Patent Publication Number: US-9419387-B2

Title: Plug for DC appliance

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2011-0011412, filed on Feb. 9, 2011 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments of the present disclosure relate to a plug for a DC appliance for safely supplying DC power to an electric device. 
     2. Description of the Related Art 
     Conventionally, power has been supplied to household appliances or electric devices of a general home by an AC power distribution system providing commercial power. The AC power distribution system supplies power to electric devices using a plug, a socket, a switch, etc. The electric device having received AC power converts AC power into DC power using a rectifier embedded therein. Typically, the AC power distribution system does not include a device for preventing arc from being generated in plug separation. 
     However, in the future, it is expected that the demand of a general home which desires to use DC power using a solar battery, a fuel cell, etc. will be rapidly increasing. DC power can reduce energy loss generated when a conventional AC power distribution system converts AC power into DC power. In the case of using AC power, provided that a unique power factor of a device is bad or poor although the device has the same power consumption, a generation end has to generate as much power as reactive power, resulting in energy inefficiency. Further, DC power can be easily stored, so that it can effectively cope with an emergency situation. 
     Due to these disadvantages, the number of household appliances including an inverter is rapidly increasing, and most digital devices use DC power. 
     Therefore, a plug suitable for DC power distribution is needed. The conventional DC power plug is identical in structure to the AC power plug, so that an in-rush current occurs in power distribution or an arc occurs in an unplugging operation, resulting in safety problems. 
     SUMMARY 
     Therefore, it is an aspect of the present disclosure to provide a plug for a DC appliance which includes a rectifier unit and a condenser unit to prevent arc from being generated in an unplugging operation. 
     It is another aspect of the present disclosure to provide a plug for a DC appliance which includes an inductor unit to prevent an in-rush current from being generated in power distribution. 
     Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure. 
     In accordance with one aspect of the present disclosure, a plug for a DC appliance includes an input unit including anode and cathode terminals inserted into a socket so as to receive a DC current; an output unit including anode and cathode terminals so as to allow the DC current input through the input unit to be output to an electric device; a connection unit including anode and cathode lines so as to interconnect the input unit and the output unit; a rectifier unit coupled between anode and cathode terminals of the input unit so as to rectify the input DC current; an inductor unit that is connected in series to the rectifier unit in such a manner that an internal current of the plug is gradually increased in response to an increase of the input DC current; and a condenser unit that is connected in series to the inductor unit, is charged with voltage in response to a current passing through the inductor unit, and discharges the charged voltage to the output unit when the input of the DC current from the input unit is interrupted. 
     The rectifier unit may flow back a current present in the plug to the output unit when the DC current input is stopped by the input unit disconnected from the socket, thereby preventing an arc phenomenon generated when the current is leaked to outside of the plug. 
     The rectifier unit may be coupled to cathode and anode terminals of the input unit, and may be coupled to anode and cathode terminals of the input unit so that a current present in the plug flows from the input unit to the output unit. 
     One terminal of the inductor unit may be coupled to the cathode of the rectifier, and other terminal thereof may be coupled to the condenser unit. 
     The inductor unit may prevent an internal current of the plug from being rapidly increased when the input unit is inserted into the socket and the DC current input is increased, thereby preventing flow of an in-rush current. 
     Inductance of the inductor unit may be adjusted in such a manner that an internal current of the plug is increased with an appropriate speed. 
     The condenser unit may reduce a voltage difference between the input unit and the output unit when the DC current input is stopped by the input unit disconnected from the socket, thereby preventing an arc phenomenon. 
     The condenser unit may be coupled between anode and cathode terminals of the output unit in such a manner that the charged voltage is discharged to the output unit when the input unit is disconnected from the socket. 
     Capacitance of the condenser unit may be adjusted in such a manner that the voltage difference between the input unit and the output unit is maintained within a predetermined range for a predetermined time beginning from a specific time where the input unit is disconnected from the socket. 
