Input voltage sampling circuit and charger

Abstract

The utility model discloses an input voltage sampling circuit and a charger. A secondary winding of a transformer in a charger circuit is connected with a load interface through a first on-off device. The input voltage sampling circuit comprises a second on-off device, a first capacitor, a first resistor and a second resistor; the second on-off device is connected with the first on-off device in parallel after being connected with the first capacitor in series; the first resistor and the second resistor are connected in series and then are connected in parallel with the first capacitor; the series connection midpoint of the first resistor and the second resistor serves as a sampling output end to output a sampling signal of the input voltage of the charger circuit, sampling of the input voltage of the charger circuit is achieved, application of an auxiliary power supply is avoided, the complexity of an internal circuit of the charger is reduced, and resource waste is reduced.

Description

Technical Field

[0001] The utility model relates to the field of circuit design, in particular to an input voltage sampling circuit and a charger. Background Art

[0002] In a charger, since the electrolytic capacitor needs to store power frequency energy, its volume has not been reduced. Therefore, the volume of the electrolytic capacitor has become a bottleneck for reducing the volume of the charger. In order to reduce the capacitance and volume of the electrolytic capacitor, it is necessary to make the charger output different powers according to different input voltages. For example, under the condition of a 110V power grid, the charger can only output a relatively small power; under the condition of a 220V power grid, the charger can output a relatively large power. Therefore, detecting the input voltage has become a key point for distinguishing different output powers.

[0003] As Figure 1 shown, in the prior art, the synchronous rectification switch S in the charger is set at a high position. In this case, an additional auxiliary power supply Vdd needs to be set so that the voltage sampled by the voltage sampling circuit can be converted from negative voltage to positive voltage for the analysis and processing of the subsequent circuit. The setting of the auxiliary power supply Vdd not only increases the complexity of the internal circuit of the charger, but also causes a certain degree of waste. Summary of the Utility Model

[0004] The utility model provides an input voltage sampling circuit and a charger to reduce the complexity of the internal circuit of the charger and reduce resource waste.

[0005] According to one aspect of the utility model, an input voltage sampling circuit is provided. In the charger circuit, the secondary winding of the transformer is connected to the load interface through a first switch.

[0006] The input voltage sampling circuit includes a second switch, a first capacitor, a first resistor, and a second resistor. The second switch and the first capacitor are connected in series and then connected in parallel with the first switch. The first resistor and the second resistor are connected in series and then connected in parallel with the first capacitor. The series midpoint of the first resistor and the second resistor serves as a sampling output terminal to output a sampling signal of the input voltage of the charger circuit.

[0007] Optionally, the first switch and the second switch adopt at least one of the structures of electrical interlock, mechanical linkage, and connection logic circuit, so that their on-off states are opposite.

[0008] Optionally, both the first switch and the second switch are unidirectional conduction devices, and their conduction directions are opposite.

[0009] According to another aspect of the utility model, a charger is provided. The charger includes a charger circuit and the input voltage sampling circuit described in any of the previous aspects.

[0010] The charger circuit includes a transformer, a first switch, a second capacitor, a load interface, and a control circuit;

[0011] The primary winding of the transformer is connected to an input power supply, and the secondary winding is connected in series with the first switch and then in parallel with the second capacitor between two terminals of the load interface; the control circuit is respectively connected to the sampling output terminal and the load interface.

[0012] Optionally, the load interface includes a USB interface, the USB interface is externally connected to a load, and the load adjusts its own power according to the power level that the charger circuit can provide.

[0013] Optionally, the USB interface includes at least one of a Mini USB interface, a Micro USB interface, a USB Type-A interface, a USB Type-B interface, and a USB Type-C interface.

[0014] Optionally, the control circuit includes a fast charging protocol chip.

[0015] Optionally, the charger circuit further includes a third switch, and the third switch is disposed between the input power supply and the same-named end of the primary winding.

[0016] Optionally, the third switch includes a field effect transistor.

[0017] Optionally, the charger circuit further includes an AC / DC converter,

[0018] The AC / DC converter is disposed between the AC power supply and the primary winding.

