Patent Publication Number: US-7592924-B2

Title: Intelligent life testing methods and apparatus for leakage current protection

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Chinese Patent Application No. 200610007854.8, filed on Feb. 21, 2006, entitled “Intelligent Life Testing Methods and Apparatus for Leakage Current Protection,” by Feng ZHANG, Hongliang CHEN, Fu WANG, Wusheng CHEN, Yulin ZHANG and Huaiyin SONG, the disclosure of which is incorporated herein by reference in its entirety. 
     This application is related to four co-pending U.S. patent applications, entitled “Intelligent Life Testing Methods and Apparatus for Leakage Current Protection Device with Indicating Means,” by Feng ZHANG, Hongliang CHEN, Fu WANG, Wusheng CHEN, Yulin ZHANG and Huaiyin SONG; Ser. No. 11/588,017; “Apparatus and Methods for Testing the Life of a Leakage Current Protection Device,” by Feng ZHANG, Hongliang CHEN, Fu WANG, Wusheng CHEN, Yulin ZHANG and Huaiyin SONG; Ser. No. 11/588,016; “Intelligent Life Testing Methods and Apparatus for Leakage Current Protection,” by Feng ZHANG, Hongliang CHEN, Fu WANG, Wusheng CHEN, Yulin ZHANG and Huaiyin SONG; Ser. No. 11/588,163; and “Intelligent Life Testing Methods and Apparatus for Leakage Current Protection,” by Wusheng CHEN, Fu WANG, and Lianyun WANG, Ser. No. 11/588,046, respectively. The above identified co-pending applications were filed on the same day that this application was filed, and with the same assignee as that of this application. The disclosures of the above identified co-pending applications are incorporated herein by reference in their entireties. 
     FIELD OF THE PRESENT INVENTION 
     The present invention generally relates to real time detection of fault with an alarming device of a leakage current protection device for appliances. More particularly, the present invention relates to intelligent life testing methods and apparatus for leakage current protection. 
     BACKGROUND OF THE PRESENT INVENTION 
     Leakage current protection can be divided into two categories according to their functionalities: ground fault circuit interrupter (hereinafter “GFCI”) and arc fault circuit interrupter (hereinafter “AFCI”). In order to achieve the goal of leakage current protection, a leakage current protection device used for appliances comprises at least two components: a trip mechanism and a leakage current detection circuit. The trip mechanism comprises a silicon controlled rectifier (hereinafter “SCR”), trip coil, and trip circuit interrupter device. The leakage current detection circuit comprises induction coils, a signal amplifier and a controller. 
     The operating principle of a GFCI used for appliances is as follows. In a normal condition, the electric current on a hot wire of an electrical socket should be the same as the electric current on a neutral wire in the same electrical socket. When a leakage current occurs, there exists a current differential between the hot wire and the neutral wire of the electrical socket. The inductive coil of the leakage current protection device monitors the current differential and transfers the current differential into a voltage signal. The voltage signal is then amplified by the signal amplifier and sent to the controller. If the current differential exceeds a predetermined threshold, the controller sends a control signal to the trip circuit interrupter to cut off the connection between the AC power and the appliance to prevent damage caused by the leakage current. 
     For an AFCI used for appliances, in a normal condition, the electric current on a hot wire of an electrical socket should be the same as the electric current on a neutral wire in the same electrical socket, and the variation of both the electric current is same. When an arc fault occurs due to aging or damages of the AFCI device, the current or voltage between the hot wire and the neutral wire of the electrical socket exhibits a series of repeated pulse signals. The inductive coil of the arc fault protection device detects the pulse signals and converts the pulse signals to a voltage signal. The voltage signal is amplified by the signal amplifier and sent to the controller. If the amplitude of the pulse signals or the their occurring frequency exceed certain predetermined threshold, the controller sends a control signal to the trip circuit interrupter to cut off the connection between the AC power and the appliance to prevent further damage caused by the arc fault. 
     Leakage current protection devices have been widespreadly used because of their superior performance. However, the leakage protection devices may fail to provide such leakage current protection, if they are installed improperly and/or they are damaged due to aging. If a faulty controller can not output a correct control signal, or a trip mechanism fails to cut off the connection between the AC power and the appliance, the leakage current protection device will not be able to provide the leakage current protection, which may cause further damages or accidents. Although most leakage current protection devices are equipped with a manual testing button, usually, users seldom use the manual testing button. Therefore, the leakage current protection devices need an additional circuit to automatically detect malfunctions, faults or the end of the life of such devices. The great relevance would be gained if a leakage current protection device is capable of automatically detecting a fault therein or its end of the life, and consequently alerting a user to take an appropriate action including repairing or replacing the leakage current detection circuit. 
     Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies. 
     SUMMARY OF THE PRESENT INVENTION 
     In one aspect, the present invention relates to an apparatus for testing the life of a leakage current protection device. The leakage current protection device has a first input, a second input, a third input, a fourth input, a first output, a second output, a trip switch having two LINE terminals that are electrically coupled to the first input and the second input, respectively, and two LOAD terminals that are electrically coupled to the inputs of an electrical appliance, respectively, a reset circuit having an input that is electrically coupled to the third input, and an output that is electrically coupled to the first output, and a trip coil circuit having a switching device that has a gate, an anode, and a cathode, a first input 1  that is electrically coupled to the output of the reset circuit and the first output, a second input that is electrically coupled to the fourth input, an output that is electrically coupled to the second output. 
     In one embodiment, the apparatus comprises a microcontroller unit (MCU) having a first input that is electrically coupled to the second output of the leakage current protection device, a second input, a first output that is electrically coupled to the third input of the leakage current protection device, a second output, a third output, a fourth output that is electrically coupled to the second input 2  of the trip coil circuit and the fourth input of the leakage current protection device, and a power supply input P. The apparatus further comprises a power grid signal synchronization monitoring circuit having an input that is electrically coupled to the first output of the leakage current protection device, and an output that is electrically coupled to the second input of the MCU; an alarm circuit having an input that is electrically coupled to the third output of the MCU, and a power supply input; a power supply circuit having an input that is electrically coupled to the first output of the leakage current protection device, and an output that is electrically coupled to the power supply input P of the MCU and the power supply input of the alarm circuit; and a ground fault simulation unit having an input that is electrically coupled to the second output of the MCU, a first output that is electrically coupled to the first input of the leakage current protection device, a second output that is electrically coupled to the second input of the leakage current protection device. 