     In accordance with another aspect of the present disclosure, a plug for a DC appliance includes an input unit including anode and cathode terminals inserted into a socket so as to receive a DC current; an output unit including anode and cathode terminals so as to allow the DC current input through the input unit to be output to an electric device; a connection unit including anode and cathode lines so as to interconnect the input unit and the output unit; a rectifier unit coupled between anode and cathode terminals of the input unit so as to rectify the input DC current; a condenser unit that is connected in parallel to the rectifier unit, is charged with voltage in response to the rectified current, and discharges the charged voltage to the output unit when the input of the DC current from the input unit is interrupted; and an inductor unit that is connected in series to the rectifier unit and the condenser unit connected in parallel to each other, thereby gradually increasing an internal current of the plug when the DC current from the input unit is increased. 
     The rectifier unit may flow back a current present in the plug to the output unit when the DC current input is stopped by the input unit disconnected from the socket, thereby preventing an arc phenomenon generated when the current is leaked to outside of the plug. 
     The rectifier unit may connect its own cathode terminal to the anode line, and may connect its own anode terminal to the cathode line so that a current present in the plug flows from the input unit to the output unit. 
     The condenser unit may reduce a voltage difference between the input unit and the output unit when the DC current input is stopped by the input unit disconnected from the socket, thereby preventing an arc phenomenon. 
     Capacitance of the condenser unit may be adjusted in such a manner that the voltage difference between the input unit and the output unit is maintained within a predetermined range for a predetermined time beginning from a specific time where the input unit is disconnected from the socket. 
     The inductor unit may prevent an internal current of the plug from being rapidly increased when the input unit is inserted into the socket and the DC current input is increased, thereby preventing flow of an in-rush current. 
     Inductance of the inductor unit may be adjusted in such a manner that an internal current of the plug is increased with an appropriate speed. 
     One terminal of the inductor unit may be coupled to an anode terminal of the input unit, and other terminal thereof may be coupled to the rectifier unit and the condenser unit connected in parallel to each other. 
     The other terminal of the inductor unit may be coupled to a cathode terminal of the rectifier unit, and may be also connected to the anode line. 
     The condenser unit may be coupled between anode and cathode terminals of the output unit in such a manner that the charged voltage is discharged to the output unit when the input unit is disconnected from the socket and the DC current input is thus stopped. 
     One terminal of the inductor unit may be coupled to an anode terminal of the output unit, and other terminal thereof may be coupled to the rectifier unit and the condenser unit connected in parallel to each other. 
     A cathode terminal of the rectifier unit may be coupled to an anode terminal of the input unit, and an anode terminal thereof may be coupled to the cathode terminal of the input unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a perspective view illustrating a plug for a DC appliance and a socket according to one embodiment of the present disclosure; 
         FIG. 2  is a circuit diagram illustrating a plug for a DC appliance according to one embodiment of the present disclosure; 
         FIG. 3  shows a current changing with time at a plug for a DC appliance including an overcurrent prevention circuit; 
         FIG. 4A  shows the flow of current in a current-leakage prevention circuit in case of a plug-in operation; 
         FIG. 4B  shows the flow of current in a current-leakage prevention circuit in case of an unplugging operation; 
         FIG. 5 , parts (a) and (b), shows a current changing with time in case of a plug-out operation of one plug including a current-leakage prevention circuit or another plug including no current-leakage prevention circuit; 
         FIG. 6A  shows the flow of current in case of a plug-in operation of the plug of the DC appliance shown in  FIG. 2 ; 
         FIG. 6B  shows the flow of current in case of an unplugging operation of the plug of the DC appliance shown in  FIG. 2 ; 
         FIG. 7  is a circuit diagram illustrating a plug for a DC appliance according to another embodiment of the present disclosure; and 
         FIG. 8  is a circuit diagram illustrating a plug for a DC appliance according to still another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIG. 1  is a perspective view illustrating a plug for a DC appliance and a socket according to one embodiment of the present disclosure. 
     Referring to  FIG. 1 , a plug  10  for a DC appliance (hereinafter referred to as a DC-appliance plug) includes a plug housing  11 , one pair of through-holes formed at one side of the plug housing  11 , and one pair of connectors  13   a  and  13   b  installed at the through-holes and protruded outside. 
     The DC-appliance plug  10  according to the embodiment of the present disclosure is detachably connected to the socket  20 , and is inserted into the socket  20 , such that it receives DC current. 
