Universal serial bus (USB) wall socket device for detecting alternating current input voltage and switching charging power

Abstract

The utility model relates to a universal serial bus (USB) wall socket device capable of detecting alternating current input voltage and switching charging power, which comprises a rectifying and filtering circuit, a switching power supply circuit, a synchronous rectifying and filtering circuit, a fast charging protocol adjusting circuit, an isolation feedback circuit, an input voltage detection circuit, a fast charging output interface circuit and a first transformer TR1, the switching power supply circuit is connected with the rectification filter circuit, the rectification filter circuit and the switching power supply circuit are both connected with the primary end of the first transformer TR1, the secondary end of the first transformer TR1 is connected with the synchronous rectification filter circuit, and the fast charging protocol adjusting circuit is connected with the synchronous rectification filter circuit. The isolation feedback circuit is connected with the fast charging protocol adjusting circuit. With the adoption of the USB wall socket device capable of detecting the alternating current input voltage and switching the charging power, the charging power can be switched by detecting the input voltage, so that the quick charging power supply can exert the optimal performance under different input voltages.

Description

Technical Field

[0001] This utility model relates to the field of USB fast charging technology, and more particularly to the field of fast charging power supply. Specifically, it refers to a USB wall socket device that can detect AC input voltage and switch charging power. Background Technology

[0002] In recent years, with the widespread adoption of smart devices (smartphones, tablets, IoT devices, etc.), charging demands have become increasingly diversified and frequent. Simultaneously, to extend user usage time, smart devices are increasingly larger in battery capacity. Furthermore, with the rapid development of fast charging power supply technology and fast charging protocols such as PD and QC, the power output of fast charging power supplies is becoming increasingly powerful, meeting the needs of fast charging for smart devices. However, higher power results in greater losses in the power semiconductors and magnetic components inside the power supply, leading to significant heat generation in the fast charging power supply. And because fast charging power sockets are limited by the size of the mounting box and have poor heat dissipation due to the wall mounting surface, the heat generation becomes even more severe when the power of the fast charging power supply increases.

[0003] To adapt to different input voltages in various regions around the world, fast charging power supplies typically need to support 100-240Vac AC input. At low input voltages, the input current is high, resulting in greater losses in power devices, transformers, and other components compared to high input voltages. This leads to significant heat generation and lower overall efficiency. Therefore, the maximum power rating of a fast charging power supply is often limited to the maximum power it can output at low input voltages, even though it can achieve higher power at high input voltages.

[0004] In summary, in the existing technology, fast charging power supplies cannot adjust the output charging power according to different input voltages, thus failing to achieve the best performance of the product. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a USB wall socket device that is simple in structure, has higher output power, and is widely applicable, enabling the detection of AC input voltage and switching of charging power.

[0006] To achieve the above objectives, the present invention provides a USB wall socket device for detecting AC input voltage and switching charging power as follows:

[0007] This USB wall socket device, which detects AC input voltage and switches charging power, is characterized by comprising a rectifier and filter circuit, a switching power supply circuit, a synchronous rectifier and filter circuit, a fast charging protocol adjustment circuit, an isolation feedback circuit, an input voltage detection circuit, a fast charging output interface circuit, and a first transformer TR1. The switching power supply circuit is connected to the rectifier and filter circuit, and both the rectifier and filter circuit and the switching power supply circuit are connected to the primary side of the first transformer TR1. The secondary side of the first transformer TR1 is connected to the synchronous rectifier and filter circuit. The fast charging protocol adjustment circuit is connected to the synchronous rectifier and filter circuit. The isolation feedback circuit is connected to the fast charging protocol adjustment circuit and is also connected to the switching power supply circuit. The input voltage detection circuit is connected to the secondary side of the first transformer TR1 and also to the fast charging protocol adjustment circuit. The fast charging output interface circuit is connected to both the synchronous rectifier and filter circuit and the fast charging protocol adjustment circuit.

