Patent Publication Number: US-10778031-B2

Title: Charger, terminal device, and charging system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 15/722,427, filed on Oct. 2, 2017, which is a continuation application of International Patent Application No. PCT/CN2015/094652 filed on Nov. 16, 2015. The International Patent Application claims priority to Chinese Patent Application No. 201510145136.6 filed on Mar. 30, 2015. All of the afore-mentioned patent applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of circuits, and in particular, to a charger, a terminal device, and a charging system in the field of circuits. 
     BACKGROUND 
     As mobile terminals such as smartphones and tablet computers gradually develop towards large-screen, battery capacity required by mobile terminals increasingly grows. To control a charging time not to be excessively long, high-power chargers start to be widely used. 
     Because a charging current of a high-power charger is relatively large, a short circuit is easily caused in a universal serial bus (USB), and in particular, in a Micro USB, and as a result, a USB or Micro USB interface is overheated and fused. Currently, a USB or Micro USB interface commonly used in a mobile terminal has a compact size, a user easily brings in a foreign matter in a usage process, and non-standard insertion and removal of a user also cause metal shell elements to rub to generate metal dust and the like, which all cause a charging short circuit in a charging process. Short circuits are distinguished by a high degree and a low degree, a short circuit of a relatively high degree may cause a relatively large current to ground, and is easily detected and avoided, but a short circuit of a slight degree causes only a relatively small current to ground, and is referred to as a micro short circuit. 
     To avoid a risk of a charging short circuit, currently, a charger of a mobile terminal generally has an overcurrent detection and protection function. Because a working current of a high-power charger is relatively large, a maximum current set for overcurrent detection is also relatively large. As a result, when a micro short circuit occurs in a charger, an overcurrent protection function may not be triggered. The micro short circuit cannot trigger overcurrent protection of the charger, but heat continuously generated by a small current generated by the micro short circuit can still accumulate to a relatively high temperature, and as a result, security accidents such as fusing, smoking, and fire outbreak occur on a USB or Micro USB plug or a Micro USB charging interface of a mobile terminal. 
     To avoid a risk of a charging micro short circuit, in another solution, a positive temperature coefficient (PTC) thermistor is built in a USB or Micro USB connector of a charging cable, and when a temperature is excessively high, a resistance value of the PTC thermistor connected to the charging cable in series increases to limit an excessively large charging current in order to avoid smoking and burning, or a negative temperature coefficient (NTC) thermistor is built in a USB or Micro USB connector of a charging cable, and when a temperature is excessively high, a resistance value of the NTC thermistor connected to the ground decreases to trigger overcurrent protection of a charger. 
     However, a position at which a micro short circuit usually occurs is located at an inner spring plate of an interface that protrudes at a USB or Micro USB end of a charging cable. However, the PTC thermistor or the NTC thermistor are disposed in a plastic body at the USB or Micro USB end of the charging cable, and a distance exists between the position at which the micro short circuit usually occurs and the position at which the PCT thermistor or the NTC thermistor are disposed. When a micro short circuit occurs at the spring plate, a temperature of the spring plate is relatively high, but a temperature sensed at the PTC thermistor or the NTC thermistor is insufficient and cannot trigger an impedance change of the PTC thermistor or the NTC thermistor, or only a resistance value of the PTC thermistor is enabled to increase so that charging decelerates. In this case, the micro short circuit easily causes the plastic body at the USB or Micro USB end of the charging cable to fuse or become black, which brings in a potential security risk for a user. 
     SUMMARY 
     Embodiments of the present disclosure provide a charger, a terminal device, and a charging system such that a micro short circuit that occurs in a charging circuit can be detected and a charging process can be controlled, thereby improving charging security. 
     According to a first aspect, a charger is provided, including a power conversion circuit, a charging interface, and an over current protection circuit, where the power conversion circuit includes a transformer and a rectifier, an alternating current is input from a primary side of the transformer, and is induced to a secondary side of the transformer by the primary side of the transformer, and a direct current is output from the secondary side of the transformer after the alternating current is rectified by the rectifier. The charging interface includes a power cable, a ground cable, and a signal cable, where a positive electrode of the rectifier is connected to the power cable, and a negative electrode of the rectifier is connected to the ground cable. The overcurrent protection circuit includes an overcurrent detection circuit and a pulse width modulation (PWM) control chip, where the overcurrent detection circuit is configured to enable the PWM control chip to control the primary side of the transformer to stop inducing the alternating current to the secondary side of the transformer when it is detected that a current of the secondary side of the transformer is greater than or equal to a first current threshold that is preset, where the first current threshold is greater than a rated output current value of the charger, and the charger further includes a resistor and a switch device, where a first end of the resistor is connected to the power cable, and a second end of the resistor is connected to the signal cable. A first end of the switch device is connected to the signal cable, a second end of the switch device is connected to the power cable, a third end of the switch device is connected to the ground cable, and in a case in which a difference between a voltage of the first end of the switch device and a voltage of the second end of the switch device is greater than or equal to a preset first voltage threshold, the second end of the switch device and the third end of the switch device are connected, and in a process in which the charger charges a terminal device, in a case in which the difference between the voltage of the first end of the switch device and the voltage of the second end of the switch device is greater than or equal to the first voltage threshold, the second end of the switch device and the third end of the switch device are connected such that the power cable and the ground cable are connected. The current, detected by the overcurrent detection circuit, of the secondary side of the transformer is greater than or equal to the first current threshold such that the PWM control chip controls the primary side of the transformer to stop inducing the alternating current to the secondary side of the transformer, where the first voltage threshold is greater than 0 volts (V) and is less than an output voltage value of the power cable. 
     With reference to the first aspect, in a first possible implementation manner of the first aspect, the charger further includes a voltage control chip and a power supply module that supplies power to the voltage control chip, where a first end of the voltage control chip is connected to the signal cable, a second end of the voltage control chip is connected to the first end of the switch device, a third end of the voltage control chip is connected to the power supply module, the voltage control chip is configured to output a low voltage at the second end of the voltage control chip when a voltage of the first end of the voltage control chip is less than or equal to a second voltage threshold such that the second end of the switch device and the third end of the switch device are connected, and the power cable and the ground cable are connected, the current, detected by the overcurrent detection circuit, of the secondary side of the transformer is greater than or equal to the first current threshold such that the PWM control chip controls the primary side of the transformer to stop inducing the alternating current to the secondary side of the transformer, and the second voltage threshold is greater than 0 V and is less than a designed minimum output voltage value of the power cable. 
     With reference to the first aspect or the first possible implementation manner of the first aspect, in a second possible implementation manner of the first aspect, the switch device includes at least one device of a p-channel metal-oxide-semiconductor field-effect transistor (PMOSFET), an electromagnetic relay, a thyristor, a triode, or a controllable silicon element. 
     With reference to the first aspect, the first possible implementation manner of the first aspect, or the second possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the signal cable includes at least one of a positive voltage data cable (D+), a negative voltage data cable (D−), a dead-end ID, or a positive receiving differential bus  1  (RX 1 +), a negative receiving differential bus  1  (RX 1 −), a positive receiving differential bus  2  (RX 2 +), a negative receiving differential bus  2  (RX 2 −), a positive transmitting differential bus  1  (TX 1 +), a negative transmitting differential bus  1  (TX 1 −), a positive transmitting differential bus  2  (TX 2 +), a negative transmitting differential bus  2  (TX 2 −), a sideband signal cable  1  (SBU 1 ), a sideband signal cable  2  (SBU 2 ), a configuration channel signal cable  1  (CC 1 ), or a configuration channel signal cable  2  (CC 2 ) of a Typc C interface defined in the USB 3.1 specification. 
     According to a second aspect, an embodiment of the present disclosure provides a charger, including a power conversion circuit, a charging interface, and an overcurrent protection circuit, where the power conversion circuit includes a transformer and a rectifier, an alternating current is input from a primary side of the transformer, and is induced to a secondary side of the transformer by the primary side of the transformer, and a direct current is output from the secondary side of the transformer after the alternating current is rectified by the rectifier. The charging interface includes a power cable, a ground cable, and a signal cable, where a positive electrode of the rectifier is connected to the power cable, and a negative electrode of the rectifier is connected to the ground cable. The overcurrent protection circuit includes an overcurrent detection circuit and a PWM control chip, where the overcurrent detection circuit is configured to enable the PWM control chip to control the primary side of the transformer to stop inducing the alternating current to the secondary side of the transformer when it is detected that a current of the secondary side of the transformer is greater than or equal to a first current threshold that is preset, where the first current threshold is greater than a rated output current value of the charger, and the charger further includes a resistor, a switch device, and an isolation control device, where a first end of the resistor is connected to the power cable, and a second end of the resistor is connected to the signal cable. The overcurrent protection circuit further includes a metal-oxide-semiconductor field effect transistor (MOSFET), a first end of the MOSFET is connected to a control pin of the PWM control chip, and a second end of the MOSFET is connected to the primary side of the transformer to control working of the primary side of the transformer. When a voltage of the first end of the MOSFET is less than or equal to a third voltage threshold, the MOSFET is turned off so that the primary side of the transformer stops inducing the alternating current to the secondary side of the transformer, where the third voltage threshold is greater than 0 V and is less than a working voltage of the PWM control chip. A first end of the switch device is connected to the signal cable, a second end of the switch device is connected to a first input end of the isolation control device, and a third end of the switch device is connected to the ground. When a voltage difference between a voltage of the first end of the switch device and a voltage of the second end of the switch device is greater than or equal to a preset first voltage threshold, the switch device is turned on to trigger the isolation control device to work, where the first voltage threshold is greater than 0 V and is less than an output voltage value of the power cable, and a second input end of the isolation control device is connected to the power cable, a first output end of the isolation control device is connected to the control pin of the PWM control chip, a second output end of the isolation control device is connected to the ground, and when the switch device is turned on, the isolation control device is triggered to work such that a voltage of the first output end of the isolation control device is less than the third voltage threshold. 
