Patent Publication Number: US-11050289-B2

Title: Power supply circuit, power supply device and control method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2017/102932, filed Sep. 22, 2017, the entire disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to a charging technology field, and more particularly, to a power supply circuit, a power supply device and a control method. 
     BACKGROUND 
     A power supply circuit typically includes a primary conversion unit and a secondary conversion unit. The primary conversion unit generally includes a primary rectifier unit and a primary filtering unit. The primary filtering unit typically adopts one or more high-capacity liquid electrolytic capacitors (such as, liquid aluminum electrolytic capacitors) to perform primary filtering on a voltage after primary rectification. 
     The liquid electrolytic capacitor has disadvantages of short life and easy cracking, resulting in a short life and insecurity of a conventional power supply circuit. 
     SUMMARY 
     The present disclosure provides a power supply circuit, a power supply device and a control method. 
     In a first aspect, a power supply circuit is provided. The power supply circuit includes: a primary rectifier unit, configured to perform rectification on input alternating current to output a first voltage having a periodically changing voltage value; a modulation unit, configured to modulate the first voltage to generate a second voltage; a transformer, configured to generate a third voltage based on the second voltage; a secondary rectifier and filtering unit, configured to perform rectification and filtering on the third voltage to generate a fourth voltage and a first current corresponding to the fourth voltage; and a control unit, configured to adjust the first current to generate an output current of the power supply circuit, the output current having a second waveform with a current value periodically changing, and each period of the second waveform containing a duration in which the current value is 0. 
     In a second aspect, a power supply device is provided. The power supply device includes a housing, a circuit board, and a power supply circuit. The circuit board is enclosed by the housing. The power supply circuit is positioned on the circuit board, and the power supply circuit is as described in the first aspect. 
     In a third aspect, a control method of a power supply circuit is provided. The control method includes: performing rectification on input alternating current to output a first voltage having a periodically changing voltage value; modulating the first voltage to generate a second voltage; generating a third voltage based on the second voltage; performing rectification and filtering on the third voltage to generate a fourth voltage and a first current corresponding to the fourth voltage; and adjusting the first current to generate an output current of the power supply circuit, the output current having a second waveform with a current value periodically changing, and each period of the second waveform containing a duration in which the current value is 0. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a power supply circuit according to an embodiment of the present disclosure. 
         FIG. 2  is a schematic diagram illustrating a waveform of a first voltage to be modulated according to an embodiment of the present disclosure. 
         FIG. 3  is a schematic diagram comparing voltage waveforms before and after modulation of a conventional power supply circuit. 
         FIG. 4  is a schematic diagram illustrating a waveform of a second voltage obtained after modulating a first voltage according to an embodiment of the present disclosure. 
         FIG. 5  is a schematic diagram illustrating a first waveform after secondary rectification and filtering according to an embodiment of the present disclosure. 
         FIG. 6  is a schematic diagram of a power supply circuit according to another embodiment of the present disclosure. 
         FIG. 7  is a schematic diagram illustrating a waveform of an output current and a waveform of a control signal for generating the waveform of the output current according to an embodiment of the present disclosure. 
         FIG. 8  is a schematic diagram of a power supply circuit according to yet another embodiment of the present disclosure. 
         FIG. 9  is a schematic diagram of a power supply circuit according to still another embodiment of the present disclosure. 
         FIG. 10  is a schematic diagram illustrating a fast charging process according to an embodiment of the present disclosure. 
         FIG. 11  is a block diagram of a power supply device according to an embodiment of the present disclosure. 
         FIG. 12  is a schematic flow chart of a control method according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the related art, both a primary rectifier unit and a primary filtering unit are provided at a primary side of a power supply circuit. The primary filtering unit generally includes one or more liquid electrolytic capacitors. The liquid electrolytic capacitor has properties of large capacity and strong filtering ability. Due to the existence of the liquid electrolytic capacitor, an output provided by the power supply circuit may be a constant direct current. However, the liquid electrolytic capacitor has disadvantages of short life and easy cracking, resulting in a short life and insecurity of the power supply circuit. Moreover, charging a battery in a device to be charged with the constant direct current will result in polarization and lithium precipitation of the battery, such that a service life of the battery may be reduced. 
     In order to improve the service life and safety of the power supply circuit, and to relieve the polarization and lithium precipitation of the battery during charging process, embodiments of the present disclosure provide a power supply circuit without the liquid electrolytic capacitor at the primary side. Such a power supply circuit may be used to charge the battery in the device to be charged. 
     The device to be charged used in embodiments of the present disclosure may refer to a mobile terminal, such as a “communication terminal” (or “terminal” for short). The “terminal” may include, 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 &amp; 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. 
     As illustrated in  FIG. 1 , the power supply circuit  10  according to an embodiment of the present disclosure may include a primary rectifier unit  11 , a modulation unit  12 , a transformer  13 , and a secondary rectifier and filtering unit  14 . In the following, respective components of the power supply circuit  10  will be described in detail respectively. 
     The primary rectifier unit  11  may be configured to perform rectification on input alternating current to output a first voltage having a periodically changing voltage value. In some cases, the input alternating current (AC) may be referred to as mains supply. The input alternating current may be 220V alternating current, or may be 110V alternating current, which is not limited in embodiments of the present disclosure. 
     A voltage waveform of the first voltage is periodically changing. As illustrated in  FIG. 2 , the waveform of the first voltage may be a pulsating waveform or a steamed bun waveform. 
     Implementation of the primary rectifier unit  11  is not limited in embodiments of the present disclosure. The primary rectifier unit  11  may be a full-bridge rectifier circuit formed of four diodes, or may be a rectifier circuit in other forms, such as a half-bridge rectifier circuit. 
     The modulation unit  12  may be configured to modulate the first voltage to generate a second voltage. In some cases, the modulation unit  12  may be referred to as a chopper unit or a chopper. In other cases, the modulation unit  12  may be referred to as a clipper unit or a clipper. In embodiments of the present disclosure, implementation of the modulation unit  12  is not limited. As an example, the modulation unit  12  may module the first voltage in a PWM (Pulse Width Modulation) mode, or may modulate the first voltage in a frequency modulation mode. 
     It should be noted that, in the related art, a voltage output from the primary rectifier unit  11  (corresponding to the first voltage in embodiments of the present disclosure) needs to be filtered by the primary filtering unit (including one or more liquid electrolytic capacitors) to form the constant direct current. A voltage waveform of the constant direct current is typically a straight line, i.e., the voltage waveform before modulation as illustrated in  FIG. 3 . Then, the modulation unit modulates the constant voltage (chops the waveform), to form the voltage after modulation as illustrated in  FIG. 3 . It can be seen from  FIG. 3  that, with the processing of the modulation unit, the constant voltage signal is chopped into many small square wave pulse signals with same amplitude. 
     In contrast, the power supply circuit provided by embodiments of the present disclosure removes the liquid electrolytic capacitor for primary filtering, and directly modulates the first voltage having the periodically changing voltage value after the primary rectification. Taking the waveform of the first voltage illustrated in  FIG. 2  as an example, the waveform of the second voltage obtained after the modulation may be as illustrated in  FIG. 4 . It can be seen from  FIG. 4  that, the second voltage also contains may small pulse signals, however, amplitudes of these pulse signals are not identical and change periodically. The dashed line in  FIG. 4  indicates an envelope of pulse signals forming the second voltage. Compared with  FIG. 2 , the envelope of pulse signals forming the second voltage is substantially same as the waveform of the first voltage. 