[0019] The input voltage sampling circuit and the charger provided by the present invention, the secondary winding of the transformer in the charger circuit is connected to the load interface through the first switch. The input voltage sampling circuit includes a second switch, a first capacitor, a first resistor, and a second resistor; the second switch and the first capacitor are connected in series and then in parallel with the first switch; the first resistor and the second resistor are connected in series and then in parallel with the first capacitor; the series midpoint of the first resistor and the second resistor serves as the sampling output terminal, and samples the input voltage of the charger circuit to output a sampling signal, realizing the sampling of the input voltage of the charger circuit, avoiding the application of an auxiliary power supply, reducing the complexity of the internal circuit of the charger, and reducing resource waste.

[0020] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. Description of the Drawings

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 It is a circuit schematic diagram of a charger in the prior art;

[0023] Figure 2 It is a circuit schematic diagram of a charger provided by an embodiment of the present invention;

[0024] Figure 3 It is a circuit schematic diagram of another charger provided by an embodiment of the present invention;

[0025] Figure 4 It is a circuit schematic diagram of yet another charger provided by an embodiment of the present invention.

[0026] Explanation of reference numerals:

[0027] 200 - charger, 201 - charger circuit, 202 - input voltage sampling circuit, 203 - load interface, 204 - control circuit, Vin - input voltage, Np - primary winding, Ns - secondary winding, S1 - first switch, S2 - second switch, C1 - first capacitor, C2 - second capacitor, Vo - output voltage, R1 - first resistor, R2 - second resistor, P - sampling output terminal, S3 - third switch, 401 - AC / DC converter, Us - input power supply. Specific embodiments

[0028] In order to enable those skilled in the art to better understand the solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present utility model are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present utility model described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0030] To solve the problems in the background art, the present utility model proposes an input voltage sampling circuit. Figure 2 The following is a schematic circuit diagram of a charger provided by an embodiment of the present utility model. Refer to Figure 2 , the charger 200 includes a charger circuit 201 and an input voltage sampling circuit 202. The secondary winding Ns of the transformer T in the charger circuit 201 is connected to the load interface 203 through a first switch S1. The input voltage sampling circuit 202 includes a second switch S2, a first capacitor C1, a first resistor R1 and a second resistor R2; the second switch S2 and the first capacitor C1 are connected in series and then connected in parallel with the first switch S1; the first resistor R1 and the second resistor R2 are connected in series and then connected in parallel with the first capacitor C1; the series midpoint of the first resistor R1 and the second resistor R2 serves as the sampling output terminal P, and outputs a sampling signal of the input voltage of the charger circuit 201.

[0031] Specifically, the input voltage Vin of the charger 200 is, in this embodiment, the voltage across the primary winding Np of the transformer T in the charger circuit 201. Corresponding to the input voltage Vin, the induced voltage across the secondary winding Ns of the transformer T in the charger circuit 201 is Vin*n 2 / n 1 , where n 2 is the voltage across the secondary winding Ns, n 1is the voltage across the two ends of the primary winding Np. During application, the on-off states of the first switch S1 and the second switch S2 are set to be opposite, that is, when the first switch S1 is controlled to be on, the second switch S2 remains off, and when the first switch S1 is controlled to be off, the second switch S2 remains on. Exemplarily, the first switch S1 and the second switch S2 can adopt at least one of the structures of electrical interlock, mechanical linkage, and connection logic circuit to make their on-off states opposite. For example, the first switch S1 and the second switch S2 can be diodes with opposite direction settings. When the first switch S1 is off, the second switch S2 is on, and the voltage across the off first switch S1 can then be expressed as Vin*n 2 / n 1 +Vo, where Vo is the output voltage at the load interface. The voltage across the first switch S1 is positively correlated with the input voltage Vin. Sampling the voltage at the output terminal P, that is, the sampling signal, can be expressed by the sampling voltage formula as

[0032] Vp = (Vin*n 2 / n 1 +Vo) / (R1 + R2)R2. After the input voltage Vin is sampled, the first switch S1 can be controlled to be on. At this time, the second switch S2 is off, and the secondary winding Ns of the transformer T is coupled with the output voltage Vo of the charger circuit 201 to provide a stable charging power supply for the load.