     In operation, the power grid signal synchronization monitoring circuit generates a first signal that is synchronized with an AC power from the first input and the second input of the leakage current protection device to form a power grid signal synchronization signal, the power grid signal synchronization signal is electrically coupled to the second input of the MCU, the MCU generates a pulse signal before the power grid signal synchronization signal reduces to zero volt during every positive half-wave of the AC power, and a second signal from the second output to the ground fault simulation unit to generate a simulated ground fault signal, the gate of the switching device receives the pulse signal and a third signal in responsive to the simulated ground fault signal, the MCU receives a DC voltage at the first input of the MCU, and the MCU compares the DC voltage with a predetermined threshold value to determine whether a fault exists in the leakage current protection device, and activates the alarm circuit if at least one fault exists. 
     In one embodiment, the MCU is programmed such that if the DC voltage is greater than the predetermined threshold value, no fault exists in the leakage current protection device, and if the DC voltage is less than the predetermined threshold value, at least one fault exists in the leakage current protection device. The apparatus provides a surge protection function. When the voltage at the first input and the second input of the leakage current protection device exceeds a second predetermined threshold value, the MCU sends a signal to a switching device to set the trip switch in a non-conductive state and to disconnect the AC power from the LINE terminal to the LOAD terminal of the trip switch, where the switching device comprises a silicon controlled rectifier, when the switching device is in a conductive state, the switching device passes current in the positive half-wave of the AC power to set the trip switch in a non-conductive state and to disconnect the AC power from the LINE terminal to the LOAD terminal of the trip switch. 
     During the time period when the trip switch is in a non-conductive state, the apparatus continues to detect faults of the leakage current protection device. When the trip switch is in a non-conductive state for a predetermined timeout period, and the MCU does not detect any fault in the leakage current protection device, the MCU sends a signal to a reset switching device to set the trip switch in a conductive state and to connect the AC power from the LINE terminal to the LOAD terminal of the trip switch, where the length of the predetermined timeout period is adjustable. Therefore, the apparatus also provides an automatic reset function. 
     When the MCU determines that at least one fault exists, the MCU sends an alarm signal to the alarm circuit, and the alarm circuit receives the alarm signal and generates an alarm. In one embodiment, the alarm circuit comprises at least one of an audio alarm circuit for generating an audible alarm and a visual alarm circuit for generating a visible alarm. 
     In another aspect, the present invention relates to a method for intelligently testing the life of a leakage current protection device. The leakage current protection device has a first input, a second input, a third input, a fourth input, a first output, a second output, a trip switch having two LINE terminals that are electrically coupled to the first input and the second input, respectively, and two LOAD terminals that are electrically coupled to the inputs of an electrical appliance, respectively, a reset circuit having an input that is electrically coupled to the third input, and an output that is electrically coupled to the first output, and a trip coil circuit having a switching device that has a gate, an anode, and a cathode, a first input 1  that is electrically coupled to the output of the reset circuit and the first output, a second input that is electrically coupled to the fourth input, an output that is electrically coupled to the second output. 
     In one embodiment, the method includes the step of providing a testing device. The testing device in one embodiment has a microcontroller unit (MCU) having a first input that is electrically coupled to the second output of the leakage current protection device, a second input, a first output that is electrically coupled to the third input of the leakage current protection device, a second output, a third output, a fourth output that is electrically coupled to the second input of the trip coil circuit and the fourth input of the leakage current protection device, and a power supply input P; a power grid signal synchronization monitoring circuit having an input that is electrically coupled to the first output of the leakage current protection device, and an output that is electrically coupled to the second input of the MCU; an alarm circuit having an input that is electrically coupled to the third output of the MCU, and a power supply input; a power supply circuit having an input that is electrically coupled to the first output of the leakage current protection device, and an output that is electrically coupled to the power supply input P of the MCU and the power supply input of the alarm circuit; and a ground fault simulation unit having an input that is electrically coupled to the second output of the MCU, a first output that is electrically coupled to the first input of the leakage current protection device, a second output that is electrically coupled to the second input of the leakage current protection device. 
     Furthermore, the method includes the steps of generating a first signal by the power grid signal synchronization monitoring circuit, which is synchronized with an AC power to form a power grid synchronization signal that is received at the second input of the MCU; and producing a pulse signal before the power grid synchronization signal reduces to zero volt and a second signal during every positive half-wave of the AC power by the MCU, wherein the pulse signal is output to the gate of the switching device, and wherein the second signal is output to the ground fault simulation unit so as to generate a simulated ground fault signal therein. 
     Moreover, the method includes the steps of receiving the pulse signal and a third signal in responsive to the simulated ground fault, at the gate of the switching device; detecting a DC voltage between the gate and the cathode of the switching device; and comparing the DC voltage to a predetermined threshold value by the MCU to determine whether a fault exists in the leakage current protection device, where the MCU is programmed such that if the DC voltage is greater than the predetermined threshold value, no fault exists in the leakage current protection device, and if the DC voltage is less than the predetermined threshold value, a fault exists in the leakage current protection device. 
     Additionally, the method includes the steps of and activating the alarm circuit by the MCU if a fault exists in the leakage current protection device to generate an alarm to alert users of the leakage current protection device. In one embodiment, the activating the alarm circuit step further comprising at least of one of following steps activating an audio alarm circuit for generating an audible alarm; and activating a visual alarm circuit for generating a visible alarm. 
     In yet another aspect, the present invention relates to an apparatus with intelligent life testing. In one embodiment, the apparatus includes a leakage current protection device having a first input; a second input; a third input; a fourth input; a first output; a second output; a trip switch having two LINE terminals that are electrically coupled to the first input and the second input, respectively, and two LOAD terminals that are electrically coupled to the inputs of an electrical appliance, respectively; a reset circuit having an input that is electrically coupled to the third input, and an output that is electrically coupled to the first output; and a trip coil circuit having a switching device that has a gate, an anode and a cathode, a first input 1  that is electrically coupled to the output of the reset circuit and the first output, and a second input 2  that is electrically coupled to the fourth input, and an output that is electrically coupled to the second output. 
     The apparatus further includes a microcontroller unit (MCU) having a first input that is electrically coupled to the second output of the leakage current protection device, a second input, a first output that is electrically coupled to the third input of the leakage current protection device, a second output, a third output, a fourth output that is electrically coupled to the second input 2  of the trip coil circuit and the fourth input of the leakage current protection device, and a power supply input P; a power grid signal synchronization monitoring circuit having an input that is electrically coupled to the first output of the leakage current protection device, and an output that is electrically coupled to the second input of the MCU; an alarm circuit having an input that is electrically coupled to the second output of the MCU, and a power supply input; a power supply circuit having an input that is electrically coupled to the first output of the leakage current protection device, and an output that is electrically coupled to the power supply input P of the MCU and the alarm circuit; and a ground fault simulation unit having an input that is electrically coupled to the second output of the MCU, a first output that is electrically coupled to the first input of the leakage current protection device, a second output that is electrically coupled to the second input of the leakage current protection device. 
