Title of Invention: Device to be charged and charging method Abstract: The present disclosure provides a device to be charged and a charging method. The device to be charged includes: a charging interface; a first charging circuit, coupled with the charging interface, configured to receive an output voltage and an output current of an adapter via the charging interface and to directly apply the output voltage and the output current of the adapter to both ends of a plurality of battery cells coupled in series in the device to be charged, so as to perform a direct charging on the plurality of battery cells. With the present disclosure, heat generated in the charging process can be reduced while ensuring the charging speed. Detailed Description: Part general_description_paragraphs: Part CROSS REFERENCE TO RELATED APPLICATIONS: This application is a continuation application of U.S. application Ser. No. 15/565,512 filed Oct. 10, 2017, which is a US national phase application of International Application No. PCT/CN2017/074825, filed on Feb. 24, 2017, which claims priority to International Application No. PCT/CN2016/101944, filed on Oct. 12, 2016, and International Application No. PCT/CN2017/073653, filed on Feb. 15, 2017. The entire contents of each of the above applications are incorporated herein by reference. Part TECHNICAL FIELD: The present disclosure generally relates to a charging technical field, and more particularly, to a device to be charged and a charging method. Part BACKGROUND: Nowadays, mobile terminals such as smart phones are increasingly favored by consumers. However, the mobile terminal consumes large power energy, and needs to be charged frequently. One feasible solution for improving a charging speed is to adopt a large current to charge a device to be charged. The larger the charging current, the faster the charging speed of the device to be charged. However, the heating problem of the device to be charged becomes serious accordingly. Thus, under the premise of ensuring the charging speed, how to reduce the heat generated in the device to be charged is an urgent problem to be resolved. Part SUMMARY: The present disclosure provides a device to be charged and a charging method, which may reduce the heat generated in the device to be charged under the premise of ensuring the charging speed. Embodiments of the present disclosure provide a device to be charged. The device to be charged includes: a charging interface; a first charging circuit, coupled with the charging interface, configured to receive an output voltage and an output current of an adapter via the charging interface and to directly apply the output voltage and the output current of the adapter to both ends of a plurality of battery cells coupled in series in the device to be charged, so as to perform a direct charging on the plurality of battery cells. Embodiments of the present disclosure provide a charging method. The charging method is applied for charging a device to be charged. The device to be charged includes a charging interface. The charging method includes: receiving an output voltage and an output current of an adapter via the charging interface; directly applying the output voltage and the output current of the adapter to both ends of a plurality of battery cells coupled in series in the device to be charged, so as to perform a direct charging on the plurality of battery cells; and equalizing voltages of respective battery cells of the plurality of battery cells. Part DETAILED DESCRIPTION: Before describing a device to be charged and a charging method according to embodiments of the present disclosure, an adapter for charging the device to be charged in the related art (hereinafter, “related adapter”) will be described. Voltage outputted by the related adapter is basically constant, such as 5V, 9V, 12V or 20V or the like, when the related adapter works in a constant voltage mode. The voltage outputted by the related adapter is unsuitable for being directly applied to both ends of a battery. It is required to convert the voltage by a conversion circuit in the device to be charged to obtain a charging voltage and/or charging current expected by the battery in the device to be charged. The charging current may be a direct current. The conversion circuit is configured to convert the voltage outputted by the related adapter, to meet a requirement of the charging voltage and/or charging current expected by the battery. As an example, the conversion circuit may be a charging management module, such as a charging integrated circuit (IC) in the device to be charged. During a charging process of the battery, the conversion circuit may be configured to manage the charging voltage and/or charging current of the battery. The conversion circuit may have at least one of a voltage feedback function and a current feedback function, so as to manage the charging voltage and/or charging current of the battery. For example, the charging process of the battery may include at least one of a trickle charging stage, a constant current charging stage and a constant voltage charging stage. In the trickle charging stage, the conversion circuit may utilize a current feedback loop to ensure that a current flowing into the battery in the trickle charging stage meets the charging current (such as a first charging current) expected by the battery. In the constant current charging stage, the conversion circuit may utilize a current feedback loop to ensure that the current flowing into the battery in the constant current charging stage meets the charging current (such as a second charging current, which may be greater than the first charging current) expected by the battery. In the constant voltage charging stage, the conversion circuit may utilize a voltage feedback loop to ensure that a voltage applied to both ends of the battery in the constant voltage charging stage meets the charging voltage expected by the battery. As an example, when the voltage outputted by the related adapter is greater than the charging voltage expected by the battery, the conversion