Charging device and power transmission method

Abstract

A charging device includes a first connector, a second connector and a control circuit. The first connector has a first detection resistor. When the first connector is connected to an electric vehicle through the first detection resistor, the first connector receives a first supply power. The second connector has a second detection resistor. The control circuit is respectively coupled to the first connector and the second connector, and is driven by the first supply power. The control circuit is configured to supply power to an external device with the first supply power, or transmits a communication signal to the electric vehicle to obtain a second supply power from the electric vehicle according to a cross voltage of the second detection resistor. The voltage of the first supply power is different from the voltage of the second supply power.

Description

Technical Field

[0001] This disclosure relates to power transmission technology, and in particular to a charging device and a power transmission method. Prior Technology

[0002] In recent years, with the increasing awareness of environmental protection, the development of electric vehicles has received more and more attention. To make the use of electric vehicles more widespread, the "charging devices" used by electric vehicles are crucial. Therefore, how to improve the convenience, application flexibility, and usability of charging devices has become a major issue. Summary of the Invention

[0003] This disclosure relates to a charging device, comprising a first connector, a second connector, and a control circuit. The first connector has a first sensing resistor. When the first connector is connected to an electric vehicle through the first sensing resistor, the first connector receives a first power supply. The second connector has a second sensing resistor. The control circuit is coupled to both the first and second connectors and is driven by the first power supply. The control circuit is used to supply power to an external device using the first power supply, or to transmit a communication signal to the electric vehicle to obtain a second power supply from the electric vehicle, based on the voltage across the second sensing resistor. The voltage of the first power supply is different from the voltage of the second power supply.

[0004] This disclosure also relates to a power transmission method, comprising: when a charging device is connected to an electric vehicle through a first sensing resistor, receiving a first supplied power from the electric vehicle; using the first supplied power to drive a controller in the charging device; determining the voltage across a second sensing resistor of the charging device through the controller; and selectively using the first supplied power to supply power to an external device or obtaining a second supplied power from the electric vehicle based on the voltage across the second sensing resistor, wherein the voltage of the first supplied power is different from the voltage of the second supplied power.

[0005] This disclosure also relates to a charging device, comprising a first connector and a control circuit. The first connector has a first detection resistor. When the first connector is connected to an electric vehicle through the first detection resistor, the first connector receives power supplied from the electric vehicle. The control circuit is coupled to the first connector and is driven using the supplied power. When the charging device is connected to an external device and receives a detection signal, the control circuit supplies power to the external device according to the supplied power and selectively provides communication signals to the electric vehicle to cause the electric vehicle to change the voltage of the supplied power.

[0006] The charging device and power transmission method disclosed herein can obtain the corresponding voltage power supply from the electric vehicle according to different types / specifications of external devices. In addition, the charging device can also be driven by the power supply provided by the electric vehicle and selectively provide communication signals to the electric vehicle. Simple Explanation of the Diagram

[0007] Figure 1 is a schematic diagram of a charging device and an electric vehicle using it, according to some embodiments of the present disclosure. Figure 2 is a schematic diagram of a charging device according to some embodiments of the present disclosure. Figure 3 is a flowchart of a power transmission method according to some embodiments of the present disclosure. Figure 4A is a schematic diagram of the operation of a charging device according to some embodiments of the present disclosure. Figures 4B-4C are schematic diagrams illustrating the operation of a charging device according to some embodiments of the present disclosure. Figure 5 is a signal waveform diagram of a charging device according to some embodiments of the present disclosure. Implementation

[0008] The following drawings disclose several embodiments of the present invention. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the invention. That is, in some embodiments of the invention, these practical details are not essential. Furthermore, for the sake of simplicity, some conventional structures and elements will be shown in the drawings in a simple schematic manner.

[0009] In this document, when an element is referred to as a "connection" or "coupled," it may mean an "electrical connection" or "electrical coupling." "Connection" or "coupled" can also be used to indicate the operation or interaction between two or more elements. Furthermore, although terms such as "first," "second," etc., are used herein to describe different elements, these terms are merely used to distinguish elements or operations described using the same technical terms. Unless the context clearly indicates otherwise, these terms do not specifically refer to or imply any order or sequence, nor are they intended to limit the invention.