     In operation, the power grid signal synchronization monitoring circuit generates a first signal that is synchronized with an AC power from the first input and the second input of the leakage current protection device to form a power grid signal synchronization signal, the power grid signal synchronization signal is electrically coupled to the second input of the MCU, the MCU generates a pulse signal before the power grid signal synchronization signal reduces to zero volt during every positive half-wave of the AC power, and a second signal from the second output to the ground fault simulation unit to generate a simulated ground fault signal, the gate of the switching device receives the pulse signal and a third signal in responsive to the simulated ground fault signal, the MCU receives a DC voltage at the first input of the MCU, and the MCU compares the DC voltage with a predetermined threshold value to determine whether a fault exists in the leakage current protection device, and activates the alarm circuit if at least one fault exists. 
     In one embodiment, the MCU is programmed such that if the DC voltage is greater than the predetermined threshold value, no fault exists in the leakage current protection device, and if the DC voltage is less than the predetermined threshold value, at least one fault exists in the leakage current protection device. The apparatus provides a surge protection function, when the voltage at the first input and the second input exceeds a second predetermined threshold value, the MCU sends a signal to the switching device to set the trip switch in a non-conductive state and to disconnect the AC power from the LINE terminals to the LOAD terminals of the trip switch, respectively. The switching device comprises a silicon controlled rectifier, when the switching device is in a conductive state, the switching device passes current in the positive half-wave of the AC power to set the trip switch in a non-conductive state and to disconnect the AC power from the LINE terminals to the LOAD terminals of the trip switch, respectively. 
     During the time period when the trip switch is in a non-conductive state, the apparatus continues to detect faults of the leakage current protection device. When the trip switch is in a non-conductive state for a predetermined timeout period, and the MCU does not detect any fault in the leakage current protection device, the MCU sends a signal to a reset switching device to set the trip switch in a conductive state and to connect the AC power from the LINE terminals to the LOAD terminals of the trip switch, respectively, wherein the length of the predetermined timeout period is adjustable. Thus, the apparatus also provides an automatic reset function. 
     In one embodiment, the MCU sends an alarm signal to the alarm circuit when the MCU determines that at least one fault exists, and the alarm circuit receives the alarm signal and generates an alarm. In one embodiment, the alarm circuit comprises at least one of an audio alarm circuit for generating an audible alarm and a visual alarm circuit for generating a visible alarm. 
     These and other aspects of the present invention will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate one or more embodiments of the invention and, together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment, and wherein: 
         FIG. 1  shows a block diagram of an apparatus for intelligently testing the life of a leakage current protection device according to one embodiment of the present invention; 
         FIG. 2  shows a circuit diagram of an apparatus for intelligently testing the life of a leakage current protection device according to one embodiment of the present invention; 
         FIG. 3  shows a power grid synchronized half wave signal, measured from a power grid synchronization monitoring circuit at an input pin  1  of the MCU shown in  FIG. 2  according to one embodiment of the present invention; 
         FIG. 4  shows a signal received at the gate of a switching device SCR 101  shown in  FIG. 2  according to one embodiment of the present invention; 
         FIG. 5  shows a voltage waveform received at the anode of the switching device SCR 101  shown in  FIG. 2  according to one embodiment of the present invention; 
         FIG. 6  shows a voltage waveform received at the anode of a diode D 102  of the trip coil circuit shown in  FIG. 2  according to one embodiment of the present invention; and 
         FIG. 7  shows an output voltage waveform of a leakage current detection circuit shown in  FIG. 2 , in relation to the power grid signal waveform, when a leakage current occurs during the negative half-wave of the AC power, according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     The present invention is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. Various embodiments of the invention are now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. Moreover, titles or subtitles may be used in the specification for the convenience of a reader, which has no influence on the scope of the invention. Additionally, some terms used in this specification are more specifically defined below. 
     DEFINITIONS 
     The terms used in this specification generally have their ordinary meanings in the art, within the context of the invention, and in the specific context where each term is used. 
     Certain terms that are used to describe the invention are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner in describing the apparatus and methods of the invention and how to make and use them. For convenience, certain terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; the scope and meaning of a term is the same, in the same context, whether or not it is highlighted. Whether or not a term is capitalized is not considered definitive or limiting of the meaning of a term. As used in the description herein and throughout the claims that follow, a capitalized term shall have the same meaning as an uncapitalized term, unless the context of the usage specifically indicates that a more restrictive meaning for the capitalized term is intended. It will be appreciated that the same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification, including examples of any terms discussed herein, is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification. Furthermore, subtitles may be used to help a reader of the specification to read through the specification, which the usage of subtitles, however, has no influence on the scope of the invention. 
     As used herein, “around”, “about” or “approximately” shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about” or “approximately” can be inferred if not expressly stated. 
     As used herein, the terms “unit” and “circuit” are interchangeable, and refer to a configuration of electrically or electromagnetically electrically coupled components or devices. 
     The term “switch”or “switching device”, refers to a device for changing the course (or flow) of a circuit, i.e., a device for making or breaking an electric circuit, or for selecting between multiple circuits. As used herein, a switch or switching device has two states: a conductive state and a non-conductive state. When the switching device is in the conductive state, a current is allowed to pass through. When the switching device is in the non-conductive state, no current is allowed to pass through. 
     As used herein, short names, acronyms and/or abbreviations “AC” refers to alternate current; “DC” refers to direct current; “AFCI” refers to arc fault circuit interrupter; “GFCI” refers to ground fault circuit interrupter; “LED” refers to light emitting diode; “MCU” refers to microcontroller unit; and “SCR” refers to silicon controlled rectifier. 
     OVERVIEW OF THE INVENTION 
     The present invention, among other things, discloses an apparatus and method for testing the life of a leakage current protection device. The leakage current protection device has a leakage current detection circuit and a trip mechanism having a switch device. The switch device has a gate, an anode and a cathode. The leakage current detection circuit of the leakage current protection device has two inductive coils adapted for detecting a leakage current. In one embodiment, the apparatus includes a ground fault simulation unit, a fault detector of the leakage current detection circuit and the trip mechanism, and a life testing detection control unit having a microcontroller unit (MCU) for controlling operation of the fault detector. In operation, a first signal (pulse signal) is sent to the gate of the switching device to generate a first voltage at the cathode of the switching device, a second signal is sent to the ground fault simulation unit to generate a simulated ground fault for the leakage current detection circuit to generate a second voltage at the gate of the switching device, and the first and second voltages are measured to determine whether a fault exists in the leakage current detection circuit and the trip mechanism. In other words, the apparatus of the present invention in operation detects a leakage current in the leakage current protection device, compares the leakage current with a predetermined threshold and consequently outputs a leakage current protection (and/or alarm) signal if a fault occurs and/or the life of leakage current protection device reaches its end. In this sense, the invented apparatus is an intelligently testing apparatus of the life of devices. 