circuit may be configured to perform a buck conversion on the voltage outputted by the related adapter to enable a buck-converted charging voltage to meet the requirement of the charging voltage expected by the battery. As another example, when the voltage outputted by the related adapter is less than the charging voltage expected by the battery, the conversion circuit may be configured to perform a boost conversion on the voltage outputted by the related adapter to enable a boost-converted charging voltage to meet the requirement of the charging voltage expected by the battery. As another example, assume that the related adapter outputs a constant voltage of 5V. When the related adapter charges a single battery cell (such as a lithium battery cell, a charging cut-off voltage of a single battery cell is typically 4.2V), the conversion circuit (for example, a buck circuit) may perform a buck conversion on the voltage outputted by the related adapter, such that the charging voltage obtained after the buck conversion meets a requirement of the charging voltage expected by the single battery cell. As yet another example, assume that the related adapter outputs a constant voltage of 5V. When the related adapter charges a plurality of (two or more) battery cells (such as lithium battery cell, a charging cut-off voltage of a single battery cell is typically 4.2V) coupled in series, the conversion circuit (for example, a boost circuit) may perform a boost conversion on the voltage outputted by the related adapter, such that the charging voltage obtained after the boost conversion meets a requirement of the charging voltage expected by the plurality of battery cells. Limited by a poor conversion efficiency of the conversion circuit, a part of electric energy is lost in a form of heat, and the heat may gather inside the device to be charged. A design space and a space for heat dissipation of the device to be charged are small (for example, the physical size of a mobile terminal used by a user becomes thinner and thinner, while plenty of electronic elements are densely arranged in the mobile terminal to improve performance of the mobile terminal), which not only increases difficulty in designing the conversion circuit, but also results in that it is hard to dissipate the heat gathered in the device to be charged in time, thus further causing an abnormity of the device to be charged. For example, the heat gathered on the conversion circuit may cause a thermal interference on electronic elements neighboring the conversion circuit, thus causing abnormal operations of the electronic elements. For another example, the heat gathered on the conversion circuit may shorten the service life of the conversion circuit and neighboring electronic elements. For yet another example, the heat gathered on the conversion circuit may cause a thermal interference on the battery, thus causing abnormal charging and/or abnormal discharging of the battery. For still another example, the heat gathered on the conversion circuit may increase the temperature of the device to be charged, thus affecting user experience during the charging. For still yet another example, the heat gathered on the conversion circuit may short-circuit the conversion circuit, such that the voltage outputted by the related adapter is directly applied to both ends of the battery, thus causing an over-voltage charging of the battery, which brings safety hazard if the over-voltage charging lasts for a long time, for example, the battery may explode. The adapter according to embodiments of the present disclosure may obtain status information of the battery. The status information of the battery at least includes electric quantity information and/or voltage information of the battery. The adapter adjusts the voltage outputted by itself according to the obtained status information of the battery, to meet the requirement of the charging voltage and/or charging current expected by the battery. The output voltage after the adjustment may be directly applied to both ends of the battery for charging the battery (hereinafter, “direct charging”). The voltage outputted by the adapter may be a voltage with a stable voltage value or a voltage with a pulsating waveform. The adapter may have a voltage feedback function and/or a current feedback function, so as to realize a closed-loop feedback control on the charging voltage and/or charging current of the battery. In some embodiments, the adapter may adjust the voltage outputted by itself according to the obtained status information of the battery as follows. The adapter may obtain the status information of the battery in real time, and adjust the voltage outputted by itself according to the status information of the battery obtained in real time, to meet the charging voltage and/or charging current expected by the battery. In some embodiments, the adapter may adjust the voltage outputted by itself according to the status information of the battery obtained in real time as follows. During the charging process, with the increasing of the charging voltage of the battery, the adapter may obtain status information of the battery at different time points in the charging process, and adjust the voltage outputted by itself in real time according to the status information of the battery at different time points in the charging process, to meet the requirement of the charging voltage and/or charging current expected by the battery. The output voltage after the adjustment of the adapter may be directly applied to both ends of the battery to charge the battery. For example, the charging process of the battery may include at least one of a trickle charging stage, a constant current charging stage and a constant voltage charging stage. In the trickle charging stage, the adapter may output the first charging current (the first charging current may be a constant direct current or a current with a pulsating waveform) to charge the battery, so as to meet the requirement of the charging current expected by the battery. In the constant current charging