Switching circuit and inversion equipment

Abstract

The invention discloses a switching circuit and inversion equipment, the switching circuit comprises a first square wave power supply, a first capacitor, a first diode and an output capacitor, the switching circuit is constructed through the first square wave power supply, the first capacitor, the first diode and the output capacitor, and the output capacitor can supply power for driving of a switching tube. Due to the fact that an isolation alternating current conversion circuit is omitted, the size is reduced, and cost is reduced. And by adding the second square wave power supply for power supply, the power supply mode of the cyclo inverter topology is also optimized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic circuit, in particular to a switching circuit and an inverter device. BACKGROUND

[0002] The driving power supply scheme of the switching tube can be realized by an isolated driving power supply circuit taking power from the primary side of the AC conversion circuit.

[0003] However, since the isolated driving power supply circuit needs to use an isolated AC conversion circuit, it leads to problems such as large size and high cost. SUMMARY

[0004] The present application provides a switching circuit and an inverter device to alleviate the technical problems of large size and high cost of the driving power supply circuit of the switching tube.

[0005] In a first aspect, the present application provides a switching circuit, which comprises a first square wave power supply, a first capacitor, a first diode, and an output capacitor, a first end of the first capacitor is connected with a first end of the first square wave power supply; an anode of the first diode is connected with a second end of the first capacitor; a first end of the output capacitor is connected with a cathode of the first diode, and a second end of the output capacitor is connected with a second end of the first square wave power supply.

[0006] In a second aspect, the present application provides an inverter device, which comprises an inverter and the above-mentioned switching circuit, the inverter comprises a primary side circuit, an AC conversion circuit, and a secondary side circuit connected in sequence, the secondary side circuit comprises a first bridge arm and a second bridge arm connected in parallel; the first square wave power supply is for a transistor in the first bridge arm or the second bridge arm.

[0007] The switching circuit and the inverter device provided by the present application, through the switching circuit composed of the first square wave power supply, the first capacitor, the first diode, and the output capacitor, the output capacitor can provide driving power for the switching tube, since the isolated AC conversion circuit is saved, not only the size is reduced, but also the cost is reduced.

[0008] Since the switching circuit uses a square wave power supply, it can take power from the AC side of the secondary side of the AC conversion circuit of the inverter, and does not need an isolated AC conversion circuit, which also improves the conversion efficiency; and compared with taking power from the AC side, which needs rectification, filtering, voltage reduction, and other processing, the above-mentioned switching circuit saves these processing, which can also reduce the size and cost. BRIEF DESCRIPTION OF DRAWINGS

[0009] The technical solutions and other beneficial effects of the present application will be apparent through the following detailed description of the specific embodiments of the present application combined with the accompanying drawings.

[0010] Figure 1The first circuit schematic diagram of the switching circuit provided in the embodiments of this application.

[0011] Figure 2 This is a second circuit diagram illustrating the charging process of the switching circuit provided in an embodiment of this application.

[0012] Figure 3 This is a second circuit diagram illustrating the discharge process of the switching circuit provided in an embodiment of this application.

[0013] Figure 4 This is a third circuit diagram of a switching circuit provided in an embodiment of this application.

[0014] Figure 5 This is a schematic diagram of the first structure of the inverter device provided in the embodiments of this application.

[0015] Figure 6 for Figure 5 The diagram shows the voltage change of the inverter device.

[0016] Figure 7 This is a fourth circuit diagram of a switching circuit provided in an embodiment of this application.

[0017] Figure 8 The fifth circuit schematic diagram of the switching circuit provided in the embodiments of this application.

[0018] Figure 9 The sixth circuit schematic diagram of the switching circuit provided in the embodiments of this application.

[0019] Figure 10 The seventh circuit schematic diagram of the switching circuit provided in the embodiments of this application.

[0020] Figure 11 The circuit diagram of the inverter device provided in the embodiment of this application.

[0021] Figure 12 for Figure 11 The diagram shows the voltage change of the inverter device. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Features thus defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified.