     The transformer  13  may be configured to generate a third voltage based on the second voltage. In other words, the transformer  13  may be configured to couple the second voltage from the primary side of the transformer  13  to the secondary side of the transformer  13 , to obtain the third voltage. For example, the transformer  13  may be configured to perform voltage transformation related operation on the second voltage to obtain the third voltage. The transformer  13  may be a common transformer, or may be a high-frequency transformer of which a working frequency ranges from 50 KHz to 2 MHz. The transformer  13  may include a primary winding and a secondary winding. Forms of the primary winding and the secondary winding, and connection modes between the primary winding and secondary winding and other units in the power supply circuit  10  are related to types of a switching power supply used by the power supply circuit. For example, the power supply circuit  10  may be based on a flyback switching power supply, a forward switching power supply, or a push-pull switching power supply. With different types of the switching power supply on which the power supply circuit is based, the specific forms and the connection modes of the primary winding and the secondary winding of the transformer may be different, which is not limited in embodiments of the present disclosure.  FIG. 1  merely illustrates one possible connection mode of the transformer  13 . 
     The secondary rectifier and filtering unit  14  may include a secondary rectifier unit and a secondary filtering unit. The filtering mode of the secondary filtering unit is not limited in embodiments of the present disclosure. As an example, the secondary filtering unit may adopt a SR (synchronous rectifier) chip to perform synchronous rectification on the voltage (or current) induced by the secondary winding of the transformer. As another example, the secondary filtering unit may adopt a diode to perform secondary rectification. The secondary filtering unit may be configured to perform secondary filtering on the voltage after the secondary rectification. The secondary filtering unit may include one or more solid capacitors, or may include a combination of solid capacitors and common capacitors (such as, ceramic capacitors). 
     After the processing of the secondary rectifier and filtering unit  14 , a fourth voltage and a first current corresponding to the fourth voltage may be obtained. In the following, a waveform of the first current is referred to as a first waveform. The solid line in  FIG. 5  illustrates one example of the first waveform. It can be seen from  FIG. 5  that, the first waveform does not have a constant current value, but have a periodically changing current value, the reason which is explained as follows. 
     Since the liquid electrolytic capacitor is removed from the primary side of the power supply circuit  10 , the second voltage input into the transformer  13  consists of many small pulse signals whose amplitudes periodically changes. Likewise, the third voltage transmitted to the secondary side by the transformer  13  also consists of many small pulse signals whose amplitudes periodically change. The secondary filtering capacitor is provided in the secondary rectifier and filtering unit  14 . However, compared with the liquid electrolytic capacitor, the secondary filtering capacitor typically adopts some low-capacity solid capacitors. A capacitance of the solid capacitor is generally low, and a filtering ability of the solid capacitor is relatively lower. Therefore, the secondary filtering capacitor is mainly configured to filter many small pulse signals outputted after the secondary rectification into a continuous signal which periodically changes. The waveform of this continuous signal is similar to the envelope of these small pulse signals. 
     Further, it can be seen from  FIG. 5  that, the first waveform is not a complete pulsating waveform. Neither Peaks nor valleys of the first waveform reach peaks and valleys of the pulsating waveform (dashed line in  FIG. 5 ). The reasons why peaks of the first waveform do not reach the peaks of the pulsating waveform are mainly in that the power supply circuit  10  generally monitors the output voltage and/or the output current of itself, and performs voltage limiting operation on the output voltage and/or performs current limiting operation on the output current. the voltage limiting and/or current limiting operation will limit the peaks of the pulsating waveform under a preset magnitude, such that the first waveform after peak clipping as illustrated in  FIG. 5  is formed. 
     The reasons why valleys of the first waveform do not reach the valleys of the pulsating waveform are mainly in that the secondary filtering capacitor in the secondary rectifier and filtering unit has a clamping role for a voltage on a charging line at the secondary side, such that the voltage and current on the charging line at the secondary side cannot reach zero point. In detail, when the voltage on the charging line at the secondary side drops to be equal to the voltage value of the secondary filtering capacitor, the secondary filtering capacitor enters a discharging state, such that the voltage on the charging line does not continue to drop, thus clamping the valley of the first waveform at a certain value greater than zero. The specific size of this value is related to the capacitance of the secondary filtering capacitor, which is not limited in embodiments of the present disclosure. 
     It can be seen from the above description that, in the power supply circuit  10  provided by embodiments of the present disclosure, the liquid electrolytic capacitor at the primary side is removed, such that the volume of the power supply circuit is reduced, and the service life and safety of the power supply circuit is improved. 
     The power supply circuit  10  may be used to charge the battery in the device to be charged. During the charging process, if the battery may be controlled to charge and discharge periodically, polarization and lithium precipitation of the battery may be reduced significantly, thus improving the service life and safety of the battery. However, based on the above description related to the secondary filtering, the secondary filtering capacitor in the secondary rectifier and filtering unit  14  has the clamping role for the voltage on the charging line of the power supply circuit  10 , resulting in that the valleys of the waveform of the first current obtained after the secondary filtering (i.e., the first waveform) cannot reach zero points. if the first current is directly outputted as the output current of the power supply circuit  10 , since the first current cannot reach zero points, the battery in the device to be charged may be always in the charging state, which cannot ensure the periodical discharging of the battery. 
     Further, in embodiments of the present disclosure, in order to ensure that the battery can charge and discharge periodically, the power supply circuit  10  may further include a control unit  15 . The control unit  15  may be configured to adjust the first current to generate the output current of the power supply circuit  10 . The output current of the power supply circuit  10  may have a second waveform with a periodically changing current value, and each period of the second waveform includes a duration in which the current value is zero. 
     Each period of the second waveform includes a duration in which the current value is zero and a duration in which the current value is not zero. For the sake of description, the duration in which the current value is zero is referred to as a first duration, and the duration in which the current value is not zero is referred to as a second duration. The second waveform is a waveform of the output current. The current value of the output current in the first duration being zero means that there is no output from the power supply circuit  10  in the first duration. At this time, since the battery in the device to be charging typically needs to charge the system of the device to be charged continuously, the battery is in the discharging state. The current value of the output current in the second duration being not zero means that the output of the power supply circuit  10  is recovered in the second duration. At this time, the battery in the device to be charged is in the charging state. It can be seen that, since each period of the second waveform has the first duration in which the current value is zero and the second duration in which the current value is not zero, the battery in the device to be charged may enter a periodical charging and discharging state, thus significantly reducing the polarization and lithium precipitation of the battery, and improving the service life and safety of the battery. 
     The control unit  15  may be an MCU (micro-control unit). The control unit  15  may control other units in the power supply circuit  10  by sending a control signal to other units in the power supply circuit  10 . The control unit  15  may adjust the first current in various ways, and accordingly, the control unit  15  may be coupled to the other units of the power supply circuit  10  in various ways, which is not limited in embodiments of the present disclosure. Illustration may be made below with reference to  FIGS. 6-9 . 
