CN219497058U

CN219497058U - Circuit for identifying USB interface function and electronic equipment

Info

Publication number: CN219497058U
Application number: CN202320696051.7U
Authority: CN
Inventors: 陈悦; 刘建仁; 向国祥; 胡凯
Original assignee: Shenzhen H&T Intelligent Control Co Ltd
Current assignee: Shenzhen H&T Intelligent Control Co Ltd
Priority date: 2023-03-27
Filing date: 2023-03-27
Publication date: 2023-08-08
Anticipated expiration: 2033-03-27

Abstract

The application discloses a circuit and electronic equipment of discernment USB interface function, discernment USB interface function's circuit includes. The switching device comprises a first switching branch, a second switching branch, a third switching branch and a controller. The first switch branch is conducted when the USB interface is connected with external equipment so as to output a first level signal. The first switching branch is disconnected when the USB interface is not connected with external equipment. The second switching branch is turned off when receiving the first level signal and turned on when the first switching branch is turned off to output the second level signal. The third switch branch is conducted when receiving the first level signal, and outputs a third level signal to the controller so that the controller determines the USB interface function as the first function. The third switching branch is opened when the first switching branch is opened, so that the controller determines that the USB interface function is the second function. Through the mode, the functions of the USB interface can be identified, so that the application scene applicable to the USB interface is increased, and the practicability is improved.

Description

Circuit for identifying USB interface function and electronic equipment

Technical Field

The present disclosure relates to the field of electronic circuits, and in particular, to a circuit for identifying a USB interface function and an electronic device.

Background

In the design of electronic products, the USB Type-a interface is often used, which is a common interface Type. The USB Type-a interface is typically provided with 4 electrical pins, a power pin, a ground pin, and two data transfer pins, respectively.

However, the identification of the operating mode of the USB Type-a interface cannot be achieved by the 4 pins of the USB Type-a interface. The working modes comprise a Host mode and a Device mode. In other words, for the USB Type-A interface, a fixed mode, such as a Host mode, is typically set. Only the function corresponding to the Host mode can be realized. And then lead to USB Type-A interface only to be applicable to partial application scenario, the practicality is relatively poor.

Disclosure of Invention

The application aims at providing a circuit and electronic equipment for identifying the function of a USB interface, and the function of the USB interface can be identified, so that the application scene applicable to the USB interface is increased, and the practicability is improved.

To achieve the above object, in a first aspect, the present application provides a circuit for identifying a USB interface function, including:

the first switching branch, the second switching branch, the third switching branch and the controller;

the first end of the first switch branch is connected with a power pin of a USB interface, the second end of the first switch branch, the first end of the second switch branch, the first end of the third switch branch and the second end of the third switch branch are all connected with a first power supply, and the second end of the second switch branch and the third end of the third switch branch are all connected with the controller;

the first switch branch is used for being conducted when the USB interface is connected with external equipment so as to output a first level signal, and the first level signal is respectively input into the second switch branch and the third switch branch;

the first switch branch is further used for being disconnected when the USB interface is not connected with the external device;

the second switch branch is used for being turned off when the first level signal is received, and is used for being turned on in response to the first power supply when the first switch branch is turned off so as to output a second level signal to the controller;

the third switch branch is used for being conducted when the first level signal is received, and outputting a third level signal to the controller based on the first power supply, so that the controller responds to the disconnection of the second switch branch and the third level signal to determine that the USB interface function is a first function;

the third switching branch is further configured to open when the first switching branch is open, such that the controller determines the USB interface function as a second function in response to the opening of the second level signal from the third switching branch.

In an optional manner, the circuit for identifying the USB interface function further includes a voltage dividing branch, a first current limiting branch, a second current limiting branch, and a pull-up branch;

the first end of the voltage division branch is connected with a power pin of the USB interface, the second end of the voltage division branch is connected with the first end of the first switch branch, the first end of the first current limit branch and the first end of the pull-up branch are both connected with the first power supply, the second end of the first current limit branch is respectively connected with the first end of the second current limit branch and the first end of the second switch branch, the second end of the second current limit branch is connected with the first end of the third switch branch, and the second end of the pull-up branch is connected with the second end of the third switch branch;

the voltage dividing branch circuit is used for dividing the voltage of the first power supply and outputting a first voltage when the USB interface is connected with the external equipment;

the first current limiting branch is used for limiting the input current of the second switch branch;

the second current limiting branch circuit is used for limiting the input power supply of the third switching branch circuit;

the pull-up branch is used for pulling up the level of the third end of the third switch branch to be high level based on the voltage drop of the first power supply when the third switch branch is conducted.

