommodate variable frequency control of the LLC resonant soft-switching converter, a self-sensing synchronous rectifier circuit is employed in the secondary, replacing traditional diodes with low-on-resistance MOS transistors. Due to the high output current, the synchronous rectifier circuit utilizes MOS transistors in parallel. Furthermore, an analog controller is employed for control. The analog controller is placed on the primary side, and the primary PFM signal directly provides a drive signal to the switching transistors in the LLC resonant soft-switching converter circuit. The secondary PFM signal is then directly supplied to the secondary synchronous rectifiers by the self-sensing synchronous rectifier controller.

[0086] The above-described embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. An LLC resonant soft-switching converter based on self-detection synchronous rectification, characterized in that: include: Input filter circuit, LLC resonant circuit, transformer, self-detection synchronous rectification circuit, output filter circuit, output voltage sampling circuit, op amp compensation circuit, optocoupler isolation circuit, LLC resonant control circuit and primary PFM drive circuit; The input filter circuit filters the input voltage signal to obtain a DC component of the input voltage; the LLC resonant circuit converts the DC component of the input voltage into an AC square wave signal through a switch tube, and converts the AC square wave signal into a high-frequency resonant signal through the LLC resonant cavity; the transformer electrically isolates and converts the amplitude of the high-frequency resonant signal; the self-detection synchronous rectifier circuit rectifies and outputs the high-frequency resonant signal after electrical isolation and amplitude conversion, and controls the rectifier tube to output a first output voltage signal containing an AC component through a synchronous rectifier controller; The output filter circuit filters the first output voltage signal to obtain an output voltage DC component; the output voltage sampling circuit divides and reduces the output voltage DC component to obtain a proportionally reduced second output voltage signal; the operational amplifier compensation circuit compares the second output voltage signal with a reference signal and outputs a voltage error feedback signal based on the comparison result; the optocoupler isolation circuit electrically isolates the voltage error feedback signal; the LLC resonant control circuit adjusts the PFM signal that drives the operating frequency of the switch tube based on the voltage error feedback signal and inputs the PFM signal into the primary PFM drive circuit; the primary PFM drive circuit conditions the PFM signal and uses the conditioned PFM signal to control the switching of the half-bridge switch tube in the LLC resonant circuit.

2. The LLC resonant soft-switching converter based on self-detection synchronous rectification according to claim 1 is characterized in that: The transformer is a transformer with a secondary center tap; the transformer comprises a primary winding, a first secondary winding and a second secondary winding; the opposite-name end of the first secondary winding is connected to the same-name end of the second secondary winding.

3. The LLC resonant soft-switching converter based on self-detection synchronous rectification according to claim 2, characterized in that: The LLC resonant circuit includes a resonant inductor Lr, an excitation inductor Lm, and a resonant capacitor Cr; a first end of the resonant inductor Lr is connected to the middle node of the half-bridge switch tube in the LLC resonant circuit, a second end of the resonant inductor Lr is connected to the first end of the resonant capacitor Cr, a second end of the resonant capacitor Cr is connected to the same-name end of the excitation inductor Lm, and an opposite-name end of the excitation inductor Lm is connected to the input reference ground PGND; the same-name end of the excitation inductor Lm is connected to the same-name end of the primary winding of the transformer T, and the opposite-name end of the excitation inductor Lm is connected to the opposite-name end of the primary winding of the transformer T; The LLC resonance control circuit includes an LLC resonance controller N1, a resistor RH, a resistor RL, a resistor Rss, a capacitor Css, a capacitor C F The pin Line of the LLC resonant controller N1 is connected to the second end of the resistor RH and the first end of the resistor RL respectively. The first end of the resistor RH is connected to the input voltage Vin, and the second end of the resistor RL is connected to the input reference ground PGND. The pin Rfmin of the LLC resonant controller N1 is connected to the input reference ground PGND via the resistor Rss and the capacitor Css. The pin CSS of the LLC resonant controller N1 is connected to the node between the resistor Rss and the capacitor Css. The pin CF of the LLC resonant controller N1 is connected to the capacitor C F The first end is connected to the capacitor C F The second terminal is connected to the input reference ground PGND.

