USB plugging test circuit

Abstract

The invention discloses a USB plugging test circuit. The output end of a first charging and discharging unit is connected with the inverted input end of a first comparison unit, and the input end of the first charging and discharging unit is connected with the output end of the first comparison unit; the normal phase input end of the first comparison unit is connected with a first reference voltage; the output end of the second charging and discharging unit is connected with the inverted input end of the second comparison unit, and the input end is connected with the output end of the second comparison unit; the non-inverting input end of the second comparison unit is connected with a second reference voltage; the first charge-discharge unit and the second charge-discharge unit have the same charge-discharge duration; the output end of the first comparison unit is connected with the input end of the delay unit and is connected with a USB power switch enable signal; the output end of the delay unit is connected with the input end of the phase inverter; the output end of the phase inverter is connected with the output end of the second charging and discharging unit; and the output end of the second comparison unit is connected with the USB data switch enable signal. When the USB is accessed, a power supply is accessed firstly and then data is accessed; and the power supply and the data are switched off when being pulled out.

Description

Technical Field

[0001] The invention relates to the technical field of USB testing, in particular to a USB plug-in and pull-out testing circuit. Background Art

[0002] When a device with a USB interface communicates with an external device, it needs to communicate with different PC USB ports through the USB interface. During the communication process, it is necessary to confirm whether different PC ends can recognize the device normally and whether it can be recognized after multiple plug-ins and unplugs to ensure the compatibility of the device's USB communication.

[0003] Therefore, the existing USB interface test method is usually to check whether the device manager on the PC can normally identify the device by plugging and unplugging the USB port continuously. However, frequent plugging and unplugging of the USB port has low test efficiency, and constantly plugging and unplugging the USB port shortens the life of the USB port on the PC side of the partner. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a USB plug-in test circuit to improve the test efficiency without shortening the life of the USB port socket.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A USB plug-in test circuit, comprising: A first comparing unit, a first charging and discharging unit, a second comparing unit, a second charging and discharging unit, a delay unit and an inverter; The output end of the first charge and discharge unit is connected to the inverting input end of the first comparison unit, and the input end of the first charge and discharge unit is connected to the output end of the first comparison unit; the non-inverting input end of the first comparison unit is connected to a first reference voltage; The output end of the second charge and discharge unit is connected to the inverting input end of the second comparison unit, and the input end of the second charge and discharge unit is connected to the output end of the second comparison unit; the non-inverting input end of the second comparison unit is connected to the second reference voltage; The first charge-discharge unit and the second charge-discharge unit have the same charge-discharge duration; The output end of the first comparison unit is connected to the input end of the delay unit and is used to be connected to the USB power switch enable signal; The output end of the delay unit is connected to the input end of the inverter; The output end of the inverter is connected to the output end of the second charge and discharge unit; The output end of the second comparison unit is used to be connected to a USB data switch enable signal.

[0006] The beneficial effects of the present invention are as follows: the inverting voltage of the first comparison unit is adjusted by the first charge and discharge unit, and the inverting voltage of the second comparison unit is adjusted by the second charge and discharge unit, and the first comparison unit is connected to the second comparison unit through a delay unit and an inverter; the output end of the first comparison unit outputs a high level before the output end of the second comparison unit outputs a high level, and the output end of the first comparison unit outputs a low level before the output end of the second comparison unit outputs a low level, so that when the USB is connected, the power supply is connected first and then the data switch enable signal is connected; when the USB is unplugged, the power supply is disconnected first and then the data switch enable signal is disconnected, so as to realize the simulation of continuous plugging and unplugging of the USB and complete the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 Schematic diagram of the circuit structure of a USB plug-in test circuit in an embodiment of the present invention; Figure 2 A test application connection diagram of a USB plug-in test circuit in an embodiment of the present invention; Description of labels: 1. First charge and discharge unit; 11. Charge and discharge assembly; 12. Time adjustment assembly; 2. Second charge and discharge unit; 3. Delay unit; 4. Charge control unit; U1A, first comparison unit; U1B, second comparison unit; U2A, inverter; R1, first resistor; R2, second resistor; R3, third resistor; R4, fourth resistor; R5, fifth resistor; C1, first capacitor; C2, second capacitor; C3, third capacitor; S1, switch; Q1, first transistor; Q2, second transistor; D1, diode. DETAILED DESCRIPTION