[0008] Preferably, the rectifier and filter circuit receives the AC input voltage and rectifies and filters it to obtain a DC voltage V1. After the switching power supply circuit is turned on, the two ends of the primary terminal of the first transformer TR1 receive the DC voltage V1, and the secondary terminal of the first transformer TR1 synchronously senses the secondary voltage V2. The input voltage detection circuit converts the secondary voltage V2 into a detection voltage Vi. The fast charging protocol adjustment circuit receives the detection voltage Vi and determines the voltage value of the detection voltage Vi. If the voltage value of the detection voltage Vi is lower than a preset value, the power input voltage is low, and the fast charging protocol is set to the default power. If the voltage value of the detection voltage Vi is higher than the preset value, the power input voltage is high, and the fast charging protocol is set to high power.

[0009] Preferably, the device further includes a first polarized capacitor CE1, a first resistor R1, a second MOSFET Q2, a third resistor R3, and a second diode D2. The first polarized capacitor CE1 is connected to a rectifier-filter circuit, with its negative terminal grounded and its positive terminal connected to a first transformer TR1. The rectifier-filter circuit receives an AC input voltage and obtains a DC voltage across the first polarized capacitor CE1. One end of the first resistor R1 is connected to the first transformer TR1, and the other end is connected to a switching power supply circuit. The gate of the second MOSFET Q2 is connected to the switching power supply circuit, its source is connected to the primary terminal of the first transformer TR1, and its drain is connected to the third resistor R3, with the other end of the third resistor grounded. The positive terminal of the second diode D2 is connected to the switching power supply circuit, and its negative terminal is grounded.

[0010] Preferably, the device further includes a third MOSFET Q3, a second polarized capacitor CE2, and a first MOSFET Q1. The isolation feedback circuit includes a first optocoupler U1. The gate of the third MOSFET Q3 is connected to the synchronous rectification and filtering circuit. The source of the third MOSFET Q3 is connected to the secondary side of the first transformer TR1. The drain of the third MOSFET Q3 is connected to the fast charging protocol adjustment circuit. The second polarized capacitor CE2 is connected across the secondary side of the first transformer TR1, and the negative terminal of the second polarized capacitor CE2 is grounded. The first optocoupler U1 is connected between the fast charging protocol adjustment circuit and the switching power supply circuit. The gate of the first MOSFET Q1 is connected to the fast charging protocol adjustment circuit. The source of the first MOSFET Q1 is connected to the secondary side of the first transformer TR1. The drain of the first MOSFET Q1 is connected to the fast charging output interface circuit.

[0011] Preferably, the input voltage detection circuit includes a first diode D1, a second resistor R2, a fourth resistor R4, and a first capacitor C1. The anode of the first diode D1 is connected to the secondary side of the first transformer TR1, the cathode of the first diode D1 is connected to the second resistor R2, the fourth resistor R4 is connected to the second resistor R2, and the other end of the fourth resistor R4 is grounded. The two ends of the first capacitor C1 are connected to the two ends of the fourth resistor R4. The fast charging protocol adjustment circuit is connected at the midpoint between the second resistor R2 and the fourth resistor R4. The first diode D1 rectifies the secondary voltage V2 of the first transformer TR1, and the second resistor R2 and the fourth resistor R4 divide the secondary voltage V2 to obtain the detection voltage Vi.

[0012] This invention relates to a USB wall socket device that detects AC input voltage and switches charging power. By detecting the AC input voltage, it switches to a fast charging protocol, thereby adjusting the power output of the fast charging power supply. When used in areas with low input voltage, the fast charging power supply outputs its default power, meeting the fast charging needs of the device. When used in areas with high input voltage, the fast charging power supply switches to a higher output power, providing faster charging speeds and a better user experience. In summary, this invention detects the input voltage and switches the charging power accordingly, ensuring that the fast charging power supply performs optimally under different input voltage conditions. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the module of the USB wall socket device of this utility model that realizes the detection of AC input voltage and switching of charging power.

[0014] Figure 2 This is a schematic diagram of the circuit structure of the USB wall socket device of this utility model that detects AC input voltage and switches charging power.

[0015] Figure 3 This is a schematic diagram of the external structure of the USB wall socket device of this utility model that detects AC input voltage and switches charging power.