[0024] Please see Figures 1 to 12 This embodiment provides a switching circuit 100, such as Figure 1 As shown, the switching circuit 100 includes a first square wave power supply Vin1, a first capacitor C1, a first diode D1, and an output capacitor Co. The first capacitor C1, the first diode D1, and the output capacitor Co are connected in series across the two ends of the first square wave power supply Vin1. The anode of the first diode D1 is connected to the first capacitor C1, and the cathode of the first diode D1 is connected to the output capacitor Co.

[0025] It is understood that the switching circuit 100 provided in this embodiment is constructed by the first square wave power supply Vin1, the first capacitor C1, the first diode D1 and the output capacitor Co. The output capacitor Co can provide power for driving the switching transistor M1. Since the isolation AC conversion circuit 302 is saved, not only is the size reduced, but the cost is also reduced.

[0026] Since the switching circuit 100 uses a square wave power supply, it can draw power from the AC side of the secondary side of the AC conversion circuit 302 of the inverter 300, and there is no need to isolate the AC conversion circuit 302, which improves the conversion efficiency. Moreover, compared with the rectification, filtering, and step-down processing required when drawing power from the AC side, the above-mentioned switching circuit 100 can reduce the size and cost by saving these processes.

[0027] It should be noted that the higher the frequency of the voltage output by the first square wave power supply Vin1, the smaller the drop in the output voltage (Vo) across the output capacitor Co. Therefore, the frequency of the voltage output by the first square wave power supply Vin1 can be selected as high frequency. The first capacitor C1 can act as a voltage divider. The voltage output by the first square wave power supply Vin1 includes high and low levels. At the high level, the first capacitor C1 and the output capacitor Co are charged, and the current flows as follows: Figure 1 The dashed arrow indicates a clockwise direction; at low level, due to the unidirectional conduction characteristic of the first diode D1, the current cannot flow as... Figure 1 The flow is counterclockwise as indicated by the dashed arrow. The first capacitor C1 and the output capacitor Co cannot discharge. At this time, the electrical energy stored in the output capacitor Co can power the subsequent load. The output voltage across the output capacitor Co is the voltage division of the output voltage of the first square wave power supply Vin1 by the first capacitor C1 and the output capacitor Co.

[0028] In some of these embodiments, such as Figure 2 , Figure 3 as well as Figure 4 As shown, the switching circuit 100 also includes a freewheeling unit 10. The first end of the freewheeling unit 10 is connected to the anode of the first diode D1 and the second end of the first capacitor C1. The second end of the freewheeling unit 10 is connected to the second end of the output capacitor Co and the second end of the first square wave power supply Vin1.

[0029] It should be noted that during the process of the output capacitor Co supplying power to the downstream load, the first capacitor C1 cannot discharge. Therefore, after connecting the load, the voltage across the first capacitor C1 will increase, while Vo will decrease. In order to prevent Vo from continuously decreasing, a discharge path needs to be constructed for the first capacitor C1 to ensure that power is continuously supplied to the output capacitor Co through the first capacitor C1 during the power supply process. In this way, the freewheeling unit 10 can prevent Vo from dropping to 0V.

[0030] In some of these embodiments, such as Figure 2 , Figure 3 As shown, the freewheeling unit 10 includes a second diode D2. The cathode of the second diode D2 is connected to the anode of the first diode D1 and the second terminal of the first capacitor C1. The anode of the second diode D2 is connected to the second terminal of the output capacitor Co and the second terminal of the first square wave power supply Vin1.

[0031] It should be noted that the charging process begins when the first square wave power supply Vin1 outputs a high level, such as... Figure 2 As shown, due to the unidirectional conduction of the second diode D2, the current flows in a clockwise direction through the first capacitor C1, the first diode D1, and the output capacitor Co in sequence, charging the first capacitor C1 and the output capacitor Co, and increasing the voltage across both the first capacitor C1 and the output capacitor Co.