In an alternative manner, the first switching branch comprises a first switching tube;

the first end of the first switching tube is connected with the power supply pin of the USB interface, the second end of the first switching tube is grounded, and the third end of the first switching tube is connected with the first end of the second switching branch and the first end of the third switching branch respectively.

In an alternative way, the second switching branch comprises a second switching tube;

the first end of the second switching tube is respectively connected with the second end of the first switching branch and the first end of the third switching branch, the second end of the second switching tube is grounded, and the third end of the second switching tube is connected with the controller.

In an alternative way, the third switching leg comprises a third switching tube;

the first end of the third switching tube is connected with the second end of the first switching branch and the first end of the second switching branch respectively, the second end of the third switching tube is connected with the first power supply, and the third end of the third switching tube is connected with the controller.

In an alternative manner, the voltage dividing branch includes a first resistor and a second resistor;

the first resistor is connected with the second resistor in series, the non-series connection end of the first resistor is connected with the power pin of the USB interface, the connection point between the first resistor and the second resistor is connected with the first end of the first switch branch, and the non-series connection end of the second resistor is grounded.

In an alternative manner, the first current limiting branch includes a third resistor and a fourth resistor;

the third resistor is connected with the fourth resistor in series, the non-series connection end of the third resistor is connected with the first power supply, and the non-series connection end of the fourth resistor is connected with the first end of the second switch branch.

In an alternative manner, the second current limiting branch includes a fifth resistor;

the first end of the fifth resistor is connected with the second end of the first switch branch and the first end of the second switch branch respectively, and the second end of the fifth resistor is connected with the first end of the third switch branch.

In an alternative manner, the pull-up leg includes a sixth resistor;

the first end of the sixth resistor is connected with the first power supply, and the second end of the sixth resistor is connected with the second end of the third switch branch.

In a second aspect, the present application provides an electronic device comprising a USB interface and a circuit for identifying a USB interface function as described above;

the circuit for identifying the USB interface function is connected with the USB interface, and the circuit for identifying the USB interface function is used for identifying the function of the USB interface.

The beneficial effects of this application are: the circuit for identifying the USB interface function comprises a first switch branch, a second switch branch, a third switch branch and a controller. When the USB interface is connected with external equipment, the first switch branch is conducted and outputs a first level signal. The first level signal is input into the second switch branch and the third switch branch respectively. In one aspect, the second switching leg is opened upon receipt of the first level signal; on the other hand, the third switching branch is conducted when receiving the first level signal, and outputs a third level signal to the controller based on the first power supply. Then, when the second switching branch is disconnected, if the controller receives the third level signal, the controller determines that the USB interface function is the first function. When the USB interface is not connected with external equipment, the first switch branch is disconnected. At this time, the third switching leg is also opened. Meanwhile, the second switch branch is conducted in response to the first power supply and outputs a second level signal to the controller. Then, when the third switching branch is opened, if the controller receives the second level signal, the controller determines that the USB interface function is the second function. Thereby realizing the process of identifying the function of the USB interface. In addition, the first function and the second function can be respectively executed by two modes of the Device and the Host, so that in different application scenes, the corresponding functions can be executed based on different modes.

Drawings

One or more embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which the figures of the drawings are not to be taken in a limiting sense, unless otherwise indicated.

FIG. 1 is a schematic diagram of a circuit for identifying USB interface functions according to an embodiment of the present disclosure;

FIG. 2 is a schematic structural diagram of a USB interface according to an embodiment of the present disclosure;

FIG. 3 is a schematic diagram of a circuit for identifying USB interface functions according to another embodiment of the present disclosure;

fig. 4 is a schematic structural diagram of a circuit for identifying a USB interface function according to an embodiment of the present application.

Detailed Description

For the purposes of making the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a circuit 100 for identifying a USB interface function according to an embodiment of the present application. As shown in fig. 1, the circuit 100 for identifying a USB interface function includes a first switching leg 10, a second switching leg 20, a third switching leg 30, and a controller 40.