       FIG. 6  illustrate an embodiment in which the control unit  15  adjusts the first current to form the output current crossing zero points. As illustrated in  FIG. 6 , the power supply circuit  10  may further include a first switch unit  60  configured to control the charging line  61  of the power supply circuit  10  to switch on or off. The charging line  61  may be configured to transmit electric energy. In other words, the charging line  61  may be configured to transmit a charging voltage and/or a charging current to the device to be charged. Taking the power supply circuit  10  charging the device to be charged via a USB (universal serial bus) as an example, the charging line  61  may be for example a VBUS of the USB. 
     The first switch unit  62  may be any element having a line on-off control function. As illustrated in  FIG. 6 , the first switch unit  62  may be a MOS (metal oxide semiconductor) transistor. A gate of the MOS transistor may be coupled to the control unit  15 , for receiving the control signal sent by the control unit  15 . A source and a drain of the MOS transistor may be coupled in serial in the charging line  61 , such that the charging line  61  may be controlled to switch on or off under the control of the control signal. 
     Further, the control unit  15  may be configured to control the first switch unit  62  to switch off in a part of each period of the first waveform, to switch off the output of the power supply circuit  10 . 
     The ways for selecting the above part of each period is not limited in embodiments of the present disclosure, and any one or more durations of each period of the first waveform may be selected as the above part of each period. 
     As an example, the above part of each period may be the duration where the valley of the first waveform is located. In other words, the control unit  15  may control the first switch unit  62  to switch off in a part of all of the duration in which the first waveform is at the valley, to switch off the output of the power supply circuit  10 . Compared with controlling the first switch unit  62  to switch off in the duration of each period other than the duration where the valley is located, controlling the first switch unit  62  to switch off in the duration of each period where the valley is located may ensure a charging efficiency of the battery to the maximum extent while satisfying the periodical charging and discharging of the battery. 
     Assume that the control unit  15  controls the first switch unit  62  to switch off in a part or all of the duration in which the first waveform is at the valley, the control unit  15  determines the duration where the valley of the first waveform is located in various ways. As an example, the control unit  15  samples the first current, and determines the duration where the valley of the first waveform is located according to the sampling value of the first current. As another example, the period of the first waveform has a synchronization relationship with many other signals in the power supply circuit  10 , for example, the voltage signal or current signal outputted by the primary rectifier unit, the voltage signal or current signal outputted by the secondary rectifier unit, and the like. These signals are referred to as synchronization signals of the first current in the following. The control unit  15  may determine the duration where the valley of the first waveform is located according to the waveform of the synchronization signal, and the synchronization relationship between the waveform of the synchronization signal and the first waveform. 
     Taking the first waveform being the waveform represented by the solid line in  FIG. 5  as an example, the control unit  15  may send the control signal as illustrated in  FIG. 7  to the first switch unit  62 , to control the power supply circuit  10  to stop outputting in the duration where the valley of the first waveform is located, such that the second waveform including the duration in which the current value is zero as illustrated in  FIG. 7  may be formed. 
       FIG. 8  illustrates another embodiment in which the control unit  15  adjusts the first current to form the output current crossing zero points. As illustrated in  FIG. 8 , the power supply circuit  10  may further include a load circuit  81  coupled in parallel with a charging loop of the power supply circuit  10 , and a second switch unit  82  configured to control the load circuit  81  to switch on or off. 
     The charging loop may be formed by the charging line and a ground line. Taking the power supply circuit charging the device to be charged via the BUS as an example, the charging loop may be formed by the VBUS and GND. 
     In embodiments of the present disclosure, in order to achieve a purpose that the output current of the power supply circuit may reach 0, the load circuit  81  is introduced in the power supply circuit  10 . With the configuration of load on the load circuit  81 , all the electric energy transmitted on the charging loop may be consumed by the load in the load circuit  81  when the second switch unit  82  is switched on. 
     In embodiments of the present disclosure, implementation of the load on the load circuit  81  is not limited. The load may be for example a resistor, or may be other elements that can be used to consume electric energy. Moreover, a size of the load may be determined according to actual situation, as long as all the electric energy on the charging loop may be consumed by the load circuit  81  when the second switch unit  82  is switched on. 
     The control unit  15  may be configured to control the second switch unit  82  to switch on in a part of each period of the first waveform. When the second switch unit is switched on, the load circuit  81  is in a working state, and the electric energy on the charging loop may be consumed by the load circuit  81  and may not be outputted to the outside of the power supply circuit  10 . Therefore, when the load circuit  81  is in the working state, the output current of the power supply circuit  10  is zero. 
     The above part of each period mentioned in embodiments of the present disclosure (i.e., the duration in which the load circuit  81  is in the working state) may be selected in ways same as those in the embodiment of  FIG. 6 , and reference may be made to the foregoing description related to the embodiment of  FIG. 6 , which will not be elaborated for avoiding repetition. 
       FIG. 9  illustrates yet another embodiment in which the control unit  15  adjusts the first current to form the output current crossing zero points. As illustrated in  FIG. 9 , the secondary rectifier and filtering unit  14  may include a filtering circuit  141  (it is to be understood that, the secondary rectifier and filtering unit  14  may include elements related to secondary rectification, but for sake of clarity,  FIG. 9  only illustrates elements related to this embodiment in the secondary rectifier and filtering unit  14 ). The filtering circuit  141  may consists of one or more capacitors (such as solid capacitors) coupled in parallel. The filtering circuit  141  may further include a third switch unit  142  configured to control the filtering circuit  141  to switch on or off. When the third switch unit  142  is switched on, the filtering circuit  141  is in the working state, having a clamping role for the voltage on the charging line of the power supply circuit  10 , resulting in that the output current of the power supply circuit  10  cannot reach zero. In this embodiment, in order to enable to the output current of the power supply circuit  10  to reach zero, the control unit  15  controls the third switch unit  142  to switch off in a target duration of each period of the first waveform, in which the target duration is the duration where the valley of the first waveform is located. Since the target duration is the duration where the valley of the first waveform is located, the capacitor in the filtering circuit  141  should be in the discharging state in the target duration. However, in the target duration, since the control unit  15  controls the filtering circuit  141  via the third switch unit  142  to stop working, the capacitor in the filtering circuit  141  cannot discharge, and thus there is no output form the power supply circuit  10 . In this way, the output current of the power supply circuit is zero in the target duration. 
     Further, in the embodiment corresponding to  FIG. 9 , the third switch unit  142  may include a MOS transistor. A positive electrode of the filtering capacitor  143  may be coupled to the charging line (such as VBUS) of the power supply circuit  10 , a negative electrode of the filtering capacitor  143  may be coupled to a source of the MOS transistor, a drain of the MOS transistor may be coupled to ground (such as GND), and a gate of the MOS transistor may be coupled to the control unit  15 . The source of the MOS transistor being coupled to the negative electrode of the filtering capacitor  143  may enable a cathode of a bulk diode in the MOS transistor to ground, such that the filtering capacitor  143  may not discharge to the bulk diode when the MOS transistor is switched on. 