[0032] When the first square wave power supply Vin1 outputs a low level, it enters the discharge process, such as Figure 3 As shown, the first capacitor C1 discharges through the second diode D2. After repeated charging and discharging in each cycle, the voltage across the first capacitor C1 will approach 0V, and Vo will approach the peak value of the output voltage of the first square wave power supply Vin1. Therefore, by adding the freewheeling second diode D2, Vo can be prevented from dropping to 0V due to load consumption.

[0033] In some of these embodiments, such as Figure 4 As shown, the freewheeling unit 10 includes a switching transistor M1. The first terminal of the switching transistor M1 is connected to the anode of the first diode D1 and the second terminal of the first capacitor C1. The second terminal of the switching transistor M1 is connected to the second terminal of the output capacitor Co and the second terminal of the first square wave power supply Vin1. The control terminal of the switching transistor M1 is connected to a control signal.

[0034] It should be noted that when the first square wave power supply Vin1 outputs a high level, the control signal can control the switching transistor M1 to turn off, thereby realizing the charging process; when the first square wave power supply Vin1 outputs a low level, the control signal can control the switching transistor M1 to turn on, thereby realizing the discharging process.

[0035] Meanwhile, if the output voltage of the first square wave power supply Vin1 is high, Vo will also be high, which will lead to damage to the subsequent components. Therefore, the freewheeling second diode D2 is replaced with a controllable switching transistor M1. By controlling the switching transistor M1, the magnitude of Vo can be adjusted, thus enabling the switching circuit 100 to output a stable and safe Vo.

[0036] In some of these embodiments, such as Figure 4 As shown, the switching circuit 100 also includes a hysteresis comparator unit 20, which is connected to the switching transistor M1 and the output capacitor Co.

[0037] It should be noted that the hysteresis comparator unit 20 is used to adjust the switching state of the switching transistor M1 according to Vo, thereby controlling Vo within a certain range to achieve voltage regulation. For example, when Vo is higher than the first threshold voltage (Vth1), the switching transistor M1 will be turned on to prevent Vo from continuing to rise; when the load is consumed, causing Vo to fall below the second threshold voltage (Vth2), the switching transistor M1 will be turned off, allowing it to continue charging the output capacitor Co to increase Vo, where Vth1 is greater than Vth2. This scheme can effectively control Vo within a certain range and prevent the switching transistor M1 from frequently switching near its rated voltage.

[0038] In some of these embodiments, such as Figure 4As shown, the hysteresis comparator unit 20 includes at least one of a first resistor R1, a Zener diode Z1, a second resistor R2, a third resistor R3, a comparator COMP, a third diode D3, and a fourth resistor R4. The first terminal of the first resistor R1 is connected to the first terminal of the output capacitor Co; the cathode of the Zener diode Z1 is connected to the second terminal of the first resistor R1, and the anode of the Zener diode Z1 is connected to the ground terminal GND; the first terminal of the second resistor R2 is connected to the first terminal of the first resistor R1; the first terminal of the third resistor R3 is connected to the second terminal of the second resistor R2, and the second terminal of the third resistor R3 is connected to the ground terminal GND; the first input terminal of the comparator COMP is connected to the second terminals of the second resistor R2 and the first terminal of the third resistor R3, the second input terminal of the comparator COMP is connected to the first terminal of the first resistor R1 and the cathode of the Zener diode Z1, and the output terminal of the comparator COMP is connected to the control electrode of the switching transistor M1; the anode of the third diode D3 is connected to the second input terminal of the comparator COMP, and the cathode of the third diode D3 is connected to the anode of the first diode D1; the fourth resistor R4 is connected in series with the third diode D3.

[0039] Optionally, such as Figure 4 As shown, the hysteresis comparator unit 20 also includes a fifth resistor R5. The first end of the fifth resistor R5 is connected to the cathode of the Zener diode Z1 and the second end of the first resistor R1, and the second end of the fifth resistor R5 is connected to the second input terminal of the comparator COMP.

[0040] It should be noted that the circuit structure of the hysteresis comparator 20 may be, but is not limited to, the various embodiments provided in this application, or may be other circuits capable of achieving stable Vo.