     A silicon controlled rectifier (SCR) constitutes a key component of the trip mechanism of the leakage current protection device. In such a device, when a leakage current or arc fault occurs, the conduction of the current through the SCR must be guaranteed. Otherwise, the trip coil circuit is broken and the trip mechanism fails to operate properly. 
     It is experimentally showed that a proper operation of the trip mechanism depends not only on whether the trip coil conducts current, but also on the other conditions such as the current level and the duration of current conduction. The current level must be strong enough and the duration of current conduction must be long enough. Since the trip coil and the SCR are electrically coupled to a 10 to 240V AC power, the descending edge of the positive cycle of the AC power is selected to turn on the SCR when the instant value exceeds a pre-determined value. While the SCR is set in its conductive state, the leakage current detection circuit is tested to determine whether the current passes through the SCR. Immediately after the SCR is turned on, the AC power crosses zero volt level and enters the negative cycle, the SCR is turned off. Since the SCR is turned on only for a very brief moment, the current passing through the SCR is small enough to ensure the trip mechanism is not tripped. 
     In addition to a switching device (e.g. an SCR), the trip mechanism also includes a trip coil and a trip switch. The trip switch has to two pairs of terminals. One pair is corresponding to a pair of LINE terminals for connecting to an AC power source and the other pair is corresponding to a pair of LOAD terminals for connecting to one or more electrical appliances. When the trip switch is in the conductive state, the first LINE terminal is electrically coupled to the first LOAD terminal and the second LINE terminal is electrically coupled to the second LOAD terminal, respectively. When the trip switch is in the non-conductive state, the first and second LINE terminals are electrically decoupled from the first and second LOAD terminal, respectively. The trip switch is operated by the trip coil. When the trip coil is set in its conductive state, a current is allowed to pass through. When the trip switch is set in its non-conductive state, the AC power at the pair of LINE terminals is disconnected from the pair of LOAD terminals. 
     According to the present invention, the apparatus detects faults within the leakage current detection circuit for the leakage current protection device and the trip mechanism in the real time for testing the life of the leakage current protection device. In a descending edge of every positive half-wave of an AC power, or at a predetermined time, the apparatus sets the switching device SCR in its conductive state in a substantially short period of time, and tests whether the leakage current detection circuit for the leakage current protection device and the trip mechanism work properly. Shortly after the SCR is set in the conductive state, the voltage of the AC power crosses the zero line and thus sets the switching device SCR into its non-conductive state. The duration of the switching device SCR in the conductive state is so short such that the current passing through is not strong enough to activate the trip mechanism. If they are not working properly, at least one of an audio alarm circuit and a visual alarm circuit is activated. The present invention can be found many applications in different types of leakage current protection devices including GFCI and AFCI. 
     These and other aspects of the present invention are further described below. 
     IMPLEMENTATIONS AND EXAMPLES OF THE INVENTION 
     Without intent to limit the scope of the invention, exemplary configurations and their related results according to the embodiments of the present invention are given below. Note again that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the invention. 
     Referring to  FIGS. 1 and 2 , and first to  FIG. 1 , a block diagram of an apparatus for intelligently testing the life of a leakage current protection device is shown according to one embodiment of the present invention. The apparatus  300  includes a leakage current protection circuit  100 , an intelligent life testing and alarm circuit  200  based on an MCU  209 , and a ground fault simulation unit  250  for generating a simulated leakage current. 
     The leakage current protection circuit  100  has a first input  151 , a second input  153 , a third input  155 , a fourth input  157 , a first output  172 , a second output  174 , a reset circuit  103  having an input  103   a  that is electrically coupled to the third input  155  and an output  103   b  that is electrically coupled to the first output  172 , and a trip coil circuit  104  having a first input  104   a   1  that is electrically coupled to the output  103   b  of the reset circuit  103  and the first output  172 , a second input  104   a   2  that is electrically coupled to the fourth input  157  and an output  104   b  that is electrically coupled to the second output  174 . 
     The trip coil circuit  104  also includes a switching device SCR 101  that has a gate, an anode, and a cathode, as shown in  FIG. 2 . The leakage current protection device  100  further has a trip switch SW 101  having two LINE terminals that are electrically coupled to the first input  151  and the second input  153 , respectively, and two LOAD terminals that are electrically coupled to the inputs of an electrical appliance, respectively. 
     The intelligent life testing and alarm circuit  200  has an MCU  209 , a power grid signal synchronization monitoring circuit  204 , a power supply circuit  201  and an alarm circuit  208 . The MCU  209  includes a first input A 1  that is electrically coupled to the second output  174  of the leakage current protection device  100 , a second input A 2 , a first output B 1  that is electrically coupled to the third input  155  of the leakage current protection device  100 , a second output B 2 , a third output B 3 , a fourth output B 4  that is electrically coupled to the second input  104   a   2  of the trip coil circuit  104  and the fourth input  157  of the leakage current protection device  100 , and a power supply input P. The power grid signal synchronization monitoring circuit  204  has an input  204   a  that is electrically coupled to the first output  172  of the leakage current protection device  100 , and an output  204   b  that is electrically coupled to the second input A 2  of the MCU  209 . The alarm circuit  208  has an input  208   a  that is electrically coupled to the third output B 3  of the MCU  209 , and a power supply input  208   p . The power supply circuit  201  has an input  201   a  that is electrically coupled to the first output  172  of the leakage current protection device  100 , and an output  201   b  that is electrically coupled to the power supply input P of the MCU  209  and the power supply input  208   p  of the alarm circuit  208 . 
     The ground fault simulation unit  250  includes an input  250   a  that is electrically coupled to the second output B 2  of the MCU  209 , a first output  250   b   1  that is electrically coupled to the first input  151  of the leakage current protection device  100  and a second output  250   b   2  that is electrically coupled to the second input  153  of the leakage current protection device  100 . 
     In operation, the power grid signal synchronization monitoring circuit  204  generates a first signal that is synchronized with an AC power from the first input  151  and the second input  153  of the leakage current protection device  100  to form a power grid signal synchronization signal, the power grid signal synchronization signal is electrically coupled to the second input A 2  of the MCU  209 , the MCU  209  generates a pulse signal before the power grid signal synchronization signal reduces to zero volt during every positive half-wave of the AC power, and a second signal from the second output B 2  to the ground fault simulation unit  250  to generate a simulated ground fault signal, the gate of the switching device SCR 101  receives the pulse signal and a third signal in responsive to the simulated ground fault signal, the MCU  209  receives a DC voltage at the first input A 1  of the MCU  209 , and the MCU  209  compares the DC voltage with a predetermined threshold value to determine whether a fault exists in the leakage current protection device  100 , and activates the alarm circuit  208  if at least one fault exists. 