[0016] Figure 4 This is a schematic diagram of the internal structure of the USB wall socket device of this invention, which detects AC input voltage and switches charging power. Detailed Implementation

[0017] To more clearly describe the technical content of this utility model, the following description is provided in conjunction with specific embodiments.

[0018] This utility model discloses a USB wall socket device for detecting AC input voltage and switching charging power, comprising a rectifier and filter circuit, a switching power supply circuit, a synchronous rectifier and filter circuit, a fast charging protocol adjustment circuit, an isolation feedback circuit, an input voltage detection circuit, a fast charging output interface circuit, and a first transformer TR1. The switching power supply circuit is connected to the rectifier and filter circuit, and both the rectifier and filter circuit and the switching power supply circuit are connected to the primary terminal of the first transformer TR1. The secondary terminal of the first transformer TR1 is connected to the synchronous rectifier and filter circuit. The fast charging protocol adjustment circuit is connected to the synchronous rectifier and filter circuit. The isolation feedback circuit is connected to the fast charging protocol adjustment circuit and is also connected to the switching power supply circuit. The input voltage detection circuit is connected to the secondary terminal of the first transformer TR1 and also to the fast charging protocol adjustment circuit. The fast charging output interface circuit is connected to both the synchronous rectifier and filter circuit and the fast charging protocol adjustment circuit.

[0019] In a preferred embodiment of this utility model, the rectifier and filter circuit receives the AC input voltage and performs rectification and filtering to obtain a DC voltage V1. After the switching power supply circuit is turned on, the two ends of the primary terminal of the first transformer TR1 receive the DC voltage V1, and the secondary terminal of the first transformer TR1 synchronously senses the secondary voltage V2. The input voltage detection circuit converts the secondary voltage V2 into a detection voltage Vi. The fast charging protocol adjustment circuit receives the detection voltage Vi and determines the voltage value of the detection voltage Vi. If the voltage value of the detection voltage Vi is lower than a preset value, the power input voltage is low, and the fast charging protocol is set to the default power. If the voltage value of the detection voltage Vi is higher than the preset value, the power input voltage is high, and the fast charging protocol is set to high power.

[0020] In a preferred embodiment of this utility model, the device further includes a first polarized capacitor CE1, a first resistor R1, a second MOSFET Q2, a third resistor R3, and a second diode D2. The first polarized capacitor CE1 is connected to a rectifier-filter circuit, with its negative terminal grounded and its positive terminal connected to a first transformer TR1. The rectifier-filter circuit receives an AC input voltage and obtains a DC voltage across the first polarized capacitor CE1. One end of the first resistor R1 is connected to the first transformer TR1, and the other end is connected to a switching power supply circuit. The gate of the second MOSFET Q2 is connected to the switching power supply circuit, its source is connected to the primary terminal of the first transformer TR1, and its drain is connected to the third resistor R3, with the other end of the third resistor R3 grounded. The positive terminal of the second diode D2 is connected to the switching power supply circuit, and its negative terminal is grounded.

[0021] In a preferred embodiment of this utility model, the device further includes a third MOSFET Q3, a second polarized capacitor CE2, and a first MOSFET Q1. The isolation feedback circuit includes a first optocoupler U1. The gate of the third MOSFET Q3 is connected to the synchronous rectification and filtering circuit, the source of the third MOSFET Q3 is connected to the secondary side of the first transformer TR1, and the drain of the third MOSFET Q3 is connected to the fast charging protocol adjustment circuit. The second polarized capacitor CE2 is connected across the secondary side of the first transformer TR1, and the negative terminal of the second polarized capacitor CE2 is grounded. The first optocoupler U1 is connected between the fast charging protocol adjustment circuit and the switching power supply circuit. The gate of the first MOSFET Q1 is connected to the fast charging protocol adjustment circuit, the source of the first MOSFET Q1 is connected to the secondary side of the first transformer TR1, and the drain of the first MOSFET Q1 is connected to the fast charging output interface circuit.