[0041] Figure 5 This is a schematic diagram of a first structure of an inverter device 500 provided in an embodiment of this application. The inverter device 500 includes a driver 200 and a switching circuit 100. The switching circuit 100 provides Vo to the driver 200, wherein the first square wave power supply Vin1 is a transistor or a MOSFET. Under the power supply of Vo, power supply VCC, and ground GND, the driver 200 outputs a corresponding first drive signal DRV1 according to the input pulse width modulation signal PWM to control the switching state of the first square wave power supply Vin1.

[0042] Figure 6 for Figure 5 The diagram shows the voltage change of the inverter device 500. One transistor, serving as the first square wave power supply Vin1, is in a normally-on state for half a power frequency cycle in the inverter 300. Since there is no voltage across this transistor, Vo will decrease during this half-cycle of the normally-on state.

[0043] In some of these embodiments, such as Figures 7 to 10As shown, the switching circuit 100 also includes a second capacitor C2 and a second square wave power supply Vin2. The first end of the second capacitor C2 is connected to the second end of the first capacitor C1; the first end of the second square wave power supply Vin2 is connected to the second end of the second capacitor C2, and the second end of the second square wave power supply Vin2 is connected to the second end of the output capacitor Co.

[0044] It should be noted that the second square wave power supply Vin2 can also be a transistor or a MOSFET. In this embodiment, the complementary first square wave power supply Vin1 and the second square wave power supply Vin2 can be in a normally-on state during different half-cycles of the power frequency, thereby improving... Figure 6 This addresses the issue of Vo decreasing during half a power frequency cycle in the normally on state, ensuring continuous Vo stability. This is achieved by adding a second square wave power supply, Vin2, which also optimizes the power supply method of the cyclo inverter topology.

[0045] In some of these embodiments, such as Figure 8 As shown, the switching circuit 100 also includes a fourth diode D4 and a fifth diode D5. The anode of the fourth diode D4 is connected to the second terminal of the first capacitor C1, and the cathode of the fourth diode D4 is connected to the anode of the first diode D1. The cathode of the fifth diode D5 is connected to the anode of the first diode D1, and the anode of the fifth diode D5 is connected to the first terminal of the second capacitor C2.

[0046] It should be noted that the fourth diode D4 and the fifth diode D5 are used to select either the first square wave power supply Vin1 or the second square wave power supply Vin2 as the power supply, which can ensure the stability of Vo.

[0047] In some of these embodiments, such as Figure 9 As shown, the switching circuit 100 also includes a sixth diode D6 and a seventh diode D7. The anode of the sixth diode D6 is connected to the second terminal of the first square wave power supply Vin1 and the second terminal of the second square wave power supply Vin2, and the cathode of the sixth diode D6 is connected to the anode of the fourth diode D4. The anode of the seventh diode D7 is connected to the anode of the sixth diode D6, and the cathode of the seventh diode D7 is connected to the anode of the fifth diode D5.

[0048] It should be noted that after adding the fourth diode D4 and the fifth diode D5, when the first square wave power supply Vin1 or the second square wave power supply Vin2 outputs a low level, the corresponding first capacitor C1 or second capacitor C2 cannot discharge, which will also cause Vo to become lower and lower. Therefore, in this embodiment, the sixth diode D6 and the seventh diode D7, which have a freewheeling function, can provide a discharge path for the first capacitor C1 and the second capacitor C2.

[0049] In some of these embodiments, such as Figure 10As shown, the switching circuit 100 also includes an eighth diode D8 and a ninth diode D9. The anode of the eighth diode D8 is connected to the cathode of the sixth diode D6, and the cathode of the eighth diode D8 is connected to the first terminal of the output capacitor Co. The anode of the ninth diode D9 is connected to the cathode of the seventh diode D7, and the cathode of the ninth diode D9 is connected to the first terminal of the output capacitor Co.

[0050] It should be noted that the eighth diode D8 and the ninth diode D9, which provide clamping function in this embodiment, can prevent the switching transistor M1 from being damaged by overvoltage.

[0051] In some embodiments, this embodiment provides an inverter device 500, such as... Figure 5 and Figure 11 As shown, the inverter device 500 includes the aforementioned switching circuit 100.