     The MCU  209  is programmable. In one embodiment, the MCU  209  is programmed such that if the DC voltage is greater than the predetermined threshold value, no fault exists in the leakage current protection device  100 , and if the DC voltage is less than the predetermined threshold value, at least one fault exists in the leakage current protection device  100 . The apparatus  300  provides a surge protection function. When the voltage at the first input  151  and the second input  153  of the leakage current protection device  100  exceeds a second predetermined threshold value, the MCU  209  sends a signal to a switching device SCR 101  to set the trip switch SW 101  in its non-conductive state and to disconnect the AC power from the LINE terminals to the LOAD terminals of the trip switch SW 101 . The switching device SCR 101  comprises a silicon controlled rectifier. When the switching device SCR 101  is in its conductive state, the switching device SCR 101  passes current in the positive half-wave of the AC power to set the trip switch SW 101  in its non-conductive state and to disconnect the AC power from the LINE terminals to the LOAD terminals of the trip switch SW 101 . 
     During the time period when the trip switch SW 101  is in the non-conductive state, the apparatus  300  continues to detect faults of the leakage current protection device  100 . When the trip switch SW 101  is in the non-conductive state for a predetermined timeout period and the MCU  209  does not detect any fault in the leakage current protection device  100 , the MCU  209  sends a signal to a reset switching device SCR 102  to set the trip switch SW 101  in the conductive state and to connect the AC power from the LINE terminals to the LOAD terminals of the trip switch SW 101 . The length of the predetermined timeout period is adjustable. Accordingly, the apparatus  200  also provides an automatic reset function. 
     When the MCU  209  determines that at least one fault exists, the MCU  209  sends an alarm signal to the alarm circuit  208 , and the alarm circuit  208  receives the alarm signal and generates an alarm. In one embodiment, the alarm circuit  208  comprises at least one of an audio alarm circuit  202  for generating an audible alarm and a visual alarm circuit  203  for generating a visible alarm. 
       FIG. 2  shows a circuit diagram of an apparatus for intelligently testing the life of a leakage current protection device according to one embodiment of the present invention. The apparatus  300  includes a ground fault simulation unit  250  for generating a simulated leakage current, a leakage current protection circuit  100 , and an intelligent life testing and alarm circuit  200  based on an MCU  209 . 
     The ground fault simulation unit  250  has a switching device SCR 301  having a gate, an anode and a cathode, and two resistors R 301  and R 302 . The first resistor R 301  is electrically connected between the hot wire (through the line phase terminal  151 ) of an AC power supply and the cathode of the switching device SCR 301 . The anode of the switching device SCR 301  is connected to the line neutral terminal  153   a  of the trip switch SW 101  which is electrically connected to the neutral wire  153  of the AC power supply after passing through two inductive coils L 1  and L 2 . The resistor R 302  is connected between the gate of the switching device SCR 301  and an output pin  7  (B 2 ) of the MCU  209 . A signal output from the output pin  7  (B 2 ) of the MCU  209  is sent to the gate of the switching device SCR 301  to set the switching device SCR 301  in either its conductive or its non-conductive state, depending on the output signal of the MCU  209 . When the voltage at the output pin  7  (B 2 ) of the MCU  209  reaches a predetermined voltage level, the voltage at the gate of the switching device SCR 301  sets the switching device SCR 301  in the conductive state, thereby causing an imbalance between the currents passing through the line phase terminal  151  (hot wire) and the line neutral terminal  153 , which can be detected by the leakage current detection circuit  107  electrically coupled with the inductive coils L 1  and L 2 . 
     The leakage current protection device  100  comprises two inductive coils L 1  and L 2  adapted for detecting a leakage current, a leakage current detection circuit  107 , a half-wave rectification circuit  101 , a manual testing circuit  102 , a reset circuit  103 , a trip coil circuit  104  and a trip switch SW 101 . The trip switch SW 101  has a pair of LINE terminals (a line phase terminal  151   a  and a line neutral terminal  153   a ) in one side and a pair of LOAD terminals  151   b  and  153   b  in another side, where the line phase terminal  151   a  and the line neutral terminal  153   a  pass through both inductive coils L 1  and L 2  and are connected to a line phase terminal  151  and a line neutral terminal  153 , respectively, of an AC power supplier, and a pair of LOAD terminals  151   b  and  153   b  are connected to one or more loads. When the trip switch SW 101  is in its conductive state, the AC power is supplied from the LINE terminals to the LOAD terminals. When the trip switch SW 101  is in its non-conductive state, no AC power is supplied from the pair of LINE terminals to the pair of LOAD terminals. Each of inductive coils L 1  and L 2  electrically coupled to the leakage current detection circuit  107 . 
     The half-wave rectification circuit  101  includes a rectifier diode D 101  having a cathode and an anode connected to the line phase terminal  151 , and a current limiting resistor R 101  having two terminals with one connected to the cathode of the rectifier diode D 101  and the other connected to an input  107   a  of the leakage current detection circuit  107 . The line phase terminal  151  is corresponding to the first input of the leakage current protection device  100 , while the line neutral terminal  153  is corresponding to the second input of the leakage current protection device  100 , as shown in  FIG. 1 . The half-wave rectification circuit  101  provides a DC power to the leakage current detection circuit  107 . 
     The manual testing circuit  102  has a push-on release-off switch SW 102  having two terminals and a resistor R 102  having two terminals with one electrically coupled to the line phase terminal  151  and the other connected to one terminal of the push-on release-off switch SW 102 , whose other terminal is connected to a LAOD terminal  151   b  of the trip switch SW 101 . The LAOD terminal  151   b  of the trip switch SW 101  is connected to the line phase terminal  151   a  of the trip switch SW 101  when the trip switch SW 101  is in its conductive state. Thus, the push-on release-off switch SW 102  and the resistor R 102  are connected in series. The manual testing circuit  102  is adapted for manually testing the leakage current protection device. 
     The reset circuit  103  comprises a switching device SCR 102  having a gate, an anode and a cathode, a capacitor C 101  having two terminals and a reset coil S 2  having two terminals. As shown in  FIG. 2 , the switching device SCR 102  and the reset coil S 2  are connected in series, and the switching device SCR 102  and the capacitor C 101  are connected in parallel. Specifically, the reset coil S 2  has one terminal electrically coupled to the line phase terminal  151  and the other terminal connected to the anode of the switching device SCR 102 , and the capacitor C 101  has its one terminal connected to the gate of the switching device SCR 102  and the other terminal connected to the cathode of the switching device SCR 102 , which is grounded. The gate of the switching device SCR 102  is in turn connected to a pin  2  (B 1 ) of the MCU  209 . An input signal to the gate of the switching device SCR 102  makes the switching device SCR 102  either in its conductive or its non-conductive state. When the switching device SCR 102  is in the conductive state, the reset coil S 2  is electrically coupled to an AC power supply (through the line phase terminal  151 ) and the reset coil S 2  maintains the trip switch SW 101  in the conductive state such that the AC power is connected from the LINE terminals  151   a  and  153   a  to the LOAD terminals  151   b  and  153   b  of the trip switch SW 101 . 