[0022] In a preferred embodiment of this utility model, the input voltage detection circuit includes a first diode D1, a second resistor R2, a fourth resistor R4, and a first capacitor C1. The positive terminal of the first diode D1 is connected to the secondary terminal of the first transformer TR1, the negative terminal of the first diode D1 is connected to the second resistor R2, the fourth resistor R4 is connected to the second resistor R2, and the other end of the fourth resistor R4 is grounded. The two ends of the first capacitor C1 are connected to the two ends of the fourth resistor R4. The fast charging protocol adjustment circuit is connected at the midpoint between the second resistor R2 and the fourth resistor R4. The first diode D1 rectifies the secondary voltage V2 of the first transformer TR1, and the second resistor R2 and the fourth resistor R4 divide the secondary voltage V2 to obtain the detection voltage Vi.

[0023] This invention adjusts the power output of a fast charging power supply by detecting the AC input voltage and switching the fast charging protocol. The power supply is based on an 86-type chassis or similar USB fast charging power supply and employs an input voltage detection circuit to detect the input voltage of the fast charging power supply. When a low input voltage is detected, such as 110Vac, the fast charging protocol is set to the default power, and the maximum output power of the fast charging power supply is the default power. When a high input voltage is detected, such as 220Vac, the fast charging protocol is switched to a higher power, allowing the fast charging power supply to output greater power to charge devices.

[0024] This utility model includes several USB TYPE-C fast charging ports and USB TYPE-A fast charging ports. By detecting the AC input voltage of the fast charging power supply and switching the fast charging protocol, the power of the fast charging power supply can be adjusted, thereby enabling the fast charging power supply to output greater power when the input voltage is high.

[0025] like Figure 1 As shown, the AC input voltage is rectified and filtered by the rectifier and filter circuit to obtain a DC voltage. This DC voltage is connected to the switching power supply circuit, and after being converted into an output DC voltage by the switching power supply circuit and the synchronous rectifier and filter circuit, this voltage is controlled by the fast charging protocol adjustment circuit and the isolation feedback circuit. When the device end and the fast charging interface end are successfully connected according to the protocol, the switching power supply can output the output voltage and current required by the device end.

[0026] The AC input voltage detection circuit works as follows: After rectification and filtering, the input voltage is converted into a DC voltage V1. When the primary switching power supply circuit is turned on, the DC voltage V1 is applied across the primary winding of the transformer. According to the transformer's operating principle, the secondary winding will also synchronously induce a secondary voltage V2. If the primary-to-secondary turns ratio of the transformer is N, then V2 = V1 / N. The secondary voltage V2 is converted into a detection voltage Vi by the input voltage detection circuit, and Vi is connected to the fast charging protocol adjustment circuit.

[0027] When the AC input voltage changes, the rectified DC voltage V1 also changes accordingly, and the secondary voltage V2 changes proportionally to the DC voltage V1. The value Vi, resulting from the conversion of the secondary voltage V2 by the input voltage detection circuit, also changes. The fast charging protocol adjustment circuit detects the value of Vi. When it is lower than a preset value, the power input voltage is determined to be low, and the fast charging protocol is set to the default power. When Vi is detected to be higher than the preset value, the power input voltage is determined to be high, and the fast charging protocol is switched to high power, allowing the fast charging power supply to output greater power.

[0028] As described above, this utility model detects the input voltage and switches the maximum output power of the fast charging power supply, thereby enabling the fast charging power supply to output greater power when the input voltage is high, bringing a better charging experience to the device.

[0029] In a specific embodiment of this utility model, an AC-DC switching power supply is used as the main power supply architecture. The power output is a Type-C interface. The maximum power output of the power supply varies depending on the input voltage, as detailed below:

[0030] Input: 100-130Vac 50 / 60Hz; Output: 5V3A, 9V3A, 12V3A, 15V3A, 20V2.25A, maximum 45W;

[0031] Input: 200-240Vac 50 / 60Hz; Output: 5V3A, 9V3A, 12V3A, 15V3A, 20V3.25A, maximum 65W.

[0032] After the AC input is rectified and filtered, a DC voltage is obtained across the first polarity capacitor CE1. The switching power supply circuit is powered through the first resistor R1 and the second diode D2. The high-voltage side DC voltage is then used to power the secondary winding by controlling the switching of the second MOSFET Q2 and the transformation of the first transformer TR1.

