Buck-boost switching circuit, switching control method, buck-boost converter and electric appliance

Abstract

The application relates to a boost-buck switching circuit, a switching control method, a boost-buck converter and an electrical appliance. The boost-buck switching circuit comprises a boost circuit, a buck circuit, a switching switch, a boost sampling circuit and a buck sampling circuit. The voltage across the first capacitor is a boosted voltage, and the on-off time duty cycle of a boost switch tube is used to adjust the size of the boosted voltage. The voltage across the second capacitor is a bucked voltage, and the on-off time duty cycle of a buck switch tube is used to adjust the bucked voltage. The switching switch is used to control the switching between the boost circuit and the buck circuit. By adjusting the on-off time duty cycle of the boost and / or buck switch tube, the voltage change value on the switching switch contact before and after the switching switch performs a switching action can be less than a preset arc generation threshold value, the current overshoot during the boost-buck switching can be prevented, the switching switch can be prevented from generating an arc phenomenon, and thus the boost-buck converter can be protected, and the normal use of the electrical appliance can be ensured.

Description

Technical Field

[0001] This application belongs to the technical field of buck-boost converters, specifically relating to a buck-boost switching circuit, a switching control method, a buck-boost converter, and electrical components. Background Technology

[0002] A buck-boost converter can be used to generate a constant output voltage. The input voltage of a buck-boost converter can be higher, lower, or equal to the output voltage. The converter can operate in buck mode, boost mode, and / or buck-boost mode. When the input voltage is higher than the output voltage, the buck-boost converter is considered to be in buck mode. When the input voltage is lower than the output voltage, the buck-boost converter is considered to be in boost mode. Traditional electrical controllers use boost circuits to improve the power factor and thus meet harmonic requirements; at low power, buck circuits are used to meet the voltage reduction requirements. Therefore, switching between boost and buck circuits is necessary. Related technologies use switchable buck-boost circuit topologies, where switching is accomplished via relays. The advantages are low voltage stress on the power switching transistors and low cost. However, during switching, current overshoot can cause arcing at the relay contacts, affecting the normal operation of the electrical appliance. Summary of the Invention

[0003] To at least partially overcome the problem of current overshoot causing arcing at relay contacts during switching in traditional buck-boost switching circuits, this application provides a buck-boost switching circuit, a switching control method, a buck-boost converter, and electrical appliances.

[0004] In a first aspect, this application provides a buck-boost switching circuit, comprising:

[0005] Boost circuit, buck circuit, switching switch, boost sampling circuit and buck sampling circuit;

[0006] The boost sampling circuit includes a first capacitor, a first boost voltage divider element, and a second boost voltage divider element. The first boost voltage divider element and the second boost voltage divider element are connected in series and then connected in parallel with the first capacitor.

[0007] The step-down sampling circuit includes a second capacitor, a first step-down voltage divider element, and a second step-down voltage divider element. The first step-down voltage divider element and the second step-down voltage divider element are connected in series and then connected in parallel with the second capacitor.

[0008] The boost circuit includes a boost switching transistor and a boost inductor. The gate of the boost switching transistor is connected to the connection point between the first boost voltage divider element and the second boost voltage divider element. The boost inductor is connected in series with the first capacitor.

[0009] The voltage reduction circuit comprises a voltage reduction switch tube and a voltage reduction inductor, the gate of the voltage reduction switch tube is connected to the voltage increase inductor; the drain of the voltage reduction switch tube is connected to the connection point between the first voltage reduction voltage dividing element and the second voltage reduction voltage dividing element, and the voltage reduction inductor is connected in series with the second capacitor;

[0010] The voltage across the first capacitor is the voltage after voltage increase, and the on-off time duty cycle of the voltage increase switch tube is used to adjust the voltage after voltage increase;

[0011] The voltage across the second capacitor is the voltage after voltage reduction, and the on-off time duty cycle of the voltage reduction switch tube is used to adjust the voltage after voltage reduction;

[0012] The switching switch is connected to the voltage increase inductor at one end and connected to the voltage reduction inductor at the other end, and is used to control the switching between the voltage increase circuit and the voltage reduction circuit.