     With reference to the second aspect, in a first possible implementation manner of the second aspect, the switch device includes at least one device of a PMOSFET, an electromagnetic relay, a thyristor, a triode, or a controllable silicon element. 
     With reference to the second aspect or the first possible implementation manner of the second aspect, in a second possible implementation manner of the second aspect, the signal cable includes at least one of a D+, a D−, a dead-end ID, or an RX 1 +, an RX 1 −, an RX 2 +, an RX 2 −, a TX 1 +, a TX 1 −, a TX 2 +, a TX 2 −, an SBU 1 , an SBU 2 , a CC 1 , or a CC 2  of a Typc C interface defined in the USB 3.1 specification. 
     According to a third aspect, an embodiment of the present disclosure provides a terminal device, including a charging input circuit, an apparatus for controlling a charging micro short circuit, a battery, and an application processor, where the charging input circuit charges the battery, the apparatus for controlling a charging micro short circuit is configured to determine whether a micro short circuit occurs on the charging input circuit, and send a signal to the application processor when the micro short circuit occurs on the charging input circuit such that the application processor controls an output device of the terminal device to emit an alert signal to prompt an owner of the terminal device that the micro short circuit occurs on the charging input circuit of the terminal device, and the apparatus for controlling a charging micro short circuit includes a voltage comparator and a processing unit, where the voltage comparator is configured to acquire a voltage of a power cable of the charging input circuit and a voltage of a signal cable of the charging input circuit, and obtain a difference between the voltage of the power cable of the charging input circuit and the voltage of the signal cable of the charging input circuit, and the processing unit is configured to determine, according to the difference between the voltage of the power cable of the charging input circuit and the voltage of the signal cable of the charging input circuit, whether a micro short circuit occurs on the charging input circuit, and in a case in which the micro short circuit occurs on the charging input circuit, send, to the application processor of the terminal device, a signal used to indicate that the micro short circuit occurs on the charging input circuit such that the application processor controls the output device of the terminal device to emit an alert signal to prompt the owner of the terminal device that the micro short circuit occurs on the charging input circuit of the terminal device. 
     With reference to the third aspect, in a first possible implementation manner of the third aspect, the terminal device further includes a charging control chip, and the charging control chip controls the charging input circuit to stop current input when the micro short circuit occurs on the charging input circuit. 
     With reference to the third aspect or the first possible implementation manner of the third aspect, in a second possible implementation manner of the third aspect, when the difference between the voltage of the power cable of the charging input circuit and the voltage of the signal cable of the charging input circuit is greater than a voltage threshold, and a time for which the difference between the voltage of the power cable of the charging input circuit and the voltage of the signal cable of the charging input circuit is greater than the voltage threshold is greater than a preset time threshold, the processing unit is further configured to determine that the micro short circuit occurs on the power cable of the charging input circuit, and send, to the application processor of the terminal device, a signal used to indicate that the micro short circuit occurs on the power cable of the charging input circuit such that the application processor controls the output device of the terminal device to emit an alert signal to prompt the owner of the terminal device that the micro short circuit occurs on the charging input circuit of the terminal device, where the voltage threshold is determined by the processing unit according to a wiring resistance of the power cable of the charging input circuit and a current that passes through the power cable of the charging input circuit, and the preset time threshold is greater than a designed communication signal period of the signal cable of the charging input circuit. 
     With reference to the third aspect or the first possible implementation manner of the third aspect, in a third possible implementation manner of the third aspect, when the difference between the voltage of the power cable of the charging input circuit and the voltage of the signal cable of the charging input circuit is less than 0 V, and a time for which the difference between the voltage of the power cable of the charging input circuit and the voltage of the signal cable of the charging input circuit is less than 0 V is greater than a preset time threshold, the processing unit is further configured to determine that the micro short circuit occurs on the signal cable of the charging input circuit, and send, to the application processor of the terminal device, a signal used to indicate that the micro short circuit occurs on the signal cable of the charging input circuit such that the application processor controls the output device of the terminal device to emit an alert signal to prompt the owner of the terminal device that the micro short circuit occurs on the charging input circuit of the terminal device, where the preset time threshold is greater than a designed communication signal period of the signal cable of the charging input circuit. 
     With reference to the third aspect or any possible implementation manner of the first possible implementation manner of the third aspect to the third possible implementation manner of the third aspect, in a fourth possible implementation manner of the third aspect, the apparatus for controlling a charging micro short circuit is a charging integrated circuit (IC) or a power management unit (PMU). 
     According to a fourth aspect, an embodiment of the present disclosure provides a charging system, including a charger and the terminal device according to the third aspect or any one of the first possible implementation manner of the third aspect to the fourth possible implementation manner of the third aspect, where the charger includes a charging interface, the charging interface includes a power cable, a ground cable, and a signal cable, and the power cable of the charging interface is connected to the signal cable of the charging interface using a resistor. 
     With reference to the fourth aspect, in a first possible implementation manner of the fourth aspect, a resistance value of the resistor is greater than or equal to 5 ohms. 
     According to a fifth aspect, an embodiment of the present disclosure provides a terminal device, including a charging input circuit, an apparatus for controlling a charging micro short circuit, a battery, and an application processor, where the charging input circuit charges the battery, the apparatus for controlling a charging micro short circuit is configured to determine whether a micro short circuit occurs on the charging input circuit, and in a case in which the micro short circuit occurs on the charging input circuit, send a signal to the application processor such that the application processor controls an output device of the terminal device to emit an alert signal to prompt an owner of the terminal device that the micro short circuit occurs on the charging input circuit of the terminal device, and the apparatus for controlling a charging micro short circuit includes a voltage comparator and a processing unit, where the voltage comparator is configured to acquire a voltage of a signal cable of the charging input circuit, and compare a reference voltage and the voltage of the signal cable of the charging input circuit, to obtain a difference between the voltage of the signal cable of the charging input circuit and the reference voltage, where the reference voltage is greater than 0 V and is less than a designed minimum output voltage value of a power cable of the charging input circuit, and the processing unit is configured to determine, according to the difference between the voltage of the signal cable of the charging input circuit and the reference voltage, whether a micro short circuit occurs on the signal cable of the charging input circuit, and in a case in which the micro short circuit occurs on the signal cable of the charging input circuit, send, to the application processor of the terminal device, a signal used to indicate that the micro short circuit occurs on the signal cable of the charging input circuit such that the application processor controls the output device of the terminal device to emit an alert signal to prompt the owner of the terminal device that the micro short circuit occurs on the charging input circuit of the terminal device. 
     With reference to the fifth aspect, in a first possible implementation manner of the fifth aspect, the terminal device further includes a charging control chip, and the charging control chip controls the charging input circuit to stop current input when the micro short circuit occurs on the signal cable of the charging input circuit. 
     With reference to the fifth aspect or the first possible implementation manner of the fifth aspect, in a second possible implementation manner of the fifth aspect, when the difference between the voltage of the signal cable of the charging input circuit and the reference voltage is greater than 0 V, and a time for which the difference between the voltage of the signal cable of the charging input circuit and the reference voltage is greater than 0 V is greater than a preset time threshold, the processing unit is further configured to determine that the micro short circuit occurs on the signal cable of the charging input circuit, and send, to the application processor of the terminal device, a signal used to indicate that the micro short circuit occurs on the signal cable of the charging input circuit such that the application processor controls the output device of the terminal device to emit an alert signal to prompt the owner of the terminal device that the micro short circuit occurs on the charging input circuit of the terminal device, where the preset time threshold is greater than a designed communication signal period of the signal cable of the charging input circuit. 
     With reference to the fifth aspect, the first possible implementation manner of the fifth aspect, or the second possible implementation manner of the fifth aspect, in a third possible implementation manner of the fifth aspect, the apparatus for controlling a charging micro short circuit is a charging IC or a PMU. 
     According to a sixth aspect, an embodiment of the present disclosure further provides a charging system, including a charger and the terminal device according to the fifth aspect or any possible implementation manner of the first possible implementation manner of the fifth aspect to the third possible implementation manner of the fifth aspect, where the charger includes a charging interface, the charging interface includes a power cable, a ground cable, and a signal cable, and the power cable of the charging interface is connected to the signal cable of the charging interface using a resistor. 
     With reference to the sixth aspect, in a first possible implementation manner of the sixth aspect, a resistance value of the resistor is greater than or equal to 5 ohms. 
     Based on the foregoing technical solutions, according to the charger, the terminal device, and the charging system provided in the embodiments of the present disclosure, a resistor is disposed between a power cable and a signal cable on a side of the charger, using a voltage drop generated on the signal cable because a micro short circuit occurs, a switch device is triggered to connect the power cable and a ground cable, and as a result, a secondary side of a transformer generates an overcurrent, and an overcurrent protection circuit detects the overcurrent and controls the charger to stop outputting a charging current to the terminal device, thereby controlling a charging process and improving charging security. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To describe the technical solutions in the embodiments of the present disclosure more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments of the present disclosure. The accompanying drawings in the following description show merely some embodiments of the present disclosure, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1A  is a schematic diagram of a USB interface; 
         FIG. 1B  is a schematic diagram of a Micro USB interface; 
         FIG. 2  is a schematic structural diagram of a charger; 
         FIG. 3  is a schematic diagram of a circuit of a charger according to an embodiment of the present disclosure; 
         FIG. 4  is a schematic diagram of a circuit of a charger according to another embodiment of the present disclosure; 
         FIG. 5  is a schematic diagram of a circuit of a charger according to still another embodiment of the present disclosure; 
         FIG. 6  is a schematic structural diagram of a circuit of a terminal device according to an embodiment of the present disclosure; and 
         FIG. 7  is a schematic structural diagram of a circuit of a terminal device according to another embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following clearly describes the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings in the embodiments of the present disclosure. The described embodiments are some but not all of the embodiments of the present disclosure. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure. 