[0033] In the charger 200, the subsequent circuit of the input voltage sampling circuit 202 (which can include the control circuit 204 shown in the figure) can adaptively adjust the charging power for the load according to the sampling signal, realizing the adaptive adjustment of the charging power of the charger 200, so that the charger 200 can be applied under different power supply conditions. Exemplarily, the control circuit 204 at the subsequent stage of the input voltage sampling circuit 202 can, according to the sampling signal, the output voltage Vo, and the sampling voltage formula, inversely calculate the voltage across the two ends of the primary winding Np of the transformer T, which is the input voltage Vin. Further, the control circuit 204 at the subsequent stage of the input voltage sampling circuit 202 can also calculate the maximum power that the charger circuit 201 can provide at this time according to the determined input voltage Vin, generate a communication signal according to the maximum power, and send it to the load through the load interface 203. The load can adjust the charging power it requests from the charger 200 according to the power level that the charger 200 can provide.

[0034] The input voltage sampling circuit provided by the embodiment of the present utility model. In the charger circuit, the secondary winding of the transformer is connected to the load interface through a first switch. The input voltage sampling circuit includes a second switch, a first capacitor, a first resistor, and a second resistor; the second switch and the first capacitor are connected in series and then connected in parallel with the first switch; the first resistor and the second resistor are connected in series and then connected in parallel with the first capacitor; the series midpoint of the first resistor and the second resistor serves as the sampling output terminal, outputting the sampling signal of the input voltage of the charger circuit, realizing the sampling of the input voltage of the charger circuit, avoiding the application of the auxiliary power supply, reducing the complexity of the internal circuit of the charger, and reducing resource waste.

[0035] Optionally, Figure 3 is a circuit schematic diagram of another charger provided by the embodiment of the present utility model. On the basis of the foregoing embodiment, referring to Figure 3 , the charger 200 includes a charger circuit 201 and an input voltage acquisition circuit 202. The charger circuit 201 is provided with a third switch S3, and the third switch S3 is disposed between the input power supply Vin and the same-named end of the primary winding Np. The first switch S1 and the second switch S2 are both unidirectional conduction devices, and the conduction directions are opposite.

[0036] Specifically, the charger circuit 201 may include a flyback converter. The third switch S3 in the flyback converter may include at least one of a switch and a field effect transistor. Exemplarily, the third switch S3 may include an enhancement-mode N-channel field effect transistor. The first switch S1 may be unidirectionally conductive from the end far from the different-named end of the secondary winding Ns of the transformer T to the end close to the different-named end of the secondary winding Ns of the transformer T. Exemplarily, the first switch S1 may include a first diode with an anode connected to the load interface 203 and a cathode connected to the different-named end of the secondary winding Ns of the transformer T. Similar to the first switch S1, the second switch S2 may be unidirectionally conductive from the end far from the different-named end of the secondary winding Ns in the transformer T to the end close to the different-named end of the secondary winding Ns of the transformer T. Exemplarily, the second switch S2 is a second diode with an anode connected to the different-named end of the secondary winding Ns of the transformer T and a cathode connected to the first capacitor C1.

[0037] Exemplarily, in the charger circuit 201, the primary winding Np of the transformer T is connected in series with the third switch S3 and then connected in parallel with the input voltage Vin, and the input voltage Vin can be a rectified DC voltage. The signals at both ends of the secondary winding Ns of the transformer T are rectified and filtered by the first diode and the second capacitor C2 and then connected to the load interface 203. The cathode of the first diode can be connected to the terminal of the secondary winding Ns with the opposite name. One end of the second capacitor C2 is connected to the anode of the first diode, and the other end is connected to the terminal of the secondary winding Ns with the same name. The charger circuit 201 further includes a load interface 203, which is connected in parallel with the second capacitor C2 and is used to dock with the load and transmit data. The input voltage sampling circuit 202 is connected in parallel across the two ends of the second diode. The input voltage sampling circuit 202 includes a second diode, a first capacitor C1, a first resistor R1, and a second resistor R2. The anode of the second diode is connected to the terminal of the secondary winding Ns with the opposite name, the cathode of the second diode is connected to one end of the first capacitor C1, the other end of the first capacitor C1 is connected to one end of the second capacitor C2, one end of the first resistor R1 is connected between the second diode and the first capacitor C1, and the other end is connected in series with the second resistor R2 and then connected to one end of the second capacitor C2. The charger circuit 201 may further include a control circuit 204. One input terminal of the control circuit 204 is connected to the sampling output terminal P of the input voltage sampling circuit 202, and the output terminal of the control circuit 204 is connected to the load interface 203. The control circuit 204 can detect the output voltage Vo and the sampling signal of the charger circuit 201, and then substitute the output voltage Vo and the sampling signal into the input voltage formula to determine the input voltage Vin of the charger circuit 201. The input voltage formula is where Vp is the voltage at point P, that is, the sampling signal.