[0052] It is understood that since the inverter device 500 provided in this embodiment includes the aforementioned switching circuit 100, it can also be constructed using the first square wave power supply Vin1, the first capacitor C1, the first diode D1, and the output capacitor Co. The output capacitor Co can provide power for driving the switching transistor M1. Since the isolation AC conversion circuit 302 is saved, not only is the size reduced, but the cost is also reduced.

[0053] Since the switching circuit 100 uses a square wave power supply, it can draw power from the AC side of the secondary side of the AC conversion circuit 302 of the inverter 300, and there is no need to isolate the AC conversion circuit 302, which improves the conversion efficiency. Moreover, compared with the rectification, filtering, and step-down processing required when drawing power from the AC side, the above-mentioned switching circuit 100 can reduce the size and cost by saving these processes.

[0054] In some embodiments, the inverter device 500 further includes a driver 200, which is connected to the output terminal and ground terminal GND of the switching circuit 100 to power the driver 200 through the Vo output by the switching circuit 100. The driver 200 can output a fifth drive signal DRV5, a sixth drive signal DRV6, a seventh drive signal DRV7, and an eighth drive signal DRV8.

[0055] In some of these embodiments, such as Figure 11 As shown, the inverter device 500 also includes an inverter 300, which includes a primary circuit 301, an AC conversion circuit 302, and a secondary circuit 303 connected in sequence.

[0056] In some of these embodiments, such as Figure 11As shown, the primary-side circuit 301 includes a first field-effect transistor S1, a second field-effect transistor S2, a third field-effect transistor S3, and a fourth field-effect transistor S4. The first terminal of the first field-effect transistor S1 is connected to the positive terminal of the DC voltage (Udc), the second terminal of the first field-effect transistor S1 is connected to the first terminal of the second field-effect transistor S2, the second terminal of the second field-effect transistor S2 is connected to the negative terminal of the DC voltage (Udc), the first terminal of the third field-effect transistor S3 is connected to the first terminal of the first field-effect transistor S1, the second terminal of the third field-effect transistor S3 is connected to the first terminal of the fourth field-effect transistor S4, and the second terminal of the fourth field-effect transistor S4 is connected to the second terminal of the second field-effect transistor S2.

[0057] In this embodiment, the DC voltage (Udc) can be converted into the corresponding AC voltage (Up) by controlling the switching states of the first field-effect transistor S1, the second field-effect transistor S2, the third field-effect transistor S3, and the fourth field-effect transistor S4.

[0058] In some of these embodiments, such as Figure 11 As shown, the primary-side circuit 301 also includes a third capacitor Cdc. The first end of the third capacitor Cdc is connected to the first terminal of the first field-effect transistor S1, and the second end of the third capacitor Cdc is connected to the second terminal of the second field-effect transistor S2.

[0059] In some of these embodiments, such as Figure 11 As shown, the AC converter circuit 302 includes a transformer T1 and a first inductor Lr. The primary winding of the transformer T1 is connected to an AC voltage (Up). The first end of the secondary winding of the transformer T1 is connected to the first end of the first inductor Lr. The second end of the first inductor Lr is connected to the secondary circuit 303. The second end of the secondary winding of the transformer T1 is connected to the secondary circuit 303.

[0060] The turns ratio of the primary and secondary windings of transformer T1 is 1:n. The current flowing through the second terminal of the secondary winding of transformer T1 is.

[0061] In some of these embodiments, such as Figure 11 As shown, the secondary circuit 303 includes a first bridge arm H1 and a second bridge arm H2 connected in parallel. The first bridge arm H1 includes a first upper bridge arm H11 and a first lower bridge arm H12 connected in parallel.