The first end of the first switch branch 10 is connected to the power pin of the USB interface 200, the second end of the first switch branch 10, the first end of the second switch branch 20, the first end of the third switch branch 30, and the second end of the third switch branch 30 are all connected to the first power V1, and the second end of the second switch branch 20 and the third end of the third switch branch 30 are all connected to the controller 40.

Specifically, the first switching branch 10 is configured to be turned on when the USB interface 200 is connected to an external device, so as to output a first level signal. The first level signal is input to the second switching branch 20 and the third switching branch 30, respectively. The first switching branch 10 is also used to disconnect when the USB interface 200 is not connected to an external device. The second switching branch 20 is configured to be turned off when receiving the first level signal, and to be turned on in response to the first power V1 when the first switching branch 10 is turned off, so as to output the second level signal to the controller 40. The third switch branch 30 is configured to be turned on when receiving the first level signal, and output a third level signal to the controller 40 based on the first power V1, so that the controller 40 determines the function of the USB interface 200 as the first function in response to the disconnection of the second switch branch 20 and the third level signal. The third switching branch 30 is further configured to be opened when the first switching branch 10 is opened, so that the controller 40 determines the function of the USB interface 200 as the second function in response to the opening of the second level signal from the third switching branch 30.

The external device is a device with a USB Type-A interface, such as a USB flash disk.

The controller 40 may employ a micro control unit (Microcontroller Unit, MCU) or a digital signal processing (Digital Signal Processing, DSP) controller, etc.

The first level signal, the second level signal and the third level signal may be the same or different.

In this embodiment, when the USB interface 200 is connected to an external device, the first switching leg 10 is turned on and outputs a first level signal. The first level signal is input to the second switching branch 20 and the third switching branch 30, respectively. Then, the second switching leg 20 is turned off and the third switching leg 30 is turned on. After the third switching branch 30 is turned on, the third switching branch 30 outputs a third level signal to the controller 40 based on the first power V1. Meanwhile, in this embodiment, the control logic preset in the controller 40 is that the controller 40 can determine that the function of the USB interface 200 is the first function once the third voltage level is received. That is, at this time, the controller 40 determines the function of the USB interface 200 as the first function.

When the USB interface is not connected to an external device, the first switching leg 10 is opened. At this time, the third switching leg 30 is also opened. Meanwhile, the second switching branch 20 is turned on in response to the first power V1, and outputs a second level signal to the controller 40. Then, when the third switching leg 30 is opened and the controller 40 receives the second level signal, the controller 40 determines the function of the USB interface 200 as the second function. In this embodiment, the control logic preset in the controller 40 determines that the function of the USB interface 200 is the second function once the controller 40 receives the second voltage level.

In summary, the process of identifying the functions of the USB interface 200 is implemented.

Referring to fig. 1 and fig. 2 together, one structure of a USB interface 200 is illustrated in fig. 2. The USB interface 200 of this embodiment is a USB Type-A interface. In the related art, the USB Type-a interface has 4 pins, which are a VCC pin (i.e., a power pin), a D-pin (a first data transmission pin), a d+ pin (i.e., a second data transmission pin), and a GND pin (i.e., a ground pin), respectively. The VCC pin is used for connecting a power supply; the D-pin and the D+ pin are used for transmitting data; the GND pin is used for grounding. The 4 pins cannot directly identify the working mode of the USB Type-A interface. In other words, for the USB Type-a interface, a fixed mode, such as a Host mode, is generally set, so that only a function corresponding to the Host mode can be implemented.

In order to implement the pattern recognition function in the related art, an additional pin is generally added to the USB Type-a interface. On the one hand, the added pins result in increased costs; on the other hand, the USB Type-a interface currently in the market is still 4 pins, and the pin adding method cannot be adopted for the USB Type-a interface, so that the pin adding method has a certain limitation.

For the purposes of the present application, first, the first function and the second function may be functions executed by two modes, namely, the Device mode and the Host mode, respectively, so that in different application scenarios, the corresponding functions may be executed based on different modes. Therefore, the purpose of being applicable to application scenes of two modes, namely Device and Host, is achieved, namely the application scene applicable to the USB interface 200 is increased, and the practicability is improved. Second, no extra pins are required to be added, and no cost increase is caused. In addition, the circuit 100 for identifying the USB interface function provided by the application can be suitable for USB Type-A interfaces with 4 pins, and has lower limitation, namely stronger practicability.

