LCCC type capacitive isolated DCDC conversion device

Abstract

The invention discloses an LCCC type capacitive isolated DCDC conversion device, and relates to the field of power conversion. In the device, an inverter circuit is used for performing switching modulation on a direct-current input voltage signal by utilizing a GaN MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), and converting the direct-current input voltage signal into a high-frequency alternating-current voltage signal; the resonance circuit is an LC type resonance circuit containing an isolation capacitor and is used for realizing insulation isolation of a high-voltage side and a low-voltage side and transmission of a power flow and transmitting a high-frequency alternating-current voltage signal to the low-voltage side; the synchronous rectification circuit is used for obtaining a high-frequency alternating-current voltage signal of the low-voltage side from the resonant circuit and converting the high-frequency alternating-current voltage signal of the low-voltage side into a direct-current signal of the low-voltage side by means of a GaN MOSFET; and the step-down chopper circuit is used for adjusting and stabilizing the low-voltage side direct-current signal so as to realize voltage-stabilized output of the low-voltage side. The device can realize voltage conversion from a high-voltage side to a low-voltage side in a high-power application scene without using a transformer, so that the size and the weight of the device are reduced, the power density is increased, and the conversion efficiency is improved.

Description

Technical Field

[0001] The present application relates to the technical field of power conversion, and in particular to an LCCC type capacitive isolation type DCDC conversion device. Background Art

[0002] DC-DC converters are devices that convert DC voltage to another DC voltage and are widely used in power conversion in industrial and other fields. With the continuous advancement of power electronics technology, high-voltage, high-frequency, and high-power applications are gradually increasing. Considering voltage isolation and safety, the use of isolated DC-DC converters is increasing. Isolated DC-DC converters are based on conventional non-isolated DC-DC converters and incorporate a high-frequency transformer to achieve voltage isolation. However, the greater the power demand of the application, the larger the transformer required in the isolated DC-DC converter. This can seriously impact equipment layout during actual use. A larger transformer also further reduces power density and results in increased losses during the conversion process. Therefore, there is an urgent need to develop a compact, high-power-density, and high-efficiency isolated DC-DC converter that can replace the transformer. Summary of the Invention

[0003] In response to the problems existing in the above-mentioned prior art, the purpose of this application is to provide an LCCC-type capacitive isolation DCDC conversion device, which can realize voltage conversion from the high-voltage side to the low-voltage side in high-power application scenarios without using a transformer, thereby reducing the volume and weight of the device, increasing power density and improving conversion efficiency.

[0004] To achieve the above objectives, this application provides the following solutions.

[0005] The present application provides an LCCC type capacitive isolation type DC / DC converter device, comprising: an inverter circuit, a resonant circuit, a synchronous rectification circuit, and a step-down chopper circuit connected in sequence;

[0006] The inverter circuit is used to perform switching modulation on a DC input voltage signal using a GaN MOSFET (Gallium Nitride Metal-Oxide-Semiconductor Field-Effect Transistor) to convert the DC input voltage signal into a high-frequency AC voltage signal.

[0007] The resonant circuit is an LC resonant circuit containing an isolation capacitor, which is used to achieve insulation isolation between the high and low voltage sides and transfer power flow, and transmit high-frequency AC voltage signals to the low voltage side;

[0008] The synchronous rectification circuit is used to obtain a high-frequency AC voltage signal on the low-voltage side from the resonant circuit, and convert the high-frequency AC voltage signal on the low-voltage side into a low-voltage DC signal with the help of GaN MOSFET;

[0009] The step-down chopper circuit is used to adjust and stabilize the DC signal on the low-voltage side to achieve a stable voltage output on the low-voltage side.

[0010] Optionally, the inverter circuit is a single-phase full-bridge inverter circuit, including GaN MOSFETs G1, G2, G3, and G4; wherein GaN MOSFETs G1 and G3 form a group, and G2 and G4 form a group, and the conversion of DC voltage to AC voltage is achieved by alternating conduction of the two groups of GaN MOSFETs, thereby generating a high-frequency AC voltage signal U0 at the output end.

[0011] Optionally, in the inverter circuit, when GaN MOSFETs G1 and G3 are closed and G2 and G4 are disconnected, the high-frequency AC voltage signal U0 at the output end is positive; when GaN MOSFETs G2 and G4 are closed and G1 and G3 are disconnected, the high-frequency AC voltage signal U0 at the output end is negative.