     In the related art, a power supply circuit for charging the device to be charged is proposed. This power supply circuit operates in a constant voltage mode. In the constant voltage mode, the output voltage of this power supply circuit keeps substantially constant, for example, 5V, 9V, 12V or 20V. 
     The output voltage of the power supply circuit is not suitable for being directly applied to both ends of the battery. Instead, the output voltage of the power supply circuit needs to be converted by a conversion circuit in the device to be charged, such that a charging voltage and/or a charging current expected by the battery in the device to be charged is obtained. 
     The conversion circuit is configured to convert the output voltage of the power supply circuit, 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). 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 output voltage of the power supply circuit is greater than the charging voltage expected by the battery, the conversion circuit may be configured to perform a buck conversion on the output voltage of the power supply circuit to enable a buck-converted charging voltage to meet the requirement of the charging voltage expected by the battery. As another example, when the output voltage of the power supply circuit is less than the charging voltage expected by the battery, the conversion circuit may be configured to perform a boost conversion on the output voltage of the power supply circuit 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 power supply circuit outputs a constant voltage of 5V. When the battery includes 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 output voltage of the power supply circuit, such that the charging voltage obtained after the buck conversion meets a requirement of the charging voltage expected by the battery. 
     As yet another example, assume that the power supply circuit outputs a constant voltage of 5V. When the power supply circuit 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 output voltage of the power supply circuit, such that the charging voltage obtained after the boost conversion meets a requirement of the charging voltage expected by the battery. 
     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, 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; and/or for another example, the heat gathered on the conversion circuit may shorten the service life of the conversion circuit and neighboring electronic elements; and/or 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; and/or 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; and/or for still yet another example, the heat gathered on the conversion circuit may short-circuit the conversion circuit, such that the output voltage of the power supply circuit is directly applied to both ends of the battery, thus causing abnormal charging of the battery, which brings safety hazard if the over-voltage charging lasts for a long time, for example, the battery may explode. 
     Embodiments of the present disclosure further provide a power supply circuit  10 . The control unit  15  in the power supply circuit  10  may be configured to communicate with the device to be charged, to adjust an output power of the power supply circuit  10 , such that the output voltage and/or the output current of the power supply circuit  10  matches a charging stage where the battery in the device to be charged is currently. 
     It should be understood that, the charging stage where the battery is currently may include at least one of a trickle charging stage, a constant current charging stage and a constant voltage charging stage. 
     Taking the charging stage where the battery is currently being the constant voltage charging stage as an example, communicating with the device to be charged, to adjust the output power of the power supply circuit, such that the output voltage and/or the output current of the power supply circuit matches the charging stage where the battery in the device to be charged is currently, includes: in the constant voltage charging stage, communicating with the device to be charged, to adjust the output power of the power supply circuit, such that the output voltage of the power supply circuit matches the charging voltage corresponding to the constant voltage charging stage. 
     Taking the charging stage where the battery is currently being the constant current charging stage as an example, communicating with the device to be charged, to adjust the output power of the power supply circuit, such that the output voltage and/or the output current of the power supply circuit matches the charging stage where the battery in the device to be charged is currently, includes: in the constant current charging stage, communicating with the device to be charged, to adjust the output power of the power supply circuit, such that the output current of the power supply circuit matches the charging current corresponding to the constant current charging stage. 
     The power supply circuit  10  having communication function provided by embodiments of the present disclosure will be illustrated in detail below. 
     The power supply circuit  10  may obtain status information of the battery. The status information of the battery may include present electric quantity information and/or voltage information of the battery. The power supply circuit  10  may adjust the output voltage of the power supply circuit  10  itself according to he obtained status information of the battery, to meet the requirement of the charging voltage and/or charging current expected by the battery. The voltage outputted by the power supply circuit  10  after adjustment may be directly applied to both ends of the battery for charging the battery (hereinafter, referred to as “direct charging”). Further, during the constant current charging stage of the process of charging the battery, the voltage outputted by the power supply circuit  10  after adjustment may be directly applied to both ends of the battery for charging the battery. 
     The power supply circuit  10  may have a voltage feedback function and a current feedback function, so as to manage the charging voltage and/or charging current of the battery. 
     The power supply circuit  10  adjusting the output voltage of the power supply circuit  10  itself according to the obtained status information of the battery may mean that, the power supply circuit  10  may obtain the status information of the battery in real time, and adjust the output voltage of the power supply circuit  10  itself according to the obtained real-time status information of the battery, to meet the charging voltage and/or charging current expected by the battery. 
     The power supply circuit  10  adjusting the output voltage of the power supply circuit  10  itself according to the obtained real-time status information of the battery may mean that, as the voltage of the battery continuously increases during the charging process, the power supply circuit  10  may obtain the present status information of the battery at different time points in the charging process, and adjust the output voltage of the power supply circuit  10  itself in real time according to the present status information of the battery, to meet the requirement of the charging voltage and/or charging current expected by 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 power supply circuit  10  may output a first charging current in the trickle charging stage to charge the battery, so as to meet the requirement of the charging current expected by the battery (the first charging current may be the constant direct current). In the constant current charging stage, the power supply circuit  10  may utilize a current feedback loop to ensure that the current outputted by the power supply circuit  10  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 also be a current with a pulsating waveform, and may be greater than the first charging current, which may mean 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 power supply circuit  10  may utilize a voltage feedback loop to ensure that a voltage outputted from the power supply circuit  10  to the device to be charged in the constant voltage charging stage (i.e., the constant direct voltage) keeps constant. 
     For example, the power supply circuit  10  mentioned in embodiments of the present disclosure may be mainly configured to control the constant current charging stage of the battery in the device to be charged. In other embodiments, controlling the trickle charging stage and the constant voltage charging stage of the battery in the device to be charged may also be completed cooperatively by the power supply circuit  10  and an additional charging chip in the device to be charged. Compared to that in the constant current charging stage, the charging power accepted by the battery in the trickle charging stage and the constant voltage charging stage is less, and the efficiency conversion loss and the heat accumulation of the charging chip in the device to be charged is acceptable. 
     It should be noted that, the constant current charging stage or the constant current stage mentioned in embodiments of the present disclosure may refer to a charging mode in which the output current of the power supply circuit  10  is controlled, and does not require the output current of the power supply circuit  10  to keep completely constant and unchanged. For example, the constant current may refer to that, a peak value or a mean value of the current with the pulsating waveform outputted by the power adapter is basically constant, or keeps constant during a certain time period. For example, in practice, the power supply circuit  10  typically performs charging by means of multi-stage constant current charging in the constant current charging stage. 
     The multi-stage constant current charging may include N constant current stages, where N is an integer no less than 2. The first charging stage of the multi-stage constant current charging starts with a predetermined charging current. N constant current stages in the multi-stage constant current charging are performed in sequence from the first charging stage to the (N-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 of the current 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, in a case where the output current of the power supply circuit  10  is the current having the current value periodically changing (such as the pulsating direct current), the constant current mode may refer to a charging mode in which the peak value or the mean value of the current periodically changing is controlled, i.e., the peak value of the output current of the power supply circuit  10  is controlled to not exceed the current corresponding to the constant current mode. Moreover, in a case where the output current of the power supply circuit  10  is the alternating current, the constant current mode refers to a charging mode in which the peak value of the alternating current is controlled. 