[0013] Further, the voltage increase sampling further comprises:

[0014] The first freewheeling diode is connected in series between the voltage increase inductor and the gate of the voltage reduction switch tube, and when the current in the circuit disappears, the loop composed of the first freewheeling diode and the voltage increase inductor absorbs the induced electromotive force generated by the voltage increase inductor.

[0015] Further, the voltage reduction sampling further comprises:

[0016] The second freewheeling diode is connected to the voltage reduction inductor, and when the current in the circuit disappears, the loop composed of the second freewheeling diode and the voltage reduction inductor absorbs the induced electromotive force generated by the voltage reduction inductor.

[0017] Further, it further comprises:

[0018] The filter circuit is used for filtering the input alternating current power supply.

[0019] Further, it further comprises:

[0020] The rectifier circuit is used for rectifying the alternating current power supply after filtering to output a direct current voltage.

[0021] In a second aspect, the application provides a voltage increase and reduction switching control method, which is suitable for the voltage increase and reduction switching circuit as described in the first aspect, and comprises:

[0022] Obtaining the first voltage value corresponding to the connection point between the first voltage increase voltage dividing element and the second voltage increase voltage dividing element, and the second voltage value corresponding to the connection point between the first voltage reduction voltage dividing element and the second voltage reduction voltage dividing element;

[0023] The on-off time duty cycle of the boost switch tube and / or the on-off time duty cycle of the buck switch tube is controlled according to the first voltage value and the second voltage value, so that the current variation value corresponding to the switching of the switching switch before and after the switching of the boost circuit and the buck circuit is less than a preset arc generation threshold.

[0024] Further, when the buck circuit is switched to the boost circuit, the method comprises:

[0025] The on-off time duty cycle of the buck switch tube is increased, so that the second voltage value gradually increases;

[0026] When the difference between the first voltage value and the second voltage value is less than a preset voltage difference threshold, the buck switch tube is controlled to be turned on;

[0027] When the first voltage value is equal to the second voltage value, the switching switch is controlled to be attracted;

[0028] After the switching switch is attracted, the buck switch tube is controlled to be turned off.

[0029] Further, after the buck switch tube is turned off, the method further comprises:

[0030] The on-off time duty cycle of the boost switch tube is controlled to output the target voltage.

[0031] Further, when the boost circuit is switched to the buck circuit, the method comprises:

[0032] The buck switch tube is controlled to be turned on;

[0033] After the on time of the buck switch tube meets the switching tube action time requirement, the switching switch is controlled to be turned off.

[0034] Further, after the off time of the switching switch meets the switching switch action time requirement, the method further comprises:

[0035] The on-off time duty cycle of the buck switch tube is controlled to output the target voltage.

[0036] In a third aspect, the application provides a boost-buck converter, comprising:

[0037] The boost-buck switching circuit according to the first aspect.

[0038] In a fourth aspect, the application provides an electrical appliance, comprising:

[0039] The boost-buck converter according to the third aspect.

[0040] The technical scheme provided by the embodiments of the application can have the following beneficial effects:

[0041] The application provides a boost-buck switching circuit, a switching control method, a boost-buck converter and an electrical appliance.

[0042] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory and are not restrictive of the application. BRIEF DESCRIPTION OF DRAWINGS

[0043] The accompanying drawings incorporated herein and forming a part of the specification illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0044] Figure 1 A circuit diagram of a boost-buck switching circuit provided for an embodiment of the application.

[0045] Figure 2 A flowchart of a boost-buck switching control method provided for an embodiment of the application.

[0046] Figure 3 A flowchart of another boost-buck switching control method provided for an embodiment of the application.

[0047] Figure 4A flowchart of another boost-buck switching control method is provided for an embodiment of the present application. DETAILED DESCRIPTION

[0048] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0049] Figure 1 A functional structure diagram of a boost-buck switching circuit is provided for an embodiment of the present application, as shown in the figure, the boost-buck switching circuit comprises: Figure 1

[0050] a boost circuit, a buck circuit, a switching switch 111, a boost sampling circuit and a buck sampling circuit;

[0051] The boost sampling circuit comprises a first capacitor 101, a first boost voltage dividing element 102 and a second boost voltage dividing element 103, the first boost voltage dividing element 101 and the second boost voltage dividing element 102 are connected in series and then connected in parallel with the first capacitor 101;