[0008] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0009] A USB plug-in and unplug test circuit comprises: a first comparison unit, a first charge-discharge unit, a second comparison unit, a second charge-discharge unit, a delay unit and an inverter; the output end of the first charge-discharge unit is connected to the inverting input end of the first comparison unit, and the input end of the first charge-discharge unit is connected to the output end of the first comparison unit; the positive input end of the first comparison unit is connected to a first reference voltage; the output end of the second charge-discharge unit is connected to the inverting input end of the second comparison unit, and the input end of the second charge-discharge unit is connected to the output end of the second comparison unit; the positive input end of the second comparison unit is connected to a second reference voltage; the charge-discharge time lengths of the first charge-discharge unit and the second charge-discharge unit are the same; the output end of the first comparison unit is connected to the input end of the delay unit and is used to be connected to a USB power switch enable signal; the output end of the delay unit is connected to the input end of the inverter; the output end of the inverter is connected to the output end of the second charge-discharge unit; the output end of the second comparison unit is used to be connected to a USB data switch enable signal.

[0010] From the above description, it can be seen that the beneficial effects of the present invention are: the inverting voltage of the first comparison unit is adjusted by the first charge and discharge unit, and the inverting voltage of the second comparison unit is adjusted by the second charge and discharge unit, and the first comparison unit is connected to the second comparison unit through a delay unit and an inverter; so that the output end of the first comparison unit outputs a high level before the output end of the second comparison unit outputs a high level, and the output end of the first comparison unit outputs a low level before the output end of the second comparison unit outputs a low level, so that when the USB is connected, the power supply is connected first and then the data switch enable signal is connected; when the USB is unplugged, the power supply is disconnected first and then the data switch enable signal is disconnected, so as to realize the simulation of continuous plugging and unplugging of the USB and complete the test.

[0011] Furthermore, the first charge and discharge unit includes a charge and discharge component and a time adjustment component; the time adjustment component is respectively connected to the positive input end of the first comparison unit, the output end of the first comparison unit and the input end of the charge and discharge component; the output end of the charge and discharge component is connected to the negative input end of the first comparison unit.

[0012] From the above description, it can be seen that by setting a charging and discharging component and a time adjustment component, the charging and discharging function is realized by the charging and discharging component, and the charging and discharging time is adjusted by the time adjustment component, so that the charging and discharging time of the first charging and discharging unit can be the same as that of the second charging and discharging unit, thereby avoiding the problem that after multiple charges and discharges, the charging and discharging time of the first charging and discharging unit is different from that of the second charging and discharging unit and cannot be effectively tested.

[0013] Furthermore, the charging and discharging component includes a first resistor and a first capacitor; one end of the first resistor is respectively connected to one end of the first capacitor and the inverting input end of the first comparison unit; the other end of the first resistor is connected to the output end of the first comparison unit; and the other end of the first capacitor is grounded.

[0014] From the above description, it can be seen that the charging and discharging component is composed of the first resistor and the first capacitor, so that when discharging, the first capacitor is discharged through the first resistor, and when charging, the output end of the first comparison unit outputs a high level and charges the first capacitor through the first resistor.

[0015] Furthermore, the time adjustment component includes a second resistor, a third resistor and a fourth resistor; one end of the second resistor is used to connect to a power supply; the other end of the second resistor is respectively connected to one end of the third resistor, one end of the fourth resistor and the positive phase input end of the first comparison unit; the other end of the third resistor is connected to the output end of the first comparison unit; the other end of the fourth resistor is used to be grounded.

[0016] From the above description, it can be seen that by respectively setting the second resistor, the third resistor and the fourth resistor at the non-phase input terminal and the output terminal of the first comparison unit, the duration of the high level output by the first comparison unit can be adjusted, thereby achieving the effect of adjusting the charging and discharging time.

[0017] The second charging and discharging unit includes a charging and discharging component and a time adjustment component.

[0018] It can be seen from the above description that by providing a charge-discharge component and a time adjustment component, the charge-discharge component can realize the charge-discharge function, and the charge-discharge time can be adjusted by the time adjustment component.

[0019] Further, the delay unit includes a fifth resistor and a second capacitor; one end of the fifth resistor is connected to the output end of the first comparison unit; the other end of the fifth resistor is respectively connected to one end of the second capacitor and the input end of the inverter; the other end of the second capacitor is grounded.