[0062] The first upper bridge arm H11 includes a fifth field-effect transistor (FET) S5 and a sixth field-effect transistor (FET) S6. The first terminal of the fifth FET S5 serves as the first terminal of the first square wave power supply Vin1, and the second terminal of the fifth FET S5 serves as the second terminal of the first square wave power supply Vin1, connected to the ground terminal GND. The gate of the fifth FET S5 is connected to the fifth drive signal DRV5. The first terminal of the sixth FET S6 serves as the second terminal of the second square wave power supply Vin2, connected to the ground terminal GND. The second terminal of the sixth FET S6 serves as the first terminal of the second square wave power supply Vin2, and the gate of the sixth FET S6 is connected to the sixth drive signal DRV6.

[0063] The first lower bridge arm H12 includes a seventh field-effect transistor (FET) S7 and an eighth field-effect transistor (FET) S8. The first terminal of the seventh FET S7 serves as the first terminal of the second square wave power supply Vin2, and the second terminal of the seventh FET S7 serves as the second terminal of the second square wave power supply Vin2, connected to the ground terminal GND. The gate of the seventh FET S7 is connected to the seventh drive signal DRV7. The first terminal of the eighth FET S8 serves as the second terminal of the first square wave power supply Vin1, connected to the ground terminal GND. The second terminal of the eighth FET S8 serves as the first terminal of the first square wave power supply Vin1, and the gate of the eighth FET S8 is connected to the eighth drive signal DRV8.

[0064] Figure 12 for Figure 11 The diagram shows the voltage variation of the inverter device 500. The fifth and sixth field-effect transistors S5 and S6, which are complementary to the power frequency, are used as the first square wave power supply Vin1 and the second square wave power supply Vin2, respectively. These transistors can alternately provide high-level input voltages during the alternating half-cycles, thereby stabilizing Vo and effectively preventing its drop.

[0065] Similarly, by using the seventh field-effect transistor S7 and the eighth field-effect transistor S8, which are complementary to the power frequency, as the first square wave power supply Vin1 and the second square wave power supply Vin2, a high-level input voltage can be provided in turn during the alternating half-cycles, thereby stabilizing Vo and effectively preventing Vo from dropping.

[0066] In some of these embodiments, please continue to refer to Figure 11 The second bridge arm H2 includes a fourth capacitor Cr1 and a fifth capacitor Cr2. The first end of the fourth capacitor Cr1 is connected to the first terminal of the fifth field-effect transistor S5. The second end of the fourth capacitor Cr1 is connected to the second end of the secondary winding of the transformer T1 and the first end of the fifth capacitor Cr2. The second end of the fifth capacitor Cr2 is connected to the second terminal of the eighth field-effect transistor S8.

[0067] It should be noted that in other embodiments, the second bridge arm H2 can also adopt the same structure as the first bridge arm H1. The first bridge arm H1 and the second bridge arm H2 can adjust the frequency of the AC voltage (Us) output by the AC converter circuit 302.

[0068] In some of these embodiments, please continue to refer to Figure 11 The secondary circuit 303 also includes a second inductor Lf, a first switch K1, and a third inductor Lg. The first terminal of the second inductor Lf is connected to the first terminal of the fourth capacitor Cr1, the second terminal of the second inductor Lf is connected to the first terminal of the first switch K1, and the second terminal of the first switch K1 is connected to the first terminal of the third inductor Lg. The second terminal of the third inductor Lg and the second terminal of the fifth capacitor Cr2 are used to output AC voltage (Ug). Here, io represents the current corresponding to the AC voltage (Ug).

[0069] It should be noted that the aforementioned inverter 500 can be applied in the field of photovoltaic technology, but can also be applied in other suitable scenarios.

[0070] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0071] The switching circuit 100 and inverter device 500 provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A switching circuit, characterized in that, The switching circuit includes: First square wave power supply; A first capacitor, the first terminal of which is connected to the first terminal of the first square wave power supply; The first diode, the anode of the first diode is connected to the second terminal of the first capacitor; An output capacitor, the first end of which is connected to the cathode of the first diode, and the second end of which is connected to the second end of the first square wave power supply.

2. The switching circuit according to claim 1, characterized in that, The switching circuit further includes a freewheeling unit, the first end of which is connected to the anode of the first diode and the second end of the first capacitor, and the second end of which is connected to the second end of the output capacitor and the second end of the first square wave power supply.