[0038] In the input voltage sampling circuit provided in this embodiment, both the first switch and the second switch are unidirectional conduction devices, and their conduction directions are opposite. It can be applied to a flyback converter to realize the acquisition of the input voltage. The switches in this acquisition circuit can be unidirectional conduction devices such as diodes, which can adjust their own on-off states according to the voltage direction, avoiding the additional control of the switches, reducing the control difficulty while improving the performance of the charger circuit.

[0039] The present invention also provides a charger. On the basis of the foregoing embodiment, continue to refer to Figure 2, the charger 200 includes a charger circuit 201 and an input voltage sampling circuit 202 mentioned in any embodiment of the present invention. The charger circuit 201 includes a transformer T, a first switch S1, a second capacitor C2, a load interface 203, and a control circuit 204. The primary winding Np of the transformer T is connected to the input power supply Vin, and the secondary winding Ns is connected in series with the first switch S1 and then connected in parallel with the second capacitor C2 between the two terminals of the load interface 203. The control circuit 204 is connected to the sampling output terminal P and the load interface 203 respectively.

[0040] Specifically, the load interface 203 refers to the interface on the charger circuit 201 for externally connecting the load to be charged. Exemplarily, the load interface 203 may include a USB interface. The USB interface is externally connected to the load, and the load adjusts its own power according to the power level that the charger circuit 201 can provide. Among them, the USB interface may include at least one of a Mini USB interface, a Micro USB interface, a USB Type-A interface, a USB Type-B interface, and a USB Type-C interface.

[0041] The control circuit 204 is a data analysis and processing circuit at the rear stage of the input voltage sampling circuit 202. It can determine the current maximum power of the charger 200 according to the sampling signal, thereby generating a communication signal to communicate with the load. The load can adjust the power level it requests from the charger 200 according to the power provided by the charger 200. Exemplarily, the control circuit 204 may include a fast charging protocol chip, and the fast charging protocol chip may include WT6636F.

[0042] Exemplarily, the input voltage Vin of the charger 200 is, in this embodiment, the voltage across the two ends of the primary winding Np of the transformer T in the charger circuit 201. Corresponding to the input voltage Vin, the induced voltage across the two ends of the secondary winding Ns of the transformer T in the charger circuit 201 is Vin*n 2 / n 1 , where, n 2 is the voltage across the two ends of the secondary winding Ns, and n 1 is the voltage across the two ends of the primary winding Np. During the application process, the on-off states of the first switch S1 and the second switch S2 are set to be opposite, that is, when the first switch S1 is controlled to be on, the second switch S2 remains off, and when the first switch S1 is controlled to be off, the second switch S2 remains on. Exemplarily, the first switch S1 and the second switch S2 may adopt at least one of electrical interlock, mechanical linkage, and connection logic circuit structures to make their on-off states opposite. For example, the first switch S1 and the second switch S2 may be diodes with opposite direction settings. When the first switch S1 is off, the second switch S2 is on, and the voltage across the two ends of the off first switch S1 can then be expressed as Vin*n2 / n 1 +Vo, where Vo is the output voltage at the load interface. The voltage across the first switch S1 is positively correlated with the input voltage Vin. Sampling the voltage at the sampling output terminal P, i.e., the sampling signal, can be expressed by the sampling voltage formula as

[0043] Vp = (Vin * n 2 / n 1 +Vo) / (R1 + R2)R2. After the input voltage Vin is sampled, the first switch S1 can be controlled to conduct. At this time, the second switch S2 is cut off, and the secondary winding Ns of the transformer T is coupled with the output voltage Vo of the charger circuit 201 to provide a stable charging power supply for the load.