     The trip coil circuit  104  comprises a switching device SCR 101  having a gate, an anode and a cathode, a capacitor C 102  having two terminals, a diode D 102  having an anode and a cathode and a trip coil S 1  having two terminals, as shown in  FIG. 2 . The trip coil S 1  has its one terminal electrically coupled to the line phase terminal  151  and the other terminal connected to the anode of the switching device SCR 101 . The capacitor C 102  has its one terminal connected to the gate of the switching device SCR 101  and the other terminal connected to the cathode of diode D 102 , respectively. The cathode of the switching device SCR 101  is connected to the anode of the diode D 102 , whose cathode is grounded. Furthermore, the gate of the switching device SCR 101  is also connected to both the output  107   b  of the leakage current detection circuit  107  and a pin  4  (B 4 ) of the MCU  209 . The cathode of the switching device SCR 101  (the anode of the diode D 102 ) is also connected to a pin  3  (A 1 ) of the MCU  209 . 
     For such a configuration, when the switching device SCR 101  is in its conductive state, the trip coil S 1  is connected to an AC power supply (through the line phase terminal  151 ) and the trip coil S 1  sets the trip switch SW 101  into its non-conductive state (a trip state). The trip switch SW 101  maintains its state until a current passes through either the trip coil S 1  or the reset coil S 2 . The trip switch SW 101  responds to the action of the trip coil S 1  and the reset coil S 2 . When the leakage current detection circuit  107  detects a leakage current, the signal from the leakage current detection circuit  107  is connected to the gate of the switching device SCR 101  and this signal sets the switching device SCR 101  to the conductive state. The power supply energizes the trip coil S 1  to set the trip switch SW 101  in a non-conductive state so that the AC power is disconnected from the LINE terminals  151   a  and  153   a  to the LOAD terminals  151   b  and  153   b  of trip switch SW 101 , i.e. in the trip state. The reset circuit  103 , on the other hand, energizes the reset coil S 2  through the switching device SCR 102  to reset the trip switch SW 101  back to the conductive state so that the AC power is connected from the LINE terminal  151   a  and  153   a to the LOAD terminals  151   b  and  153   b  of the trip switch SW 101 . 
     The intelligent life testing and alarm circuit  200  has the MCU  209 , a power supply  201  electrically coupled to the MCU  209 , a power grid signal synchronization monitoring circuit  204 , and an alarm unit  202  and/or  203 . 
     The MCU  209  includes a general purpose integrated circuit with a timer function, or an application specific integrated circuit such as a 555 timer chip. 
     The power supply circuit  201  comprises a rectifying diode D 201 , a resistor R 201 , a regulator diode Z 201 , a first voltage stabilizing capacitor C 201 , a second voltage stabilizing capacitor C 202 , and a light emitting diode LED 201 . The anode of the diode D 201  is electrically connected to the hot wire of the AC power through the line phase terminal  151 . The cathode terminal of the diode D 201  is electrically connected to a first end of the resistor R 201 . A second end of the resistor R 201  is electrically connected to a terminal Vcc and provides a DC power supply voltage to the terminal Vcc. The regulator diode Z 201  has its cathode and anode electrically connected to the terminal Vcc and the ground, respectively. The first voltage stabilizing capacitors C 201  has its two terminals electrically connected to the electrically connected to the terminal Vcc and the ground, respectively, as well. The regulator diode Z 201  and first voltage stabilizing capacitors C 201  coupled to each other in parallel to form a voltage regulator to further regulate the voltage of the terminal Vcc. The light emitting diode LED 201  has its anode electrically connected to the terminal Vcc and its cathode electrically connected to one terminal of the second voltage stabilizing capacitor C 202 , which is electrically connected to a pin  10  (P) of the MCU  209  for supplying the power from the power supply circuit  201  to the MCU  209 . The other terminal of the second voltage stabilizing capacitor C 202  is electrically connected to the anode of the regulator diode Z 20 , which is electrically connected to the ground. The regulator diode Z 201  and the voltage stabilizing capacitor C 202  are adapted for regulating the power supply to an appropriate voltage for the MCU  209 . The LED 201  may also be used as an indication of working conditions of the leakage current protection device unit  100 . 
     The power grid signal synchronization monitoring circuit  204  includes a voltage divider having a first resistor R 206  and a second resistor R 207 . The input to the circuit  294  is a DC power supplied from the cathode of the diode D 201 . The first resistor R 206  and the second resistor R 207  forming the voltage divider are adapted for reducing the DC voltage to an appropriate value of voltages, inputting to the input pin  1  (A 2 ) of the MCU  209 . The output signal to the MCU  209  is a synchronized half-wave waveform used as a sampling of the power grid alternate current waveform. 
     The alarm unit includes at least of an audio alarm circuit  202  and a visual alarm circuit  203 . As shown in  FIG. 2 , the alarm unit comprises both the audio alarm circuit  202  and the visual alarm circuit  203 . 
     In this embodiment shown in  FIG. 2 , the audio alarm circuit  202  has a speaker, a switching device SCR 201 , and a voltage dividing resistor R 202 . A transistor or an SCR may be used as the switching device, depending upon applications. A DC voltage output from the half-wave rectifier D 201  is applied to the speaker through the voltage dividing resistor R 202  and the switching device SCR 201 . Normally, the switching device SCR 201  is in a non-conductive state and the speaker remains silent. When an output from the pin  9  (B 2 ) of the MCU  209 , electrically connected to the gate of the switching device SCR 201  turns the switching device SCR 201  to its conductive state, the speaker produces an audible alarm. An optional integrated circuit may be used to generate special alarm sounds. 
     In this embodiment shown in  FIG. 2 , the visual alarm circuit  203  has a resistor R 203 , a light emitting diode LED 202 , a switch SW 201  and a resistor R 204 . The switch SW 201  has its one terminal electrically connected to the cathode of the diode D 201  of the power supply circuit  201  and the other terminal electrically connected to one terminal of the resistor R 204  whose other terminal is electrically connected to the pin  8  (B 3 ) of the MCU  209 . The resistor R 203  is electrically connected between the other terminal of the resistor R 204  and the anode of the light emitting diode LED 202  whose cathode is grounded. Normally, the output at the pin  8  (B 3 ) of the MCU  209  is in a low voltage state and the LED 202  is not lit. When the MCU  209  detects the malfunction of the leakage current detection circuit  107  or the trip coil S 1 , the output at the pin  8  of the MCU  209  is in a high voltage state, which causes the light emitting diode LED 202  to generate a visible alarm. The switch SW 201  is a mechanical contact switch associated with trip protections. When the leakage current protection device  100  trips, the switch SW 201  is set in its conductive state, causing the lighting of the LED 202 . The lighting of the LED 202  indicates either the leakage current protection device unit  100  is in a trip condition or the leakage current detection circuit  100  is not working properly. 