[0012] Optionally, the resonant circuit includes a resonant capacitor C2, a resonant inductor L1, an isolation capacitor C3 and an isolation capacitor C4; wherein, one end of the resonant capacitor C2 is connected to the positive pole of the inverter circuit output end, and the other end of the resonant capacitor C2 is connected to one end of the isolation capacitor C3; one end of the resonant inductor L1 is connected to the negative pole of the inverter circuit output end, and the other end of the resonant inductor L1 is connected to one end of the isolation capacitor C4; a high-frequency AC voltage signal U1 on the low-voltage side is generated between the other end of the isolation capacitor C3 and the other end of the isolation capacitor C4.

[0013] Optionally, the isolation capacitor C3 and the isolation capacitor C4 are both safety capacitors made of gallium nitride material.

[0014] Optionally, the synchronous rectification circuit adopts a full-bridge rectification form, including a diode D1, a capacitor C5 and GaNMOSFETs G5, G6, G7, and G8; wherein the GaN MOSFETs G5, G6, G7, and G8 constitute a full-bridge rectification circuit; the input end of the full-bridge rectification circuit is connected to the high-frequency AC voltage signal U1 on the low-voltage side; the output end of the full-bridge rectification circuit is connected in parallel with the diode D1 and the capacitor C5, and generates a low-voltage side DC signal U2.

[0015] Optionally, in the synchronous rectification circuit, GaN MOSFETs G5 and G7 form a group, and G6 and G8 form a group; when the high-frequency AC voltage signal U1 on the low-voltage side is a positive half-cycle, GaN MOSFETs G6 and G8 are closed, G5 and G7 are disconnected, and the output end of the full-bridge rectifier circuit forms a half-wave rectified voltage with positive top and negative bottom; when the high-frequency AC voltage signal U1 on the low-voltage side is a negative half-cycle, GaNMOSFETs G5 and G7 are closed, G6 and G8 are disconnected, and the output end of the full-bridge rectifier circuit also forms a half-wave rectified voltage with positive top and negative bottom; this process is alternated, and finally a full-wave rectified voltage is formed at the output end of the synchronous rectification circuit, generating a low-voltage side DC signal U2.

[0016] Optionally, the step-down chopper circuit includes GaN MOSFET G9 and G 10 , chopper inductor L2 and output filter capacitor C6; wherein the drain of the GaN MOSFET G9 is connected to one end of the low-voltage side DC signal U2; the source of the GaN MOSFET G9 is respectively connected to the GaN MOSFET G 10 The drain of the GaN MOSFET G 10 The source of the output filter capacitor C6 and the other end of the output filter capacitor C6 are connected to the other end of the low-voltage side DC signal U2; the two ends of the output filter capacitor C6 generate a regulated output signal V out .

[0017] Optionally, in the step-down chopper circuit, when the GaN MOSFET G9 is turned on, the output terminal generates a regulated output signal V out Directly supply power to the output side; after the preset time, turn off the GaN MOSFET G9, at which time the chopper inductor L2 releases the stored energy, generating reverse electromotive force, which is then 10 After one cycle, the process of turning on and off the GaN MOSFET G9 is repeated, and the load voltage is reduced by controlling the time that the GaN MOSFET G9 is in the on state.

[0018] Optionally, an input filter capacitor C1 is connected in parallel to the input end of the inverter circuit.

[0019] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0020] In an LCCC-type capacitive isolated DCDC converter provided by the present application, a high-frequency AC voltage signal is generated on the high-voltage side through an inverter circuit composed of GaNMOSFET, which is injected into a resonant circuit containing an isolation capacitor that replaces the transformer. The low-voltage side obtains input power from the isolation capacitor through a synchronous rectification circuit, and achieves a regulated output through a step-down chopper circuit, forming a capacitive, transformer-free, isolated DCDC converter. It can realize the conversion from the high-voltage side to the low-voltage side in high-power application scenarios without using a transformer, and form a regulated output on the low-voltage side. It has the significant characteristics of small size, light weight, high power density and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 This is a schematic diagram of the overall structure of an LCCC type capacitive isolation DCDC converter;

[0023] Figure 2 It is the basic circuit form and voltage waveform diagram of the inverter circuit;

[0024] Figure 3 It is a schematic diagram of the basic circuit form of the resonant circuit;

[0025] Figure 4 It is a basic circuit diagram of a synchronous rectification circuit;

[0026] Figure 5 It is a basic circuit diagram of the step-down chopper circuit. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0028] The purpose of this application is to propose an LCCC-type capacitive isolated DCDC conversion device, which can realize voltage conversion from the high-voltage side to the low-voltage side in high-power application scenarios without the use of a transformer, thereby reducing the size and weight of the device, increasing power density and improving conversion efficiency.