[0044] In the charger 200, the subsequent circuit of the input voltage sampling circuit 202 (which may include the control circuit 204 shown in the figure) can adaptively adjust the charging power for the load according to the sampling signal, realizing the adaptive adjustment of the charging power of the charger 200, so that the charger 200 can be applied under different power supply conditions. Exemplarily, the control circuit 204 at the subsequent stage of the input voltage sampling circuit 202 can inversely calculate the voltage across the primary winding Np of the transformer T, which is the input voltage Vin, according to the sampling signal, the output voltage Vo, and the sampling voltage formula. Further, the control circuit 204 at the subsequent stage of the input voltage sampling circuit 202 can also calculate the maximum power that the charger circuit 201 can provide at this time according to the determined input voltage Vin, generate a communication signal according to the maximum power, and send it to the load through the load interface 203. The load can adjust the charging power it requests from the charger 200 according to the power level that the charger 200 can provide.

[0045] The charger provided by the embodiment of the present invention, the charger circuit and any input voltage sampling circuit in the present invention. The charger circuit includes a transformer, a first switch, a second capacitor, a load interface, and a control circuit. The primary winding of the transformer is connected to the input power supply, and the secondary winding is connected in series with the first switch and then connected in parallel with the second capacitor between the two terminals of the load interface; the control circuit is respectively connected to the sampling output terminal and the load interface, realizing the sampling of the input voltage of the charger circuit, avoiding the application of the auxiliary power supply, reducing the complexity of the internal circuit of the charger, and reducing resource waste.

[0046] Optionally, on the basis of the foregoing embodiment, continue to refer to Figure 3 , the charger circuit 201 further includes a third switch S3, and the third switch S3 is arranged between the input power supply and the same-name end of the primary winding Np.

[0047] Specifically, the charger circuit 201 may include a flyback converter. The third switch S3 in the flyback converter may include at least one of a switch and a field effect transistor. Exemplarily, the third switch S3 may include an enhancement-mode N-channel field effect transistor. The first switch S1 may be unidirectionally conductive from the end far from the opposite-named end of the secondary winding Ns of the transformer T to the end close to the opposite-named end of the secondary winding Ns of the transformer T. Exemplarily, the first switch S1 may include a first diode with its anode connected to the load interface 203 and its cathode connected to the opposite-named end of the secondary winding Ns of the transformer T. Similar to the first switch S1, the second switch S2 may be unidirectionally conductive from the end far from the opposite-named end of the secondary winding Ns of the transformer T to the end close to the opposite-named end of the secondary winding Ns of the transformer T. Exemplarily, the second switch is a second diode with its anode connected to the opposite-named end of the secondary winding Ns of the transformer T and its cathode connected to the first capacitor C1.

[0048] Exemplarily, in the charger circuit 201, the primary winding Np of the transformer T is connected in series with the third switch S3 and then in parallel with the input voltage Vin. The input voltage Vin may be a rectified DC voltage. The signals at both ends of the secondary winding Ns of the transformer T are rectified and filtered by the first diode and the second capacitor C2 and then connected to the load interface 203. The cathode of the first diode may be connected to the opposite-named end of the secondary winding Ns. One end of the second capacitor C2 is connected to the anode of the first diode, and the other end is connected to the same-named end of the secondary winding Ns. The charger circuit 201 further includes a load interface 203, which is connected in parallel with the second capacitor C2 and is used to dock with the load and transmit data. The input voltage sampling circuit 202 is connected in parallel across the second diode. The input voltage sampling circuit 202 includes the second diode, the first capacitor C1, the first resistor R1, and the second resistor R2. The anode of the second diode is connected to the opposite-named end of the secondary winding Ns, the cathode of the second diode is connected to one end of the first capacitor C1, the other end of the first capacitor C1 is connected to one end of the second capacitor C2, one end of the resistor R1 is connected between the second diode and the first capacitor C1, and the other end is connected in series with the second resistor R2 and then to one end of the second capacitor C2. The charger circuit 201 may further include a control circuit 204. One input terminal of the control circuit 204 is connected to the sampling output terminal P of the input voltage sampling circuit 202, and the output terminal of the control circuit 204 is connected to the load interface 203. The control circuit 204 can detect the output voltage Vo and the sampling signal of the charger circuit 201, and then substitute the output voltage Vo and the sampling signal into the input voltage formula to determine the input voltage Vin of the charger circuit 201. The input voltage formula is where Vp is the voltage at point P, which is the sampling signal.