stage, the adapter may utilize a current feedback loop to ensure that the current outputted by the adapter and flowing into the battery in the constant current charging stage meets the requirement of the charging current expected by the battery (such as a second charging current, which may be a constant direct current or a current with a pulsating waveform, and may be greater than the first charging current. For example, when the second charging current is a current with a pulsating waveform, the second charging current being greater than the first charging current means that, a peak value of the current with the pulsating waveform in the constant current charging stage is greater than that of the current with the pulsating waveform in the trickle charging stage, while “constant current” of the constant current charging stage means that, in the constant current charging stage, a peak value or a mean value of the current with the pulsating waveform is basically constant). In the constant voltage charging stage, the adapter may utilize a voltage feedback loop to ensure that a voltage (i.e., a voltage with a pulsating waveform) outputted by the adapter to the device to be charged within the constant voltage charging stage is constant. For example, the adapter according to embodiments of the present disclosure is mainly configured to control the constant current charging stage of the battery in the device to be charged. In other embodiments, the control on the trickle charging stage and the constant voltage charging stage of the battery in the device to be charged can be realized by the adapter according to embodiments of the present disclosure in coordination with an additional charging chip in the device to be charged. Compared to the constant current charging stage, the charging power received by the battery in the trickle charging stage and the constant voltage charging stage is smaller, such that the conversion loss and heat accumulation of the charging chip in the device to be charged is acceptable. It some embodiments, the constant current charging stage or the constant current mode involved in embodiments of the present disclosure may refer to a charging stage or a charging mode in which the current outputted by the adapter is controlled. It is unnecessary to keep the current outputted by the adapter completely constant. For example, when the current outputted by the adapter is a current with a pulsating waveform, the constant current may refer to that, a peak value or a mean value of the current with the pulsating waveform outputted by the adapter is basically constant, or keeps constant during a certain time period. For example, in practice, the adapter typically adopts a multi-stage constant current mode for charging in the constant current charging stage. The multi-stage constant current charging may include M constant current stages, where M is an integer no less than 2. The first charging stage of the multi-stage constant current charging starts with a predetermined charging current. M constant current stages in the multi-stage constant current charging are performed in sequence from the first charging stage to the (M−1)th charging stage. After the constant current charging is switched from one constant current stage to the next constant current stage, the peak value or mean value of the current with the pulsating waveform may be decreased. When the battery voltage reaches a charging stop voltage threshold, the constant current charging is switched from the present constant current stage to the next constant current stage. The current change between two adjacent constant current stages may be gradual, or may be in a stepped skip manner. Further, it should be noted that, the device to be charged according to embodiments of the present disclosure may, for example, be a terminal or a communication terminal. The terminal or the communication terminal includes, but is not limited to a device configured to receive/transmit communication signals via a wired connection (for example, public switched telephone network (PSTN), digital subscriber line (DSL) connection, digital cable connection, direct cable connection and/or another data connection/network) and/or via a wireless interface (for example, cellular network, wireless local area network (WLAN), digital TV network such as digital video broadcasting handheld (DVB-H) network, satellite network, an amplitude modulation-frequency modulation (AM-FM) broadcasting transmitter, and/or a wireless interface of another communication terminal). The communication terminal configured to communicate via the wireless interface may be referred to as “wireless communication terminal”, “wireless terminal” and/or “mobile terminal”. Examples of a mobile terminal include, but are not limited to a satellite phone or a cell phone, a terminal combining a cell radio phone and a personal communication system (PCS) having capability of data process, fax, and data communication, a personal digital assistant (PDA) including a radio phone, a pager, Internet/Intranet access, a web browser, a note pad & address book, a calendar and/or a global positioning system (GPS) receiver, and a common laptop and/or handheld receiver, or other electronic devices including a radio phone transceiver. In addition, in embodiments of the present disclosure, when the voltage with the pulsating waveform outputted by the adapter is directly applied to both ends of the battery in the device to be charged to charge the battery, the charging current may be characterized by a pulsating waveform such as a steamed bun waveform. In some embodiments, the charging current may be used to charge the battery intermittently. A period of the charging current may vary with a frequency of an input alternating current (such as a frequency of an alternating current power grid). For example, the frequency corresponding to the period of the charging current may be an integral multiple or a fraction of the frequency of the power grid. Moreover, when the charging current is used to charge the battery intermittently, a current