[0029] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0030] In an exemplary embodiment, the present application provides an LCCC type capacitive isolation type DC / DC converter. Figure 1 As shown, the LCCC capacitive isolation DC / DC converter comprises: an inverter circuit 1, a resonant circuit 2, a synchronous rectification circuit 3, and a step-down chopper circuit 4 connected in sequence. In an exemplary embodiment, an input filter capacitor C1 may be connected in parallel to the input end of the inverter circuit.

[0031] The inverter circuit 1 is used to use GaN MOSFET to convert the DC input voltage signal V in Perform switch modulation and convert the DC input voltage signal V in Converted into a high-frequency AC voltage signal U0. The resonant circuit 2 is an LC-type resonant circuit containing an isolation capacitor, which is used to achieve insulation isolation between the high and low voltage sides and the transmission of power flow, and transmit the high-frequency AC voltage signal U0 to the low-voltage side. The synchronous rectification circuit 3 is used to obtain the high-frequency AC voltage signal U1 on the low-voltage side from the resonant circuit 2, and convert the high-frequency AC voltage signal U1 on the low-voltage side into a low-voltage side DC signal U2 with the help of GaN MOSFET. The step-down chopper circuit 4 is used to adjust and stabilize the low-voltage side DC signal U2 to achieve a regulated output on the low-voltage side, that is, to generate a regulated output signal V out .

[0032] In an exemplary embodiment, the basic circuit form of the inverter circuit 1 is as follows: Figure 2 Part (a) shows a single-phase full-bridge inverter circuit, including GaN MOSFETs G1, G2, G3, and G4. GaN MOSFETs G1 and G3 form a group, while G2 and G4 form another group. The alternating conduction of the two GaN MOSFET groups achieves DC-to-AC conversion, generating a high-frequency AC voltage signal U0 at the output.

[0033] Specifically, the drains of the GaN MOSFETs G1 and G2 are both connected to a DC input voltage signal V in The positive terminal of the GaN MOSFET G4 and G3 are connected to the source of the DC input voltage signal V inThe source of the GaN MOSFET G1 is connected to the drain of the GaN MOSFET G4, and their common connection point leads to the positive electrode of the high-frequency AC voltage signal U0. The source of the GaN MOSFET G2 is connected to the drain of the GaN MOSFET G3, and their common connection point leads to the negative electrode of the high-frequency AC voltage signal U0.

[0034] The working process of the inverter circuit 1 is as follows: when the GaN MOSFETs G1 and G3 are closed and G2 and G4 are open, the high-frequency AC voltage signal U0 at the output end is positive; when the GaN MOSFETs G2 and G4 are closed and G1 and G3 are open, the high-frequency AC voltage signal U0 at the output end is negative. Figure 2 As shown in part (b), the horizontal coordinates t1, t2, and t3 are different commutation moments.

[0035] In an exemplary embodiment, the basic circuit form of the resonant circuit 2 is as follows: Figure 3 As shown, it includes a resonant capacitor C2, a resonant inductor L1, an isolation capacitor C3, and an isolation capacitor C4. Among them, one end of the resonant capacitor C2 is connected to the positive electrode of the inverter circuit output end (that is, the positive electrode of U0), and the other end of the resonant capacitor C2 is connected to one end of the isolation capacitor C3. One end of the resonant inductor L1 is connected to the negative electrode of the inverter circuit output end (that is, the negative electrode of U0), and the other end of the resonant inductor L1 is connected to one end of the isolation capacitor C4. A high-frequency AC voltage signal U1 on the low-voltage side is generated between the other end of the isolation capacitor C3 and the other end of the isolation capacitor C4.