[0010] This disclosure relates to a charging device and a power transmission method. Referring to Figure 1, it shows a charging device 100 and an electric vehicle (EV) applied according to a partial embodiment of this disclosure. In this embodiment, the charging device 100 is used to connect the electric vehicle (EV) and another external device (ED) for unidirectional or bidirectional power transmission. For example, the electric vehicle (EV) can supply power to the external device (ED) through the charging device 100, or the external device (ED) can charge the electric vehicle (EV) through the charging device 100.

[0011] "External device" can be another electric vehicle, a charging station, the electric vehicle's energy storage battery, or any electrical device, such as a computer, smartphone, network sharing device, fan, lamp, etc.

[0012] In this embodiment, the charging device 100 includes a first connector 110, a second connector 120, and a control circuit 130. The connection interface of the first connector 110 is matched with the connection interface of the connection port EC of the electric vehicle EV, so as to be coupled to the connection port EC. The connection interface of the second connector 120 is matched with the connection interface of the external device ED (or its charger), so as to be coupled to the external device ED. In one embodiment, the second connector 120 has one or more AC sockets, such as type A, type B, or type C sockets, but this disclosure is not limited thereto.

[0013] The control circuit 130 is coupled between the first connector 110 and the second connector 120 to obtain power from either the electric vehicle (EV) or the external device (ED) and to supply power to the other. It should be noted that although the charging device 100 is depicted in Figure 1 as a combination of three components—the first connector 110, the second connector 120, and the control circuit 130—this disclosure is not limited thereto. In other embodiments, the first connector 110, the second connector 120, and the control circuit 130 may be integrated into a single component.

[0014] By designing the connection interfaces of the first connector 110 and the second connector 120 to correspond to the electric vehicle (EV) and the external device (ED), a power transmission path can be implemented in the "hardware configuration." However, corresponding supporting measures are still required in the "control program" because the operating voltages of the electric vehicle (EV) and the external device (ED) are not necessarily the same. For example, the charging and discharging voltage used by the electric vehicle (EV) is 240V, but the application voltage of the AC socket may be 100~120V. Therefore, if it is to be applied to different charging scenarios, the charging device 100 must have a control mechanism to obtain the required power supply.

[0015] In the following embodiments, two application methods are used as examples: V2V (Vehicle-to-Vehicle) and V2L (Vehicle-to-Load). V2V refers to the application of one electric vehicle charging another electric vehicle, with an operating voltage of 240V. V2L is the application of using the electric power of an electric vehicle to charge other electrical devices, with an operating voltage of 120V.

[0016] To enable the charging device 100 to obtain power at the corresponding voltage from the power supply device (e.g., an electric vehicle EV) according to the needs of the device to be charged (e.g., an external device ED), one approach is for the charging device 100 to detect the specifications of the external device ED and then transmit a communication signal to the electric vehicle EV, causing the electric vehicle EV to change its output voltage. However, to achieve this, the charging device 100 must have an internal battery to perform detection and communication functions, which will affect the cost and size of the charging device 100.

[0017] Another approach is to configure a sensing resistor of a specific size within the charging device 100. When the electric vehicle (EV) is connected to the charging device 100, the EV can determine the voltage required by the charging device 100 by identifying the impedance value of the sensing resistor (e.g., determining the voltage across). However, the sensing resistor can only correspond to a single specification and cannot automatically switch between different application methods.

[0018] The charging device and power transmission method disclosed herein can obtain a detection signal from the second connector and then obtain a corresponding voltage supply power from the electric vehicle. Furthermore, in some embodiments, the charging device may not require a battery and can be driven by the power supplied by the electric vehicle.