[0052] The first boost voltage dividing element 101 and the second boost voltage dividing element 102 are, for example, inductance elements;

[0053] The buck sampling circuit comprises a second capacitor 104, a first buck voltage dividing element 105 and a second buck voltage dividing element 106, the first buck voltage dividing element 105 and the second buck voltage dividing element 106 are connected in series and then connected in parallel with the second capacitor 104;

[0054] The first buck voltage dividing element 105 and the second buck voltage dividing element 106 are, for example, inductance elements;

[0055] The boost circuit comprises a boost switch tube 107 and a boost inductor 108, the gate of the boost switch tube 107 is connected to a connection point between the first boost voltage dividing element 102 and the second boost voltage dividing element 103, and the boost inductor 108 is connected in series with the first capacitor 101;

[0056] The boost circuit completes the boost operation through the boost switch tube 107 and the boost inductor 108, so that the output voltage is a preset target voltage value;

[0057] The buck circuit comprises a buck switch tube 109 and a buck inductor 110, the gate of the buck switch tube 109 is connected to the boost inductor 108, the drain of the buck switch tube 109 is connected to a connection point between the first buck voltage dividing element 105 and the second buck voltage dividing element 106, and the output end of the buck inductor 110 is connected in series with the second capacitor 104.​

[0058] The voltage reduction circuit completes the voltage reduction operation through the voltage reduction switch tube 109 and the voltage reduction inductor 110, so that the output voltage is a preset target voltage value.

[0059] The voltage across the first capacitor 101 is the voltage after voltage increase, and the on-off time duty cycle of the voltage increase switch tube 107 is used to adjust the voltage after voltage increase.

[0060] The voltage across the second capacitor 104 is the voltage after voltage reduction, and the on-off time duty cycle of the voltage reduction switch tube 109 is used to adjust the voltage after voltage reduction.

[0061] The switching switch 111 is connected to the voltage increase inductor 108 at one end and to the voltage reduction inductor 110 at the other end, and is used to control the switching between the voltage increase circuit and the voltage reduction circuit.

[0062] As shown in Figure 1 , the voltage increase sampling further includes:

[0063] The first freewheeling diode 112 is connected in series between the voltage increase inductor 108 and the gate of the voltage reduction switch tube 109, and when the current in the circuit disappears, the loop composed of the first freewheeling diode 112 and the voltage increase inductor 108 absorbs the induced electromotive force generated by the voltage increase inductor 108.

[0064] The first freewheeling diode 112 is used to freewheel when the current in the circuit disappears to protect other elements in the circuit.

[0065] The voltage reduction sampling further includes:

[0066] The second freewheeling diode 113 is connected to the voltage reduction inductor 110, and when the current in the circuit disappears, the loop composed of the second freewheeling diode 113 and the voltage reduction inductor 110 absorbs the induced electromotive force generated by the voltage reduction inductor 110.

[0067] The second freewheeling diode 113 is used to freewheel when the current in the circuit disappears to protect other elements in the circuit.

[0068] In this embodiment, the voltage increase and voltage reduction switching circuit further includes:

[0069] The filter circuit 114 is used to filter the input alternating current power supply.

[0070] The filter circuit 114 can realize the filtering of the input power supply, and only the required power supply signal is retained, providing a basis for subsequent voltage increase and voltage reduction processing.

[0071] The rectifier circuit 115 is used to rectify the filtered alternating current power supply and output a direct current voltage.

[0072] The user required DC voltage can be obtained through the rectifier circuit 115, and a basis for subsequent boost-buck processing is provided.

[0073] In the conventional boost-buck switching circuit, the switching of the boost-buck circuit is completed by a relay. However, before and after the switching, the current in the boost circuit and the current in the buck circuit are quite different, which can cause current overshoot during the switching of the circuit, and the relay contact can generate arc problem, affecting the normal use of the electrical appliance.