waveform corresponding to the charging current may be formed of one pulse or a set of pulses synchronous to the power grid. As an example, during the charging process (such as, at least one of the trickle charging stage, the constant current charging stage and the constant voltage charging stage), the battery may receive the pulsating direct current (having a direction unchanged and amplitude varying with time), the alternating current (having a direction and amplitude both varying with time) or the constant direct current (having a direction and amplitude both unchanged) outputted by the adapter. In the related art, the device to be charged typically includes only a single battery cell. When the single battery cell is charged with large charging current, a serious heating phenomenon occurs on the device to be charged. In order to ensure the charging speed of the device to be charged and relieve the heating phenomenon on the device to be charged during the charging, the structure of the battery cell in the device to be charged according to embodiments of the present disclosure is improved by incorporating a plurality of battery cells coupled in series, and a direct charging is performed on the plurality of battery cells. Embodiments of the present disclosure will be described in detail with reference to FIG. 1. FIG. 1 is a schematic structure diagram illustrating a device to be charged according to embodiments of the present disclosure. The device 10 to be charged in FIG. 1 includes a charging interface 11 and a first charging circuit 12. The first charging circuit 12 is coupled with the charging interface 11. The first charging circuit 12 receives an output voltage and an output current of an adapter via the charging interface 11, and directly applies the output voltage and the output current of the adapter to both ends of the plurality of battery cells 13 coupled in series in the device to be charged so as to perform a direct charging on the plurality of battery cells 13. In order to solve the heating problem due to a conversion circuit and to reduce power consumption, in embodiments of the present disclosure, the plurality of battery cells 13 are charged in a direct charging manner via the first charging circuit 12. The solution of direct charging can reduce the heat generated in the device to be charged to some extent. However, when the output current of the adapter is too large, for example, when the output current of the adapter reaches a value ranging from 5 A to 10 A, the device to be charged may have a serious heating problem, thus causing a safety hazard. In order to ensure the charging speed and to further relieve the heating phenomenon of the device to be charged, in embodiments of the present disclosure, the structure of the battery cell in the device to be charged is further improved, i.e., the plurality of battery cells coupled in series are incorporated. Compared to the solution of a single battery cell, to achieve the same charging speed, the charging current required by the plurality of battery cells is 1/N (N is the number of the plurality of battery cells coupled in series in the device to be charged) of that required by the single battery cell. In other words, under the premise of the same charging speed, the charging current may be reduced greatly in embodiments of the present disclosure, thus further reducing the heat generated during the charging process in the device to be charged. For example, for the single battery cell of 3000 mAh, a charging current of 9 A is required to reach a charging rate of 3 C. In order to reach the same charging speed and to reduce the heat generated during the charging process in the device to be charged, two battery cells each of which is 1500 mAh may be coupled in series, so as to replace a single battery cell of 3000 mAh. In this way, it merely requires a charging current of 4.5 A to reach the charging rate of 3 C. Compared to a charging current of 9 A, the charging current of 4.5 A causes obviously less heat. In some embodiments, since the first charging circuit 12 charges the plurality of battery cells 13 in the direct charging manner, the output voltage received by the first charging circuit 12 from the adapter needs to be greater than a total voltage of the plurality of battery cells 13. Generally, a working voltage of a single battery cell is typically within 3.0V-4.35V. For example, for two battery cells coupled in series, the output voltage of the adapter may be greater than or equal to 10V. In some embodiments, a type of the charging interface 11 is not limited in embodiments of the present disclosure. For example, the charging interface 11 may be a universal serial bus (USB) interface, which may be a common USB interface or a micro USB interface, or a Type-C interface. The first charging circuit 12 may charge the plurality of battery cells 13 via a power wire in the USB interface. The power wire in the USB interface may be a VBus wire and/or a ground wire in the USB interface. The plurality of battery cells 13 in embodiments of the present disclosure may include battery cells with the same or similar specification and parameters. The battery cells with the same or similar specification are easy to manage. The overall performance and service life of the plurality of battery cells 13 can be improved when battery cells with the same or similar specification and parameters are selected. In some embodiments, the plurality of battery cells 13 coupled in series can realize voltage-dividing on the output voltage of the adapter. In the related art, the device to be charged (or elements in the device to be charged, or a chip in the device to be charged) typically adopts a single battery cell for power supply. In embodiments of the present disclosure, the plurality of battery cells coupled in series are incorporated, which have a high total voltage unsuitable for being used to supply power for the device to be charged (or elements in the device to be charged, or a chip in the device to be charged) directly. For solving this problem, one feasible implementation