     One pair of insertion holes  22   a ,  22   b  is arranged at one surface of the socket housing  21  of the socket  20 . A positive-pole (i.e., anode) contact and a negative-pole (i.e., cathode) contact are arranged the insertion holes  22   a  and  22   b , respectively. An anode wire and a cathode wire are coupled to the anode contact and the cathode contact, respectively. 
     In the case where the connectors  13   a , 13   b  of the plug  10  are inserted into the insertion holes  22   a , 22   b  of the socket and both contacts of the socket  20  are coupled to the connectors  13   a , 13   b  of the plug  10 , DC current received from the external part is applied to the connectors  13   a , 13   b  of the plug  10 . 
     In order to prevent the plug  10  from being wrongly coupled to an anode and a cathode of the socket  20 , the plug  10  according to the embodiment includes different sizes of the anode and the cathode in such a manner that the anode and the cathode can be distinguished from each other. If necessary, the anode and the cathode may be distinguished from each other in different ways. 
     For example, provided that a user may make a distinction between an anode and a cathode of the plug by viewing an anode terminal and a cathode terminal arranged in the form of L-shape or by viewing different shapes of the anode and cathode, the above plug may be used as a DC-appliance plug  10 . In addition, a 3-terminal plug  10  comprised of an anode terminal, a cathode terminal, and a ground or guide terminal may be used as necessary. 
     In the case where the DC-appliance plug  10  is plugged in the socket  20  so that DC power is applied to the plug  10 , an in-rush current higher than a normal current may occur due to a condenser, etc. present in the electric device. Such in-rush current may apply impact to the electric device, resulting in a malfunction or a shortened lifetime of the electric device. 
     Although the conventional AC power distribution system limits such in-rush current using a relay, the DC power distribution system does not include a small-sized DC relay, so that a separate structure for preventing overcurrent is needed. 
     In addition, when the DC-appliance plug  10  inserted into the socket  20  is separated (i.e., when the DC-appliance plug  10  is unplugged), arc may be generated by parasitic capacitance of an electric line and inductance of a load device. In more detail, because a current, that remains in the plug  10  without flowing to the electric device when the plug  10  is unplugged, is discharged to the outside, the arc phenomenon is generated. 
     In the conventional AC power distribution system, a voltage periodically reaches zero ‘0’ and thus the arc phenomenon may be prevented from being generated, but a point at which a DC voltage is set to zero ‘0’ is not present in the conventional DC power distribution system, so that arc is continuously generated. If the arc phenomenon is continuously generated, the electric device may be instantaneously damaged, durability of conductive lines may be adversely affected, thereby causing a variety of electric shock accidents and a fire. 
     The circuit diagram of the DC-appliance plug that prevents an in-rush current from being generated in the plug-in operation simultaneously while preventing the arc phenomenon from being generated in the plug-out operation will hereinafter be described with reference to the annexed drawings. 
       FIG. 2  is a circuit diagram illustrating a plug for a DC appliance according to one embodiment of the present disclosure. 
     Referring to  FIG. 2 , a plug  100  for a DC appliance includes an input unit  110  to receive a DC current, an output unit  120  to output the received DC current, a connection unit  130  to couple the input unit  110  to the output unit  120 , a rectifier unit  140 , an inductor unit  150 , and a condenser unit  160 . 
     The input unit  110  includes an anode terminal T 1  and a cathode terminal T 2  located below the anode terminal T 1 , so that it is detachably coupled to the socket. That is, the input unit  110  is inserted into the socket so as to receive a DC current from the external part. 
     The input DC current is output through the output unit  120  that includes an anode terminal T 3  and a cathode terminal T 4  located below the anode terminal T 1 , so that it is used to operate the electric device. 
     The connection unit  130  includes an anode line (Line 1 ) and a cathode line (Line 2 ) located below the anode line (Line 1 ) so as to interconnect the input unit  110  and the output unit  120 . 
     The connection unit  130  is coupled to the rectifier unit  140 , the inductor unit  150 , and the condenser unit  160 , and allows the input DC current to be output to the output unit  120 . 
     The rectifier unit  140  acting as a diode may interconnect the anode terminal T 1  and the cathode terminal T 2  of the input unit  110 . In more detail, an anode terminal of the rectifier unit  140  is coupled to the cathode terminal T 2  of the input unit  110 , and the cathode terminal is coupled to the anode terminal T 1  of the input unit  110 . 