[0074] In this embodiment, the boost-buck switching circuit includes a boost circuit, a buck circuit, a switching switch, a boost sampling circuit and a buck sampling circuit. The boost sampling circuit includes a first capacitor, a first boost voltage dividing element and a second boost voltage dividing element, the first boost voltage dividing element and the second boost voltage dividing element are connected in series and connected in parallel with the first capacitor. The buck sampling circuit includes a second capacitor, a first buck voltage dividing element and a second buck voltage dividing element, the first buck voltage dividing element and the second buck voltage dividing element are connected in series and connected in parallel with the second capacitor. The boost circuit includes a boost switch tube and a boost inductor, the gate of the boost switch tube is connected to the connection point between the first boost voltage dividing element and the second boost voltage dividing element, and the boost inductor is connected in series with the first capacitor. The buck circuit includes a buck switch tube and a buck inductor, the gate of the buck switch tube is connected to the boost inductor. The drain of the buck switch tube is connected to the connection point between the first buck voltage dividing element and the second buck voltage dividing element, and the buck inductor is connected in series with the second capacitor. The voltage across the first capacitor is the boosted voltage, and the on-off time duty cycle of the boost switch tube is used to adjust the size of the boosted voltage. The voltage across the second capacitor is the bucked voltage, and the on-off time duty cycle of the buck switch tube is used to adjust the bucked voltage. One end of the switching switch is connected to the buck inductor, and the other end is connected to the buck inductor, which is used to control the switching between the boost circuit and the buck circuit. By adjusting the on-off time duty cycle of the boost switch tube and the on-off time duty cycle of the buck switch tube, the voltage change value on the switching switch contact before and after the switching switch performs the switching action can be less than the preset arc generation threshold, which can prevent current overshoot during boost-buck switching and the switching switch from generating arc phenomenon.

[0075] Figure 2 The flow chart of the boost-buck switching control method provided by an embodiment of the present application is shown in Figure 2 As shown in the figure, the boost-buck switching control method is applicable to the boost-buck switching circuit described in the above embodiments, and includes the following steps.

[0076] S21: obtaining a first voltage value corresponding to the connection point between the first boost voltage dividing element and the second boost voltage dividing element, and a second voltage value corresponding to the connection point between the first buck voltage dividing element and the second buck voltage dividing element;

[0077] S22: control the on-off time duty cycle of the boost switch tube and / or the on-off time duty cycle of the buck switch tube according to the first voltage value and the second voltage value, so that the current variation value corresponding to the switching action of the switching switch before and after the boost circuit and the buck circuit is switched is less than the preset arc generation threshold.

[0078] The preset arc generation threshold is, for example, 1A. In the embodiment, the boost-buck switching control method can control the switching current to be within 1A during switching, so that current overshoot and arc generation can be avoided.

[0079] When the buck circuit is switched to the boost circuit, as shown in FIG. 2, the boost-buck switching control method includes the following steps. Figure 3

[0080] S31: increase the on-off time duty cycle of the buck switch tube, so that the second voltage value gradually increases.

[0081] S32: control the buck switch tube to be turned on when the difference between the first voltage value and the second voltage value is less than the preset voltage difference threshold.

[0082] S33: control the switching switch to be attracted when the first voltage value is equal to the second voltage value.

[0083] S34: control the buck switch tube to be turned off after the switching switch is attracted.

[0084] S35: control the on-off time duty cycle of the boost switch tube to output the target voltage.

[0085] The voltage in the circuit is increased before the buck circuit is switched to the boost circuit, so that the voltage on the contact of the switching switch before and after the switching switch is attracted can be stabilized, and arc generation can be avoided.

[0086] When the boost circuit is switched to the buck circuit, as shown in FIG. 3, the boost-buck switching control method includes the following steps. Figure 4

[0087] S41: control the buck switch tube to be turned on.

[0088] S42: control the switching switch to be turned off after the on time of the buck switch tube meets the switching tube action time requirement.

[0089] In some embodiments, the switching tube action time requirement ranges from 0.1S to 0.5S.

[0090] S43: control the on-off time duty cycle of the buck switch tube to output the target voltage after the off time of the switching switch meets the switching switch action time requirement.

[0091] In some embodiments, the switching switch action time requirement ranges from 0.5S to 1S.

[0092] ​​The control of the switch-on of the step-down switch tube is prior to the switch of the step-up circuit to the step-down circuit, the second voltage value in the step-down circuit is raised, and when the first voltage value and the second voltage value are equal, the switch action of the switch is controlled, so that the voltage on the contact of the switch is stable before and after the attraction of the switch, and arc is avoided.