     For ease of understanding the embodiments of the present disclosure, several related concepts are described first herein. 
     (1) PWM 
     PWM is an analog control manner, and in PWM, an offset of a base of a transistor or a gate of a metal-oxide-semiconductor (MOS) transistor is modulated according to a change of corresponding load to implement a change of a time at which the transistor or the MOS transistor is conducted, and to implement a change of regulated power supply output of a switch. In this manner, an output voltage of power supply can maintain constant when a working condition changes, which is a very effective technology that controls an analog circuit using a digital signal of a microprocessor. 
     (2) MOSFET 
     A MOSFET is a switch device that is widely used, and the MOSFET has a relatively high switching speed but also has a relatively large parasitic capacitor. When the MOSFET is turned off, the parasitic capacitor of the MOSFET is fully charged under an effect of an external voltage, and if this part of charges is not discharged before the MOSFET is turned on, the charges are consumed inside the device. 
     The MOSFET may also be briefly referred to as a MOS transistor. 
     (3) PNP Transistor 
     The transistor is formed by sandwiching one N-type semiconductor between two P-type semiconductors, that is, N-electrons of two P-N junctions are connected to serve as a base, and the two P-type semiconductors separately serve as a collector and an emitter. A current flows in from the emitter, and an electric potential of the emitter is the highest and an electric potential of the collector is the lowest. 
     (4) Short Circuit 
     A short circuit refers to a case in which two points that have different electric potentials in a normal circuit are directly in contact incorrectly or are connected by a conductor having a very small impedance (or a resistance). A short circuit may be understood as a state in which two points that should not be connected in a normal circuit are connected because of a reason, that is, a low-impedance path is formed between two points that should not be connected. A short circuit represents a circuit connection status, and is unrelated to activities such as whether a voltage is applied and whether a loop is formed and a current is formed between two points of the short circuit. For example, a data cable D+ and a ground cable (GND) of a USB interface form a path because an object (liquid, metal, dust, or the like) enters, and it may be considered that a short circuit occurs between the data cable D+ and the GND, or it is briefly referred to as that a short circuit occurs on the data cable D+ (a short circuit to the ground), regardless of whether a power supply source is connected to two ends of the data cable D+ and the GND to form a loop. When a resistance of the entered object is relatively large, a current that may be caused by the short circuit from the data cable D+ to the ground is relatively small and is referred to as a micro short circuit. 
       FIG. 1A  and  FIG. 1B  are schematic diagrams of a USB interface and a Micro USB interface respectively. As shown in  FIG. 1A , the USB interface generally includes a GND, a D+, a D−, and a power cable (Vbus). As shown in  FIG. 1B , the Micro USB interface generally includes a GND, a D+, a D−, a Vbus, and a dead-end ID. Moreover, for a Micro USB interface of a Typc C standard defined in a next-generation USB 3.1 specification, the Micro USB interface may further include another signal cable defined in the Typc C interface. 
     A signal cable in this embodiment of the present disclosure includes a signal cable used to transmit a control signal and a signal cable used to transmit a data signal. For example, the signal cable may be at least one of a D+, a D−, a dead-end ID, or an RX 1 +, an RX 1 −, an RX 2 +, an RX 2 −, a TX 1 +, a TX 1 −, a TX 2 +, a TX 2 −, an SBU 1 , an SBU 2 , a CC 1 , or a CC 2  of a Typc C interface defined in the USB 3.1 specification. 
     Because a USB interface and a Micro USB interface have a very compact structure currently, when a micro short circuit occurs on a stub of a charging circuit or a charging interface of a mobile terminal because liquid, metal, dust, or the like enters, in most cases, a micro short circuit to the ground also occurs on neighboring signal cables thereof because liquid enters. 
       FIG. 2  is a schematic structural diagram of a charger in other approaches. As shown in  FIG. 2 , the charger includes a plug, an internal circuit, and a charging interface. The charger is connected to an alternating current power source using the plug, converts an alternating current to a direct current using the internal circuit of the charger, and outputs the direct current using the charging interface. Corresponding to a USB interface, the charging interface of the charger generally also includes a GND, a D+, a D−, and a Vbus. The internal circuit includes a transformer, a rectifier, and an overcurrent protection circuit. An alternating current is input from a primary side N P  of the transformer, and is induced to a secondary side N S  of the transformer by the primary side N P  of the transformer, and a direct current is output from the secondary side N S  of the transformer after the alternating current is rectified by the rectifier. A positive electrode of the rectifier is connected to the Vbus, and a negative electrode of the rectifier is connected to the GND. The overcurrent protection circuit includes an overcurrent detection circuit and a PWM control chip, where the overcurrent detection circuit is configured to enable the PWM control chip to control the primary side N P  of the transformer to stop inducing an alternating current to the secondary side N S  of the transformer when it is detected that a current of the secondary side N S  of the transformer is greater than or equal to a preset current threshold (an overcurrent). It should be understood that  FIG. 2  shows only a schematic structure of the charger, and the structure of the charger may vary in various manners, which is not described in detail in the present disclosure. 
     Based on the foregoing case, the charger may be improved, and  FIG. 3  is a schematic diagram of a circuit of a charger  1000  according to an embodiment of the present disclosure. As shown in  FIG. 3 , the charger  1000  includes a power conversion circuit  1100 , a charging interface  1200 , and an overcurrent protection circuit  1300 , where the power conversion circuit  1100  includes a transformer  1101  and a rectifier C 1 , an alternating current (designated as AC in  FIG. 3 ) is input from a primary side N P  of the transformer  1101 , and is induced to a secondary side N S  of the transformer  1101  by the primary side N P  of the transformer  1101 , and a direct current is output from the secondary side N S  of the transformer  1101  after the alternating current is rectified by the rectifier C 1 . 
     The charging interface  1200  includes a Vbus, a GND, and a signal cable  1201 , where a positive electrode of the rectifier C 1  is connected to the Vbus, and a negative electrode of the rectifier C 1  is connected to the GND. 
     The overcurrent protection circuit  1300  includes an overcurrent detection circuit  1301  and a PWM control chip  1302 , the overcurrent detection circuit  1301  is configured to enable the PWM control chip  1302  to control the primary side N P  of the transformer  1101  to stop inducing the alternating current to the secondary side N S  of the transformer  1101  when it is detected that a current of the secondary side N S  of the transformer  1101  is greater than or equal to a first current threshold that is preset, where the first current threshold is greater than a rated output current value of the charger  1000 . 
     The charger  1000  further includes a resistor  1400  and a switch device P 1 . 
     A first end of the resistor  1400  is connected to the Vbus, and a second end of the resistor  1400  is connected to the signal cable  1201 . 
     A first end of the switch device P 1  is connected to the signal cable  1201 , a second end of the switch device P 1  is connected to the Vbus, a third end of the switch device P 1  is connected to the GND, and in a case in which a difference between a voltage of the first end of the switch device P 1  and a voltage of the second end of the switch device P 1  is greater than or equal to a preset first voltage threshold, the second end of the switch device P 1  and the third end of the switch device P 1  are connected. 
     In a process in which the charger  1000  charges the terminal device, in a case in which the difference between the voltage of the first end of the switch device P 1  and the voltage of the second end of the switch device P 1  is greater than or equal to the first voltage threshold, the second end of the switch device P 1  and the third end of the switch device P 1  are connected such that the Vbus and the GND are connected. The current, detected by the overcurrent detection circuit  1301 , of the secondary side N S  of the transformer  1101  is greater than or equal to the first current threshold such that the PWM control chip  1302  controls the primary side N P  of the transformer  1101  to stop inducing the AC to the secondary side N S  of the transformer  1101 , where the first voltage threshold is greater than 0 V and is less than an output voltage value of the Vbus. 
     Therefore, according to the charger  1000  provided in this embodiment of the present disclosure, a resistor  1400  is disposed between a power cable and a signal cable  1201 , using a voltage drop generated on the signal cable  1201  because a micro short circuit occurs, a switch device is triggered to connect the power cable and a ground cable, and as a result, a secondary side of a transformer  1101  generates an overcurrent, and the overcurrent protection circuit  1300  detects the overcurrent and controls the charger to stop outputting a charging current to the terminal device, thereby controlling a charging process and improving charging security. 
     Further, the charger  1000  includes the power conversion circuit  1100 , the charging interface  1200 , and the overcurrent protection circuit  1300  shown in  FIG. 3 . The power conversion circuit  1100  generally includes the transformer  1101 , and the transformer  1101  includes the primary side N P  and the secondary side N S . The primary side N P  is connected to the AC power source, the secondary side N S  is connected to the rectifier C 1 , and the positive electrode and the negative electrode of the rectifier C 1  are connected to the Vbus and the GND of the charging interface  1200  respectively. It should be understood that the power conversion circuit  1100  may further include another auxiliary element, which is not limited in this embodiment of the present disclosure. When the charger  1000  works, an AC is input from the primary side N P  of the transformer  1101 , and is induced to the secondary side N S  of the transformer  1101  by the primary side N P  of the transformer  1101 , and a direct current is output from the secondary side N S  of the transformer  1101  after the AC is rectified by the rectifier C 1 . The direct current is output from the Vbus, and forms a charging loop with the GND by the charged terminal device. 