It will be appreciated that in the embodiment of the present application, the Host mode is a master mode, and the Device mode is a slave mode. When the circuit 100 for identifying a USB interface function in the embodiment of the present application executes the Host mode, the circuit 100 for identifying a USB interface function needs to turn off the program download function (corresponding to the second function in the embodiment of the present application). When the circuit 100 for identifying a USB interface function in the embodiment of the present application executes the Host mode, the circuit 100 for identifying a USB interface function needs to start a program downloading function (corresponding to the first function in the embodiment of the present application), so that an external device connected to the USB interface 200 downloads a program in the circuit 100 for identifying a USB interface function.

In one embodiment, as shown in fig. 3, the circuit 100 for identifying a USB interface function further includes a voltage dividing branch 50, a first current limiting branch 60, a second current limiting branch 70, and a pull-up branch 80.

The first end of the voltage-dividing branch 50 is connected to the power pin of the USB interface 200, the second end of the voltage-dividing branch 50 is connected to the first end of the first switch branch 10, the first end of the first current-limiting branch 60 and the first end of the pull-up branch 80 are both connected to the first power V1, the second end of the first current-limiting branch 60 is connected to the first end of the second current-limiting branch 70 and the first end of the second switch branch 20, the second end of the second current-limiting branch 70 is connected to the first end of the third switch branch 30, and the second end of the pull-up branch 80 is connected to the second end of the third switch branch 30.

Specifically, the voltage dividing branch 50 is configured to divide the voltage of the first power V1 and output the first voltage when the USB interface 200 is connected to an external device. By providing the voltage dividing branch 50, the voltage input to the first switching branch 10 can be made within the voltage range in which the first switching branch 10 is allowed to input, so as to protect the first switching branch 10.

The first current limiting branch 60 is used to limit the input current of the second switching branch 20. To prevent the second switching leg 20 from being damaged by excessive current input to the second switching leg 20.

The second current limiting branch 70 is used to limit the input power of the third switching branch 30. To prevent the third switching leg 30 from being damaged by excessive current input to the third switching leg 30.

The pull-up branch 80 is configured to pull up the level of the third terminal of the third switching branch 30 to a high level based on the voltage drop of the first power V1 when the third switching branch 30 is turned on. The high level is the level of the third level signal.

Referring to fig. 4, a circuit configuration of a circuit 100 for identifying a USB interface function is schematically shown in fig. 4.

In one embodiment, as shown in fig. 4, the first switching leg 10 includes a first switching tube Q1.

The first end of the first switching tube Q1 is connected to the power pin of the USB interface 200, the second end of the first switching tube Q1 is grounded to GND, and the third end of the first switching tube Q1 is connected to the first end of the second switching branch 20 and the first end of the third switching branch 30, respectively.

Specifically, when the USB interface 200 is connected to an external device, the power pin of the USB interface 200 is powered. The voltage on the power pin of the USB interface 200 acts on the first end of the first switching tube Q1 to turn on the first switching tube Q1. When the USB interface 200 is not connected to an external device, the power pin of the USB interface 200 is powered off. There is no voltage on the first terminal of the first switching tube Q1 and the first switching tube Q1 is turned off.

In this embodiment, the first switching transistor Q1 is taken as an NPN transistor as an example. The base electrode of the NPN triode is the first end of the first switching tube Q1, the emitter electrode of the NPN triode is the second end of the first switching tube Q1, and the collector electrode of the NPN triode is the third end of the first switching tube Q1.

In addition, the first switching transistor Q1 may be any controllable switch, such as an Insulated Gate Bipolar Transistor (IGBT) device, an Integrated Gate Commutated Thyristor (IGCT) device, a gate turn-off thyristor (GTO) device, a Silicon Controlled Rectifier (SCR) device, a junction gate field effect transistor (JFET) device, a MOS Controlled Thyristor (MCT) device, or the like.

In an embodiment, the second switching leg 20 includes a second switching tube Q2.