is to adjust the working voltage of the device to be charged (or elements in the device to be charged, or a chip in the device to be charged) to support the power supply of the plurality of battery cells. However, with this implementation, the device to be charged needs to be changed greatly, thus causing a high cost. In the following, an implementation according to embodiments of the present disclosure is described in detail with reference to FIG. 2 and FIG. 3, in which the problem of how to supply power using the plurality of battery cells can be solved. In some embodiments, as illustrated in FIG. 2, the device 10 to be charged further includes a step-down circuit 21 and a power supply circuit 22. An input end of the step-down circuit 21 is coupled to both ends of the plurality of battery cells 13 respectively. The step-down circuit 21 is configured to convert the total voltage of the plurality of battery cells 13 into a first voltage V1, where aV1b, a represents the minimum working voltage of the device 10 to be charged (or elements in the device 10 to be charged, or a chip in the device 10 to be charged), and b represents the maximum working voltage of the device 10 to be charged (or elements in the device 10 to be charged, or a chip in the device 10 to be charged). The power supply circuit 22 is coupled to an output end of the step-down circuit 21. The power supply circuit 22 supplies power for the device 10 to be charged based on the first voltage. In embodiments of the present disclosure, the step-down circuit 21 is incorporated on the basis of the embodiment described with regard to FIG. 1. When the device to be charged is in a working state, the total voltage of the plurality of battery cells 13 is stepped down by the step-down circuit 21 to obtain a first voltage. Since the first voltage is between the minimum working voltage and the maximum working voltage of the device 10 to be charged, the first voltage can be directly used to supply power for the device to be charged, thus solving the problem of how to supply power using the plurality of battery cells. In some embodiments, the total voltage of the plurality of battery cells 13 varies with the electric quantity of the plurality of battery cells 13. The aforementioned total voltage of the plurality of battery cells 13 may refer to a present total voltage of the plurality of battery cells 13. For example, the working voltage of a single battery cell is in a range of 3.0V-4.35V. Assuming that the plurality of battery cells include two battery cells and the present voltage of each battery cell is 3.5V, the aforementioned total voltage of the plurality of battery cells 13 is 7V. For example, the working voltage of the single battery cell is in a range of 3.0V-4.35V, i.e., a=3.0V and b=4.35V. In order to ensure that the power supply voltage of elements in the device to be charged is normal, the step-down circuit 21 may step down the total voltage of the plurality of battery cells 13 to any value in the range of 3.0V-4.35V. There are many ways to implement the step-down circuit 21, for example, a buck circuit, a charge pump or the like can be used for stepping down voltage. In some embodiments, for simplifying the implementation of a circuit, the step-down circuit 21 may be a charge pump. With the charge pump, the total voltage of the plurality of battery cells 13 may be directly stepped down to 1/N of the present total voltage, where N is the number of the plurality of battery cells 13. A conventional buck circuit includes a switch transistor, an inductor and other elements. Since the power consumption of the inductor is large, the power consumption is high when the buck circuit is used to buck voltage. Compared to the buck circuit, the charge pump mainly utilizes a switch transistor and a capacitor to buck voltage, and the capacitor does not consume additional energy basically. Thus, the power consumption during the step-down process can be decreased when the charge pump is used. In detail, the switch transistor in the charge pump controls the charging and discharging of the capacitor in a certain manner, such that the input voltage is stepped down by a certain factor (in embodiments of the present disclosure, the factor is 1/N), and the desired voltage can be obtained. In some embodiments, as illustrated in FIG. 3, the device 10 to be charged further includes a power supply circuit 32. An input end of the power supply circuit 32 is coupled to both ends of any one of the plurality of battery cells 13. The power supply circuit 32 supplies power for the elements in the device 10 to be charged based on the voltage of a single battery cell 13. In some embodiments, the voltage after the buck conversion of the step-down circuit may have a pulsating wave, thus affecting the quality of power supply of the device to be charged. In embodiments of the present disclosure, the power supply voltage is derived from both ends of one of the plurality of battery cells 13 directly to supply power for elements in the device to be charged. Since the voltage outputted by the battery cell is stable relatively, in embodiments of the present disclosure, not only the problem of how to supply power using the plurality of battery cells can be solved but also the quality of power supply of the device to be charged can be guaranteed. Further, on the basis of the embodiment described with regard to FIG. 3, as illustrated in FIG. 4, the device 10 to be charged further includes an equalization circuit 33. The equalization circuit 13 is coupled with the plurality of battery cells 13. The equalization circuit 13 is configured to equalize voltages of respective battery cells of the plurality of battery cells 13. When the power supply mode illustrated in FIG. 3 is adopted, the battery cell that supplies power for the elements in the device to be charged (hereinafter, this battery cell is referred to as a main battery cell, and other battery cells are referred as slave battery cells) consume electric quantity constantly, such that the voltage of the main battery cell and the voltage of the