     In some embodiments, the power supply circuit  10  supports a first charging mode and a second charging mode, and a charging speed of the power supply circuit  10  charging the battery in the second charging mode is greater than a charging mode of the power supply circuit  10  charging the battery in the first charging mode. In other words, compared to the power supply circuit  10  working in the first charging mode, the power supply circuit  10  working in the second charging mode may take a shorter time to fully charge the battery with a same capacity. Further, in some embodiments, in the first charging mode, the power supply circuit  10  charges the battery via a second charging channel, and in the second charging mode, the power supply circuit  10  charges the battery via a first charging channel. 
     The first charging mode may be a normal charging mode, and the second charging mode may be a fast charging mode. The normal charging mode may refer to a charging mode in which the power supply circuit  10  outputs a relatively smaller current value (typically less than 2.5 A) or charges the battery in the device to be charged with a relatively smaller power (typically less than 15). In the normal charging mode, it typically takes several hours to fully fill a larger capacity battery (such as a battery with 3000 mAh). However, in the fast charging mode, the power supply circuit  10  can output a relatively large current (typically greater than 2.5 A, such as 4.5 A, 5 A or higher) or charges the battery in the device to be charged with a relatively large power (typically greater than or equal to 15 W). Compared to the normal charging mode, the period of time may be significantly shortened when the battery with the same capacity is fully filled by the power supply circuit  10  in the fast charging mode, and the charging is faster. 
     As indicated above, the output current of the power supply circuit  10  may have the second waveform with the current value periodically changing. The second waveform may refer to the current waveform of the output current of the power supply circuit  10  working in the second charging mode. In the first charging mode, the voltage value of the output voltage of the power supply circuit  10  is constant, and the current waveform of the output current varies with the load. 
     Further, the device to be charged may perform bidirectional communication with the power supply circuit  10  (or the control unit  15  in the power supply circuit  10 ), to control the output of the power supply circuit  10  in the second charging mode (i.e., control the charging voltage and/or the charging current provided by the power supply circuit  10  in the second charging mode). The device to be charged may include a charging interface, and the device to be charged may communicate with the power supply circuit  10  via a data wire of the charging interface. Taking the charging interface being a USB interface as an example, the data wire may be a D+ wire and/or a D− wire of the USB interface. Or, the device to be charged may perform wireless communication with the power supply circuit  10 . 
     The communicated content between the power supply circuit  10  and the device to be charged is not limited in embodiments of the present disclosure, and the control method of the device to be charged on the output of the power supply circuit  10  in the second charging mode is also not limited in embodiments of the present disclosure. For example, the device to be charged may communicate with the power supply circuit  10  to obtain the present voltage or present electric quantity of the battery in the device to be charged, and adjust the output voltage or output current of the power supply circuit  10  based on the present voltage or present electric quantity of the battery. In the following, the communicated content between the power supply circuit  10  and the device to be charged and the control method of the device to be charged on the output of the power supply circuit  10  in the second charging mode will be described in detail in combination with specific embodiments. 
     The master-slave relation of the power supply circuit  10  and the device to be charged is not limited in embodiments of the present disclosure. In other words, any of the power supply circuit  10  and the device to be charged can be configured as the master device for initiating the bidirectional communication session, accordingly, the other one can be configured as the slave device for making a first response or a first reply to the communication initiated by the master device. As a feasible implementation, during the communication, the identities of the master device and the slave device can be determined by comparing the electrical levels of the power supply circuit  10  and the device to be charged relative to the ground. 
     The specific implementation of bidirectional communication between the power supply circuit  10  and the device to be charged is not limited in embodiments of the present disclosure. In other words, any of the power supply circuit  10  and the device to be charged can be configured as the master device for initiating the communication session, accordingly, the other one can be configured as the slave device making a first response or a first reply to the communication session initiated by the master device, and the master device is able to make a second response to the first response or the first reply of the slave device, and thus a negotiation about a charging mode can be realized between the master device and the slave device. As a feasible implementation, a charging operation between the master device and the slave device is performed after a plurality of negotiations about the charging mode are completed between the master device and the slave device, such that the charging process can be performed safely and reliably after the negotiation. 
     As an implementation, the mater device is able to make a second response to the first response or the first reply made by the slave device to the communication session in a manner that, the master device is able to receive the first response or the first reply made by the slave device to the communication session and to make a targeted second response to the first response or the first reply. As an example, when the master device receives the first response or the first reply made by the slave device to the communication session in a predetermined time period, the master device makes the targeted second response to the first response or the first reply of the slave device in a manner that, the master device and the slave device complete one negotiation about the charging mode, and a charging process may be performed between the master device and the salve device in the first charging mode or the second charging mode, i.e., the power supply circuit  10  charges the device to be charged in the first charging mode or the second charging mode according to a negotiation result. 
     As another implementation, the mater device is able to make a second response to the first response or the first reply made by the slave device to the communication session in a manner that, when the master device does not receive the first response or the first reply made by the slave device to the communication session in the predetermined time period, the mater device also makes the targeted second response to the first response or the first reply of the slave device. As an example, when the master device does not receive the first response or the first reply made by the slave device to the communication session in the predetermined time period, the mater device makes the targeted second response to the first response or the first reply of the slave device in a manner that, the master device and the slave device complete one negotiation about the charging mode, and the charging process is performed between the mater device and the slave device in the first charging mode, i.e., the power supply circuit  10  charges the device to be charged in the first charging mode. 
     In some embodiments, when the device to be charged is configured as the mater device for initiating the communication session, after the power supply circuit  10  configured as the slave device makes the first response or the first reply to the communication session initiated by the master device, it is unnecessary for the device to be charged to make the targeted second response to the first response or the first reply of the power supply circuit  10 , i.e., one negotiation about the charging mode is regarded as completed between the power supply circuit  10  and the device to be charged, and the power supply circuit  10  is able to charge the device to be charged in the first charging mode or the second charging mode according to the negotiation result. 
     In some embodiments, the device to be charged may perform bidirectional communication with the power supply circuit  10  to control the output of the power supply circuit  10  in the second charging mode as follows. The device to be charged performs the bidirectional communication with the power supply circuit  10  to negotiate the charging mode between the power supply circuit  10  and the device to be charged. 
     In some embodiments, the device to be charged may perform the bidirectional communication with the power supply circuit  10  to negotiate the charging mode between the power supply circuit  10  and the device to be charged as follows. The device to be charged receives a first instruction sent by the power supply circuit  10 , in which the first instruction is configured to query the device to be charged whether to operate in the second charging mode. The device to be charged sends a reply instruction of the first instruction to the power supply circuit  10 , in which the reply instruction of the first instruction is configured to indicate whether the device to be charged agrees to operate in the second charging mode. When the device to be charged agrees to operate in the second charging mode, the device to be charged controls the power supply circuit  10  to charge the battery via the first charging channel. 
     In some embodiments, the device to be charged may perform bidirectional communication with the power supply circuit  10  to control the output of the power supply circuit  10  in the second charging mode as follows. The device to be charged performs the bidirectional communication with the power supply circuit  10  to determine the charging voltage outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged. 