[0036] In the resonant circuit 2 of the present application, an LC resonant circuit is formed by the resonant inductor L1 and the resonant capacitor C2, which can effectively reduce the loss of the GaN MOSFET in the inverter circuit during the switching process, and at the same time improve the output characteristics of the output voltage of the inverter circuit. On the basis of the LC resonant circuit, the present application connects an isolation capacitor C3 and C4 in series after the resonant capacitor C2 and the resonant inductor L1 to replace the high-frequency transformer in the traditional isolated DCDC conversion device. The isolation capacitors C3 and C4 are both safety capacitors made of gallium nitride materials. With the help of the "DC isolation and AC passing" characteristics of the capacitor itself, the voltage isolation between the high and low voltage sides can be effectively achieved; at the same time, because the gallium nitride material has good high-frequency working performance, the power flow can be transmitted to the low-voltage side through the high-frequency signal.

[0037] In an exemplary embodiment, the basic circuit form of the synchronous rectification circuit 3 is as follows: Figure 4As shown, it includes a diode D1, a capacitor C5, and GaN MOSFETs G5, G6, G7, and G8. The synchronous rectification circuit adopts a full-bridge rectification form, and GaN MOSFETs are used to replace the MOSFETs in the rectification circuit of the traditional DCDC conversion device. Among them, the GaN MOSFETs G5, G6, G7, and G8 constitute a full-bridge rectification circuit. The input end of the full-bridge rectification circuit is connected to the high-frequency AC voltage signal U1 on the low-voltage side. The output end of the full-bridge rectification circuit is connected in parallel with the diode D1 and the capacitor C5, and generates a low-voltage side DC signal U2. Among them, the diode D1 is preferably a Schottky diode; the capacitor C5 is a low-voltage side thin-film capacitor.

[0038] Specifically, the drains of the GaN MOSFETs G5 and G6 are connected to the cathode of the diode D1 and one end of the capacitor C5, and the sources of the GaN MOSFETs G8 and G7 are connected to the anode of the diode D1 and the other end of the capacitor C5. The source of the GaN MOSFET G5 is connected to the drain of the GaN MOSFET G8, and their common connection point is connected to the anode of U1. The source of the GaN MOSFET G6 is connected to the drain of the GaN MOSFET G7, and their common connection point is connected to the cathode of U1.

[0039] In the synchronous rectification circuit 3, GaN MOSFETs G5 and G7 form a group, and G6 and G8 form a group. When the high-frequency AC voltage signal U1 on the low-voltage side is in the positive half-cycle, GaN MOSFETs G6 and G8 are closed, while G5 and G7 are disconnected. A half-wave rectified voltage with a positive top and a negative bottom is formed at the output of the full-bridge rectifier circuit. When the high-frequency AC voltage signal U1 on the low-voltage side is in the negative half-cycle, GaN MOSFETs G5 and G7 are closed, while G6 and G8 are disconnected. Similarly, a half-wave rectified voltage with a positive top and a negative bottom is formed at the output of the full-bridge rectifier circuit. This process repeats, ultimately forming a full-wave rectified voltage at the output of the synchronous rectification circuit, rectifying the AC voltage into a DC voltage and generating a low-voltage DC signal U2.

[0040] In an exemplary embodiment, the basic circuit form of the step-down chopper circuit 4 is as follows: Figure 5 As shown, including GaNMOSFET G9 and G 10 , chopper inductor L2 and output filter capacitor C6. The drain of the GaN MOSFET G9 is connected to one end of the low-voltage side DC signal U2. The source of the GaN MOSFET G9 is connected to the GaN MOSFET G 10 The other end of the chopper inductor L2 is connected to one end of the output filter capacitor C6. 10The source of the output filter capacitor C6 and the other end of the output filter capacitor C6 are connected to the other end of the low-voltage side DC signal U2. The two ends of the output filter capacitor C6 generate a regulated output signal V out .

[0041] Among them, GaN MOSFET G9 is used as a fully controlled device. 10 The internal body diode is used as a freewheeling diode. C6 is the output filter capacitor on the low-voltage side, which plays the role of energy storage and reducing the ripple of the output voltage. L2 is the chopper inductor, which plays the role of energy storage and voltage reduction. In the step-down chopper circuit, when the GaN MOSFET G9 is turned on, the output terminal generates a regulated output signal V out Directly supply power to the output side. After the preset time, the GaN MOSFET G9 is turned off. At this time, the chopper inductor L2 releases the stored energy, generating reverse electromotive force, which is then 10 After one cycle, the process of turning on and off the GaN MOSFET G9 is repeated. By controlling the time that the GaN MOSFET G9 is in the on state, the load voltage can be reduced.