[0019] Figure 2 shows a schematic diagram of the internal circuit of a charging device 100 according to a partial embodiment of this disclosure. The first connector 110 includes multiple terminals, which can be divided into "power terminals" for transmitting electrical power and "signal terminals" for transmitting data, depending on the content being transmitted. In this embodiment, the "power terminals" include power supply terminals P1-P2 for transmitting alternating current and a ground terminal P3. The "signal terminals" include an identification terminal PR and a communication terminal CP, used for transmitting control and communication signals, such as determining whether the connector is correctly connected, transmitting a specific voltage to indicate a specific charging mode, etc.

[0020] The terminal configuration shown in Figure 2 is only one embodiment of this disclosure, and this disclosure is not limited thereto. In other embodiments, the connector may have different charging specifications / interfaces and may have different terminal configurations. In other words, the connector has at least one power supply terminal and at least one signal terminal, and the number and arrangement of the terminals can be adjusted according to the actual application specifications.

[0021] The first connector 110 also includes a detection resistor R11, which is coupled to the identification terminal PR. When the charging device 100 is connected to the electric vehicle EV, the electric vehicle EV can determine the impedance value of the detection resistor R11 to know the power required by the charging device 100. Since those skilled in the art will understand the method and principle by which the electric vehicle EV determines the impedance value of the detection resistor R11, it will not be described in detail here.

[0022] In one embodiment, the impedance value of the detection resistor R11 corresponds to V2V, so the electric vehicle EV will provide 240V power supply (hereinafter referred to as the first power supply) according to the detection resistor R11.

[0023] In one embodiment, as shown in Figure 2, the first connector 110 further includes a resistor R12 and a switch W11 connected in parallel. Resistor R12 and switch W11 are coupled to the detection resistor R11, wherein switch W11 is a foolproof switch; the user must press a button on the charging device 100 to open switch W11, allowing the charging device 100 to connect to the electric vehicle EV. Then, the user must release the button to short-circuit switch W11, allowing the electric vehicle EV to recognize the detection resistor R11. In some embodiments, resistor R12 can also serve as the detection resistor.

[0024] The second connector 120 is used for electrical connection with an external device ED and includes a sensing resistor R13 and at least one AC connection port 121. The AC connection port 121 is coupled to the sensing resistor R13, and the sensing resistor R13 is also coupled to a ground terminal or ground terminal P3 in the second connector 120. In one embodiment, the second connector 120 further includes a one-way switch D11, which is used to prevent current from flowing in the reverse direction through the sensing resistor R13. In addition, the sensing resistor R13 and the one-way switch D11 may be further coupled to a resistor R14 in the control circuit 130 to adaptively adjust the voltage level of the second sensing resistor according to the specifications of the controller 131 in the control circuit 130.

[0025] The control circuit 130 is coupled between the first connector 110 and the second connector 120, and is a detachable and modular component. In other words, the control circuit 130 and the second connector 120 are encapsulated in different device housings and can be connected to each other via a port or connector. When the control circuit 130 is connected to the second connector 120, the control circuit 130 can obtain a detection signal from the second connector 120 to determine whether a communication signal needs to be generated to the electric vehicle EV.

[0026] Continuing from the above, specifically, the detection signal can be the voltage of a specific node within the second connector 120, or the voltage across a specific component. As shown in Figure 2, when the control circuit 130 is coupled to the second connector 120, the control circuit 130 determines the voltage across the detection resistor R13. Based on the voltage across the detection resistor R13, the control circuit 130 can determine the type of the second connector 120 (i.e., whether it is applied to V2V or V2L) and the required charging voltage. In other embodiments, the "detection signal" can also be a handshake signal provided by the second connector 120 or an external device ED.

[0027] In this embodiment, no battery is required within the control circuit 130. When the first connector 110 is connected to the electric vehicle EV, the EV provides a first power supply, and the control circuit 130 operates based on this first power supply to detect the voltage across the detection resistor R13. After detecting the voltage across the detection resistor R13, if it is determined that the voltage required by the second connector 120 is different from the first power supply, the control circuit 130 transmits a communication signal to the electric vehicle EV through the communication terminal CP, causing the electric vehicle EV to change the voltage of its power supply. Here, the power supply corresponding to the detection resistor R13 is referred to as the "second power supply," and its voltage is different from the voltage of the first power supply.