[0093] In some embodiments, when the input power P1 (the range of P1 is 1000W-2000W) of the compressor of the electrical appliance is lower than the preset value A, the step-up switch tube does not act, and the voltage on the first capacitor is the voltage after the rectification of the mains. Meanwhile, the on-off time duty cycle of the step-down switch tube is controlled to realize the step-down output, and the voltage on the second capacitor is the voltage after the step-down.

[0094] When the input power P1 of the compressor is higher than the preset value A (the preset value can be adjusted according to the actual application), the step-up circuit is switched, the pressure difference between the first voltage value Vp1 corresponding to the connection point between the first step-up voltage dividing element and the second step-up voltage dividing element and the second voltage value Vp2 corresponding to the connection point between the first step-down voltage dividing element and the second step-down voltage dividing element is large, and the impedance between Vp1 and Vp2 is small, the unit is in the running state, and the direct disconnection of the relay will cause the arc phenomenon of the contact of the relay. When the relay is disconnected, the power supply loop of the bus capacitor is cut off, and the rear-end load continuously consumes electric energy, so that the bus voltage Vp2 on the capacitor is rapidly pulled down, and instability of the control is easily caused.

[0095] In the embodiment, the time sequence of the switch tube and the switch is controlled according to the switching mode and the bus voltage, so that the current overshoot during the step-up and step-down switching is prevented, and the arc phenomenon of the switch is prevented.

[0096] One embodiment of the present application provides a step-up and step-down converter, which comprises the step-up and step-down switching circuit as described in the above embodiments.

[0097] One embodiment of the present application provides an electrical appliance, which comprises the step-up and step-down converter as described in the above embodiments.

[0098] The on-off time duty cycle of the step-up switch tube and / or the on-off time duty cycle of the step-down switch tube is controlled according to the first voltage value and the second voltage value, so that the current change value corresponding to the switching action of the switch before and after the switch of the step-up circuit and the step-down circuit is less than the preset arc generation threshold value, the current overshoot during the step-up and step-down switching is prevented, the arc phenomenon of the switch is prevented, the step-up and step-down converter is protected, and the normal use of the electrical appliance is ensured.

[0099] It can be understood that the same or similar parts in the above embodiments can be mutually referred to, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0100] It should be noted that the terms "first", "second" and the like in the description of the application do not denote any particular importance, but are merely used to distinguish one element from another. In addition, in the description of the application, the meaning of "a plurality of" is at least two, unless otherwise specified.

[0101] Any process or method descriptions or descriptions of the flow diagrams in the present application can be understood as representing code modules, segments or portions of code which include one or more executable instructions for performing specific logic functions or steps in the process, and the various embodiments of the application include additional implementations in which the order of steps can differ from those shown or discussed, including a step can occur at about the same time as others or can be performed in reverse order or can be performed in reverse order depending upon the functionality involved. Such variations are within the scope of the application.

[0102] It should be understood that each of the portions of the present application can be implemented in hardware, software, firmware or a combination thereof. In the above-described embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, and as in another embodiment, it can be implemented by any one or a combination of the following technologies known in the art: discrete logic circuit with logic gate circuit for implementing logic functions on data signals, application specific integrated circuit with suitable combination logic gate circuit, programmable gate array (PGA), field programmable gate array (FPGA) and the like.

[0103] Those skilled in the art of the present technology can understand that all or part of the steps carried out by the above-mentioned embodiment method can be completed by a program instructing the relevant hardware, and the program can be stored in a computer readable storage medium, and the program includes one or a combination of the steps of the method embodiment when executed.

[0104] In addition, each functional unit in each embodiment of the present application can be integrated in one processing module, or each unit can be physically present separately, or two or more units can be integrated in one module. The above-mentioned integrated module can be realized in the form of hardware or in the form of software functional module. The integrated module, if realized in the form of software functional module and sold or used as an independent product, can also be stored in a computer readable storage medium.

[0105] The storage medium mentioned above can be a read-only memory, a magnetic disk or an optical disk, etc.

[0106] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples.

[0107] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary, and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

[0108] It should be noted that the present application is not limited to the above-mentioned best mode, and those skilled in the art can derive other various forms of products under the inspiration of the present application, but regardless of any changes in shape or structure, any technical solution having the same or similar technical solutions as the present application falls within the scope of the present application.