     Without limit the scope of the present invention, different units utilized in the apparatus for testing the life of a leakage current protection device according to the present invention are described briefly as follows. These units include, but not limited to, ground fault simulation unit, life testing detection control unit, fault detector for leakage current detection circuit and trip mechanism. 
     Ground Fault Simulation Unit 
     The ground fault simulation unit  250 , as shown in  FIG. 2 , comprises a switching device SCR 301  have a gate, an anode and a cathode, a resistor R 301  having a first terminal and a second terminal, and a resistor R 302 . The resistor R 302  is connected between the gate of the switching device SCR 301  and an output pin  7  (B 2 ) of the MCU  209 . The output signal from pin  7  (B 2 ) of the MCU  209  is sent to the gate of the switching device SCR 301  to set the switching device SCR 301  in either its conductive or its non-conductive state, depending on the output signal of the MCU  209 . The first terminal of the first resistor R 301  is electrically coupled to the hot wire (through the line phase terminal  151 ) of the AC power supply. The second terminal of the first resistor R 301  is connected to the cathode of the switching device SCR 301 . The anode of the switching device SCR 301  is connected to the line neutral terminal  153   a  of the trip switch SW 010  which is electrically connected to the neutral wire  153  of the AC power supply after passing through two inductive coils L 1  and L 2 . When the voltage at the output pin  7  (B 2 ) of the MCU  209  reaches a predetermined voltage level, the voltage at the gate of the switching device SCR 301  sets the switching device SCR 301  in the conductive state. Because of the configuration shown in  FIG. 2 , the switching device SCR 301  passes a current only when the AC power enters negative half-wave so that a simulated ground fault is generated between the hot wire and neutral wire of the AC power supply. When the AC power enters a positive half cycle, the switching device SCR 301  is automatically set into the non-conductive state where no current is allowed to pass through. 
     Life Testing Detection Control Unit 
     The life testing detection control unit includes an MCU  209 , and an alarm unit having an audio alarm circuit  202  and a visual alarm unit  203 . The MCU  209  can be an independent unit or a shared unit with the life testing detection control unit, the fault detector for the leakage current detection circuit and the trip mechanism. If a fault exists in the leakage current detection circuit and the trip mechanism of the leakage current protection device, the MCU  209  activates the alarm unit. When a fault occurs, the audio alarm circuit  202  generates an audible alarm, and the LED LED 202  of the visual alarm circuit  203  generates a visible alarm to alert user of the leakage current protection device. An application specific integrated circuit (ASIC) may be used to generate specific alarm sounds with the speaker. A regular speaker or a piezo buzzer may be used as the speaker in the circuit. 
     Fault Detector for Leakage Current Detection Circuit and Trip Mechanism 
     A fault detector for a leakage current detection circuit and trip mechanism includes the MCU  209 , the power supply  201  electrically coupled to the MCU  209 , the ground fault simulation unit  250 , the trip coil circuit  104 , and the alarm unit. The MCU  209  can be an independent unit or a shared unit with the life testing detection control unit according to embodiments of the present invention. The MCU  209  is a main control unit for the intelligent life testing detection device of the leakage current protection device. In one embodiment, the MCU  209  includes a general purpose integrated circuit with a timer function, or an application specific integrated circuit such as a  555  timer chip. 
     The power grid signal synchronization monitoring circuit  204  provides a power grid synchronization signal. The input to the power grid signal synchronization monitoring circuit  204  is electrically coupled to the power grid through the cathode of the diode D 201  of the power supply  201 . As shown in  FIG. 3 , the output signal  303  of the power grid signal synchronization monitoring circuit  204  shows only the positive half of the power grid waveform. The positive half of the power grid waveform passes through a voltage divider having a first resistor R 206 , and a second resistor R 207 , so that the output voltage of the power grid synchronization monitoring circuit  204  reaches an appropriate level. In one embodiment, the values of the resistance of the first resistor R 206  and the second resistor R 207  are chosen so that the ratio of voltages across the first resistor R 205  and across the second resistor R 207  is in a range of about 50-200. The power grid synchronized signal is electrically coupled to the input pin  1  (A 2 ) of the MCU  209 . When the descending edge of the waveform of the sampled signal of the synchronized signal reaches a predetermined threshold, the output pin  4  (B 4 ) of the MCU  209  sends out a short pulse  404 , as shown in  FIG. 4 . In  FIG. 4 , the pulse signal  404  is overlaid with a power grid waveform  401  to show the phase relationship between the pulse and the power grid waveform. This pulse sets the switching device SCR 101  in conductive state. After a brief delay, the voltage at the anode of the switching device SCR 101  is measured through an A/D converter of the pin  3  (A 1 ) of the MCU  209 . If the voltage is at or near a predetermined threshold while the switching device SCR 101  is in conductive state during the pulse period, then the trip coil circuit and trip mechanism is working properly. 
     The pulse  404  is very short in time, but it is long enough to set the switching device SCR 101  in the conductive state to allow a current to pass through. The voltage across a p-n junction is about 0.7 V for a silicon type SCR. The voltage across a p-n junction is about 0.3 V for a Germanium type SCR. This voltage is detected by the pin  3  (A 1 ) of the MCU  209  and is used to determine whether a fault exists in the trip mechanism. For example, if the trip coil S 1  is broken, no current is allowed to pass through the trip coil S 1  from the LINE terminal. Therefore, the voltage between the gate and the cathode of the switching device SCR 101  is very small or equals to zero. If this DC voltage is smaller than the predetermined threshold or is zero, it indicates that at least one fault exists in the trip mechanism. 
       FIG. 5  shows the voltage  501  measured at the anode of the switching device SCR 101  according to one embodiment of the present invention.  FIG. 6  shows the voltage  604  measured at the anode of the diode D 102  according to one embodiment of the present invention. 
     When the AC power enters the negative half-wave and the voltage reaches a predetermined voltage level, or at a predetermined time, the output pin  7  (B 2 ) of the MCU  209  generate a pulse signal to set the switching device SCR 301  of the ground fault simulation unit  250  in conductive state. When the switching device SCR 301  is in conductive state, the ground fault simulation unit  250  generates a leakage current, i.e., a simulated ground fault. After a short delay, the voltage at the anode of the switching device is measured at the pin  4  of the MCU  209 .  FIG. 7  shows a portion of a voltage waveform at the output of the leakage current detection circuit, when the leakage current detection circuit is working properly. In  FIG. 7 , the voltage waveform  703  at the output of the leakage current detection circuit is overlaid with a power grid waveform  701  to show the phase relationship between the voltage waveform at the output of the leakage current detection circuit and the power grid waveform. If a series of pulse as shown in the  FIG. 6  is detected by the MCU  209 , it indicates that the leakage current detection circuit is working properly. Otherwise, if no pulse is detected by the MCU  209 , it indicates that the leakage current detection circuit is not working properly. 