[0028] On the other hand, if it is determined that the voltage required by the second connector 120 is the same as that of the first power supply, the control circuit 130 will not need to transmit communication signals and can directly use the first power supply to power the external device ED.

[0029] To facilitate understanding of the operation of the charging device 100, the power transmission method used by the charging device 100 will be explained below using the flowchart shown in Figure 3 as an example. Referring to Figures 1-3, in step S301, when the user wants to use the power of the electric vehicle EV to supply power to the external device ED through the charging device 100, the user first connects the first connector 110 to the electric vehicle EV and the second connector 120 to the external device ED. At this time, the electric vehicle EV will confirm the first power supply required by the charging device 100 (e.g., 240V for V2V applications) through the detection resistor R11 (first detection resistor). Therefore, the charging device 100 receives the first power supply from the electric vehicle EV.

[0030] In this embodiment, the control circuit 130 further includes a controller 131, at least one power supply switch W12, and a conversion circuit 132. The controller 131 is used to execute various actions of the control circuit 130 in the flowchart shown in Figure 3. The power supply switch W12 is a normally open switch and is coupled between at least one power supply terminal and the second connector 120. The conversion circuit 132 may be an AC-DC conversion circuit, coupled to at least one power supply terminal P1, P2, and coupled to the controller 131. In other words, the power supply terminals P1 and P2 are respectively coupled to the conversion circuit 132 and the power supply switch W12, and are used to provide power to the controller 131 of the control circuit 130.

[0031] In step S302, when the controller 131 in the control circuit 130 receives the first supplied power through the conversion circuit 132 and the power supply terminals P1 and P2, the controller 131 will start / drive according to the first supplied power. Since the power supply switch W12 is in the off (open circuit) state, the control circuit 130 will not provide the first supplied power to the second connector 120.

[0032] In step S303, after the control circuit 130 is activated using the first power supply, the controller 131 actively detects the voltage across the detection resistor R13 (the second detection resistor) in the second connector 120 as a detection signal. The voltage across the detection resistor R13 will reflect the type of the second connector 120 (or correspond to the type of the external device ED), allowing the controller 131 to determine the required charging voltage for the second connector 120 / external device ED. In one embodiment, the controller 131 stores specification data so that it can determine the required charging voltage for the second connector 120 / external device ED by looking up a table based on the voltage across the detection resistor R13.

[0033] In step S304, the controller 131 determines whether the voltage across the detection resistor R13 (the second detection resistor) is equal to or greater than a preset value. The "preset value" can be a threshold value stored in the controller 131, such as 12V. In one embodiment, if the voltage across the detection resistor R13 is equal to or greater than the preset value, it indicates that the current charging application is "V2V," meaning the charging voltage required by the second connector 120 / external device ED is 240V. If the voltage across the detection resistor R13 is less than the preset value, it indicates that the current charging application is "V2L," meaning the charging voltage required by the second connector 120 / external device ED is 120V.

[0034] In step S305, if the voltage across the detection resistor R13 (the second detection resistor) is equal to or greater than a preset value, it indicates that the charging application is "V2V". At this time, the control circuit 130 will use the first power supply to power the external device ED. Figure 4A shows the circuit state diagram of the charging device 100 in "V2V" application. Since the second connector 120 of the "V2V" specification is different from the "V2L" specification, it is indicated by a block in the figure. In this embodiment, the control circuit 130 turns on the power supply switch W12 so that the first power supply can be transmitted to the external device ED through the power supply terminals P1~P2 and the second connector 120. At this time, the charging device 100 does not need to use the communication terminal CP to connect with the electric vehicle EV.

[0035] In some embodiments, the controller 131 may also determine that the voltage on the power supply terminals P1~P2 has stabilized (e.g., the voltage value does not change within a preset range over a period of time) before turning on the power supply switch W12 to supply power to the external device ED using the first power supply.