The first end of the second switching tube Q2 is connected to the second end of the first switching branch 10 and the first end of the third switching branch 30, the second end of the second switching tube Q2 is grounded GND, and the third end of the second switching tube Q2 is connected to the controller 40.

Specifically, when the first switching tube Q1 is turned on, the first end of the second switching tube Q2 is grounded GND through the first switching tube Q1. Corresponding to the first switch Q1 being turned on, a low level signal (i.e., corresponding to the first level signal in the embodiment of the present application) is input to the first end of the second switch Q2. At this time, the second switching tube Q2 is also turned off. The third terminal of the second switching tube Q2 is in a floating state. The floating state means that the detection of the level is indefinite, and it is possible to detect a high level and also a low level.

When the first switching tube Q1 is turned off, the first power V1 acts on the second switching tube Q2 to turn on the second switching tube Q2. The third terminal of the second switching tube Q2 is connected to the ground GND through the second switching tube Q2. The third terminal corresponding to the second switching tube Q2 outputs a low level signal (i.e., a second level signal in the embodiment of the present application) to the controller 40.

In this embodiment, the second switching transistor Q2 is taken as an NPN transistor. The base electrode of the NPN triode is the first end of the second switching tube Q2, the emitter electrode of the NPN triode is the second end of the second switching tube Q2, and the collector electrode of the NPN triode is the third end of the second switching tube Q2.

In addition, the second switching transistor Q2 may be any controllable switch, such as an Insulated Gate Bipolar Transistor (IGBT) device, an Integrated Gate Commutated Thyristor (IGCT) device, a gate turn-off thyristor (GTO) device, a Silicon Controlled Rectifier (SCR) device, a junction gate field effect transistor (JFET) device, a MOS Controlled Thyristor (MCT) device, or the like.

In an embodiment, the third switching leg 30 comprises a third switching tube Q3.

The first end of the third switching tube Q3 is connected to the second end of the first switching branch 10 and the first end of the second switching branch 20, the second end of the third switching tube Q3 is connected to the first power source V1, and the third end of the third switching tube Q3 is connected to the controller 40.

Specifically, when the first switching tube Q1 is turned on, the first end of the third switching tube Q3 is grounded GND through the first switching tube Q1. A low level signal (i.e., a first level signal corresponding to the embodiment of the present application) is input to the first terminal of the third switching tube Q3 corresponding to the first switching tube Q1. The third switching transistor Q3 is turned on. The first power source V1 is connected to the controller 40 through a third switching tube Q3, and a high level signal (i.e., a third level signal corresponding to the embodiment of the present application) is input to the controller 40 corresponding to a third terminal of the third switching tube Q3.

When the first switching tube Q1 is turned off, the third switching tube Q3 is also turned off. The third end of the third switching tube Q3 is in a floating state.

In this embodiment, the third switching transistor Q3 is a PNP transistor. The base electrode of the PNP triode is the first end of the third switching tube Q3, the emitter electrode of the PNP triode is the second end of the third switching tube Q3, and the collector electrode of the PNP triode is the third end of the third switching tube Q3.

In addition, the third switching transistor Q3 may be any controllable switch, such as an Insulated Gate Bipolar Transistor (IGBT) device, an Integrated Gate Commutated Thyristor (IGCT) device, a gate turn-off thyristor (GTO) device, a Silicon Controlled Rectifier (SCR) device, a junction gate field effect transistor (JFET) device, a MOS Controlled Thyristor (MCT) device, or the like.

In one embodiment, the voltage dividing branch 50 includes a first resistor R1 and a second resistor R2.

The first resistor R1 is connected in series with the second resistor R2, the non-series connection end of the first resistor R1 is connected with the power pin of the USB interface, the connection point between the first resistor R1 and the second resistor R2 is connected with the first end of the first switch branch 10, and the non-series connection end of the second resistor R2 is grounded GND.

Specifically, when the USB interface 200 is connected to an external device, the first resistor R1 and the second resistor R2 divide the voltage on the power pin of the USB interface 200, so that the voltage input to the first end of the first switching tube Q1 is within the voltage range that the first switching tube Q1 allows to input, thereby protecting the first switching tube Q1.

In an embodiment, the first current limiting branch 60 includes a third resistor R3 and a fourth resistor R4.