[0033] To improve efficiency, this embodiment employs synchronous rectification in the secondary winding to achieve high efficiency and low temperature rise. This is achieved by a third MOSFET Q3 and a synchronous rectification and filtering circuit. After passing through the synchronous rectification and filtering circuit, an output DC voltage V+ is obtained at the second polarity capacitor CE2. This voltage is controlled by the fast charging protocol adjustment circuit and depends on the status of the connected fast charging device and the fast charging protocol. The fast charging protocol adjustment circuit feeds back the voltage across the second polarity capacitor CE2 to the switching power supply circuit in real time via the first optocoupler U1, achieving cyclic control. The fast charging protocol adjustment circuit controls the first MOSFET Q1. When device insertion and successful protocol connection are detected, the first MOSFET Q1 is turned on, outputting the DC voltage V+ to charge the device.

[0034] The first diode D1, the second resistor R2, the fourth resistor R4, and the first capacitor C1 together form the input voltage detection circuit. The first diode D1 rectifies the secondary voltage V2 of the second winding. The secondary voltage V2 of the second winding is then divided by the second resistor R2 and the fourth resistor R4 to obtain the detection voltage Vi. Vi is connected to the fast charging protocol adjustment circuit. The first capacitor C1 is a filter capacitor to prevent the Vi signal from being interfered with and causing false detection.

[0035] In this embodiment, the transformer turns ratio N is 6, the resistance of the second resistor R2 is 470KΩ, the resistance of the fourth resistor R4 is 15KΩ, the capacitance of the first capacitor C1 is 100nF, and the default output of the fast charging power supply is 5V. The input power detection and fast charging protocol switching are as follows:

[0036] When the input is 110Vac, the voltage across the first polarity capacitor CE1 after rectification and filtering is 155V DC. When the second MOSFET Q2 in the primary winding is turned on, this voltage is applied to the primary winding of the transformer, i.e., V1 = 155V. Based on the transformer turns ratio, the secondary winding voltage V2 can be calculated to be 25.8V. After the secondary voltage V2 is divided by the second resistor R2 and the fourth resistor R4, Vi is 0.8V. Similarly, when the input is 220Vac, Vi can be calculated to be 1.6V.

[0037] The fast charging protocol adjustment circuit sets the Vi detection threshold to 1.2V. When the value is below the threshold, the fast charging protocol power is set to a maximum of 45W; when the value is above the threshold, the fast charging protocol power is set to a maximum of 65W.

[0038] By employing the above method, the input voltage detection circuit detects different input voltages, thereby switching the maximum power of the fast charging protocol. At low input voltages, the fast charging power supply outputs its default power; at high input voltages, it can support higher output power, fully utilizing the optimal performance of the fast charging power supply at different input voltages.

[0039] For the specific implementation scheme of this embodiment, please refer to the relevant descriptions in the above embodiments, which will not be repeated here.

[0040] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0041] It should be noted that in the description of this utility model, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this utility model, unless otherwise stated, "a plurality of" means at least two.

[0042] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0043] This invention relates to a USB wall socket device that detects AC input voltage and switches charging power. By detecting the AC input voltage, it switches to a fast charging protocol, thereby adjusting the power output of the fast charging power supply. When used in areas with low input voltage, the fast charging power supply outputs its default power, meeting the fast charging needs of the device. When used in areas with high input voltage, the fast charging power supply switches to a higher output power, providing faster charging speeds and a better user experience. In summary, this invention detects the input voltage and switches the charging power accordingly, ensuring that the fast charging power supply performs optimally under different input voltage conditions.

[0044] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the specification and drawings should be considered illustrative rather than restrictive.

Claims

1. A USB wall socket device for detecting AC input voltage and switching charging power, characterized in that, The device includes a rectifier and filter circuit, a switching power supply circuit, a synchronous rectifier and filter circuit, a fast charging protocol adjustment circuit, an isolation feedback circuit, an input voltage detection circuit, a fast charging output interface circuit, and a first transformer TR1. The switching power supply circuit is connected to the rectifier and filter circuit, and both the rectifier and filter circuit and the switching power supply circuit are connected to the primary side of the first transformer TR1. The secondary side of the first transformer TR1 is connected to the synchronous rectifier and filter circuit. The fast charging protocol adjustment circuit is connected to the synchronous rectifier and filter circuit. The isolation feedback circuit is connected to the fast charging protocol adjustment circuit and is also connected to the switching power supply circuit. The input voltage detection circuit is connected to the secondary side of the first transformer TR1 and is also connected to the fast charging protocol adjustment circuit. The fast charging output interface circuit is connected to both the synchronous rectifier and filter circuit and the fast charging protocol adjustment circuit.