[0036] In step S306, if the voltage across the detection resistor R13 (second detection resistor) (e.g., 3V) is less than the preset value, it means that the charging application is "V2L". At this time, the controller 131 will generate a communication signal, and the controller 131 will generate the frequency of the set communication signal according to the voltage across the detection resistor R13. This frequency will correspond to the charging voltage required by the second connector 120 / external device ED.

[0037] In one embodiment, the communication signal is a handshake signal used to enable the electric vehicle (EV) to confirm the voltage required by the charging device 100. In another embodiment, the communication signal is a pulse width modulation (PWM) signal, and the control circuit 130 can set the frequency and / or duty cycle of the PWM signal.

[0038] In step S307, after determining the frequency of the communication signal, the controller 131 will transmit the communication signal to the electric vehicle EV through the communication terminal CP to obtain a second power supply (i.e., to change the voltage of the power supply to the electric vehicle), for example, 120V.

[0039] In one embodiment, the control circuit 130 includes a communication switch W13. The communication switch W13 is coupled to the communication terminal CP of the first connector 110 and is a normally open switch. In other words, the communication switch W13 remains off before the first connector 110 is coupled to the electric vehicle EV. Similarly, the communication switch W13 remains off (open circuit) unless the control circuit 130 actively controls it to turn on. After the control circuit 130 is driven by the first power supply, if the control circuit 130 confirms that the charging application is "V2L", the control circuit 130 will turn on the communication switch W13 to transmit a communication signal to the electric vehicle EV through the communication terminal CP.

[0040] Figures 4B-4C show the circuit state diagrams of the charging device 100 in a "V2V" application. The details of steps S304, S306, and S307 described above are explained below in conjunction with Figures 4B-4C. In this embodiment, the specification of the second connector 120 corresponds to "V2L". Therefore, as shown in Figure 4B, when the control circuit 130 determines that the voltage across the detection resistor R13 is less than a preset value, the control circuit 130 will turn on the communication switch W13 to transmit a communication signal to the electric vehicle EV, causing the electric vehicle EV to change the voltage of the output power.

[0041] Next, as shown in Figure 4C, in step S308, after the electric vehicle EV provides the second power supply, the control circuit 130 will use the second power supply to power the external device ED. Specifically, the control circuit 130 can also first determine whether the voltage on the power supply terminals P1 and P2 is stable, and only after confirming that the voltage on the power supply terminals P1 and P2 is stable will it turn on the power supply switch W12 to use the second power supply to power the external device ED. Accordingly, in different charging applications, the charging device 100 can automatically obtain different voltage power supplies from the electric vehicle EV to power various types of second connectors 120 / external devices ED.

[0042] Furthermore, in some embodiments, the charging device 100 has two operating modes: The first mode involves activating the control circuit 130 to supply power to the external device ED based on the first power supply. In this mode, the charging device 100 does not need to connect with the electric vehicle EV via the communication terminal CP. The second mode involves transmitting a communication signal to the electric vehicle EV via the communication terminal CP to obtain a second power supply. As shown in Figure 2, the charging device 100 can activate / drive the control circuit 130 using either the first or second power supply via power supply terminals P1 and P2, thus eliminating the need for an internal battery.

[0043] Figure 5 shows a schematic diagram of signal waveforms according to a portion of the embodiments disclosed herein, illustrating the power supply Sv1 provided by the electric vehicle EV, the voltage across the detection resistor R11 Spr, the communication signal Scp, the output power Sv2 output by the charging device 100, and the detection signal Sd acquired by the controller 131.

[0044] Please refer to Figures 1, 2, and 5. During time segment T51, the charging device 100 is connected to the electric vehicle EV. The electric vehicle EV provides power Sv1 (first power supply) according to the detection resistor R11 (or the matching resistor R12). At this time, the power supply switch W12 in the charging device 100 is in the off state, so the power supply Sv1 is not transmitted to the second connector 120, and the output power Sv2 is zero.