     In some embodiments, the device to be charged may perform the bidirectional communication with the power supply circuit  10  to determine the charging voltage outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged as follows. The device to be charged receives a second instruction sent by the power supply circuit  10 , in which the second instruction is configured to query whether the output voltage of the power supply circuit  10  matches the present voltage of the battery in the device to be charged. The device to be charged sends a reply instruction of the second instruction to the power supply circuit  10 , in which the reply instruction of the second instruction is configured to indicate that the output voltage of the power supply circuit  10  matches the present voltage of the battery, or is higher or lower than the present voltage of the battery. In some embodiments, the second instruction can be configured to query whether the present output voltage of the power supply circuit  10  is suitable for being used as the charging voltage outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged, and the reply instruction of the second instruction can be configured to indicate the present output voltage of the power supply circuit  10  is suitable, high or low. 
     When the present output voltage of the power supply circuit  10  matches the present voltage of the battery or the present output voltage of the power supply circuit  10  is suitable for being used as the charging voltage outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged, it indicates that the present output voltage of the power supply circuit  10  may be slightly higher than the present voltage of the battery, and a difference between the output voltage of the power supply circuit  10  and the present voltage of the battery is within a predetermined range (typically in an order of hundreds of millivolts). When the present output voltage of the power supply circuit  10  is higher than the present voltage of the battery, it indicates that the difference between the output voltage of the power supply circuit  10  and the present voltage of the battery is above the predetermined range. When the present output voltage of the power supply circuit  10  is lower than the present voltage of the battery, it indicates that the difference between the output voltage of the power supply circuit  10  and the present voltage of the battery is below the predetermined range. 
     In some embodiments, the device to be charged may perform the bidirectional communication with the power supply circuit  10  to control the output of the power supply circuit  10  in the second charging mode as follows. The device to be charged may perform the bidirectional communication with the power supply circuit  10  to determine the charging current outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged 
     In some embodiments, the device to be charged may perform the bidirectional communication with the power supply circuit  10  to determine the charging current outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged as follows. The device to be charged receives a third instruction sent by the power supply circuit  10 , in which the third instruction is configured to query a maximum charging current presently supported by the device to be charged. The device to be charged sends a reply instruction of the third instruction to the power supply circuit  10 , in which the reply instruction of the third instruction is configured to indicate the maximum charging current presently supported by the device to be charged. The power supply circuit  10  determines the charging current outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged according to the maximum charging current presently supported by the device to be charged. 
     The maximum charging current presently supported by the device to be charged may be derived according to the capacity of the battery of the device to be charged, a cell system, and the like, or may be a preset value. 
     It should be understood that, the device to be charged may determine the charging current outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged according to the maximum charging current presently supported by the device to be charged in many ways. For example, the power supply circuit  10  may determine the maximum charging current presently supported by the device to be charged as the charging current outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged, or may determine the charging current outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged after comprehensively considering factors such as the maximum charging current presently supported by the device to be charged and its own current output capability. 
     In some embodiments, the device to be charged may perform the bidirectional communication with the power supply circuit  10  to control the output of the power supply circuit  10  in the second charging mode as follows. During charging in the second charging mode, the device to be charged performs the bidirectional communication with the power supply circuit  10  to adjust the output current of the power supply circuit  10 . 
     In some embodiments, the device to be charged may perform the bidirectional communication with the power supply circuit  10  to adjust the output current of the power supply circuit  10  as follows. The device to be charged receives a fourth instruction sent by the power supply circuit  10 , in which the fourth instruction is configured to query a present voltage of the battery in the device to be charged. The device to be charged sends a reply instruction of the fourth instruction to the power supply circuit  10 , in which the reply instruction of the fourth instruction is configured to indicate the present voltage of the battery. The power supply circuit  10  adjusts the output current of the power supply circuit  10  according to the present voltage of the battery. 
     In some embodiments, the device to be charged may perform the bidirectional communication with the power supply circuit  10  to control the output of the power supply circuit  10  in the second charging mode as follows. The device to be charged performs the bidirectional communication with the power supply circuit  10  to determine whether the charging interface is in poor contact. 
     In an embodiment, the device to be charged may perform the bidirectional communication with the power supply circuit  10  to determine whether the charging interface is in poor contact as follows. The device to be charged receives the fourth instruction sent by the power supply circuit  10 , in which the fourth instruction is configured to query the present voltage of the battery in the device to be charged. The device to be charged sends the reply instruction of the fourth instruction to the power supply circuit  10 , in which the reply instruction of the fourth instruction is configured to indicate the present voltage of the battery in the device to be charged. The power supply circuit  10  determines whether the charging interface is in poor contact according to the output voltage of the power supply circuit  10  and the present voltage of the battery in the device to be charged. For example, when the power supply circuit  10  determines a difference between the output voltage of the power supply circuit  10  and the present voltage of the battery in the device to be charged is greater than a predetermined voltage threshold, it indicates that an impedance obtained by dividing the voltage difference by the present current value outputted by the power supply circuit  10  is greater than a preset impedance threshold, and thus it can be determined that the charging interface is in poor contact. 
     In some embodiments, it can be determined by the device to be charged whether the charging interface is in poor contact. For example, the device to be charged sends a sixth instruction to the power supply circuit  10 , in which the sixth instruction is configured to query the output voltage of the power supply circuit  10 . The device to be charged receives a reply instruction of the sixth instruction sent by the power supply circuit  10 , in which the reply instruction of the sixth instruction is configured to indicate the output voltage of the power supply circuit  10 . The device to be charged determines whether the charging interface is in poor contact according to the output voltage of the power supply circuit  10  and the present voltage of the battery in the device to be charged. After the device to be charged determines that the charging interface is in poor contact, the device to be charged may send a fifth instruction to the power supply circuit  10 , in which the fifth instruction is configured to indicate that the charging interface is in poor contact. After receiving the fifth instruction, the power supply circuit  10  may quit the second charging mode. 
     With reference to  FIG. 10 , the communication procedure between the power supply circuit  10  and the device to be charged will be described in detail. It should be noted that, examples in  FIG. 10  are merely used to help those skilled in the related art to understand embodiments of the present disclosure. The embodiments shall not be limited to the specific numeric values or specific scenes. Apparently, various modifications and equivalents can be made by those skilled in the related art based on examples in  FIG. 10 , and those modifications and equivalents shall fall within the protection scope of the present disclosure. 
     As illustrated in  FIG. 10 , the communication procedure between the power supply circuit  10  and the device to be charged (or, referred to as the communication procedure of the fast charging) may include the following five stages. 
     Stage  1 : 
     After the device to be charged is coupled to the power supply circuit  10 , the device to be charged may detect a type of the power supply circuit  10  via the data wires D+ and D−. When detecting that the power supply circuit  10  is a power supply circuit specifically used for charging, such as an adapter, the device to be charged may absorb current greater than a predetermined current threshold I2 (which may be, for example, 1A). When the power supply circuit  10  detects that the output current of the power supply circuit  10  is greater than or equal to I2 for a predetermined time period (for example, may be a continuous time period T 1 ), the power supply circuit  10  determines that the device to be charged has completed the recognition of the type of the power supply device. Then, the power supply circuit  10  initiates a negotiation with the device to be charged, and sends an instruction 1 (corresponding to the above-mentioned first instruction) to the device to be charged to query whether the device to be charged agrees that the power supply circuit  10  charges the device to be charged in the second charging mode. 