[0020] It can be seen from the above description that the delay unit formed by the fifth resistor and the second capacitor can play an effective charging and discharging role.

[0021] Furthermore, it also includes a charging control unit; the power input terminal of the charging control unit is used to connect to the power supply; the charging control unit includes a first state and a second state; the first state connects the inverting input terminal of the first comparison unit and the inverting input terminal of the second comparison unit to the power supply; the second state disconnects the inverting input terminal of the first comparison unit and the inverting input terminal of the second comparison unit from the power supply.

[0022] It can be seen from the above description that by adding a charging control unit, the start and shut-down control of the first comparison unit and the second comparison unit can be achieved by adjusting the state of the charging control unit.

[0023] Further, the charging control unit includes a switch, a first transistor and a second transistor; one end of the switch is grounded, and the other end is respectively connected to the base of the first transistor and the base of the second transistor; the emitter of the first transistor and the emitter of the second transistor are respectively used to connect to a power supply; the collector of the first transistor is connected to the inverting input terminal of the first comparison unit; and the collector of the second transistor is connected to the inverting input terminal of the second comparison unit.

[0024] It can be seen from the above description that the control unit is composed of a switch, a first transistor and a second transistor, and the switching between the first state and the second state is realized based on the closed or open state of the switch. When the switch is closed, the first transistor and the second transistor are turned on, so that the inverting input terminal of the first comparison unit and the inverting input terminal of the second comparison unit are both high voltages, thereby outputting a low level, so that the USB power switch enable signal and the USB data switch enable signal are both disconnected; and when the switch is disconnected, the circuit works normally.

[0025] Furthermore, it also includes a diode; the anode of the diode is connected to the inverting input terminal of the second comparing unit, and the cathode of the diode is connected to the output terminal of the second comparing unit.

[0026] From the above description, it can be seen that by setting a diode between the inverting input terminal and the output terminal of the second comparison unit, the inverting voltage of the second comparison unit is clamped at a preset low level value when the inverter outputs a low level, so that the second comparison unit can stably output a high level.

[0027] Furthermore, it also includes a third capacitor; one end of the third capacitor is connected to the output end of the inverter; the other end of the third capacitor is connected to the inverting input end of the second comparing unit.

[0028] From the above description, it can be seen that by setting the third capacitor at the output end of the inverter, when the inverter outputs a low level, according to the principle that the voltage across the capacitor cannot change suddenly, the inverting input end of the second comparison unit is instantly input with a negative voltage, thereby causing the second comparison unit to output a high level.

[0029] The USB plug-in test circuit provided by the present invention can be applied to the scenario of USB plug-in test, which is described below through specific implementation methods: Embodiment 1 Please refer to Figure 1A USB plug-in test circuit includes: a first comparison unit U1A, a first charge-discharge unit 1, a second comparison unit U1B, a second charge-discharge unit 2, a delay unit 3 and an inverter U2A; wherein the first comparison unit U1A and the second comparison unit U1B can be implemented by using an LM258AD operational amplifier, or other operational amplifier devices of the same type. The output end of the first charge and discharge unit 1 is connected to the inverting input end of the first comparison unit U1A, and the input end of the first charge and discharge unit 1 is connected to the output end of the first comparison unit U1A; the positive input end of the first comparison unit U1A is connected to the first reference voltage (grounded through the fourth resistor as the first reference voltage); the output end of the second charge and discharge unit 2 is connected to the inverting input end of the second comparison unit U1B, and the input end of the second charge and discharge unit 2 is connected to the output end of the second comparison unit U1B; the positive input end of the second comparison unit U1B is connected to the second reference voltage (grounded through the resistor R6 as the second reference voltage); the charge and discharge time of the first charge and discharge unit 1 and the second charge and discharge unit 2 is the same; the output end of the first comparison unit U1A is connected to the input end of the delay unit 3, and is used to connect to the USB power switch enable signal (VBUS_en); the output end of the delay unit 3 is connected to the input end of the inverter U2A; the output end of the inverter U2A is connected to the output end of the second charge and discharge unit 2; the output end of the second comparison unit U1B is used to connect to the USB data switch enable signal (DM / DP_en). Specifically, the delay unit 3 includes a fifth resistor R5 and a second capacitor C2; one end of the fifth resistor R5 is connected to the output end of the first comparison unit U1A; the other end of the fifth resistor R5 is respectively connected to one end of the second capacitor C2 and the input end of the inverter U2A; the other end of the second capacitor C2 is grounded; and a third capacitor C3 is also provided at the output end of the inverter U2A; one end of the third capacitor C3 is connected to the output end of the inverter U2A; the other end of the third capacitor C3 is connected to the inverting input end of the second comparison unit U1B.