     The rectifier unit  140  may perform rectifying of an internal current of the plug  100  in such a manner that the internal current of the plug  100  can flow to a specific direction. The rectifier unit  140  allows an internal current of the plug  100  to flow from the input unit  110  to the output unit  120 . As a result, it is prevented that a current, that remains in the plug  100  in case of the plug-out operation, is leaked to the outside through the input unit  110 . Detailed operations of the current leakage prevention effect caused by the rectifier unit  140  will be given below. 
     The inductor unit  150  may include an inductor serially connected to the rectifier unit  140 . The inductor unit  150  is coupled to the cathode terminal of the rectifier unit  140 , and is coupled to the anode line (Line 1 ). 
     The inductor acting as a circuit element may include a coil that induces a voltage in proportion to a current variation, so that it can perform current charging. The inductor prevents an internal current of the plug from being abruptly changed. 
     Meanwhile, although the inductor unit  150  of the embodiment is shown with only one inductor for convenience of description, the scope or spirit of the inductor unit  150  is not limited thereto. If necessary, in order to properly adjust inductance (L 1 ), the inductor unit  150  may also include a plurality of inductors connected in series or in parallel to each other without departing from the scope or spirit of the present disclosure. 
     The condenser unit  160  includes a condenser connected in series to the inductor unit  150 . In addition, the condenser unit  160  may be coupled between a third terminal T 3  and a fourth terminal T 4  of the output unit  120 . 
     From the beginning of the plug-in operation, the condenser unit  160  is charged with a voltage in response to a current passing through the inductor unit  150 . then, the voltage charged in the condenser unit  160  is discharged to the output unit  120  for a predetermined period of time from the beginning of the plug-out operation. 
     Although the condenser unit  160  of the embodiment includes only one condenser for convenience of description, the scope or spirit of the condenser unit  160  is not limited thereto. If necessary, in order to properly adjust capacitance (C 1 ) of the condenser unit  160 , the condenser unit  160  may also include a plurality of condensers connected in series or in parallel without departing from the scope or spirit of the present invention. 
     The DC-appliance plug to safely output a DC current by preventing the problem that may be encountered at an abrupt change point of the input DC current will hereinafter be described with reference to the annexed drawings. 
     The abrupt change time point of the input DC current is any of a plug-in time point and a plug-out time point. 
     The DC-appliance plug  100  for preventing an in-rush current caused by the plug-in operation according to the embodiment of the present disclosure will hereinafter be described. 
     The DC-appliance plug  100  according to the embodiment of the present disclosure includes the inductor unit  150  so as to prevent an in-rush current from being generated. 
     In more detail, the amount of a current flowing in the inductor  150  in case of the plug-in operation is abruptly increased. The increased in-rush current means that magnetic flux induced to the inside of the inductor unit  150  is increased, and the inductor unit  150  restricts the increasing magnetic flux until the magnetic flux is saturated. That is, the inductor unit  150  restricts magnetic flux saturation such that it prevents a current flowing in the inductor unit  150  from being rapidly increased. 
       FIG. 3  shows a current changing with time at a plug for a DC appliance in case of the plug-in operation. 
     Referring to  FIG. 3 , a current flowing in the plug is increased in case of the plug-in operation. A current (denoted by a chain line) of a plug having no inductor unit may be abruptly increased in the plug-in operation (t 1 ), so that an in-rush current I 2  higher than a normal current I 1  flows and is converged into a normal current according to the lapse of time. 
     In contrast, a current (denoted by a solid line) of a plug having the inductor unit is linearly increased for a predetermined time (t 2 −t 1 ) from the beginning of the plug-in time (t 1 ). In more detail, a current of the DC-appliance plug having the inductor unit is gradually increased to a normal current (I 1 ) for a predetermined time (t 2 −t 1 ), and is constantly maintained from the time (t 2 ) at which the current reaches the normal current (I 1 ). 
     In other words, the inductor unit linearly increases a current of the circuit until the current reaches a saturation current indicating a chargeable threshold value. If the current reaches the saturation current, the inductor unit serves as a conductive line. 
     As a result, the DC-appliance plug according to the embodiment of the present disclosure may prevent an in-rush current from being generated in the plug-in operation. 