salve battery cell are not equalized (or, the voltage of the main battery cell and the voltage of the slave battery cell are inconsistent). The overall performance of the plurality of battery cells 13 is decreased when the voltages of respective battery cells 13 are not equalized, thus affecting the service life of the plurality of battery cells 13. In addition, it is hard to manage the plurality of battery cells 13 when the voltages of respective battery cells 13 are not equalized. Thus, in embodiments of the present disclosure, the equalization circuit 33 is introduced, to equalize the voltages of respective cells of the plurality of battery cells 13, thus improving the overall performance of the plurality of battery cells 13 and facilitating the unified management of the plurality of battery cells 13. There are many ways to implement the equalization circuit 33. For example, a load may be coupled to both ends of the slave battery cell to consume the electric quantity of the slave battery cell, such that the electric quantity of the slave battery cell may be consistent with the electric quantity of the main battery cell. In an embodiment, the slave battery cell may be used to charge the main battery cell, until the voltage of the main battery cell is consistent with the voltage of the slave battery cell. As an example, the plurality of battery cells 13 may include a first battery cell 131 and a second battery cell 132 (see FIG. 15). The equalization circuit 33 is configured to transfer electric quantity between the first battery cell and the second battery cell in an electromagnetic coupling manner. In embodiments of the present disclosure, the equalization circuit is configured to equalize the voltages of respective battery cells in the electromagnetic coupling manner, such that the overall performance of the plurality of battery cells 13 is improved and it is convenient to manage the plurality of battery cells 13. In an embodiment, the first battery cell 131 may be the slave battery cell and the second battery cell 132 may be the main battery cell. The first battery cell 131 may transfer electric quantity to the second battery cell 132 via the equalization circuit 33. In an embodiment, each of the first battery cell 131 and the second battery cell 132 may include one battery cell or may include at least two battery cells, which is not limited herein. In an embodiment, when each of the first battery cell 131 and the second battery cell 132 includes one battery cell, the first battery cell 131 may be any one of the plurality of battery cells 13, and the second battery cell 132 may be any battery cell other than the first battery cell 131 in the plurality of battery cells 13. As an example, as illustrated in FIG. 11, the equalization circuit 33 may include a first circuit 41 and a second circuit 42. The first circuit 41 is coupled with the first battery cell 131, and the second circuit 42 is coupled with the first battery cell 131 and the second battery cell 132 respectively. When the first circuit 41 is switched on, the first circuit 41 is configured to couple energy outputted by the first battery cell 131 to the second circuit 42 in an electromagnetic coupling manner, such that the second circuit 42 generates a first charging current based on the energy from the first circuit 41, and charges the first battery cell and the second battery cell with the first charging current. In embodiments of the present disclosure, the first circuit 41 in the equalization circuit 33 couples the energy outputted by the first battery cell 131 to the second circuit 42, and the second circuit 42 generates the first charging current based on the energy from the first circuit 41, and charges the first battery cell 131 and the second battery cell 132 with the first charging current. When the first circuit is switched on, the equalization circuit 33 transfers the energy obtained from the firs battery cell 131 to the first battery cell 131 and the second battery cell 132, so as to realize an electric quantity transfer between the first battery cell 131 and the second battery cell 132. In an embodiment, as illustrated in FIG. 12, the equalization circuit 33 further includes a third circuit 43. The third circuit 43 is coupled with the second battery cell 132. When the third circuit 43 is switched on, the third circuit 43 is configured to couple energy outputted by the second battery cell 132 to the second circuit 42 in an electromagnetic coupling manner, such that the second circuit 42 generates a second charging current based on the energy from the third circuit 43, and charges the first battery cell 131 and the second battery cell 132 with the second charging current. In embodiments of the present disclosure, when the third circuit 43 is switched on, the equalization circuit 33 can also transfer the energy obtained from the second battery cell 132 to the first battery cell 131 and the second battery cell 132, so as to realize the electric quantity transfer between the first battery cell 131 and the second battery cell 132. In an embodiment, in an example illustrated in FIG. 12, when the voltage of the first battery cell 131 is greater than that of the second battery cell 132, the first circuit 41 and the second circuit 42 may be switched on, and the third circuit 43 may be switched off, such that the energy of the first battery cell 131 is transferred to the first battery cell 131 and the second battery cell 132. When the voltage of the second battery cell 132 is greater than that of the first battery cell 131, the first circuit 41 may be switched off, and the second circuit 42 and the third circuit 43 may be switched on, such that the energy of the second battery cell 132 is transferred to the first battery cell 131 and the second battery cell 132. In this way, voltage equalization of respective battery cells can be realized. FIG. 13 is a schematic structure diagram illustrating an equalization circuit according to another embodiment of the present disclosure. As illustrated in FIG. 13, the equalization circuit 33 includes a fourth