[0042] It can be seen that in the LCCC type capacitive isolation type DCDC converter provided by the present application, the inverter circuit 1 is mainly composed of GaNMOSFET G1, G2, G3, G4, and the input voltage V in After entering the inverter circuit, it is switched and modulated by GaN MOSFET to convert the input DC signal into a high-frequency AC signal of 12MHz. The resonant circuit 2 is mainly composed of a resonant capacitor C2, a resonant inductor L1, and isolation capacitors C3 and C4. While playing the role of a resonant circuit in a traditional DCDC converter, this part achieves insulation isolation between the high and low voltage sides by adding safety capacitors C3 and C4, and realizes the transmission of power flow through high-frequency signals. The synchronous rectification circuit 3 is mainly composed of GaN MOSFETs G5, G6, G7, G8, Schottky diode D1, and a low-voltage side film capacitor C5. This part obtains a high-frequency AC signal U1 from the isolation capacitors C3 and C4, and converts the high-frequency AC signal into a DC signal U2 on the low-voltage side with the help of GaN MOSFET. The step-down chopper circuit 4 is mainly composed of GaN MOSFETs G9, G 10 , chopper inductor L2 and output filter capacitor C6 on the low-voltage side. This part adjusts and stabilizes the rectified low-voltage side DC signal U2 to achieve the low-voltage side signal V out regulated output.

[0043] Current isolated DC-DC converters all use transformers to achieve electrical isolation between input and output. Compared to the prior art, the LCCC capacitive isolated DC-DC converter provided in this application has at least the following advantages:

[0044] 1) Compared with traditional high-power isolated DCDC converters, this application achieves a multiple reduction in volume and weight. For high-power application scenarios, traditional isolated DCDC converters require a high-frequency transformer that is both large in volume and weight to achieve voltage isolation and power flow transmission. This application replaces the high-frequency transformer with a safety capacitor that plays an isolation role. With the help of the capacitor's characteristic of blocking direct current and passing alternating current, voltage isolation can be achieved, and power flow transmission can be achieved with the help of high-frequency signals. In this way, the role of the high-frequency transformer is achieved through the isolation capacitor, which is much smaller in volume and weight, so that the volume and weight of the entire DCDC converter can be reduced by several times.

[0045] 2) Compared to traditional high-power isolated DC-DC converters, this application achieves a doubling of power density. Power density typically refers to the rated / nominal output power of a converter divided by the volume occupied by the device. In this application, while maintaining the same output power, the large high-frequency transformer in a traditional isolated DC-DC converter is replaced with a safety capacitor that is several times smaller than the transformer, thereby achieving a doubling of power density.

[0046] 3) Compared with traditional high-power isolated DC-DC converters, this application achieves improved efficiency. During use, the windings and core of high-frequency transformers generate a lot of heat, which seriously affects the conversion efficiency of the DC-DC converter. After the application uses safety capacitors to replace high-frequency transformers, the heating condition can be greatly improved and the efficiency can be significantly improved. At the same time, the circuits in this application all use gallium nitride materials, which have lower heat dissipation requirements than the circuit materials in traditional isolated DC-DC converters, so the efficiency can be further improved.

[0047] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0048] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. An LCCC type capacitive isolation type DCDC converter, characterized in that: include: An inverter circuit, a resonant circuit, a synchronous rectification circuit and a step-down chopper circuit connected in sequence; The inverter circuit is used to perform switch modulation on a DC input voltage signal using a GaN MOSFET to convert the DC input voltage signal into a high-frequency AC voltage signal; The resonant circuit is an LC type resonant circuit containing an isolation capacitor, which is used to achieve insulation isolation between the high and low voltage sides and transfer of power flow, and transfer high-frequency AC voltage signals to the low voltage side; The synchronous rectification circuit is used to obtain a high-frequency AC voltage signal on the low-voltage side from the resonant circuit, and convert the high-frequency AC voltage signal on the low-voltage side into a low-voltage DC signal by means of a GaNMOSFET; The step-down chopper circuit is used to adjust and stabilize the DC signal on the low-voltage side to achieve a regulated output on the low-voltage side.

2. The LCCC type capacitive isolation type DCDC converter according to claim 1, characterized in that: The inverter circuit is a single-phase full-bridge inverter circuit, including GaN MOSFETs G1, G2, G3, and G4; wherein GaN MOSFETs G1 and G3 form a group, and G2 and G4 form a group, and the conversion of DC voltage to AC voltage is achieved by alternating conduction of the two groups of GaN MOSFETs, thereby generating a high-frequency AC voltage signal U0 at the output end.