3. The switching circuit according to claim 2, characterized in that, The freewheeling unit includes a second diode, the cathode of which is connected to the anode of the first diode and the second terminal of the first capacitor, and the anode of which is connected to the second terminal of the output capacitor and the second terminal of the first square wave power supply.

4. The switching circuit according to claim 2, characterized in that, The freewheeling unit includes a switching transistor. The first terminal of the switching transistor is connected to the anode of the first diode and the second terminal of the first capacitor. The second terminal of the switching transistor is connected to the second terminal of the output capacitor and the second terminal of the first square wave power supply. The control terminal of the switching transistor is connected to a control signal.

5. The switching circuit according to claim 4, characterized in that, The switching circuit also includes a hysteresis comparator unit, which is connected to the switching transistor and the output capacitor.

6. The switching circuit according to claim 5, characterized in that, The hysteresis comparison unit includes: A first resistor, the first end of which is connected to the first end of the output capacitor; A Zener diode, wherein the cathode of the Zener diode is connected to the second terminal of the first resistor, and the anode of the Zener diode is connected to the ground terminal; The second resistor has its first end connected to the first end of the first resistor; The third resistor has a first end connected to the second end of the second resistor, and the second end of the third resistor is connected to the ground terminal. The comparator has its first input terminal connected to the second terminal of the second resistor and the first terminal of the third resistor, its second input terminal connected to the first terminal of the first resistor and the cathode of the Zener diode, and its output terminal connected to the control electrode of the switching transistor. The third diode has its anode connected to the second input terminal of the comparator, and its cathode connected to the anode of the first diode. A fourth resistor, which is connected in series with the third diode.

7. The switching circuit according to claim 6, characterized in that, The hysteresis comparator unit further includes a fifth resistor, the first end of which is connected to the cathode of the Zener diode and the second end of the first resistor, and the second end of which is connected to the second input terminal of the comparator.

8. The switching circuit according to any one of claims 1-7, characterized in that, The switching circuit also includes: A second capacitor, wherein the first terminal of the second capacitor is connected to the second terminal of the first capacitor; The second square wave power supply has its first terminal connected to the second terminal of the second capacitor, and its second terminal connected to the second terminal of the output capacitor.

9. The switching circuit according to claim 8, characterized in that, The switching circuit also includes: A fourth diode, wherein the anode of the fourth diode is connected to the second terminal of the first capacitor, and the cathode of the fourth diode is connected to the anode of the first diode; The fifth diode has its cathode connected to the anode of the first diode, and its anode connected to the first terminal of the second capacitor.

10. The switching circuit according to claim 9, characterized in that, The switching circuit also includes: The sixth diode has its anode connected to the second terminal of the first square wave power supply and the second terminal of the second square wave power supply, and its cathode connected to the anode of the fourth diode. The seventh diode has its anode connected to the anode of the sixth diode and its cathode connected to the anode of the fifth diode.

11. The switching circuit according to claim 10, characterized in that, The switching circuit also includes: The eighth diode has its anode connected to the cathode of the sixth diode, and its cathode connected to the first terminal of the output capacitor. The ninth diode has its anode connected to the cathode of the seventh diode, and its cathode connected to the first terminal of the output capacitor.

12. An inverter device, characterized in that, The inverter device includes: An inverter, comprising a primary circuit, an AC conversion circuit, and a secondary circuit connected in sequence, wherein the secondary circuit comprises a first bridge arm and a second bridge arm connected in parallel. The switching circuit according to any one of claims 1-11, wherein the first square wave power supply is a transistor in the first bridge arm or the second bridge arm.

13. The inverter device according to claim 12, characterized in that, The first bridge arm includes a first upper bridge arm and a first lower bridge arm connected together, and each of the first upper bridge arm and the first lower bridge arm includes two transistors; The first square wave power supply is one of the two transistors, and the second square wave power supply is the other of the two transistors.

14. The inverter device according to claim 13, characterized in that, The inverter device also includes a driver, which is connected to the output terminal of the switching circuit and the control electrode of the transistor.

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