circuit 44 and a fifth circuit 45. The fourth circuit 44 is coupled with the first battery cell 131 and the second battery cell 132 respectively, and the fifth circuit 45 is coupled with the first battery cell 131. When both the fourth circuit 44 and the fifth circuit 45 are switched on, the fourth circuit 44 is configured to couple energy outputted by the first battery cell 131 and the second battery cell 132 to the fifth circuit 45 in an electromagnetic coupling manner, such that the fifth circuit 45 generates a second charging current based on the energy from the fourth circuit 44, and charges the first battery cell 131 with the second charging current. In embodiments of the present disclosure, the fourth circuit 44 in the equalization circuit 33 couples the energy outputted by the first battery cell 131 and the second battery cell 132 to the fifth circuit 45, and the fifth circuit 45 generates the second charging current based on the energy from the fourth circuit 44, and charges the first battery cell 131 with the second charging current. When the fourth circuit 44 is switched on, the equalization circuit 33 transfers the energy obtained from the first battery cell 131 and the second battery cell 132 to the first battery cell 131, so as to realize an electric quantity transfer between the first battery cell 131 and the second battery cell 132. In an embodiment, as illustrated in FIG. 14, the equalization circuit 33 further includes a sixth circuit 46. The sixth circuit 46 is coupled with the second battery cell 132. When both the fourth circuit 44 and the sixth circuit 46 are switched on, the fourth circuit 44 is configured to couple energy outputted by the first battery cell 131 and the second battery cell 132 to the sixth circuit 46 in an electromagnetic coupling manner, such that the sixth circuit 46 generates a third charging current based on the energy from the fourth circuit 44, and charges the second battery cell 132 with the third charging current. In embodiments of the present disclosure, when the sixth circuit 46 is switched on, the equalization circuit 33 can transfer the energy obtained from the first battery cell 131 and the second battery cell 132 to the second battery cell 132, so as to realize the electric quantity transfer between the first battery cell 131 and the second battery cell 132. In an embodiment, in an example illustrated in FIG. 14, when the voltage of the second battery cell 132 is greater than that of the first battery cell 131, the fourth circuit 44 and the fifth circuit 45 may be switched on, and the sixth circuit 46 may be switched off, such that the energy of the first battery cell 131 and the second battery cell 132 is transferred to the first battery cell 131. When the voltage of the first battery cell 131 is greater than that of the second battery cell 132, the fifth circuit 45 may be switched off, and the fourth circuit 44 and the sixth circuit 46 may be switched on, such that the energy of the first battery cell 131 and the second battery cell 132 is transferred to the second battery cell 132. In this way, voltage equalization of respective battery cells can be realized. FIG. 15 is a circuit schematic illustrating an equalization circuit according to an embodiment of the present disclosure. As illustrated in FIG. 15, the first circuit 41 may include a first inductor M1 and a switch transistor Q1. The second circuit 42 may include a second inductor M2 and a rectifier diode. The third circuit 43 may include a third inductor M3 and a switch transistor Q2. The first inductor M1 and the second inductor M2 are coupled with each other, and the second inductor M2 and the third inductor M3 are coupled with each other. In an example illustrated in FIG. 15, the switch transistor Q1 or the switch transistor Q2 may be configured to generate a pulse current. For example, when the switch transistor Q1 works and the switch transistor Q2 is switched off, the equalization circuit 33 may transfer the electric quantity of the first battery cell 131 to the first battery cell 131 and the second battery cell 132 in an electromagnetic coupling manner. Similarly, when the switch transistor Q2 works and the switch transistor Q1 is switched off, the equalization circuit 33 may transfer the electric quantity of the second battery cell 132 to the first battery cell 131 and the second battery cell 132 in an electromagnetic coupling manner. FIG. 16 is a circuit schematic illustrating an equalization circuit according to another embodiment of the present disclosure. As illustrated in FIG. 16, the fourth circuit 44 may include a fourth inductor M4 and a switch transistor Q4. The fifth circuit 45 may include a fifth inductor M5 and a switch transistor Q5. The sixth circuit 46 may include a sixth inductor M6 and a switch transistor Q6. The fourth inductor M4 and the fifth inductor M5 are coupled with each other, and the fourth inductor M4 and the sixth inductor M6 are coupled with each other. In an example illustrated in FIG. 16, the switch transistor Q4 is configured to generate a pulse current. The switch transistor Q5 is configured to control the fifth circuit 45 to switch on or off and the switch transistor Q6 is configured to control the sixth circuit 46 to switch on or off. For example, when the switch transistor Q4 works, the switch transistor Q5 is switched on, and the switch transistor Q6 is switched off, the equalization circuit 33 may transfer the electric quantity of the first battery cell 131 and the second battery cell 132 to the first battery cell 131 in an electromagnetic coupling manner. Similarly, when the switch transistor Q4 works, the switch transistor Q5 is switched off, and the switch transistor Q6 is switched on, the equalization circuit 33 may transfer the electric quantity of the first battery cell 131 and the second battery cell 132 to the second battery cell 132 in an electromagnetic coupling manner. As the output power of the adapter increases, a lithium precipitation may occur when the adapter charges the battery cell in the device to be charged, thus shortening the