[0049] The charger provided in this embodiment further includes a third switch, which is arranged between the input power supply and the same-name terminal of the primary side. The first switch and the second switch are both unidirectional conductive devices, and the conductive directions are opposite, which can be applied to the flyback converter to realize the collection of the input voltage. The switch in the collection circuit can be a unidirectional conductive device such as a diode, which can adjust its own on-off state according to the voltage direction, avoiding additional control of the switch, and reducing its control difficulty on the basis of improving the performance of the charger.

[0050] Optionally, Figure 4 A circuit diagram of another charger provided by an embodiment of the utility model, based on the above embodiment, referring to Figure 4 The charger circuit 201 also includes an AC / DC converter 401, which is arranged between the AC power source Us and the primary winding Np. The AC voltage provided by the AC power source Us of the charger 200 can be rectified by the AC / DC converter 401 to generate a DC voltage at both ends of the primary winding Np of the transformer T, which is the input voltage Vin collected by the utility model. The control circuit 204 calculates the input voltage Vin of the charger 200 according to the sampling signal output by the sampling output terminal P of the input voltage sampling circuit 202, and then calculates the power level that the charger 200 can provide, and transmits the power level that the charger 200 can provide to the load through the load interface 203. The load adjusts the power it and the charger 200 request according to the power level that the charger 200 can provide.

[0051] The utility model provides an input voltage sampling circuit and a charger, in which the secondary winding of the transformer in the charger circuit is connected to the load interface via a first switch. The input voltage sampling circuit includes a second switch, a first capacitor, a first resistor, and a second resistor; the second switch and the first capacitor are connected in series and then connected in parallel with the first switch; the first resistor and the second resistor are connected in series and then connected in parallel with the first capacitor; the series midpoint of the first resistor and the second resistor serves as a sampling output terminal, outputting a sampling signal of the input voltage of the charger circuit, thereby realizing the sampling of the input voltage of the charger circuit, avoiding the use of an auxiliary power supply, reducing the complexity of the internal circuit of the charger, and reducing resource waste.

[0052] The above specific implementations do not constitute a limitation on the protection scope of the present utility model. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present utility model shall be included in the protection scope of the present utility model.

Claims

1. An input voltage sampling circuit, characterized in that: The secondary winding of the transformer in the charger circuit is connected to the load interface via the first switch; The input voltage sampling circuit includes a second switch, a first capacitor, a first resistor and a second resistor; the second switch and the first capacitor are connected in series and then connected in parallel with the first switch; the first resistor and the second resistor are connected in series and then connected in parallel with the first capacitor; the midpoint of the series connection of the first resistor and the second resistor serves as a sampling output terminal to output a sampling signal of the input voltage of the charger circuit.

2. The input voltage sampling circuit according to claim 1, characterized in that: The first switch and the second switch adopt at least one structure of electrical interlocking, mechanical linkage and connection logic circuit, so that the on-off states of the two are opposite.

3. The input voltage sampling circuit according to claim 1 or 2, characterized in that: The first switch and the second switch are both unidirectional conducting devices, and the conducting directions are opposite.

4. A charger, characterized in that: It comprises a charger circuit and an input voltage sampling circuit as claimed in any one of claims 1 to 3; The charger circuit includes a transformer, a first switch, a second capacitor, a load interface and a control circuit; The primary winding of the transformer is connected to the input power supply, the secondary winding is connected in series with the first switch and then in parallel with the second capacitor between the two terminals of the load interface; the control circuit is connected to the sampling output end and the load interface respectively.

5. The charger according to claim 4, characterized in that: The load interface comprises a USB interface, the USB interface is externally connected to a load, and the load adjusts its own power according to the power level that the charger circuit can provide.

6. The charger according to claim 5, characterized in that: The USB interface includes at least one of a Mini USB interface, a MicroUSB interface, a USB Type-A interface, a USB Type-B interface, and a USB Type-C interface.

7. The charger according to claim 4, characterized in that: The control circuit includes a fast charging protocol chip.

8. The charger according to claim 4, characterized in that: The charger circuit further includes a third switch, which is arranged between the input power source and the same-name end of the primary winding.

9. The charger according to claim 8, characterized in that: The third switch includes a field effect transistor.

10. The charger according to any one of claims 5 to 8, characterized in that: The charger circuit also includes an AC / DC converter, The AC / DC converter is arranged between the AC power source and the primary winding.

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