Claims

1. A buck-boost switching circuit, characterized in that, include: Boost circuit, buck circuit, switching switch, boost sampling circuit and buck sampling circuit; The boost sampling circuit includes a first capacitor, a first boost voltage divider element, and a second boost voltage divider element. The first boost voltage divider element and the second boost voltage divider element are connected in series and then connected in parallel with the first capacitor. The step-down sampling circuit includes a second capacitor, a first step-down voltage divider element, and a second step-down voltage divider element. The first step-down voltage divider element and the second step-down voltage divider element are connected in series and then connected in parallel with the second capacitor. The boost circuit includes a boost switching transistor and a boost inductor. The gate of the boost switching transistor is connected to the connection point between the first boost voltage divider element and the second boost voltage divider element. The boost inductor is connected in series with the first capacitor. The buck circuit includes a buck switching transistor and a buck inductor. The gate of the buck switching transistor is connected to the boost inductor. The drain of the buck switching transistor is connected to the connection point between the first buck voltage divider element and the second buck voltage divider element. The buck inductor is connected in series with the second capacitor. The voltage across the first capacitor is the boosted voltage, and the duty cycle of the boost switch is used to adjust the magnitude of the boosted voltage. The voltage across the second capacitor is the stepped-down voltage, and the duty cycle of the step-down switch is used to adjust the stepped-down voltage. One end of the switching switch is connected to the boost inductor and the other end is connected to the buck inductor, and is used to control the switching between the boost circuit and the buck circuit.

2. The buck-boost switching circuit according to claim 1, characterized in that, The boost sampling also includes: The first freewheeling diode is connected in series between the boost inductor and the gate of the buck switching transistor. When the current disappears in the circuit, the loop formed by the first freewheeling diode and the boost inductor absorbs the induced electromotive force generated by the boost inductor.

3. The buck-boost switching circuit according to claim 1, characterized in that, The reduced-pressure sampling also includes: The second freewheeling diode is connected to the step-down inductor. When the current disappears in the circuit, the loop formed by the second freewheeling diode and the step-down inductor absorbs the induced electromotive force generated by the step-down inductor.

4. The buck-boost switching circuit according to claim 1, characterized in that, Also includes: A filtering circuit is used to filter the input AC power supply.

5. The buck-boost switching circuit according to claim 4, characterized in that, Also includes: A rectifier circuit is used to rectify the filtered AC power supply and output a DC voltage.

6. A buck-boost switching control method, applicable to the buck-boost switching circuit as described in any one of claims 1 to 5, characterized in that, include: Obtain the first voltage value corresponding to the connection point between the first boost voltage divider element and the second boost voltage divider element, and the second voltage value corresponding to the connection point between the first buck voltage divider element and the second buck voltage divider element; The duty cycle of the boost switch and / or the duty cycle of the buck switch are controlled according to the first voltage value and the second voltage value, so that the current change value before and after the switching action of the switching switch between the boost circuit and the buck circuit is less than the preset arc generation threshold.

7. The buck-boost switching control method according to claim 6, characterized in that, When switching from a buck circuit to a boost circuit, the following applies: Increase the duty cycle of the buck switching transistor to gradually increase the second voltage value; When the difference between the first voltage value and the second voltage value is less than a preset voltage difference threshold, the buck switch is turned on. When the first voltage value is equal to the second voltage value, the control switch is activated; After the switching switch is engaged, the step-down switching transistor is disengaged.

8. The buck-boost switching control method according to claim 7, characterized in that, After the control step-down switch transistor is disconnected, it also includes: The duty cycle of the boost switch is controlled to output the target voltage.

9. The buck-boost switching control method according to claim 6, characterized in that, When switching from a boost circuit to a buck circuit, the following applies: Controls the conduction of the step-down switch transistor; After the conduction time of the step-down switching transistor meets the switching transistor's operating time requirement, the control switch is turned off.

10. The buck-boost switching control method according to claim 9, characterized in that, After the disconnection time of the changeover switch meets the changeover switch action time requirement, it also includes: The duty cycle of the buck converter is controlled to output the target voltage.

11. A buck-boost converter, characterized in that, include: The buck-boost switching circuit as described in any one of claims 1 to 5.

12. An electrical appliance, characterized in that, include: The buck-boost converter as described in claim 11.

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