4. The LLC resonant soft-switching converter based on self-detection synchronous rectification according to claim 3 is characterized in that: The primary PFM drive circuit includes a primary switch tube S1 and a primary switch tube S2; the source of the primary switch tube S1 is connected to the drain of the primary switch tube S2 and serves as an intermediate node of the half-bridge switch tube in the LLC resonant circuit, and the intermediate node is connected to the first end of the resonant inductor Lr; the drain of the primary switch tube S1 is connected to the input voltage Vin, and the gate of the primary switch tube S1 is connected to the first output end of the LLC resonant control circuit; the source of the primary switch tube S2 is connected to the input reference ground PGND, and the gate of the primary switch tube S2 is connected to the second output end of the LLC resonant control circuit; A first parasitic diode is connected between the source and drain of the primary switch tube S1, with the anode of the first parasitic diode connected to the source of the primary switch tube S1 and the cathode of the first parasitic diode connected to the drain of the primary switch tube S1. A second parasitic diode is connected between the source and drain of the primary switch tube S2, with the anode of the second parasitic diode connected to the source of the primary switch tube S2 and the cathode of the second parasitic diode connected to the drain of the primary switch tube S2. The primary switch tubes S1 and S2 are high-voltage MOS tubes; the secondary synchronous rectifier tubes S3 and S4 are low-voltage MOS tubes.

5. The LLC resonant soft-switching converter based on self-detection synchronous rectification according to claim 4 is characterized in that: The input filter circuit includes an input filter capacitor Cin; the input filter capacitor Cin is connected in parallel between the input voltage Vin and the input reference ground PGND; the output filter circuit includes an output filter capacitor Co; the output filter capacitor Co is connected in parallel between the output voltage Vo and the output reference ground SGND.

6. The LLC resonant soft-switching converter based on self-detection synchronous rectification according to claim 5, characterized in that: The output voltage sampling circuit includes a capacitor Co, a resistor RL, a resistor Rupper, and a resistor Rflower; a first end of the capacitor Co is respectively connected to the opposite-name terminal of the first secondary winding and the same-name terminal of the second secondary winding of the transformer T, a second end of the capacitor Co is connected to the output reference ground SGND, and the resistor RL is connected in parallel across the capacitor Co; a voltage at the first end of the capacitor Co serves as the output voltage Vo; a first end of the resistor Rupper is connected to the first end of the capacitor Co, a second end of the resistor Rupper is connected to the first end of the resistor Rflower, and a second end of the resistor Rflower is connected to the output reference ground SGND.

7. The LLC resonant soft-switching converter based on self-detection synchronous rectification according to claim 6, characterized in that: The self-detection synchronous rectification circuit includes a synchronous rectification controller N3, a secondary synchronous rectifier S3 and a secondary synchronous rectifier S4; the drain of the secondary synchronous rectifier S3 is connected to the same-name end of the first secondary winding of the transformer T1, the source of the secondary synchronous rectifier S3 is connected to the source of the secondary synchronous rectifier S4, and the gate of the secondary synchronous rectifier S3 is connected to the pin SR2 of the synchronous rectification controller N3; the gate of the secondary synchronous rectifier S4 is connected to the pin SR1 of the synchronous rectification controller N3, and the gate of the secondary synchronous rectifier S4 is connected to the opposite-name end of the second secondary winding of the transformer T; the secondary synchronous rectifier S3 and the secondary synchronous rectifier S4 are both low-voltage MOS tubes, and are driven and controlled by self-detection of the secondary synchronous rectifiers.