     An end of the primary side N P  of the transformer  1101  of the charger  1000  is connected to the overcurrent protection circuit  1300 . The overcurrent protection circuit  1300  includes the overcurrent detection circuit  1301  and the PWM control chip  1302 . The overcurrent detection circuit  1301  includes an induction coil (not shown), used to feedback a sample such that the PWM control chip  1302  of the overcurrent protection circuit  1300  determines whether an overcurrent occurs. When detecting that an overcurrent occurs, the PWM control chip  1302  turns off the primary side N P  of the transformer  1101 , that is, turns off a path for inputting the AC, and in this case, the secondary side N S  cannot generate an induced electromotive force, and the Vbus of the charger  1000  stops outputting a current. It should be understood that, circuits of an internal circuit of the charger  1000  may further include another device to implement a corresponding function of the other device, which is not limited in this embodiment of the present disclosure. 
     Generally, the charging interface  1200  further includes the signal cable  1201  in addition to the Vbus and the GND, and the signal cable  1201  may be, for example, a D+ or a D−. According to the charger  1000  in this embodiment of the present disclosure, the resistor  1400  is disposed between the signal cable  1201  and the Vbus of the charging interface  1200 . For example, a D+ of the charger  1000  is pulled up to the Vbus using a resistor R. 
     In a case in which a USB interface has a very compact structure, generally, when a micro short circuit is generated on the signal cable  1201 , a micro short circuit is also generated on the Vbus, and correspondingly, when a micro short circuit is generated on the Vbus, a micro short circuit is also generated on the signal cable  1201 . In a case in which a micro short circuit occurs on a D+ at a Micro USB interface, if a resistance value R is set, the D+ generates a current to the ground. In a case in which the resistance value of the resistor R is sufficiently large, a voltage at the D+ experiences an obvious voltage drop relative to a charging voltage, and a logical low level is formed, where the logical low level may be used to control the primary side N P  of the transformer  1101  of the power conversion circuit  1100  to be turned off to stop current output of the power conversion circuit  1100 , thereby avoiding occurrence of the micro short circuit. 
     Further, the switch device P 1  is disposed in the charger  1000 , the first end of the switch device P 1  is connected to the signal cable  1201 , the second end of the switch device P 1  is connected to the Vbus, and the third end of the switch device P 1  is connected to the GND. A working principle of the switch device P 1  is that when the difference between the voltage of the first end of the switch device P 1  and the voltage of the second end of the switch device P 1  is greater than or equal to the preset first voltage threshold, the second end of the switch device P 1  and the third end of the switch device P 1  are connected. The first voltage threshold should be greater than 0 V and is less than the output voltage value of the Vbus. 
     In a process in which the charger  1000  charges the terminal device, in a case in which the difference between the voltage of the first end of the switch device P 1  (a voltage of the signal cable  1201 ) and the voltage of the second end of the switch device P 1  (a voltage of the Vbus) is greater than or equal to the first voltage threshold, the second end of the switch device P 1  and the third end of the switch device P 1  are connected such that the Vbus and the GND are connected. The current, detected by the overcurrent detection circuit  1301 , of the secondary side N S  of the transformer  1101  is greater than or equal to the first current threshold such that the PWM control chip  1302  controls the primary side N P  of the transformer  1101  to stop inducing the AC to the secondary side N S  of the transformer  1101 , where the first voltage threshold is greater than 0 V and is less than the output voltage value of the Vbus. 
     That is, in a process in which the charger  1000  charges the terminal device, in a case in which the difference between the voltage of the Vbus and the voltage of the signal cable  1201  is greater than or equal to the first voltage threshold, the switch device P 1  connects the Vbus and the GND such that an excessively large current occurs between the Vbus and the GND to trigger overcurrent protection such that the PWM control chip  1302  turns off the primary side N P  of the transformer  1101 , and finally, the charger  1000  stops current output. 
     The resistance value of the resistor  1400  may be determined according to requirements. For example, the resistance value R is 1 kilo (K) ohms, and calculation is performed in a case in which an output voltage of the Vbus is generally 5 volts (V). When a D+ generates a micro short circuit current of over 3 milliamperes (mA), a voltage of the D+ is less than 2 V. 2 V may serve as a logical low level to trigger the switch device P 1  to work to generate an overcurrent. 
     It should be understood that, in this embodiment of the present disclosure, a micro short circuit can be detected sensitively, and relative to the foregoing example, if a slighter micro short circuit needs to be detected, a resistor R having a larger resistance value may be selected such that a smaller micro short circuit current generates a sufficient voltage drop on R, and the signal cable  1201  is pulled down to a low level for detection and recognition by a terminal or the charger  1000 . Therefore, the resistance value of the resistor R in this embodiment of the present disclosure should satisfy a voltage drop, generated by the resistor  1400 , of a micro short circuit current is sufficiently large. When the micro short circuit occurs, a voltage of the signal cable  1201  may be enabled to enter a secure logical low level range (for example, a 5 V transistor-transistor logic (TTL) level and a 5 V complementary metal-oxide semiconductor (CMOS) level, where a secure low level range is lower than 0.4 V). 
     Generally, a typical micro short circuit current is around 0.5 amperes (A), and is generally greater than 0.2 A. In this way, a resistance value of a corresponding resistor is 22 ohms such that a micro short circuit current of 0.2 A generates a logical low level (which corresponds to a 4.4 V voltage drop). Therefore, in this embodiment of the present disclosure, preferably, a resistance value of a resistor is greater than or equal to 22 ohms. 
     It should be understood that the signal cable  1201  in this embodiment of the present disclosure may include at least one of a D+, a D−, a dead-end ID, or an RX 1 +, an RX 1 −, an RX 2 +, an RX 2 −, a TX 1 +, a TX 1 −, a TX 2 +, a TX 2 −, an SBU 1 , an SBU 2 , a CC 1 , or a CC 2  of a Typc C interface defined in the USB 3.1 specification. 
     It should be understood that the switch device P 1  may include at least one device of a PMOSFET, an electromagnetic relay, a thyristor, a triode, or a controllable silicon element. That is, the switch device P 1  may be a single element or a combination of at least two elements described above. 
     It should be further understood that the first end of the switch device P 1  may be directly connected to the signal cable  1201 , or may be indirectly connected to the signal cable  1201 . For example, another element may be connected between the first end of the switch device P 1  and the signal cable  1201  to precisely control the voltage of the first end of the switch device P 1 . 
     Optionally, in this embodiment of the present disclosure, as shown in  FIG. 4 , the charger  1000  may further include a voltage control chip IC 1  and a power supply module M 1  that supplies power to the voltage control chip IC 1 . 
     A first end of the voltage control chip IC 1  is connected to the signal cable  1201 , a second end of the voltage control chip IC 1  is connected to the first end of the switch device P 1 , and a third end of the voltage control chip IC 1  is connected to the power supply module M 1 . The voltage control chip IC 1  is configured to output a low voltage at the second end of the voltage control chip IC 1  when a voltage of the first end of the voltage control chip IC 1  is less than or equal to a second voltage threshold such that the second end of the switch device P 1  and the third end of the switch device P 1  are connected, and the Vbus and the GND are connected. The current, detected by the overcurrent detection circuit  1301 , of the secondary side of the transformer  1101  is greater than or equal to the first current threshold such that the PWM control chip  1302  controls the primary side N P  of the transformer  1101  to stop inducing the AC to the secondary side N S  of the transformer  1101 , and the second voltage threshold is greater than 0 V and is less than a designed minimum output voltage value of the Vbus. 
     Further, as shown in  FIG. 4 , in the charger  1000  in this embodiment of the present disclosure, the signal cable  1201  of the charging interface  1200  may be, for example, a D+ or a D−, the resistor  1400  is disposed between the signal cable  1201  and the Vbus, the switch device P 1  is disposed among the signal cable  1201  of the charging interface  1200 , the Vbus of the charging interface  1200 , and the GND of the charging interface  1200 , and the voltage control chip IC 1  is disposed between the signal cable  1201  and the first end of the switch device P 1  to precisely control turning on and off of the switch device P 1 . The power supply module M 1  may supply power to the voltage control chip IC 1 . 
     In a case in which a USB interface has a very compact structure, generally, when a micro short circuit is generated on the signal cable  1201 , a micro short circuit is also generated on the Vbus, and correspondingly, when a micro short circuit is generated on the Vbus, a micro short circuit is also generated on the signal cable  1201 . In a case in which a micro short circuit occurs on a D+ at a Micro USB interface, a resistor whose resistance value is R is set, and the D+ generates a current to the ground. In a case in which the resistance value of the resistor R is sufficiently large, a voltage at the D+ experiences an obvious voltage drop relative to a charging voltage, and a logical low level is formed. The low level is read by the first end of the voltage control chip IC 1  (for example, an IN pin of IC 1 ), and when a voltage of the signal cable  1201  is less than the second voltage threshold, the second end of the voltage control chip IC 1  (for example, an OUT pin of IC 1 ) is triggered to pull down the first end of the switch device P 1  (for example, an emitter of a PMOSFET) such that the switch device P 1  is turned on to trigger an overcurrent to occur between the Vbus and the GND, thereby stimulating the overcurrent protection circuit  1300  to perform overcurrent protection and the Vbus to stop current output. 