     When the power supply circuit  10  receives a reply instruction of the instruction 1 sent by the device to be charged and the reply instruction of the instruction 1 indicates that the device to be charged disagrees that the power supply circuit  10  charges the device to be charged in the second charging mode, the power supply circuit  10  detects the output current of the power supply circuit  10  again. When the output current of the power supply circuit  10  is still greater than or equal to I2 within a predetermined continuous time period (for example, may be a continuous time period T 1 ), the power supply circuit  10  sends the instruction 1 again to the device to be charged to query whether the device to be charged agrees that the power supply circuit  10  charges the device to be charged in the second charging mode. The power supply circuit  10  repeats the above actions in stage  1 , until the device to be charged agrees that the power supply circuit  10  charges the device to be charged in the second charging mode or until the output current of the power supply circuit  10  is no longer greater than or equal to I2. 
     After the device to be charged agrees that the power supply circuit  10  charges the device to be charged in the second charging mode, the communication procedure goes into stage  2   
     Stage  2 : 
     For the output voltage of the power supply circuit  10 , there may be several levels. The power supply circuit  10  sends an instruction 2 (corresponding to the above-mentioned second instruction) to the device to be charged to query whether the output voltage of the power supply circuit  10  (the present output voltage) matches the present voltage of the battery in the device to be charged. 
     The device to be charged sends a reply instruction of the instruction 2 to the power supply circuit  10 , for indicating that the output voltage of the power supply circuit  10  matches the present voltage of the battery in the device to be charged, or is higher or lower than the present voltage of the battery in the device to be charged. When the reply instruction of the instruction 2 indicates that the output voltage of the power supply circuit  10  is higher or lower, the power supply circuit  10  may adjust the output voltage of the power supply circuit  10  to be lower or higher, and sends the instruction 2 to the device to be charged again to query whether the output voltage of the power supply circuit  10  matches the present voltage of the battery. The above actions in stage  2  are repeated, until the device to be charged determines that the output voltage of the power supply circuit  10  matches the present voltage of the battery in the device to be charged. Then, the communication procedure goes into stage  3 . The output voltage of the power supply circuit  10  may be adjusted in various ways. For example, a plurality of voltage levels from low to high may be set for the output voltage of the power supply circuit  10  in advance. The higher the voltage level is, the larger the output voltage of the power supply circuit  10  is. When the reply instruction of the instruction 2 indicates that the output voltage of the power supply circuit  10  is higher, the voltage level of the output voltage of the power supply circuit  10  may be reduced by one level from the present voltage level. When the reply instruction of the instruction 2 indicates that the output voltage of the power supply circuit  10  is lower, the voltage level of the output voltage of the power supply circuit  10  may be increased by one level from the present voltage level. 
     Stage  3 : 
     The power supply circuit  10  sends an instruction 3 (corresponding to the above-mentioned third instruction) to the device to be charged to query the maximum charging current presently supported by the device to be charged. The device to be charged sends a reply instruction of the instruction 3 to the power supply circuit  10  for indicating the maximum charging current presently supported by the device to be charged, and then the communication procedure goes into stage  4 . 
     Stage  4 : 
     The power supply circuit  10  determines the charging current outputted by the power supply circuit  10  in the second charging mode for charging the device to be charged according to the maximum charging current presently supported by the device to be charged. Then, the communication procedure goes into stage  5 , i.e., the constant current charging stage. 
     Stage  5 : 
     When the communication procedure goes into the constant current charging stage, the power supply circuit  10  may send an instruction 4 (corresponding to the above-mentioned fourth instruction) to the device to be charged at intervals to query the present voltage of the battery in the device to be charged. The device to be charged may send a reply instruction of the instruction 4 to the power supply circuit  10 , to feed back the present voltage of the battery. The power supply circuit  10  may determine according to the present voltage of the battery whether the charging interface is in poor contact and whether it is necessary to decrease the output current of the power supply circuit  10 . 
     When the power supply circuit  10  determines that the charging interface is in poor contact, the power supply circuit  10  may send an instruction 5 (corresponding to the above-mentioned fifth instruction) to the device to be charged, and the power supply circuit  10  would quit the second charging mode, and then the communication procedure is reset and goes into stage  1  again. 
     In some embodiments, in stage  2 , the time period from when the device to be charged agrees the power supply circuit  10  to charge the device to be charged in the second charging mode to when the power supply circuit  10  adjusts the output voltage of the power supply circuit  10  to a suitable charging voltage may be controlled in a certain range. If the time period exceeds a predetermined range, the power supply circuit  10  or the device to be charged may determine that the communication procedure is abnormal, such that the communication procedure is reset and goes into stage  1 . 
     In some embodiments, in stage  2 , when the output voltage of the power supply circuit  10  is higher than the present voltage of the battery in the device to be charged by ΔV (ΔV may be set to 200-500 mV), the device to be charged may send a reply instruction of the instruction 2 to the power supply circuit  10 , for indicating that the output voltage of the power supply circuit  10  matches the voltage of the battery in the device to be charged. 
     In some embodiments, in stage  4 , the adjusting speed of the output current of the power supply circuit  10  may be controlled to be in a certain range, thus avoiding an abnormity occurring in the charging process due to the too fast adjusting speed. 
     In some embodiments, in stage  5 , the variation degree of the output current of the power supply circuit  10  may be controlled to be less than or equal to 5%. 
     In some embodiments, in stage  5 , the power supply circuit  10  can monitor the path impedance of a charging loop in real time. In detail, the power supply circuit  10  can monitor the path impedance of the charging loop according to the output voltage of the power supply circuit  10 , the output current of the power supply circuit  10  and the present voltage of the battery fed back by the device to be charged. When the path impedance of the charging loop is greater than a sum of the path impedance of the device to be charged and the impedance of the charging wire, it may be considered that the charging interface is in poor contact, and thus the power supply circuit  10  stops charging the device to be charged in the second charging mode. 
     In some embodiments, after the power supply circuit  10  starts to charge the device to be charged in the second charging mode, time intervals of communications between the power supply circuit  10  and the device to be charged may be controlled to be in a certain range, thus avoiding abnormity in the communication procedure due to the too short time interval of communications. 
     In some embodiments, the stop of the charging process (or the stop of the charging process that the power supply circuit  10  charges the device to be charged in the second charging mode) may be a recoverable stop or an unrecoverable stop. 
     For example, when it is detected that the battery in the device to be charged is fully charged or the charging interface is poor contact, the charging process is stopped and the charging communication procedure is reset, and the charging process goes into stage  1  again. Then, the device to be charged disagrees that the power supply circuit  10  charges the device to be charged in the second charging mode, and the communication procedure would not go into stage  2 . The stop of the charging process in such a case may be considered as an unrecoverable stop. 