     An alarm is generated by the MCU  209  and sent to at least one of the audio alarm circuit  202  and visual alarm circuit  203  of the life testing detection control unit when at least one fault exists in the leakage current detection circuit and the trip mechanism of the leakage current protection device. The audio alarm circuit  202  produces an audible alarm and the visual alarm circuit  203  produces a visible alarm. 
     In one embodiment, the intelligent life testing detection device of the leakage current protection device provides surge protection functionality. When the voltage of an AC power input reaches an unusual level, such voltage surge may cause damage to electrical appliances electrically coupled to the load terminal of a leakage current protection device. During a normal operation, the input voltage of the AC power is monitored by the power grid synchronization monitoring circuit  204 . If the monitored voltage reaches a predetermined threshold, the output pin  4  of the MCU  209  sets the switching device SCR 101  in conductive state so that the trip mechanism is activated and the AC power from the LINE terminal of the leakage current protection device to the LOAD terminal is disconnected. Therefore, the surge protection functionality is provided by the intelligent life testing detection device of the leakage current protection device. An alarm signal is sent to the alarm unit to alert user of the leakage current protection device. 
     In another embodiment, the intelligent life testing detection device of the leakage current protection device can be automatically reset. When the intelligent life testing detection device of the leakage current protection device is in the trip condition, the intelligent life testing detection device of the leakage current protection device is still working properly. After a predetermined period of time, the MCU  209  attempts to reset the intelligent life testing detection device of the leakage current protection device by sending out pulse through pin  2  (B 1 ) of the MCU  209  to set the switching device SCR 102  of the reset circuit  103 . If the leakage current no longer exists, then the intelligent life testing detection device of the leakage current protection device is successfully reset and the AC power is reconnected from the LINE terminal to the LOAD terminal of the leakage current protection device. Therefore, the intelligent life testing detection device of the leakage current protection device provides an automatically reset function. 
     Another aspect of the present invention provides a method of intelligently testing the life of a leakage current protection device having a leakage current detection circuit and a trip mechanism. In one embodiment, the method comprises the steps of:
         detecting fault in leakage current protection device with a fault detector; and   alerting user of the leakage current protection device with a life testing detection unit having an MCU and an alarm unit when at least one fault is detected in the leakage current protection device.       

     The step of alerting user of the leakage current protection device with the alarm unit when at least one fault is detected in the leakage current protection device comprises at least one of the steps of:
         alerting user of the leakage current protection device that at least one fault exists in the leakage current protection device with an audio alarm circuit  202 ; and   alerting user of the leakage current protection device that at least one fault exists in the leakage current protection device with a visual alarm circuit  203 .       

     The audio alarm circuit  202  is adapted to produce an audible alarm. The visual alarm circuit  203  is adapted to produce a visible alarm. 
     The step of detecting fault in leakage current protection device with the fault detector comprising the step of detecting fault in a leakage current detection circuit of the leakage current protection device with a fault detector. The fault detector comprises:
         a ground fault simulation unit  250 ;   a trip coil circuit  104  having a switching device SCR 101 , a trip coil S 1 , and a trip switching SW 101  having a LINE terminal for connecting to an AC power and a LOAD terminal;   a power grid signal synchronization monitoring circuit  204 ; and   a reset circuit  103  having a reset coil S 2 , a reset switching device SCR 102  and the trip switching SW 101 .       

     The step of detecting fault in leakage current protection device with the fault detector comprising the steps of:
         sending a pulse signal to the gate of the switching device SCR 101  at a predetermined phase of the AC power during positive half-wave of the AC power to generate a voltage at the cathode of the switching device SCR 101 ;   sending a signal to the ground fault simulation unit  250  to generate a simulated ground fault for leakage current detection circuit during negative half of the AC power to generate a voltage at the gate of the switching device SCR 101 ;   receiving the voltage at the cathode of the switching device SCR 101  during the positive half-wave of the AC power,   receiving the voltage at the gate of the switching device SCR 101  during the negative half-wave of the AC power; and   analyzing the received voltages to determine whether at least one fault exists in the leakage current detection circuit and the trip mechanism.       

     The switching device SCR 101  is able to establish the voltage at the cathode of the switching device SCR 101  when no fault exists in the trip mechanism of the leakage current detection device, during the positive half-wave of the AC power. The switching device SCR 101  is able to establish the voltage at the gate of the switching device SCR 101  when no fault exists in the leakage current detection circuit of the leakage current detection device, during the negative half-wave of the AC power. If the received voltage at the cathode of the switching device SCR 101  is less than a predetermined threshold value, during the positive half-wave of the AC power, it is determined that at least one fault exists in the trip mechanism of the leakage current detection device. If the received voltage at the gate of the switching device SCR 101  is less than a predetermined threshold value, during the negative half-wave of the AC power, it is determined that at least one fault exists in the leakage current detection circuit of the leakage current detection device. 
     In another embodiment, the method for intelligently testing the life of a leakage current protection device includes the steps of: (i) providing a testing device, having a microcontroller unit (MCU); a power grid signal synchronization monitoring circuit; an alarm circuit; a power supply circuit; and a ground fault simulation unit, as described above; (ii) generating a first signal by the power grid signal synchronization monitoring circuit, which is synchronized with an AC power to form a power grid synchronization signal that is received at the second input A 2  of the MCU; (iii) producing a pulse signal before the power grid synchronization signal reduces to zero volt and a second signal during every positive half-wave of the AC power by the MCU, wherein the pulse signal is output to the gate of the switching device SCR 101 , and wherein the second signal is output to the ground fault simulation unit so as to generate a simulated ground fault signal therein; (iv) receiving the pulse signal and a third signal in responsive to the simulated ground fault at the gate of the switching device SCR 101 ; (v) detecting a DC voltage between the gate and the cathode of the switching device SCR 101 ; (vi) comparing the DC voltage to a predetermined threshold value by the MCU to determine whether a fault exists in the leakage current protection device, wherein the MCU is programmed such that if the DC voltage is greater than the predetermined threshold value, no fault exists in the leakage current protection device, and if the DC voltage is less than the predetermined threshold value, a fault exists in the leakage current protection device; and (vii) activating the alarm circuit by the MCU if a fault exists in the leakage current protection device to generate an alarm to alert users of the leakage current protection device. The activating the alarm circuit step further comprising at least of one of the following steps: activating an audio alarm circuit for generating an audible alarm; and activating a visual alarm circuit for generating a visible alarm. 
     The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. 
     The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.