     It should be understood that the switch device P 1  may include at least one device of a PMOSFET, an electromagnetic relay, a thyristor, a triode, or a controllable silicon element. That is, the switch device P 1  may be a single element or a combination of at least two elements described above. The voltage control chip IC 1  may be a chip that has a function of precisely determining an input voltage and outputting different control signals according to the input voltage. The power supply module M 1  may be a sub-coil that is added beside an induction coil in the overcurrent protection circuit to supply power to the voltage control chip IC 1 , which is not limited in the present disclosure. In this embodiment of the present disclosure, precise control over a micro short circuit can be implemented. 
     Therefore, according to the charger provided in this embodiment of the present disclosure, a resistor is disposed between a power cable and a signal cable, using a voltage drop generated on the signal cable because a micro short circuit occurs, a switch device is triggered to connect the power cable and a ground cable, and as a result, a secondary side of a transformer generates an overcurrent, and an overcurrent protection circuit detects the overcurrent and controls the charger to stop outputting a charging current to the terminal device, thereby controlling a charging process and improving charging security. 
       FIG. 5  is a schematic diagram of a circuit of a charger  2000  according to an embodiment of the present disclosure. As shown in  FIG. 5 , the charger  2000  includes a power conversion circuit  2100 , a charging interface  2200 , and an overcurrent protection circuit  2300 . 
     The power conversion circuit  2100  includes a transformer  2101  and a rectifier C 2 , an alternating current (designated as AC in  FIG. 5 ) is input from a primary side N P  of the transformer  2101 , and is induced to a secondary side N S  of the transformer  2101  by the primary side N P  of the transformer  2101 , and a direct current is output from the secondary side N S  of the transformer  2101  after the AC is rectified by the rectifier C 2 . 
     The charging interface  2200  includes a Vbus, a GND, and a signal cable  2201 , where a positive electrode of the rectifier C 2  is connected to the Vbus, and a negative electrode of the rectifier C 2  is connected to the GND. 
     The overcurrent protection circuit  2300  includes an overcurrent detection circuit  2301  and a PWM control chip  2302 , where the overcurrent detection circuit  2301  is configured to enable the PWM control chip  2302  to control the primary side N P  of the transformer  2101  to stop inducing the AC to the secondary side N S  of the transformer  2101  when it is detected that a current of the secondary side N S  of the transformer  2101  is greater than or equal to the first current threshold that is preset, where the first current threshold is greater than a rated output current value of the charger  2000 . 
     The charger  2000  further includes a resistor  2400 , a switch device P 2 , and an isolation control device O 1 . 
     A first end of the resistor  2400  is connected to the Vbus, and a second end of the resistor  2400  is connected to the signal cable  2201 . 
     The overcurrent protection circuit  2300  further includes a MOSFET (MOS 1 ), a first end of the MOS 1  is connected to a control pin of the PWM control chip  2302 , a second end of the MOS 1  is connected to the primary side N P  of the transformer  2101  to control working of the primary side N P  of the transformer  2101 . A third end of the MOS 1  is grounded. In a case in which a voltage of the first end of the MOS 1  is less than or equal to a third voltage threshold, the MOS 1  is turned off such that the primary side N P  of the transformer  2101  stops inducing the AC to the secondary side N S  of the transformer  2101 , where the third voltage threshold is greater than 0 V and is less than a working voltage of the PWM control chip  2302 . 
     A first end of the switch device P 2  is connected to the signal cable  2201 , a second end of the switch device P 2  is connected to a first input end of the isolation control device O 1 , a third end of the switch device P 2  is connected to the ground. In a case in which a voltage difference between a voltage of the first end of the switch device P 2  and a voltage of the second end of the switch device P 2  is greater than or equal to a preset first voltage threshold, the switch device P 2  is turned on to trigger the isolation control device O 1  to work, where the first voltage threshold is greater than 0 V and is less than an output voltage value of the Vbus. 
     A second input end of the isolation control device O 1  is connected to the Vbus, a first output end of the isolation control device O 1  is connected to the control pin of the PWM control chip  2302 , and a second output end of the isolation control device O 1  is connected to the ground. When the switch device P 2  is turned on, the isolation control device O 1  is triggered to work such that a voltage of the first output end of the isolation control device O 1  is less than the third voltage threshold. 
     Therefore, according to the charger  2000  provided in this embodiment of the present disclosure, the resistor  2400  is disposed between the power cable and the signal cable  2201 , using a voltage drop generated on the signal cable  2201  because a micro short circuit occurs, the isolation control device is triggered to turn off the MOSFET that is in the overcurrent protection circuit and that controls working of the primary side of the transformer  2101 , to control the charger  2000  to stop outputting a charging current to the terminal device, thereby controlling a charging process and improving charging security. 
     It should be understood that the isolation control device O 1  may be a device such as an optical coupler or a magnetic coupler that has an isolation function. Preferably, the isolation control device O 1  is an optical coupler, and descriptions are all provided below using an example in which the isolation control device O 1  is an optical coupler. 
     Further, as shown in  FIG. 5 , in the charger  2000  in this embodiment of the present disclosure, the signal cable  2201  of the charging interface  2200  may be, for example, a D+ or a D−, the resistor  2400  is disposed between the signal cable  2201  and the Vbus, and the switch device P 2  and an optical coupler O 1  are disposed between the signal cable  2201  and the control pin GATE of the PWM control chip  2302  of the overcurrent protection circuit  2300 . 
     In a case in which a USB interface has a very compact structure, generally, when a micro short circuit is generated on the signal cable  2201 , a micro short circuit is also generated on the Vbus, and correspondingly, when a micro short circuit is generated on the Vbus, a micro short circuit is also generated on the signal cable  2201 . For example, in a case in which a micro short circuit occurs on a D+ at a Micro USB interface, if a resistance value R is set, the D+ generates a current to the ground. In a case in which the resistance value of the resistor R is sufficiently large, a voltage at the D+ experiences an obvious voltage drop relative to a charging voltage, and a logical low level is formed. A difference between a voltage of the Vbus and the logical low level triggers the switch device P 2  such that the switch device P 2  is turned on, a current is generated between a first input end and a second input end of the optical coupler O 1 , and a first output end of the optical coupler O 1  enables a voltage of the control pin GATE of the PWM control chip  2302  to be pulled down to become a low voltage, where the low voltage is less than the third voltage threshold, and the third voltage threshold is greater than 0 V and is less than the working voltage of the PWM control chip  2302 . The low voltage of the GATE enables the MOS 1  to be turned off such that the primary side N P  of the transformer  2101  of the power conversion circuit  2100  stops working, the secondary side N S  of the transformer  2101  cannot generate an induced current, and the Vbus stops current output. 
     It should be understood that, in this embodiment of the present disclosure, an isolation control function of the optical coupler O 1  is used to conduct a level signal of the signal cable  2201  to a side of the overcurrent protection circuit  2300  of the charger  2000 , and when a micro short circuit occurs on the signal cable  2201  and a level of the signal cable  2201  decreases, a coil of the primary side of the transformer  2101  directly stops working, and the Vbus stops current output. The micro short circuit can be precisely controlled by selecting an optical coupler O 1  of a suitable specification. The optical coupler O 1  may also be an isolator having a similar function, and an output of the isolator to the primary side N P  of the transformer  2101  is transferred to a control pin of the PWM control chip  2302  such that the primary side N P  of the transformer  2101  stops working. 
     It should be understood that the switch device P 2  may include at least one device of a PMOSFET, an electromagnetic relay, a thyristor, a triode, or a controllable silicon element. That is, the switch device P 2  may be a single element or a combination of at least two elements described above. Preferably, the switch device P 2  is a PNP transistor. 
     It should be understood that the signal cable  2201  in this embodiment of the present disclosure may include at least one of a D+, a D−, a dead-end ID, or an RX 1 +, an RX 1 −, an RX 2 +, an RX 2 −, a TX 1 +, a TX 1 −, a TX 2 +, a TX 2 −, an SBU 1 , an SBU 2 , a CC 1 , or a CC 2  of a Typc C interface defined in the USB 3.1 specification. 
     Therefore, according to the charger  2000  provided in this embodiment of the present disclosure, the resistor  2400  is disposed between the Vbus and a signal cable  2201 , using a voltage drop generated on the signal cable  2201  because a micro short circuit occurs, the isolation control device O 1  is triggered to turn off a MOSFET (the MOS 1 ) that is in the overcurrent protection circuit  2301  and that controls working of the primary side N P  of the transformer  2101  to control the charger  2000  to stop outputting a charging current to a terminal device, thereby controlling a charging process and improving charging security. 
     An embodiment of the present disclosure further provides an improved terminal device.  FIG. 6  is a schematic diagram of a circuit of a terminal device  3000  according to an embodiment of the present disclosure. As shown in  FIG. 6 , the terminal device  3000  includes a charging input circuit  3100 , an apparatus  3200  for controlling a charging micro short circuit, a battery  3300 , and an application processor  3400 . 
     The charging input circuit  3100  charges the battery  3300 . The apparatus  3200  for controlling a charging micro short circuit is configured to determine whether a micro short circuit occurs on the charging input circuit  3100 , and sends a signal to the application processor  3400  when the micro short circuit occurs on the charging input circuit  3100  such that the application processor  3400  controls an output device of the terminal device  3000  to emit an alert signal to prompt an owner of the terminal device  3000  that the micro short circuit occurs on the charging input circuit  3100  of the terminal device  3000 . 
     The apparatus  3200  for controlling a charging micro short circuit includes a voltage comparator  3201  and a processing unit  3202 . 
     The voltage comparator  3201  is configured to acquire a voltage of a Vbus of the charging input circuit  3100  and a voltage of a signal cable N 1  of the charging input circuit  3100 , and obtain a difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100 . 