     The DC-appliance plug that prevents arc from being generated in the plug-out operation according to the embodiment of the present disclosure will hereinafter be described in detail. 
     The DC-appliance plug  100  includes a rectifier unit  140  and a condenser unit  160  so as to prevent the above-mentioned arc from being generated. 
     The rectifier unit  140  rectifies a residual current of the plug  100  in a predetermined direction in case of the unplugging operation, so that it can prevent current leakage from being generated. 
     In addition, the condenser unit  160  reduces a difference in voltage between the input unit  110  and the output unit  120  of the plug  100  in case of the unplugging operation, so that it can be used as a supplementary means for the arc prevention effect. 
     The flow of an internal current of the plug  100  including the rectifier unit  140  and the condenser unit  160  and the arc-phenomenon prevention effect will hereinafter be described with reference to  FIGS. 4A and 4B . 
     Referring to  FIG. 4A , if the plug  100  is inserted into the socket  20 , an electric current is applied to an anode line (Line 1 ) and a cathode line (Line 2 ) of the plug  100 , such that a DC voltage is applied from the input unit  110  to the output unit  120 . The DC voltage is supplied to the electric device through the output unit  120  of the plug  100 , so that is electrically charged in the condenser unit  160 . 
     Referring to  FIG. 4B , if the plug is plugged out of the socket  20 , the input unit  110  of the plug  110  is opened, so that the applying of DC voltage is interrupted. 
     If the applying of DC voltage is interrupted, the rectifier unit  140  is not applied to the electric device  30 , and a residual current of the plug  100  flows in a predetermined direction. That is, the rectifier unit  140  enables the residual current caused by the unplugging operation to flow back to the inside of the plug  100 , so that the residual current is consumed in the plug  100  and the electric device  30 . 
     As a result, the arc phenomenon generated when the residual current of the plug  100  is leaked outside through the input unit  110  is prevented from being generated. 
     In addition, the condenser unit  160  charged with voltage is discharged in the case of the plug-out operation. 
     In more detail, in the case where the plug  100  is unplugged, a voltage of the input unit  110  of the plug  100  is identical to a voltage of the output unit  120  by a charge voltage charged in the condenser unit  160 . By the condenser unit  160 , a discharge current is leaked to the electric device  30  with lapse of time, so that a charging potential of the condenser unit  160  is reduced. As a result, the arc phenomenon problem, caused by a difference in electric potential between the input unit and the output unit when the plug is unplugged, can be solved. 
       FIG. 5 , part (a), shows a current variation with lapse of time when a plug that does not include the rectifier unit and the condenser unit is unplugged, and  FIG. 5 , part (b), shows a current variation with lapse of time when a plug including the rectifier unit and the condenser unit is unplugged. 
     Referring to  FIG. 5 , part (a), as a voltage (denoted by a chain line) of the plug is reduced from the beginning of the unplugging time (t 2 ) of the plug including no rectifier unit and no condenser unit, a current (denoted by a solid line) is abruptly changed, resulting in the occurrence of arc. 
     In contrast, referring to  FIG. 5 , part (b), a current (denoted by a solid line) of the plug including the rectifier unit and the condenser unit is stably reduced along with a plug voltage (denoted by a chain line) that begins to reduce from the beginning of the unplugging time (t 2 ), so that the arc problem can be solved. 
     The flow of a current of a DC power distribution circuit according to an embodiment of the present disclosure will hereinafter be described with reference to  FIGS. 6A and 6B . 
     Referring to  FIG. 6A , both terminals of the input unit  110  and the socket  20  of the plug  100  are coupled to each other. If a DC voltage is applied to the plug  100 , a current flows from the input unit  110  to the output unit  120  such that it moves to the electric device  30  coupled to the output unit  120 . 
     In this case, the inductor unit  150  is charged with a current so that an internal current of the plug  100  is linearly increased, a voltage is charged in the condenser unit  160  by the current passing through the inductor unit  150 , so that the resultant current is output to the output unit  120 . 
     If a predetermined time has elapsed after the inductor unit  150  starts charging, a charging current of the inductor unit  150  is saturated so that the inductor  100  is used as a conductive line and constant current flows in the entirety of the conductive line of the plug  100 . 