8. The LLC resonant soft-switching converter based on self-detection synchronous rectification according to claim 7, characterized in that: The optocoupler isolation circuit includes an optocoupler isolator N2, a resistor R1, a resistor R2, a resistor RFmin, a resistor RFmax1 and a resistor RFmax2; the optocoupler isolator N2 includes a phototransistor and a light-emitting diode; the anode of the light-emitting diode is connected to the output voltage Vo through the resistor R1, the first end of the resistor R2 is connected to the anode of the light-emitting diode, and the second end of the resistor R2 is connected to the output end of the operational amplifier compensation circuit; the collector of the phototransistor is connected to the first end of the resistor RFmax2, and the second end of the resistor RFmax2 is connected to the pin STBY of the LLC resonant controller N1; the first end of the resistor RFmax1 is connected to the pin STBY of the LLC resonant controller N1, the second end of the resistor RFmax1 is respectively connected to the pin Rfmin of the LLC resonant controller N1, the first end of the resistor Rss, and the first end of the resistor RFmin, and the second end of the resistor RFmin is connected to the input reference ground PGND.

9. The LLC resonant soft-switching converter based on self-detection synchronous rectification according to claim 8, characterized in that: The operational amplifier compensation circuit includes an operational compensator N4, a capacitor C1, a capacitor C2 and a resistor R3; the non-inverting input terminal of the operational compensator N4 is connected to the reference voltage VREF, and the reverse input terminal is connected to the second output voltage signal; the first terminal of the capacitor C2 is connected to the reverse input terminal of the operational compensator N4, and the second terminal of the capacitor C2 is connected to the output terminal of the operational compensator N4; the first terminal of the capacitor C1 is connected to the reverse input terminal of the operational compensator N4, and the second terminal is connected to the output terminal of the operational compensator N4 via the resistor R3.

10. The control method of the LLC resonant soft-switching converter based on self-detection synchronous rectification according to claims 1 to 9, characterized in that: The method comprises the following steps: S1, the input filter circuit filters the input voltage signal to obtain the input voltage DC component; The S2 and LLC resonant circuits process the DC component of the input voltage. The primary switch tubes S1 and S2 alternately switch on and off to convert the DC input voltage signal into an AC square wave signal. The AC square wave signal is processed by the LLC resonant cavity composed of the resonant inductor Lr, the resonant inductor Lm and the resonant capacitor Cr to generate a high-frequency resonant signal. S3, the transformer performs electrical isolation and amplitude conversion on the high-frequency resonant signal; S4 and the self-detection synchronous rectification circuit rectify and output the high-frequency resonant signal after electrical isolation and amplitude conversion, and control the secondary synchronous rectifier tubes S3 and S4 through the synchronous rectification controller N3 to output a first output voltage signal containing an AC component, and input the first output voltage signal into the output filter circuit; S5. The output filter circuit filters the first output voltage signal, attenuates the AC component on the output voltage bus through the filter capacitor Co, obtains the output voltage DC component Vo, and uses the output voltage DC component Vo as the input signal of the output voltage sampling circuit; S6. The output voltage sampling circuit divides and reduces the DC component of the output voltage, and the proportionally reduced second output voltage signal obtained by the voltage dividing resistors Rupper and Rlower is used as the input signal of the operational amplifier compensation circuit; S7, the op amp compensation circuit compares the second output voltage signal with the reference signal, and uses the output voltage error feedback signal Ve as the input signal on the diode side of the optocoupler isolation circuit through the compensation circuit composed of the op amp compensator N4, resistor R3, capacitor C1 and capacitor C2; S8, the optocoupler isolation circuit electrically isolates the voltage error feedback signal Ve, and inputs the electrically isolated voltage error feedback signal into the STBY pin of the LLC resonant controller N1 in the LLC resonant control circuit; S9, the LLC resonant control circuit adjusts the PFM signal that drives the operating frequency of the switch tube, transmits the output voltage error feedback signal to the LLC resonant control controller, and inputs the PFM signal that adjusts the operating frequency of the switch tube into the primary PFM drive circuit; S10, the primary PFM drive circuit conditions the PFM signal and controls the operation of the half-bridge switches S1 and S2 in the LLC resonant circuit, thereby forming a feedback closed-loop control of the DC component Vo of the output voltage.

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