[0030] The first charge and discharge unit 1 includes a charge and discharge component 11 and a time adjustment component 12; the time adjustment component 12 is respectively connected to the positive input terminal of the first comparison unit U1A, the output terminal of the first comparison unit U1A and the input terminal of the charge and discharge component 11; the output terminal of the charge and discharge component 11 is connected to the negative input terminal of the first comparison unit U1A, specifically: The charge and discharge assembly 11 includes a first resistor R1 and a first capacitor C1; one end of the first resistor R1 is respectively connected to one end of the first capacitor C1 and the inverting input end of the first comparison unit U1A; the other end of the first resistor R1 is connected to the output end of the first comparison unit U1A; the other end of the first capacitor C1 is grounded.

[0031] The time adjustment component 12 includes a second resistor R2, a third resistor R3 and a fourth resistor R4; one end of the second resistor R2 is used to connect to the power supply (5.0V); the other end of the second resistor R2 is respectively connected to one end of the third resistor R3, one end of the fourth resistor R4 and the positive phase input end of the first comparison unit U1A; the other end of the third resistor R3 is connected to the output end of the first comparison unit U1A; the other end of the fourth resistor R4 is grounded. That is, the configuration of the high level duration of the output end of the first comparison unit U1A is adjusted by the first resistor R1, the first capacitor C1, the second resistor R2, the third resistor R3 and the fourth resistor R4.

[0032] Similarly, the second charge and discharge unit 2 also includes a charge and discharge component 11 and a time adjustment component 12; Figure 1 As shown, the resistor R6 and the resistor R10 form the time adjustment component 12 of the second charge and discharge unit 2, and the resistor R7 and the capacitor C4 form the charge and discharge component 11 of the second discharge unit; that is, the configuration of the high level duration of the output end of the second comparison unit U1B is adjusted by the resistor R6, the resistor R10, the resistor R7 and the capacitor C4; so that the high level duration of the output end of the first comparison unit U1A is close to the high level duration of the output end of the second comparison unit U1B. At the same time, a diode D1 is provided between the inverting input end and the output end of the second comparison unit U1B, the positive electrode of the diode D1 is connected to the inverting input end of the second comparison unit U1B, and the negative electrode of the diode D1 is connected to the output end of the second comparison unit U1B.

[0033] In an optional embodiment, the circuit is further provided with a charging control unit 4; the power input terminal of the charging control unit 4 is used to connect to the power supply (5.0V); the charging control unit 4 includes a first state and a second state; in the first state, the inverting input terminal of the first comparison unit U1A and the inverting input terminal of the second comparison unit U1B are connected to the power supply; the inverting input terminal of the first comparison unit U1A and the inverting input terminal of the second comparison unit U1B are disconnected from the power supply, and the specific circuit structure is as follows: The charging control unit 4 includes a switch S1, a first transistor Q1 and a second transistor Q2; one end of the switch S1 is grounded, and the other end is connected to the base of the first transistor Q1 and the base of the second transistor Q2 respectively; the emitter of the first transistor Q1 and the emitter of the second transistor Q2 are respectively used to connect to the power supply (5.0V); the collector of the first transistor Q1 is connected to the output end of the first charging and discharging unit 1 and the inverting input end of the first comparing unit U1A; the collector of the second transistor Q2 is connected to the output end of the second charging and discharging unit 2 and the inverting input end of the second comparing unit U1B.

[0034] Please refer to Figure 2, the above USB plug-in test circuit is used as a switch control circuit for USB plug-in test, connected to the USB end of the device under test and to the USB end of the PC partner respectively. The specific working principle is as follows: Among them, the output end of the first comparison unit U1A is connected to the enable signal (VBUS_en) of the USB power VBUS switch, and the high level is valid, that is, the high level makes the USB_VBUS of the device under test connected to the USB_VBUS of the PC partner machine; the output end of the second comparison unit U1B is connected to the USB data switch enable signal DM / DP switch enable signal (DM / DP_en), and the high level is valid, that is, the high level makes the USB data switch enable signal DM / DP of the device under test connected to the USB data switch enable signal DM / DP of the PC partner machine.