     Therefore, it is prevented that an internal current of the plug  100  is abruptly increased by the inductor unit  150 . The higher the inductance L 1  of the inductor unit  150 , the greater the in-rush current prevention effect. 
     The inductance L 1  is the ratio of back electromotive force (back-EMF) generated by electromagnetic induction in response to a variation of current flowing in the circuit, or the ratio of a time variance of a current flowing in a wire to a backelectromotive force generated in the wire. If the inductance L 1  is increased, a current charging speed of the inductor unit  150  is reduced. In other words, this means that a time consumed until a current passing through the inductor  110  reaches a saturation current is increased. 
     Under the condition that an internal current of the plug  100  reaches a constant or steady state because a predetermined time has elapsed upon completion of the plug-in operation, if the plug is pulled out of the socket (i.e., the unplugged state as shown in  FIG. 6B ), the rectifier unit  121  flows back the internal current of the plug to the output unit  120 . 
     The internal current of the plug  100  includes not only a current that is not yet applied from the plug  100  to the electric device  30  in case of the unplugging operation, but also a current charged in the inductor unit  150  due to a voltage variation (voltage drop) generated by the unplugging operation. 
     In more detail, the rectifier unit  140  rectifies the flow of a current flowing an anode terminal to a cathode terminal of the rectifier unit  140  so as to prevent the internal current of the plug  100  from being leaked to outside through the input unit  110  of the plug  100 . That is, the internal current of the plug  100  first flows in the plug  100  and is then output to the electric device  30 . 
     In addition, upon completion of the unplugging operation, the condenser unit  160  discharges a charged voltage so that the current flows in the output unit  120 . As a result, the charged voltage drop occurs in the condenser unit  160 . 
     Capacitance C 1  of the condenser unit  160 , in case of the unplugging operation, may be adjusted for arc prevention in such a manner that a voltage between the input unit  110  and the output unit  120  of the plug is uniformly maintained for a predetermined time so that the arc is not generated. 
     However, provided that the capacitance C 1  is excessively adjusted, the tendency of voltage accumulation of the condenser unit  160  becomes stronger so that it may cause an in-rush current to occur in the plug-in operation. Accordingly, it is preferable that capacitance C 1  be properly adjusted. 
     In the DC-appliance plug  100  according to the embodiment of the present disclosure, the rectifier unit  140  and the condenser unit  160  are arranged in the DC-appliance plug  100 , so that the arc phenomenon is not generated when the plug  100  is pulled out of the socket. 
     In addition, an additional inductor unit  150  is included in the plug  100 , such that it can prevent the occurrence of an in-rush current that may be generated when the plug  100  is inserted into the socket (i.e., in case of the plug-in operation). 
     Therefore, durability of the electric device, plug, and conductive lines can be improved only through simple circuit configuration, and a user can safely use DC current. 
       FIG. 7  is a circuit diagram illustrating a plug for a DC appliance according to another embodiment of the present disclosure. 
     Referring to  FIG. 7 , the DC-appliance plug  200  according to the embodiment of the present disclosure includes an input unit  210  that includes an anode terminal T 1  and a cathode terminal T 2  located below the anode terminal T 1 ; an output unit  220  to output an input DC current through an anode terminal T 3  and a cathode terminal T 4  located below the anode terminal T 3 ; a connection unit  230  that includes an anode line (Line 1 ) and a cathode line (Line 2 ) to interconnect the input unit  210  and the output unit  220 ; a rectifier unit  240  to rectify a current flowing in a DC power distribution circuit in a predetermined direction; an inductor unit  250  to prevent a current from being abruptly changed by linearly increasing a current flowing in the DC power distribution circuit; and a condenser unit  260  that is changed with voltage in response to a current passing through the inductor unit  250  and discharges the charged voltage through the output unit  220 . 
     Specifically, the DC-appliance plug  200  according to the embodiment of the present disclosure includes the rectifier unit  240  and the condenser unit  260  that are connected in parallel to each other. 
     In more detail, the cathode terminal of the rectifier unit  240  is located on the anode line (Line 1 ), and the anode terminal is located on the cathode line (Line 2 ). 