3. The LCCC type capacitive isolation type DCDC converter according to claim 2, characterized in that: In the inverter circuit, when GaN MOSFETs G1 and G3 are closed and G2 and G4 are disconnected, the high-frequency AC voltage signal U0 at the output end is positive; when GaN MOSFETs G2 and G4 are closed and G1 and G3 are disconnected, the high-frequency AC voltage signal U0 at the output end is negative.

4. The LCCC type capacitive isolation type DCDC converter according to claim 1, characterized in that: The resonant circuit includes a resonant capacitor C2, a resonant inductor L1, an isolation capacitor C3 and an isolation capacitor C4; wherein one end of the resonant capacitor C2 is connected to the positive electrode of the inverter circuit output end, and the other end of the resonant capacitor C2 is connected to one end of the isolation capacitor C3; one end of the resonant inductor L1 is connected to the negative electrode of the inverter circuit output end, and the other end of the resonant inductor L1 is connected to one end of the isolation capacitor C4; a high-frequency AC voltage signal U1 on the low-voltage side is generated between the other end of the isolation capacitor C3 and the other end of the isolation capacitor C4.

5. The LCCC type capacitive isolation type DCDC converter according to claim 4, characterized in that: The isolation capacitor C3 and the isolation capacitor C4 are both safety capacitors made of gallium nitride material.

6. The LCCC type capacitive isolation type DCDC converter according to claim 4, characterized in that: The synchronous rectification circuit adopts a full-bridge rectification form, including a diode D1, a capacitor C5 and GaN MOSFETs G5, G6, G7 and G8; wherein the GaN MOSFETs G5, G6, G7 and G8 constitute a full-bridge rectification circuit; the input end of the full-bridge rectification circuit is connected to the high-frequency AC voltage signal U1 on the low-voltage side; the output end of the full-bridge rectification circuit is connected in parallel with the diode D1 and the capacitor C5, and generates a low-voltage side DC signal U2.

7. The LCCC type capacitive isolation type DCDC converter according to claim 6, characterized in that: In the synchronous rectification circuit, GaN MOSFET G5 and G7 form a group, and G6 and G8 form a group; when the high-frequency AC voltage signal U1 on the low-voltage side is a positive half-cycle, GaN MOSFET G6 and G8 are closed, G5 and G7 are disconnected, and the output end of the full-bridge rectification circuit forms a half-wave rectification voltage with positive top and negative bottom; when the high-frequency AC voltage signal U1 on the low-voltage side is a negative half-cycle, GaN MOSFET G5 and G7 are closed, G6 and G8 are disconnected, and the output end of the full-bridge rectification circuit also forms a half-wave rectification voltage with positive top and negative bottom; this process is alternated, and finally a full-wave rectification voltage is formed at the output end of the synchronous rectification circuit to generate a low-voltage side DC signal U2.

8. The LCCC type capacitive isolation type DCDC converter according to claim 6, characterized in that: The step-down chopper circuit includes GaN MOSFET G9 and G 10 , chopper inductor L2 and output filter capacitor C6; wherein the drain of the GaN MOSFET G9 is connected to one end of the low-voltage side DC signal U2; the source of the GaN MOSFET G9 is respectively connected to the GaN MOSFETG 10 The drain of the GaN MOSFET G 10 The source of the output filter capacitor C6 and the other end of the output filter capacitor C6 are connected to the other end of the low-voltage side DC signal U2; the two ends of the output filter capacitor C6 generate a regulated output signal V out .

9. The LCCC capacitive isolation DCDC converter according to claim 8, characterized in that: In the step-down chopper circuit, when the GaN MOSFET G9 is turned on, the output terminal generates a regulated output signal V out Directly supply power to the output side; after the preset time, turn off the GaN MOSFET G9, at which time the chopper inductor L2 releases the stored energy, generating a reverse electromotive force, which is then 10 After one cycle, the process of turning on and off the GaN MOSFET G9 is repeated, and the load voltage is reduced by controlling the time that the GaN MOSFET G9 is in the on state.

10. The LCCC capacitive isolation DCDC converter according to claim 1, characterized in that: An input filter capacitor C1 is connected in parallel to the input end of the inverter circuit.

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