The third resistor R3 is connected in series with the fourth resistor R4, the non-series connection end of the third resistor R3 is connected to the first power source V1, and the non-series connection end of the fourth resistor R4 is connected to the first end of the second switching branch 20.

Specifically, the third resistor R3 and the fourth resistor R4 can limit the input current of the first end of the second switching tube Q2. To prevent the second switching tube Q2 from being damaged by excessive current input to the second switching tube Q2.

In one embodiment, the second current limiting branch 70 includes a fifth resistor R5.

The first end of the fifth resistor R5 is connected to the second end of the first switching leg 10 and the first end of the second switching leg 20, and the second end of the fifth resistor R5 is connected to the first end of the third switching leg 30.

Specifically, the fifth resistor R5 can limit the input current of the first terminal of the third switching transistor Q3. To prevent the third switching tube Q3 from being damaged by an excessive current inputted to the third switching tube Q3.

In one embodiment, pull-up leg 80 includes a sixth resistor R6.

The first end of the sixth resistor R6 is connected to the first power source V1, and the second end of the sixth resistor R6 is connected to the second end of the third switching leg 30.

Specifically, when the third switching transistor Q3 is turned on, the first power supply V1 pulls up the third terminal of the third switching transistor Q3 to a high level through the sixth resistor R6.

In summary, when the USB interface 200 is connected to an external device, the first switching tube Q1 and the third switching tube Q3 are turned on, and the second switching tube Q2 is turned off. At this time, the controller 40 may determine that the operation mode of the USB interface 200 is the Device mode, and turn on the program downloading function, i.e., the function of the USB interface 200 is the first function.

When the USB interface 200 is not connected to an external device, the first switching tube Q1 and the third switching tube Q3 are both turned off, and the second switching tube Q2 is turned on. At this time, the controller 40 may determine that the operation mode of the USB interface 200 is the Host mode, and turn off the program download function, i.e., the function of the USB interface 200 is the second function.

Therefore, the circuit 100 for identifying the USB interface function can be suitable for application scenarios of two modes, namely Device and Host, that is, compared with the related art, the application scenario suitable for the USB interface 200 is increased, and the practicability is improved.

In addition, it should be noted that, when the USB interface 200 is connected to an external device, the voltage of the power pin of the USB interface 200 may be greater than the operating voltage of the controller 40, and the level on the power pin of the USB interface 200 cannot be directly identified by the controller 40. Based on this, the embodiment of the present application sets the circuit 100 for identifying the USB interface function, so as to implement the process of identifying the level on the power pin of the USB interface 200, and further implement the process of identifying two modes, namely Device and Host.

The embodiment of the application also provides an electronic device, which includes a USB interface and the circuit 100 for identifying a USB interface function in any embodiment of the application.

The circuit 100 for identifying a USB interface function is connected to the USB interface, and the circuit 100 for identifying a USB interface function is used for identifying a USB interface function.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting thereof; the technical features of the above embodiments or in the different embodiments may also be combined under the idea of the present application, the steps may be implemented in any order, and there are many other variations of the different aspects of the present application as described above, which are not provided in details for the sake of brevity; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A circuit for identifying a USB interface function, comprising:

2. The circuit for identifying a USB interface function of claim 1, further comprising a voltage dividing leg, a first current limiting leg, a second current limiting leg, and a pull-up leg;

3. The circuit for identifying a USB interface function of claim 1, wherein the first switching leg includes a first switching tube;

4. The circuit for identifying a USB interface function of claim 1, wherein the second switching leg includes a second switching tube;

5. The circuit for identifying a USB interface function of claim 1, wherein the third switching leg includes a third switching tube;

6. The circuit for identifying a USB interface function of claim 2, wherein the voltage dividing branch includes a first resistor and a second resistor;

7. The circuit for identifying a USB interface function of claim 2, wherein the first current limiting branch includes a third resistor and a fourth resistor;

8. The circuit for identifying a USB interface function of claim 2, wherein the second current limiting branch includes a fifth resistor;

9. The circuit for identifying a USB interface function of claim 2, wherein the pull-up leg includes a sixth resistor;

10. An electronic device comprising a USB interface and a circuit for identifying a function of the USB interface as claimed in any one of claims 1 to 9;