[0035] When the switch S1 is closed, the first transistor Q1 and the second transistor Q2 are in the on state; the 5V power supply acts on the inverting input terminals of the first comparison unit U1A and the second comparison unit U1B respectively through the first transistor Q1 and the second transistor Q2, so that the positive input voltage of the first comparison unit U1A and the second comparison unit U1B is lower than the inverting input voltage, so that the first comparison unit U1A and the second comparison unit U1B both output a low level, and at this time, the USB power supply and data switch enable signal of the device under test are disconnected from the USB of the PC partner.

[0036] When the test starts, the switch S1 is turned on, and the first transistor Q1 and the second transistor Q2 are in the cut-off state; the first capacitor C1 is discharged through the first resistor R1, that is, the voltage at the inverting input terminal of the first comparison unit U1A gradually decreases. When the inverting voltage of the first comparison unit U1A is lower than its positive voltage, the first comparison unit U1A outputs a high level, and the USB power supply of the device under test is connected to the USB of the matching machine.

[0037] Then, the second capacitor C2 is charged through the fifth resistor R5, so that the voltage of the second capacitor C2 rises to the high-level input threshold of the inverter U2A, so that the inverter U2A outputs a low level. According to the principle that the voltage across the capacitor cannot change suddenly, the inverting input terminal of the second comparison unit U1B is instantly input with a negative voltage, and the positive electrode of the diode D1 is 0V at this time. Through the clamping of the diode D1, the inverting voltage of the second comparison unit U1B is clamped at about -0.7V. At this time, the positive voltage of the second comparison unit U1B is greater than the inverting voltage, so the output terminal of the second comparison unit U1B outputs a high level, and the USB data switch enable signal DM / DP of the device under test is connected to the USB data switch enable signal DM / DP of the matching machine. The simulation of USB insertion into the PC is realized, first connecting the power supply VBUS, and then connecting the data switch enable signal DM / DP.

[0038] Thereafter, the output end of the first comparison unit U1A outputs a high level to charge the first capacitor C1 through the first resistor R1. When the inverting voltage of the first comparison unit U1A is higher than its positive voltage, the first comparison unit U1A outputs a low level, and the USB power supply of the device under test is disconnected from the USB of the matching machine.

[0039] Similarly, the output end of the second comparison unit U1B outputs a high level to charge the capacitor C4 through the resistor R7. When the reverse voltage of the second comparison unit U1B is higher than its positive voltage, the second comparison unit U1B outputs a low level, and the USB data switch enable signal DM / DP of the device under test is disconnected from the USB data switch enable signal DM / DP of the matching machine.

[0040] Since the time when the output terminal of the first comparison unit U1A outputs a high level is nearly the same as the time when the output terminal of the second comparison unit U1B outputs a high level, and the output terminal of the first comparison unit U1A outputs a high level in advance of the output terminal of the second comparison unit U1B, the second comparison unit U1B will delay the output terminal of the first comparison unit U1A to output a low level. This achieves the simulation of unplugging the USB from the PC, first disconnecting the power supply VBUS, and then disconnecting the data switch enable signal DM / DP.

[0041] Subsequently, the first comparison unit U1A and the second comparison unit U1B repeat the above charge and discharge cycle to simulate the continuous plugging and unplugging of the USB into the PC. The above process is implemented based on the circuit without software intervention, which improves the test efficiency without shortening the life of the USB port socket on the PC end.

[0042] In summary, the USB plug-in test circuit provided by the present invention adjusts the inverting voltage of the first comparison unit through the first charge-discharge unit, and adjusts the inverting voltage of the second comparison unit through the second charge-discharge unit, and the first comparison unit is connected to the second comparison unit through a delay circuit and an inverter; so that the output end of the first comparison unit outputs a high level before the output end of the second comparison unit outputs a high level, and the output end of the first comparison unit outputs a low level before the output end of the second comparison unit outputs a low level, so that when the USB is connected, the power supply is connected first and then the data switch enable signal is connected; when the USB is unplugged, the power supply is disconnected first and then the data switch enable signal is disconnected, so as to simulate the continuous plug-in and unplugging of the USB and complete the test. The test process does not require manual multiple plug-ins and unplugs, and USB compatibility testing can be performed, which improves work efficiency and does not shorten the life of the USB port socket on the PC end of the matching machine. At the same time, the USB plug-in test is realized based on the circuit structure without the need for software intervention.