     The rectifier unit  240  is coupled in parallel to the condenser unit  260  coupled between the third terminal T 3  and the fourth terminal T 4  of the output unit  220 . That is, the cathode terminal of the rectifier unit  240  is coupled to the anode terminal T 3  of the output unit  220 , and the anode terminal thereof is coupled to the cathode terminal T 4  of the output unit  220 . 
     In addition, according to this embodiment, the inductor unit  250  is connected in series to the rectifier unit  240  and the condenser unit  260  that are coupled in parallel to each other. 
     One terminal of the inductor unit  250  is coupled to the anode terminal T 1  of the input unit  210 , and the other terminal thereof is coupled to the rectifier unit  240  and the condenser unit  260  that are coupled in parallel to each other. That is, the inductor unit  250  is coupled to the input side, and the rectifier unit  240  and the condenser unit  260  are coupled to the output side. 
     In more detail, one terminal of the inductor unit  250  is coupled to the anode terminal T 1  of the input unit  210 , and the other terminal thereof is coupled to the cathode terminal of the rectifier unit  240 . 
     Besides, the effect of preventing the in-rush current of the DC-appliance plug  200  simultaneously while preventing the arc problem is identical to that of the above-mentioned description, and as such a detailed description thereof will herein be omitted for convenience of description. 
       FIG. 8  is a circuit diagram illustrating a plug for a DC appliance according to still another embodiment of the present disclosure. 
     Referring to  FIG. 8 , the DC-appliance plug  300  according to the embodiment of the present disclosure includes an input unit  310  that includes an anode terminal T 1  and a cathode terminal T 2  located below the anode terminal T 1 ; an output unit  320  to output an input DC current through an anode terminal T 3  and a cathode terminal T 4  located below the anode terminal T 3 ; a connection unit  330  that includes an anode line (Line 1 ) and a cathode line (Line 2 ) to interconnect the input unit  310  and the output unit  320 ; a rectifier unit  340  to rectify an internal current of the plug  300  in a predetermined direction; an inductor unit  350  to prevent an internal current from being abruptly changed by linearly increasing an internal current of the plug  300 ; and a condenser unit  360  that is changed with voltage in response to a current passing through the inductor unit  350  and discharges the charged voltage through the output unit  320 . 
     Specifically, the DC-appliance plug  300  according to the embodiment of the present disclosure includes the rectifier unit  340  and the condenser unit  360  that are connected in parallel to each other. 
     In more detail, the cathode terminal of the rectifier unit  340  is located on the anode line (Line 1 ), and the anode terminal is located on the cathode line (Line 2 ). 
     The rectifier unit  340  is coupled in parallel to the condenser unit  360 , and is coupled to the input unit  310 . That is, the cathode terminal of the rectifier unit  340  is coupled to the anode terminal T 1  of the input unit  310 , and the anode terminal thereof is coupled to the cathode terminal T 2  of the input unit  310 . 
     In addition, according to this embodiment, the inductor unit  350  is connected in series to the rectifier unit  340  and the condenser unit  360  that are coupled in parallel to each other. 
     One terminal of the inductor unit  350  is coupled to the anode terminal T 3  of the output unit  320 , and the other terminal thereof is coupled to the rectifier unit  340  and the condenser unit  360  that are coupled in parallel to each other. That is, the inductor unit  350  is located on the anode line (Line 1 ), so that it is coupled to upper terminals of the condenser unit  360  and the condenser unit  360  that are coupled in parallel to each other. 
     Besides, the effect of preventing the in-rush current simultaneously while preventing the arc problem is identical to that of the above-mentioned description, and as such a detailed description thereof will herein be omitted for convenience of description. 
     As is apparent from the above description, according to the above-mentioned plug for the DC appliance of the embodiment of the present disclosure, a rectifier and a condenser are arranged in the plug for the DC appliance, so that the embodiment can prevent the occurrence of arc that may be generated when a plug is pulled out of an outlet. 
     In addition, an inductor is additionally arranged in the plug of the DC appliance, so that an in-rush current that may be generated when a plug is put into an outlet is prevented from being generated. 
     As a result, durability of the electric device, plug, and conductive lines can be improved only through simple circuit configuration, and a user can safely use DC current. 
     Although a few embodiments of the present disclosure have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.