[0045] Continuing from the above, during time interval T51, controller 131 will determine the voltage across the detection resistor R13 to obtain the detection signal Sd. In this embodiment, controller 131 will confirm that the current application is "V2L" based on the voltage across the detection resistor R13. Therefore, during time interval T52, controller 131 will generate the communication signal Scp.

[0046] During time interval T52, controller 131 activates communication switch W13 to transmit communication signal Sep to electric vehicle EV via communication terminal CP of first connector 110. Therefore, electric vehicle EV will change the voltage of supplied power Sv1 according to the frequency of communication signal Sep. The voltage of communication signal Sep changes between time intervals T52 and T53. In some embodiments, controller 131 may transmit a handshake signal first during time interval T52, and then provide communication signal Sep during time interval T53, so that electric vehicle EV changes the voltage of output power. The timing of communication signal Sep transmission is not limited to the waveform shown in Figure 5; the voltage magnitude (amplitude) of communication signal Sep may vary depending on the type of electric vehicle EV.

[0047] During time interval T54, controller 131 determines that the voltage of the supplied power Sv1 has changed to 120V (second supplied power). At this time, controller 131 can further determine whether the supplied power Sv1 is stable. During time interval T55, after confirming that the supplied power Sv1 is stable, controller 131 will turn on the power supply switch W12 to generate output power Sv2 based on the supplied power Sv1, supplying power to the external device ED.

[0048] As previously described, in one embodiment, the first connector 110, the second connector 120, and the control circuit 130 may be three different components and can be assembled into one unit. Therefore, the control circuit 130 can be used with the first connector 110 or the second connector 120 with different connection interfaces to meet different charging needs. In other embodiments, the first connector 110, the second connector 120, and the control circuit 130 may also be packaged / integrated into a single device to achieve a more compact size.

[0049] The various components, method steps, or technical features in the foregoing embodiments can be combined with each other, and are not limited to the order of textual description or graphical presentation in this disclosure.

[0050] Although the present disclosure has been described above with reference to embodiments, it is not intended to limit the present disclosure. Anyone skilled in the art may make various modifications and alterations without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be determined by the claims defined in the appended patent application.

[0051] 100: Charging device 110: First Connector 120: Second connector 121: AC Connection Port 130: Control Circuit 131: Controller 132: Conversion Circuit CP: Communication Terminal D11: One-way switch EC: Connector Port ED: External device EV: Electric Vehicle P1-P2: Power supply terminals P3: Grounding terminal PR: Identification terminal R11: Detection resistor R12: Resistor R13: Detection resistor R14: Resistor S301-S308: Steps Sv1: Supply electricity Spr: Transvoltage signal SCP: Communication Signal Sd: Detection signal Sv2: Output power T51: Time Segment T52: Time Segment T53: Time Segment T54: Time Segment T55: Time Segment W11: Switch W12: Power switch W13: Communication Switch

[0052] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A charging device comprising: a first connector having a first sensing resistor, wherein when the first connector is connected to an electric vehicle through the first sensing resistor, the first connector receives a first power supply; a second connector having a second sensing resistor; and a control circuit coupled to the first connector and the second connector, and driven by the first power supply; wherein the control circuit is configured to, based on the voltage across the second sensing resistor, use the first power supply to power an external device, or transmit a communication signal to the electric vehicle to obtain a second power supply from the electric vehicle, wherein the voltage of the first power supply is different from the voltage of the second power supply.

2. The charging device as claimed in claim 1, wherein the communication signal is a pulse width modulation signal, and the control circuit is configured to set a frequency of the communication signal according to the voltage across the second detection resistor.

3. The charging device as claimed in claim 1, wherein when the voltage across the second detection resistor is greater than a preset value, the control circuit uses the first power supply to power the external device.

4. The charging device as claimed in claim 1, wherein the control circuit generates the communication signal when the voltage across the second detection resistor is less than a preset value.