     The processing unit  3202  is configured to determine, according to the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100 , whether a micro short circuit occurs on the charging input circuit  3100 , and send, to the application processor  3400  of the terminal device  3000 , a signal used to indicate that the micro short circuit occurs on the charging input circuit  3100  when the micro short circuit occurs on the charging input circuit  3100  such that the application processor  3400  controls the output device of the terminal device  3000  to emit an alert signal to prompt the owner of the terminal device  3000  that the micro short circuit occurs on the charging input circuit  3100  of the terminal device  3000 . 
     Further, in a case in which a micro short circuit occurs on the Vbus of the charging input circuit  3100  because liquid, metal dust, or the like enters a charging interface and a stub of the charging input circuit  3100  on a side of a charger or a charging interface on a side of the terminal device  3000 , a power cable of the charging interface of the charger may be connected to a signal cable of the charging interface of the charger using a resistor. 
     In a circuit that includes the charger and the terminal device  3000 , in a case in which no short circuit occurs on the signal cable, the power cable of the charging interface of the charger is connected to the signal cable of the charging interface of the charger using a resistor, and a voltage of the power cable of an internal circuit of the charger may be obtained by collecting a voltage of the signal cable of the internal circuit of the charger. Because the voltage of the power cable of the charger may be collected on the side of the charger using the signal cable, and the voltage of the signal cable of the internal circuit of the charger is equal to the voltage of the signal cable N 1  of the charging input circuit  3100  of the terminal device  3000 , the voltage of the power cable of the internal circuit of the charger may be obtained by collecting the voltage of the signal cable N 1  of the charging input circuit  3100  of the terminal device  3000 . On the side of the charged terminal device  3000 , the voltage of the signal cable N 1  of the charging input circuit  3100  is sampled, and is compared with a voltage of the Vbus of the charging input circuit  3100  to determine whether a voltage drop from the side of the charger to the side of the terminal device  3000  exceeds a proper range, which is used as a basis for determining whether a micro short circuit occurs on the Vbus. 
     In a circuit that includes the charger and the terminal device  3000 , in a case in which a short circuit occurs on the signal cable, the power cable of the charging interface of the charger is connected to the signal cable of the charging interface of the charger using a resistor whose resistance value is R. Because the resistor whose resistance value is R is disposed between the power cable of the charging interface of the charger and the signal cable of the charging interface of the charger, a current to the ground is generated on the signal cable. In a case in which the resistance value R of the resistor is sufficiently large, the voltage of the signal cable N 1  of the charging input circuit  3100  of the terminal device  3000  experiences an obvious voltage drop relative to a charging voltage, and it may be determined, according to the voltage drop, that a micro short circuit occurs on the signal cable N 1  of the charging input circuit  3100 . 
     Therefore, according to the terminal device  3000  provided in this embodiment of the present disclosure, the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is obtained through comparison such that it may be determined whether a micro short circuit occurs on the charging input circuit  3100 . When the micro short circuit occurs on the charging input circuit  3100 , an alert signal used to indicate that the micro short circuit occurs on the charging input circuit  3100  is sent such that the owner of the terminal device  3000  is prompted that the micro short circuit occurs on the charging input circuit  3100  of the terminal device  3000 , which can improve charging security. 
     The apparatus  3200  for controlling a charging micro short circuit in this embodiment of the present disclosure may be a charging IC or a PMU of the terminal device  3000 . The voltage comparator  3201  of the apparatus  3200  for controlling a charging micro short circuit compares the voltage of the signal cable N 1  of the charging input circuit  3100  and the voltage of the Vbus of the charging input circuit  3100 . The processing unit  3202  determines, according to the difference between the voltages, whether the micro short circuit occurs on the charging input circuit  3100 . When the micro short circuit occurs on the charging input circuit  3100 , the processing unit  3202  sends to the application processor  3400  of the terminal device  3000 , a signal used to indicate that the micro short circuit occurs on the charging input circuit  3100  such that the application processor  3400  controls the output device of the terminal device  3000  to emit an alert signal. 
     The alert signal may be a sound signal emitted by a horn of the terminal device  3000 , may be an optical signal emitted by a screen, an indicator, a flash, or the like, or may be a vibration signal emitted by a vibration apparatus in the terminal device  3000 , which is not limited in this embodiment of the present disclosure. The terminal device  3000  emits the alert signal such as sound and light to notify a user of an exception of a charging micro short circuit, and may further prompt the user to clean a Micro USB interface, replace a charging cable, or the like. 
     Optionally, in an embodiment, when the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is greater than a voltage threshold, and a time for which the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is greater than the voltage threshold is greater than a preset time threshold, the processing unit  3202  is further configured to determine that the micro short circuit occurs on the Vbus of the charging input circuit  3100 , and sends, to the application processor  3400  of the terminal device  3000 , a signal used to indicate that the micro short circuit occurs on the Vbus of the charging input circuit  3100  such that the application processor  3400  controls the output device of the terminal device  3000  to emit an alert signal to prompt the owner of the terminal device  3000  that the micro short circuit occurs on the charging input circuit  3100  of the terminal device  3000 . 
     The voltage threshold is determined by the processing unit  3202  according to a wiring resistance of the Vbus of the charging input circuit  3100  and a current that passes through the Vbus of the charging input circuit  3100 , and the preset time threshold is greater than a designed communication signal period of the signal cable N 1  of the charging input circuit  3100 . 
     Further, according to a specific specification of a charger, a maximum allowable voltage drop of the Vbus from the charger to the Micro USB interface of the terminal device  3000  is generally 200 millivolts (mV). When no micro short circuit occurs on a signal cable, for a data cable such as D+/D−, because there is no current consumption, there is almost no voltage drop from a signal cable of a charging interface of the charger to the signal cable N 1  of the charging input circuit  3100  of the terminal device  3000 . That is, in a case in which no micro short circuit occurs at either the charging interface of the charger or the Vbus and the signal cable N 1  of the charging input circuit  3100  of the terminal device  3000 , the difference between the voltage of the Vbus of the charging input circuit  3100  of the terminal device  3000  and the voltage of the signal cable N 1  of the charging input circuit  3100  of the terminal device  3000  should not be greater than 200 mV. 
     In a specific example, when the difference, which is collected by the voltage comparator  3201 , between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is greater than 200 mV, and the time for which the difference is steadily greater than 200 mV is greater than the preset time threshold, it is considered that the micro short circuit occurs on the Vbus of the charging input circuit  3100 . The preset time threshold should be greater than the designed communication signal period of the signal cable N 1  of the charging input circuit  3100 , and may be several seconds or longer such that the preset time threshold is sufficiently longer than a signal period of the signal cable N 1  during normal communication to avoid that when the terminal device  3000  is inserted into a USB interface of another terminal device (for example, a desktop computer) to communicate with the other terminal device, a shift that occurs when D+/D− or the like transfers a digital signal causes incorrect determining. 
     Optionally, in an embodiment, when the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is less than 0 V, and a time for which the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is less than 0 V is greater than a preset time threshold, the processing unit  3202  is further configured to determine that the micro short circuit occurs on the signal cable N 1  of the charging input circuit  3100 , and send, to the application processor  3400  of the terminal device  3000 , a signal used to indicate that the micro short circuit occurs on the signal cable N 1  of the charging input circuit  3100  such that the application processor  3400  controls the output device of the terminal device  3000  to emit an alert signal to prompt the owner of the terminal device  3000  that the micro short circuit occurs on the charging input circuit  3100  of the terminal device  3000 . 
     The preset time threshold is greater than a designed communication signal period of the signal cable N 1  of the charging input circuit  3100 . 
     Further, in a case in which a micro short circuit occurs on the signal cable N 1  of the charging input circuit  3100 , a resistor whose resistance value is R is disposed between the power cable of the charging interface of the charger and the signal cable of the charging interface of the charger. Because the short circuit occurs on the signal cable N 1 , a current to the ground is generated on the signal cable N 1 , and in a case in which the resistance value R of the resistor is sufficiently large, the voltage of the signal cable N 1  of the charging input circuit  3100  experiences an obvious voltage drop relative to a charging voltage such that the voltage of the signal cable N 1  of the charging input circuit  3100  is less than the voltage of the Vbus of the charging input circuit  3100 , that is, the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is less than 0. 
     In a specific example, when the difference, which is collected by the voltage comparator  3201 , between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is less than 0, and the time for which the difference is steadily greater than 200 mV is greater than the preset time threshold, it is considered that the micro short circuit occurs on the signal cable N 1  of the charging input circuit  3100 . The preset time threshold should be greater than the designed communication signal period of the signal cable N 1  of the charging input circuit  3100 , and may be several seconds or longer such that the preset time threshold is sufficiently longer than a signal period of the signal cable N 1  during normal communication to avoid that when the terminal device is inserted into a USB interface of another terminal device (for example, a desktop computer) to communicate with the other terminal device, a shift that occurs when D+/D− or the like transfers a digital signal causes incorrect determining. 
     When the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is greater than 0 and is less than a voltage threshold, it is determined that normal charging is performed currently. For example, when a difference between a voltage of the Vbus and a voltage of a data cable D−/D+ is greater than 0 and is less than 200 mV, it is determined that normal charging is performed currently. When the voltage of the data cable D−/D+ is always 0 V, it is considered that a used charger may be a charger of a non-standard configuration, and the application processor  3400  of the terminal device  3000  may be triggered to prompt that the charger is not a dedicated charger, and stop a charging action. 