service life of the battery cell. In order to improve the reliability and safety of the battery cell, in some embodiments, the adapter may be controlled to output a pulsating direct current (or called as a unidirectional pulsating output current, or called as a current with a pulsating waveform, or called as a steamed bun current). Since the first charging circuit 12 charges the plurality of battery cells 13 in a direct charging manner, the pulsating direct current outputted by the adapter may be directly applied to both ends of the plurality of battery cells 13. As illustrated in FIG. 5, the magnitude of the pulsating direct current changes periodically. Compared to the constant direct current, the pulsating direct current may reduce the lithium precipitation and improve the service life of the battery cell. In addition, compared to the constant direct current, the pulsating direct current may reduce a probability and intensity of arc discharge of a contact of a charging interface and improve the service life of the charging interface. There are many ways to set the output current of the adapter as the pulsating direct current. For example, a primary filter circuit and a secondary filter circuit may be removed from the adapter, such that the obtained output current of the adapter is the pulsating direct current. In some embodiments, the output current of the adapter received by the first charging circuit 12 may be an alternating current (for example, the primary filter circuit, a secondary rectifier circuit and the secondary filter circuit are removed from the adapter, and then the obtained output current of the adapter is the alternating current), which also can reduce the lithium precipitation and improve the service life of the battery cell. In some embodiments, the output voltage and the output current of the adapter received by the first charging circuit 12 via the charging interface 11 may be a voltage and a current outputted by the adapter in a constant current mode (the constant current charging mode or the constant current charging stage) respectively. In some embodiments, as illustrated in FIG. 6, the plurality of battery cells 13 may be encapsulated in one battery 51. Further, the battery 51 may include a battery protection plate 52, by means of which over-voltage and over-current protection, electric quantity balance management and electric quantity management or the like may be realized. In some embodiments, the plurality of battery cells 13 may be encapsulated in a plurality of batteries. In some embodiments, as illustrated in FIG. 7, the device 10 to be charged may further include a second charging circuit 61. The second charging circuit 61 may include a step-up circuit 62. The step-up circuit 62 has both ends coupled to the charging interface 11 and the plurality of battery cells 13 respectively. The step-up circuit 62 may receive the output voltage of the adapter via the charging interface 11, step up the output voltage of the adapter to a second voltage, and apply the second voltage to both ends of the plurality of battery cells 13 to charge the plurality of battery cells 13. The output voltage of the adapter received by the second charging circuit 61 is less than the total voltage of the plurality of battery cells 13, and the second voltage is greater than the total voltage of the plurality of battery cells 13. It can be seen that, the first charging circuit 12 charges the plurality of battery cells 13 in a direct charging manner. In the direct charging manner, it is required that the output voltage of the adapter is greater than the total voltage of the plurality of battery cells 13. For example, in a case that two battery cells are coupled in series, if the present voltage of each battery cell is 4V, it is required that the output voltage of the adapter is at least greater than 8V when the first charging circuit 12 is used to charge the two battery cells. However, an output voltage of a normal adapter (such as the related adapter above mentioned) is typically 5V, which is unable to charge the plurality of battery cells 13 via the first charging circuit 12. For compatibility with the normal adapter, the second charging circuit 61 is incorporated in embodiments of the present disclosure, and the second charging circuit 61 includes the step-up circuit 62 which may step up the output voltage of the adapter to the second voltage greater than the total voltage of the plurality of battery cells 13, such that the problem that the normal adapter cannot charge the plurality of battery cells 13 coupled in series is solved. The voltage value of the output voltage of the adapter received by the second charging circuit 61 is not limited in embodiments of the present disclosure, as long as the output voltage of the adapter is less than the total voltage of the plurality of battery cells 13, and the plurality of battery cells 13 can be charged after the output voltage of adapter is stepped up by the second charging circuit 61. The specific form of the step-up circuit is not limited in embodiments of the present disclosure. For example, a boost circuit or a charge pump can be used to boost the voltage. In some embodiments, the second charging circuit 61 may be designed as a conventional charging circuit, i.e., a conversion circuit (such as a charging IC) is disposed between the charging interface and the battery cell. The conversion circuit may perform a constant voltage and constant current control on the charging process of the adapter, and adjust the output voltage of the adapter according to actual situations, for example, boost or buck voltage. In embodiments of the present disclosure, the voltage boost function of the conversion circuit is used for boosting the output voltage of the adapter to the second voltage greater than the total voltage of the plurality
{'bibliographic_information': "{'country': 'US', 'doc-number': '16701264', 'kind': 'B2', 'date': '20191203', 'invention_title': 'Device to be charged and charging method'}", 'source_file': './grant/2021/ipg210209.xml', 'source_data': 'USPTO-Grant'}