5. The charging device as claimed in claim 1, wherein the first connector further comprises: an identification terminal coupled to the first detection resistor; a communication terminal coupled to a communication switch of the control circuit and used to transmit the communication signal; and at least one power supply terminal for transmitting the first power supply or the second power supply.

6. The charging device as claimed in claim 5, wherein after the control circuit is driven by the first power supply, the control circuit is used to turn on the communication switch to transmit the communication signal.

7. The charging device as claimed in claim 5, wherein the control circuit includes a power supply switch coupled to the at least one power supply terminal, and the control circuit turns on the power supply switch to supply power to the external device after determining that the voltage of the at least one power supply terminal is stable.

8. The charging device as claimed in claim 7, wherein the at least one power supply terminal is respectively connected to the power supply switch and a controller of the control circuit for transmitting the first power supply or the second power supply to the controller.

9. A power transmission method, comprising: receiving a first power supply from an electric vehicle when a charging device is connected to an electric vehicle via a first sensing resistor; driving a control circuit in the charging device using the first power supply; determining a voltage across a second sensing resistor of the charging device via the control circuit; and selectively using the first power supply to power an external device or to obtain a second power supply from the electric vehicle based on the voltage across the second sensing resistor, wherein the voltage of the first power supply is different from the voltage of the second power supply.

10. The power transmission method as claimed in claim 9, wherein the step of selectively using the first power supply to power an external device or obtaining the second power supply from the electric vehicle comprises: using the first power supply to power the external device when the voltage across the second detection resistor is greater than a preset value.

11. The power transmission method as claimed in claim 9, wherein the step of selectively using the first power supply to power an external device or obtaining the second power supply from the electric vehicle comprises: generating a communication signal to obtain the second power supply from the electric vehicle when the voltage across the second detection resistor is less than a preset value.

12. The power transmission method as claimed in claim 11, wherein the communication signal is a pulse width modulation signal, and the step of generating the communication signal to obtain the second power supply from the electric vehicle comprises: setting a frequency of the communication signal based on the voltage across the second detection resistor.

13. The power transmission method as described in claim 11 further comprises: when it is determined that the voltage across the second detection resistor is less than the preset value, turning on a communication switch of the control circuit, wherein the control circuit transmits the communication signal to the electric vehicle through a communication terminal coupled to the communication switch.

14. The power transmission method as claimed in claim 9, wherein the charging device receives the first supplied power and the second supplied power through at least one power supply terminal, and the power transmission method further comprises: after determining that the voltage of the at least one power supply terminal is stable, turning on a power supply switch in the control circuit to supply power to the external device using the first supplied power or the second supplied power provided by the electric vehicle.

15. A charging device comprising: a first connector having a first detection resistor, wherein when the first connector is connected to an electric vehicle through the first detection resistor, the first connector receives a power supply from the electric vehicle; and a control circuit coupled to the first connector and driven by the power supply; wherein when the charging device is connected to an external device and receives a detection signal, the control circuit is configured to supply power to the external device according to the power supply and to selectively provide a communication signal to the electric vehicle to cause the electric vehicle to change the voltage of the power supply.

16. The charging device as claimed in claim 15 further comprises: a second connector coupled to the control circuit and connected to the external device via a second sensing resistor, wherein the control circuit is used to obtain the voltage across the second sensing resistor as the sensing signal to set a frequency of the communication signal.

17. The charging device as claimed in claim 16, wherein the first connector further comprises: an identification terminal coupled to the first detection resistor; a communication terminal coupled to a communication switch of the control circuit and used to transmit the communication signal; and at least one power supply terminal for transmitting the supplied power.

18. The charging device as claimed in claim 17, wherein when the voltage across the second detection resistor is greater than a preset value, the control circuit shuts off the communication switch and uses the supplied power to supply power to the external device.

19. The charging device as claimed in claim 17, wherein when the voltage across the second detection resistor is less than a preset value, the control circuit turns on the communication switch to transmit the communication signal to the electric vehicle.

20. The charging device as claimed in claim 17, wherein the communication open relationship remains closed before the first connector is coupled to the electric vehicle.

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