     Optionally, in this embodiment of the present disclosure, the signal cable N 1  of the charging input circuit  3100  may include at least one of a D+, a D−, a dead-end ID, or an RX 1 +, an RX 1 −, an RX 2 +, an RX 2 −, a TX 1 +, a TX 1 −, a TX 2 +, a TX 2 −, an SBU 1 , an SBU 2 , a CC 1 , or a CC 2  of a Typc C interface defined in the USB 3.1 specification. 
     Optionally, in an embodiment, the terminal device  3000  further includes a charging control chip (not shown). 
     In a case in which the micro short circuit occurs on the charging input circuit  3100 , the charging control chip controls the charging input circuit  3100  to stop current input. In this way, not only the alert signal is emitted for the owner of the terminal device  3000 , but also a current charging process is interrupted, which can further improve charging process security. 
     Optionally, in this embodiment of the present disclosure, the voltage threshold is determined by the processing unit  3202  according to a wiring resistance of the Vbus of the charging input circuit  3100  and a current that passes through the Vbus of the charging input circuit  3100 . In addition, the voltage threshold may also be preset according to an empirical value. 
     When no micro short circuit exists on the signal cable N 1  of the charging input circuit  3100 , the wiring resistance of the Vbus of the charging input circuit  3100  may be calculated using the following method. 
     The terminal device  3000  further includes a charging control chip (not shown) and a storage unit (not shown), where the charging control chip is configured to control a charging current value, the charging control chip is in communication connection with the processing unit  3202 , and the storage unit is in communication connection with the processing unit  3202 . 
     The processing unit  3202  is further configured to acquire a first charging current value using the charging control chip, and acquire, using the voltage comparator  3201 , a first difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100 , acquire a second charging current value using the charging control chip, acquire a second difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  using the voltage comparator  3201 , and determine the wiring resistance of the Vbus of the charging input circuit  3100  according to the first charging current value, the second charging current value, the first difference, and the second difference, and during charging, acquire a current third charging current value using the charging control chip, acquire, using the voltage comparator  3201 , a current third difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100 , and determine, according to the third charging current value and the wiring resistance, a proper difference between the Vbus of the charging input circuit  3100  and the signal cable N 1  of the charging input circuit  3100 . 
     The storage unit is configured to store the wiring resistance. 
     Further, the charging control chip has a function of controlling a charging current value. The processing unit  3202  has a logical operation capability to some extent, and has a function similar to a single-chip microcomputer (such as a Micro Control Unit (MCU)) or a thin central processing unit (CPU). Detection logic is as follows. 
     When a new terminal device is powered on, generally, no micro short circuit exists, in this case: 
     1) During initial charging, a relatively large current is used for charging, and the processing unit  3202  reads a current first charging current value I 1  from the charging control chip, and reads, from the voltage comparator  3201 , a first difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  (for example, a data cable D+/D−) of the charging input circuit  3100 . Because the Vbus of the charging input circuit  3100  has a voltage drop caused by a wiring resistance and a contact resistance in a case of the large current, the processing unit  3202  obtains by reading that the voltage of the signal cable N 1  of the charging input circuit  3100  is greater than the voltage of the Vbus of the charging input circuit  3100  by a. 
     2) The processing unit  3202  sends a command to the charging control chip to request the charging control chip to decrease or increase a charging current at a particular moment. Assuming that a charging current decreases by ΔI, the processing unit  3202  reads a current second charging current value I 2  from the charging control chip, where ΔI=I 1 −I 2 , and reads, from the voltage comparator  3201 , a second difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  (for example, a data cable D+/D−) of the charging input circuit  3100 . Because the Vbus of the charging input circuit  3100  has a voltage drop caused by a wiring resistance and a contact resistance in a case of the large current, the voltage of the signal cable N 1  of the charging input circuit  3100  is greater than the voltage of the Vbus of the charging input circuit  3100  by b. Because a current transferred by the Vbus of the charging input circuit  3100  to the charging control chip decreases, the numerical value b is less than a. 
     3) The processing unit  3202  may calculate the wiring resistance R of the Vbus of the charging input circuit  3100  according to the first charging current value I 1 , the second charging current value I 2 , the first difference a, and the second difference b:
 
 R =( a−b )/( I   1   −I   2 )=( a−b )/Δ I.  
 
     4) The storage unit records the wiring resistance R of the Vbus of the charging input circuit  3100 . 
     At any moment during subsequent charging: 
     1) The processing unit  3202  may acquire a current third charging current value I 3  using the charging control chip, and the wiring resistance R of the Vbus of the charging input circuit  3100  that is recorded in the storage unit, and calculate a proper difference ΔV=R×I 3  between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100 . 
     2) The processing unit  3202  acquires, using the voltage comparator  3201 , a current third difference c between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100 . 
     3) The processing unit  3202  determines, according to a result of comparing the proper difference ΔV with the third difference c, whether a micro short circuit occurs on the Vbus of the charging input circuit  3100 . 
     In this embodiment of the present disclosure, the wiring resistance R of the Vbus of the charging input circuit  3100  is actually calculated. Therefore, a voltage threshold can be set more accurately, and it can be determined more accurately whether a micro short circuit occurs on the charging input circuit  3100 . 
     Therefore, according to the terminal device  3000  provided in this embodiment of the present disclosure, the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is obtained through comparison such that it may be determined whether a micro short circuit occurs on the charging input circuit  3100 . When the micro short circuit occurs on the charging input circuit  3100 , an alert signal used to indicate that the micro short circuit occurs on the charging input circuit  3100  is sent such that the owner of the terminal device  3000  is prompted that the micro short circuit occurs on the charging input circuit  3100  of the terminal device  3000 , which can improve charging security. 
     An embodiment of the present disclosure further provides a charging system, including a charger and the terminal device  3000  described in the foregoing embodiment. The charger includes a charging interface, the charging interface includes a power cable, a ground cable, and a signal cable, and the power cable of the charging interface is connected to the signal cable of the charging interface using a resistor. 
     It should be understood that, in this embodiment of the present disclosure, a resistance value of the resistor should satisfy a voltage drop, generated by the resistor, of a micro short circuit current of the signal cable is sufficiently large, and when a micro short circuit occurs, a voltage of the signal cable may be less than a designed minimum output voltage of the Vbus. For example, a designed output voltage range of the Vbus is 4.5 V to 5.5 V. In this case, when an output voltage of the Vbus is 5.5 V, a voltage drop greater than 1 V should be generated when the micro short circuit current passes through the resistor such that the voltage of the signal cable is less than the designed minimum voltage 4.5 V of the Vbus, and the voltage comparator may determine that a micro short circuit occurs. 
     Generally, a typical micro short circuit current is around 0.5 A, and is generally greater than 0.2 A. In this way, a resistance value of a corresponding resistor should be typically around 2 ohms such that a 0.2 A micro short circuit generates a sufficient voltage drop. When a resistance value is larger, a 0.5 V voltage drop is generated and identified more easily, and precision is improved. Therefore, preferably, the resistance value of the resistor is greater than or equal to 5 ohms. 
     Moreover, the power cable of the charging interface of the charger may also be directly connected to the signal cable of the charging interface of the charger using a conductor. Similarly, in a case in which no micro short circuit occurs on the signal cable N 1  of the charging input circuit  3100 , the foregoing method for determining whether the difference between the voltage of the Vbus of the charging input circuit  3100  and the voltage of the signal cable N 1  of the charging input circuit  3100  is greater than a voltage threshold may also be used to determine whether a micro short circuit occurs on the Vbus of the charging input circuit  3100 . 
     An embodiment of the present disclosure further provides a terminal device applicable to a case in which a micro short circuit occurs on a signal cable of a charging input circuit.  FIG. 7  is a schematic diagram of a circuit of a terminal device  4000  according to an embodiment of the present disclosure. The terminal device  4000  includes a charging input circuit  4100 , an apparatus  4200  for controlling a charging micro short circuit, a battery  4300 , and an application processor  4400 . 
     The charging input circuit  4100  charges the battery  4300 . The apparatus  4200  for controlling a charging micro short circuit is configured to determine whether a micro short circuit occurs on the charging input circuit  4100 , and send a signal to the application processor  4400  when the micro short circuit occurs on the charging input circuit  4100  such that the application processor  4400  controls an output device of the terminal device  4000  to emit an alert signal to prompt an owner of the terminal device  4000  that the micro short circuit occurs on the charging input circuit  4100  of the terminal device  4000 . 
     The apparatus  4200  for controlling a charging micro short circuit includes a voltage comparator  4201  and a processing unit  4202 . 
     The voltage comparator  4201  is configured to acquire a voltage of a signal cable N 1  of the charging input circuit  4100 , and compare a reference voltage with the voltage of the signal cable N 1  of the charging input circuit  4100  to obtain a difference between the voltage of the signal cable N 1  of the charging input circuit  4100  and the reference voltage, where the reference voltage is greater than 0 V and is less than a designed minimum output voltage value of a Vbus of the charging input circuit  4100 . 
     The processing unit  4202  is configured to determine, according to the difference between the voltage of the signal cable N 1  of the charging input circuit  4100  and the reference voltage, whether a micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100 , and when the micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100 , send, to the application processor  4400  of the terminal device  4000 , a signal used to indicate that the micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100  such that the application processor  4400  controls the output device of the terminal device  4000  to emit an alert signal to prompt the owner of the terminal device  4000  that the micro short circuit occurs on the charging input circuit  4100  of the terminal device  4000 . 