     For another example, when an abnormity occurs in the communication between the power supply circuit  10  and the device to be charged, the charging process is stopped and the charging communication procedure is reset, and the charging process goes into stage  1  again. After requirements for stage  1  are met, the device to be charged agrees that the power supply circuit  10  charges the device to be charged in the second charging mode to recover the charging process. In this case, the stop of the charging process may be considered as a recoverable stop. 
     For another example, when the device to be charged detects that an abnormity occurs in the battery, the charging process is stopped and the charging communication process is reset, and the charging process goes into stage  1  again. The device to be charged then disagrees that the power supply circuit  10  charges the device to be charged in the second charging mode. When the battery returns to normal and the requirements for stage  1  are met, the device to be charged agrees that the power supply circuit  10  charges the device to be charged in the second charging mode. In this case, the stop of fast charging process may be considered as a recoverable stop. 
     Communication actions or operations illustrated in  FIG. 10  are merely exemplary. For example, in stage  1 , after the device to be charged is coupled to the power supply circuit  10 , the handshake communication between the device to be charged and the power supply circuit  10  may be initiated by the device to be charged. In other words, the device to be charged sends an instruction 1 to query the power supply circuit  10  whether to operate in the second charging mode. When the device to be charged receives a reply instruction indicating that the power supply circuit  10  agrees to charge the device to be charged in the second charging mode from the power supply circuit  10 , the power supply circuit  10  starts to charge the battery in the device to be charged in the second charging mode. For another example, after stage  5 , there may be a constant voltage charging stage. In detail, in stage  5 , the device to be charged may feed back the present voltage of the battery to the power supply circuit  10 . The charging process goes into the constant voltage charging stage from the constant current charging stage when the present voltage of the battery reaches a voltage threshold for constant voltage charging. During the constant voltage charging stage, the charging current decreases gradually. When the current reduces to a certain threshold, it indicates that the battery in the device to be charged is fully charged, and the whole charging process is stopped. 
     Embodiments of the present disclosure further provide a power supply device. As illustrated in  FIG. 11 , the power supply device  1100  may include a housing  100 , a circuit board  200  and a power supply circuit  300 . The circuit board  200  may be enclosed by the housing  100 . The power supply circuit  300  may be positioned on the circuit board  200 . The power supply circuit  300  may be the power supply circuit  10  provided in any embodiment of the present disclosure. The power supply device  1100  may be a device specifically used for charging, such as an adapter or a power bank, or may be other devices capable of supplying power and data services, such as a computer. 
     The power supply circuit and the power supply device provided by embodiments of the present disclosure have been described above in detail with reference to  FIGS. 1-11 . A control method of a power supply circuit provided by embodiments of the present disclosure will be described below in detail with reference to  FIG. 12 . As illustrated in  FIG. 12 , the control method may include following blocks. 
     At block  1210 , rectification is performed on input alternating current to output a first voltage having a periodically changing voltage value. 
     At block  1220 , the first voltage is modulated to generate a second voltage. 
     At block  1230 , a third voltage is generated based on the second voltage. 
     At block  1240 , rectification and filtering is performed on the third voltage to generate a fourth voltage and a first current corresponding to the fourth voltage. 
     At block  1250 , the first current is adjusted to generate an output current of the power supply circuit. The output current has a second waveform with a current value periodically changing, and each period of the second waveform includes a duration in which the current value is 0. 
     In some embodiments, the first current has a first waveform with a current value periodically changing, and the first current is adjusted, to switch off outputting the output current in a part of each period of the first waveform. 
     In some embodiments, the above part of each period is a duration in which a valley of the first waveform is located. 
     In some embodiments, the method may further include communicating with a device to be charged, to adjust an output power of the power supply circuit, such that an output voltage and/or the output current of the power supply circuit matches a charging stage where a battery of the device to be charged is currently. 
     In some embodiments, the charging state in which the power supply circuit charges the battery includes at least one of a trickle charging stage, a constant current charging stage and a constant voltage charging stage. 
     In some embodiments, communicating with the device to be charged, to adjust the output power of the power supply circuit, such that the output voltage and/or the output current of the power supply circuit matches the charging stage where a battery of the device to be charged is currently, may include: in the constant voltage charging stage, communicating with the device to be charged, to adjust the output power of the power supply circuit, such that the output voltage of the power supply circuit matches a charging voltage corresponding to the constant voltage charging stage. 
     In some embodiments, communicating with the device to be charged, to adjust the output power of the power supply circuit, such that the output voltage and/or the output current of the power supply circuit matches the charging stage where a battery of the device to be charged is currently, may include: in the constant current charging stage, communicating with the device to be charged, to adjust the output power of the power supply circuit, such that the output current of the power supply circuit matches a charging current corresponding to the constant current charging stage. 
     With respect to the details of the control method, reference can be made to the above description regarding the power supply circuit, which will not be elaborated here for simplicity. 
     In above embodiments, it is possible to implement the embodiments fully or partially by software, hardware, firmware or any other combination. When implemented by software, it is possible to implement the embodiments fully or partially in a form of computer program products. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed by the computer, procedures or functions according to embodiments of the present disclosure are fully or partially generated. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or any other programmable device. The computer instructions may be stored in a computer readable storage medium, or may be transmitted from one computer readable storage medium to another computer readable storage medium. For example, the computer instructions may be transmitted from one website, computer, server or data center to another website, computer, server or data center in a wired manner (for example, via coaxial cables, fiber optics, or DSL (digital subscriber line)) or in a wireless manner (for example, via infrared, WiFi or microwave). The computer readable storage medium may be any available medium that are accessible by the computer, or a data storage device such as a server or a data center integrated with one or more available medium. The available medium may be magnetic medium (for example, floppy disk, hard disk and tape), optical medium (for example, DVD (digital video disc)), or semiconductor medium (for example, SSD (solid state disk)). 
     Those skilled in the art could be aware that, exemplary units and algorithm steps described in combination with embodiments disclosed herein may be implemented by electronic hardware, or by a combination of computer software and electronic hardware. Whether these functions are executed by hardware or software is dependent on particular use and design constraints of the technical solutions. Professionals may adopt different methods for different particular uses to implement described functions, which should not be regarded as going beyond the scope of the present disclosure. 
     In several embodiments provided by the present disclosure, it should be understood that, the disclosed system, device and method may be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the units are merely divided according to logic functions, and can be divided in other ways in actual implementation. For example, a plurality of units or components may be combined or may be integrated into another system, or some features may be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection illustrated or discussed may be via some interfaces, or direct coupling or communication connection of devices or units may be in an electrical, mechanical, or other form. 
     Units illustrated as separate components may be or may not be physically separated, and components illustrated as units may be or may not be physical units, i.e., may be located at a same place, or may be distributed onto multiple network units. Some or all of the units may be selected to implement the purpose of the solution in an embodiment according to actual demands. 
     Moreover, respective functional units in respective embodiments of the present disclosure may be integrated in one processing unit, or the respective units may be separate physical existence, or two or more units may be integrated in one unit. 
     Above description is merely specific implementation of the present disclosure. However, the protection scope of the present disclosure is not limited to this. Any change or substitute that is conceivable by those skilled in the art should be in the protection scope of the present disclosure. Thus, the protection scope of the present disclosure should be defined as the protection scope of claims.