[0043] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A USB plug-in test circuit, characterized in that: include: A first comparing unit, a first charging and discharging unit, a second comparing unit, a second charging and discharging unit, a delay unit and an inverter; The output end of the first charge and discharge unit is connected to the inverting input end of the first comparison unit, and the input end of the first charge and discharge unit is connected to the output end of the first comparison unit; the non-inverting input end of the first comparison unit is connected to a first reference voltage; The output end of the second charge and discharge unit is connected to the inverting input end of the second comparison unit, and the input end of the second charge and discharge unit is connected to the output end of the second comparison unit; the non-inverting input end of the second comparison unit is connected to the second reference voltage; The first charge-discharge unit and the second charge-discharge unit have the same charge-discharge duration; The output end of the first comparison unit is connected to the input end of the delay unit and is used to be connected to the USB power switch enable signal; The output end of the delay unit is connected to the input end of the inverter; The output end of the inverter is connected to the output end of the second charge and discharge unit; The output end of the second comparison unit is used to be connected to a USB data switch enable signal.

2. A USB plug-in test circuit according to claim 1, characterized in that: The first charging and discharging unit includes a charging and discharging component and a time adjustment component; The time adjustment component is respectively connected to the positive phase input terminal of the first comparison unit, the output terminal of the first comparison unit and the input terminal of the charge and discharge component; The output end of the charging and discharging component is connected to the inverting input end of the first comparing unit.

3. A USB plug-in test circuit according to claim 2, characterized in that: The charging and discharging assembly includes a first resistor and a first capacitor; One end of the first resistor is connected to one end of the first capacitor and the inverting input end of the first comparison unit respectively; The other end of the first resistor is connected to the output end of the first comparison unit; The other end of the first capacitor is grounded.

4. A USB plug-in test circuit according to claim 2, characterized in that: The time adjustment component includes a second resistor, a third resistor and a fourth resistor; One end of the second resistor is used to be connected to a power source; The other end of the second resistor is respectively connected to one end of the third resistor, one end of the fourth resistor and the non-inverting input end of the first comparison unit; The other end of the third resistor is connected to the output end of the first comparison unit; The other end of the fourth resistor is grounded.

5. A USB plug-in test circuit according to claim 2, 3 or 4, characterized in that: The second charging and discharging unit includes a charging and discharging component and a time adjustment component.

6. A USB plug-in test circuit according to claim 1, characterized in that: The delay unit includes a fifth resistor and a second capacitor; One end of the fifth resistor is connected to the output end of the first comparison unit; The other end of the fifth resistor is connected to one end of the second capacitor and the input end of the inverter respectively; The other end of the second capacitor is grounded.

7. A USB plug-in test circuit according to claim 1, characterized in that: Also included is a charging control unit; The power input terminal of the charging control unit is used to connect to a power source; The charging control unit includes a first state and a second state; The first state connects the inverting input terminal of the first comparison unit and the inverting input terminal of the second comparison unit to the power supply; The second state disconnects the inverting input terminal of the first comparison unit and the inverting input terminal of the second comparison unit from a power supply.

8. A USB plug-in test circuit according to claim 7, characterized in that: The charging control unit includes a switch, a first transistor and a second transistor; One end of the switch is grounded, and the other end is connected to the base of the first transistor and the base of the second transistor respectively; The emitter of the first triode and the emitter of the second triode are respectively used to be connected to a power source; The collector of the first transistor is connected to the inverting input terminal of the first comparison unit; The collector of the second transistor is connected to the inverting input terminal of the second comparing unit.

9. A USB plug-in test circuit according to claim 1, characterized in that: Also includes diodes; An anode of the diode is connected to an inverting input terminal of the second comparing unit, and a cathode of the diode is connected to an output terminal of the second comparing unit.

10. A USB plug-in test circuit according to claim 1, characterized in that: Also including a third capacitor; One end of the third capacitor is connected to the output end of the inverter; The other end of the third capacitor is connected to the inverting input end of the second comparing unit.

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