     Therefore, according to the terminal device  4000  provided in this embodiment of the present disclosure, the difference between the voltage of the signal cable N 1  of the charging input circuit  4100  and the reference voltage is compared such that it may be determined whether a micro short circuit occurs on a circuit on which the signal cable N 1  of the charging input circuit  4100  is located. When the micro short circuit occurs on the circuit on which the signal cable N 1  of the charging input circuit  4100  is located, an alert signal used to indicate that the micro short circuit occurs on the charging input circuit is sent such that the owner of the terminal device  4000  is prompted that the micro short circuit occurs on the charging input circuit  4100  of the terminal device  4000 , which can improve charging security. 
     Further, because a USB interface has a very compact structure, generally, when a micro short circuit is generated on the signal cable N 1  of the charging input circuit  4100 , a micro short circuit is also generated on the Vbus of the charging input circuit  4100 , and correspondingly, when a micro short circuit is generated on the Vbus of the charging input circuit  4100 , a micro short circuit is also generated on the signal cable N 1  of the charging input circuit  4100 . Therefore, in a case in which a micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100 , a resistor whose resistance value is R is disposed between a power cable and a signal cable of a charging interface of a charger. Because of the short circuit of the signal cable, a current to the ground is generated on the resistor, and in a case in which the resistance value R of the resistor is sufficiently large, the voltage of the signal cable experiences an obvious voltage drop relative to a charging voltage. The voltage of the signal cable is collected at the charging input circuit  4100  of the terminal device  4000 , and is compared with the reference voltage, and it is determined, according to the difference between the voltage of the signal cable N 1  of the charging input circuit  4100  and the reference voltage, whether a micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100 . 
     The apparatus  4200  for controlling a charging micro short circuit in this embodiment of the present disclosure may be a charging IC or a PMU of the terminal device  4000 . The voltage comparator  4201  of the apparatus  4200  for controlling a charging micro short circuit compares the reference voltage with the voltage of the signal cable N 1  of the charging input circuit  4100 . The processing unit  4202  determines, according to the difference between the voltages, whether the micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100 . When the micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100 , the processing unit  4202  sends to the application processor  4400  of the terminal device  4000 , a signal used to indicate that the micro short circuit occurs on the charging input circuit  4100  such that the application processor  4400  controls the output device of the terminal device  4000  to emit an alert signal. 
     The alert signal may be a sound signal emitted by a horn of the terminal device  4000 , may be an optical signal emitted by a screen, an indicator, a flash, or the like, or may be a vibration signal emitted by a vibration apparatus in the terminal device  4000 , which is not limited in this embodiment of the present disclosure. The terminal device  4000  emits the alert signal such as sound and light to notify a user of an exception of a charging micro short circuit, and may further prompt the user to clean a Micro USB interface, replace a charging cable, or the like. 
     Optionally, in an embodiment of the present disclosure, when the difference between the voltage of the signal cable N 1  of the charging input circuit  4100  and the reference voltage is greater than 0, and a time for which the difference between the voltage of the signal cable N 1  of the charging input circuit  4100  and the reference voltage is greater than 0 is greater than a preset time threshold, the processing unit  4202  is further configured to determine that the micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100 , and send, to the application processor  4400  of the terminal device  4000 , a signal used to indicate that the micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100  such that the application processor  4400  controls the output device of the terminal device  4000  to emit an alert signal to prompt the owner of the terminal device  4000  that the micro short circuit occurs on the charging input circuit  4100  of the terminal device  4000 , where the preset time threshold is greater than a designed communication signal period of the signal cable N 1  of the charging input circuit  4100 . 
     Further, in this embodiment of the present disclosure, the reference voltage is greater than 0 V and is less than the designed minimum output voltage value of the Vbus of the charging input circuit  4100 , and may be set according to requirements. For example, a common output voltage range of the power cable of the charger is defined as 5 V±5%. In this case, the designed minimum output voltage value of the Vbus of the charging input circuit  4100  is 4.75 V, and the reference voltage may be set to 4.70 V (a value that is less than the designed minimum output voltage value of the Vbus may be selected according to experience, for example, 0.05 V is selected). Because a signal cable (for example, a data cable D−/D+) is connected to a Vbus in a charging circuit on a side of a charger using a resistor, when a micro short circuit occurs on the signal cable, a current to the ground is generated on the resistor. Because the resistor causes voltage division, the voltage of the signal cable experiences a voltage drop compared with the reference voltage. The voltage of the signal cable N 1  of the charging input circuit  4100  is collected on the terminal device  4000 , and when the difference between the voltage of the signal cable N 1  of the charging input circuit  4100  and the reference voltage is greater than 0, and a time for which the difference is greater than 0 is greater than a preset time threshold, it is determined that a micro short circuit occurs on the signal cable N 1  of the charging input circuit  4100 . 
     When the voltage of the signal cable N 1  of the charging input circuit  4100  is far less than the reference voltage, for example, a voltage of a data cable D−/D+ is always 0 V, it is considered that a used charger is a charger of a non-standard configuration, and a system may be triggered to prompt that the charger is not a dedicated charger, and stop a charging action. 
     Optionally, in this embodiment of the present disclosure, the signal cable N 1  of the charging input circuit  4100  may include at least one of a D+, a D−, a dead-end ID, or an RX 1 +, an RX 1 −, an RX 2 +, an RX 2 −, a TX 1 +, a TX 1 −, a TX 2 +, a TX 2 −, an SBU 1 , an SBU 2 , a CC 1 , or a CC 2  of a Typc C interface defined in the USB 3.1 specification. 
     Therefore, according to the terminal device  4000  provided in this embodiment of the present disclosure, the difference between the voltage of the signal cable N 1  of the charging input circuit  4100  and the reference voltage is compared such that it may be determined whether a micro short circuit occurs on a circuit on which the signal cable N 1  of the charging input circuit  4100  is located. When the micro short circuit occurs on the circuit on which the signal cable N 1  of the charging input circuit  4100  is located, an alert signal used to indicate that the micro short circuit occurs on the charging input circuit  4100  is sent such that the owner of the terminal device  4000  is prompted that the micro short circuit occurs on the charging input circuit  4100  of the terminal device  4000 , which can improve charging security. 
     An embodiment of the present disclosure further provides a charging system, including a charger and the terminal device  4000  described in the foregoing embodiment. The charger includes a charging interface, the charging interface includes a power cable, a ground cable, and a signal cable, and the power cable of the charging interface is connected to the signal cable of the charging interface using a resistor. 
     In addition, in this embodiment of the present disclosure, two voltage comparators  3201 ,  4201  of the apparatus  3200  for controlling a charging micro short circuit of the terminal device  3000  and the apparatus  4200  for controlling a charging micro short circuit of the terminal device  4000  may further be combined for usage, which is not described in detail again in this embodiment of the present disclosure. 
     It should be understood that, in this embodiment of the present disclosure, a resistance value of the resistor should satisfy a voltage drop, generated by the resistor, of a micro short circuit current of the signal cable is sufficiently large, and when a micro short circuit occurs, a voltage of the signal cable may be less than a reference voltage. An example in which the reference voltage is slightly less than the designed minimum output voltage of the Vbus is used. For example, a designed output range of the Vbus is 4.5 V to 5.5 V. In this case, when an output voltage of the Vbus is 5.5 V, a voltage drop greater than 1 V should be generated when the micro short circuit current passes through the resistor such that the signal cable is less than the designed minimum voltage 4.5 V of the Vbus, and the voltage comparator may determine that a micro short circuit occurs. 
     Generally, a typical micro short circuit current is around 0.5 A, and is generally greater than 0.2 A. In this way, a resistance value of a corresponding resistor should be typically around 2 ohms such that a 0.2 A micro short circuit generates a sufficient voltage drop. When a resistance value is larger, a 0.5 V voltage drop is generated and identified more easily, and precision is improved. Therefore, preferably, the resistance value of the resistor is greater than or equal to 5 ohms. 
     It should be understood that, in this embodiment of the present disclosure, “Y corresponding to X” indicates that Y is associated with X, and that Y may be determined according to X. But it should be further understood that, that Y is determined according to X does not mean that Y is determined only according to X, and Y may also be determined according to X and/or other information. 
     A person of ordinary skill in the art may be aware that, in combination with the examples described in the embodiments disclosed in this specification, units and algorithm steps may be implemented by electronic hardware, computer software, or a combination thereof. To clearly describe the interchangeability between the hardware and the software, the foregoing has generally described compositions and steps of each example according to functions. Whether the functions are performed by hardware or software depends on particular applications and design constraint conditions of the technical solutions. A person skilled in the art may use different methods to implement the described functions for each particular application, but it should not be considered that the implementation goes beyond the scope of the present disclosure. 
     It may be clearly understood by a person skilled in the art that, for the purpose of convenient and brief description, for a detailed working process of the foregoing system, apparatus, and unit, reference may be made to a corresponding process in the foregoing method embodiments, and details are not described herein again. 
     In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described apparatus embodiment is merely exemplary. For example, the unit division is merely logical function division and may be other division in actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms. 
     The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments of the present disclosure. 
     In addition, functional units in the embodiments of the present disclosure may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit. The integrated unit may be implemented in a form of hardware, or may be implemented in a form of a software functional unit. 
     When the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, the integrated unit may be stored in a computer-readable storage medium. Based on such an understanding, the technical solutions of the present disclosure essentially, or the part contributing to the other approaches, or all or some of the technical solutions may be implemented in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for instructing a computer device (which may be a personal computer, a server, or a network device) to perform all or some of the steps of the methods described in the embodiments of the present disclosure. The foregoing storage medium includes any medium that can store program code, such as a USB flash drive, a removable hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc. 
     The foregoing descriptions are merely specific embodiments of the present disclosure, but are not intended to limit the protection scope of the present disclosure. Any modification or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the present disclosure shall fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.