2. The USB wall socket device for detecting AC input voltage and switching charging power according to claim 1, characterized in that, The rectifier and filter circuit receives the AC input voltage and rectifies and filters it to obtain a DC voltage V1. After the switching power supply circuit is turned on, the two ends of the primary end of the first transformer TR1 receive the DC voltage V1, and the secondary end of the first transformer TR1 synchronously senses the secondary voltage V2. The input voltage detection circuit converts the secondary voltage V2 into a detection voltage Vi. The fast charging protocol adjustment circuit receives the detection voltage Vi and determines the voltage value of the detection voltage Vi. If the voltage value of the detection voltage Vi is lower than the preset value, the power input voltage is low, and the fast charging protocol is set to the default power. If the detected voltage Vi is higher than the preset value, the power input voltage is high and the fast charging protocol is high power.

3. The USB wall socket device for detecting AC input voltage and switching charging power according to claim 1, characterized in that, The device further includes a first polarized capacitor CE1, a first resistor R1, a second MOSFET Q2, a third resistor R3, and a second diode D2. The first polarized capacitor CE1 is connected to a rectifier and filter circuit, with its negative terminal grounded and its positive terminal connected to a first transformer TR1. The rectifier and filter circuit receives an AC input voltage and obtains a DC voltage across the first polarized capacitor CE1. One end of the first resistor R1 is connected to the first transformer TR1, and the other end is connected to a switching power supply circuit. The gate of the second MOSFET Q2 is connected to the switching power supply circuit, its source is connected to the primary terminal of the first transformer TR1, and its drain is connected to the third resistor R3, with the other end of the third resistor grounded. The positive terminal of the second diode D2 is connected to the switching power supply circuit, and its negative terminal is grounded.

4. The USB wall socket device for detecting AC input voltage and switching charging power according to claim 1, characterized in that, The device further includes a third MOSFET Q3, a second polarized capacitor CE2, and a first MOSFET Q1. The isolation feedback circuit includes a first optocoupler U1. The gate of the third MOSFET Q3 is connected to the synchronous rectification and filtering circuit. The source of the third MOSFET Q3 is connected to the secondary side of the first transformer TR1. The drain of the third MOSFET Q3 is connected to the fast charging protocol adjustment circuit. The second polarized capacitor CE2 is connected across the secondary side of the first transformer TR1, and the negative terminal of the second polarized capacitor CE2 is grounded. The first optocoupler U1 is connected between the fast charging protocol adjustment circuit and the switching power supply circuit. The gate of the first MOSFET Q1 is connected to the fast charging protocol adjustment circuit. The source of the first MOSFET Q1 is connected to the secondary side of the first transformer TR1. The drain of the first MOSFET Q1 is connected to the fast charging output interface circuit.

5. The USB wall socket device for detecting AC input voltage and switching charging power according to claim 1, characterized in that, The input voltage detection circuit includes a first diode D1, a second resistor R2, a fourth resistor R4, and a first capacitor C1. The positive terminal of the first diode D1 is connected to the secondary side of the first transformer TR1, and the negative terminal of the first diode D1 is connected to the second resistor R2. The fourth resistor R4 is connected to the second resistor R2, and the other end of the fourth resistor R4 is grounded. The two ends of the first capacitor C1 are connected to the two ends of the fourth resistor R4. The fast charging protocol adjustment circuit is connected at the midpoint between the second resistor R2 and the fourth resistor R4. The first diode D1 rectifies the secondary voltage V2 of the first transformer TR1, and the second resistor R2 and the fourth resistor R4 divide the secondary voltage V2 to obtain the detection voltage Vi.

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