Abstract:
A circuit for indicating abnormality of a three-mode surge absorber of a public electric power is disclosed. The circuit is serially connected between the input end and output end of a public electric power supply for indicating the abnormality of a three-mode surge absorbing device of a public power supply. The circuit includes a first fuse, a first surge absorbing device, an abnormal indication circuit, a second surge absorbing device and a second fuse. Other than indicating the abnormality of the L-N, L-G, N-G surge absorbing devices, the present invention can prevent current leakage in above devices.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a power abnormality indicating circuit, and especially to circuit for indicating abnormality of a three-mode surge absorber of a public electric power. Other than indicating the abnormality of the L-N, L-G, N-G surge absorbing devices, the present invention can prevent current leakage as destroys occurs in above modes. 
     BACKGROUND OF THE INVENTION 
     The general power receptacles for surge protection use metal oxide varistors or other transient/surge absorbers for suppressing surge wave. These elements will heat as absorbing surge wave, even a large surge wave will induce a short circuit. Therefore, temperature fuses or current fuses are used to prevent abnormality. 
     In general, the cutting-off of fuses is used to determine the abnormality of a surge protection indicator. However, in order to prevent that the leakage current to the ground is too large, in general, the indicator only displays the condition of the input ends of line-neutral mode while the conditions of line-ground mode and neutral-ground mode are not displayed. 
     Referring to FIG. 1, a prior art circuit for indicating abnormality of a surge absorber is illustrated, which includes two surge absorbing devices  10  and  30  and an abnormal indication circuit  20 . The L-N end in the three-mode in public power supply is connected to the surge absorbing device  10  in series. The surge absorbing device  30  is serially connected between the L-G and N-G ends. The surge absorbing device  10  has a two-end temperature sensing fuse  101  capable of suffering from a temperature of 139° C. and a metal oxide varistor  102 . When the metal oxide varistor  102  has abnormality, it will heat gradually. Since it tightly resists against the two-end temperature sensing fuse  101 , the metal oxide varistor  102  will heat and finally burn-cut the two-end temperature sensing fuse  101  so that the surge protection indicator D 2  will extinguish due to no current flowing therethrough. 
     The surge absorbing device  30  has two metal oxide varistors  301  and  302  and a two-end temperature sensing fuse  303  capable of suffering from a temperature of 139° C. When the metal oxide varistor  301  has abnormality, it will heat gradually. Since it tightly resists against the two-end temperature sensing fuse  303 , the metal oxide varistor  301  will heat and finally burn-cut the two-end temperature sensing fuse  303 , but the two-end temperature sensing fuse  101  does not burn-cut so that the surge protection indicator D 2  will not extinguish. Namely, the fault of the surge absorbing device  30  of the L-G ends can not be detected. Furthermore, When the metal oxide varistor  302  has abnormality, it will heat gradually. Since it tightly resists against the two-end temperature sensing fuse  303 , the metal oxide varistor  302  will heat and finally burn-cut the two-end temperature sensing fuse  303 , but the two-end temperature sensing fuse  101  does not burn-cut so that the surge protection indicator D 2  will not extinguish. Namely, the fault of the surge absorbing device  30  of the N-G ends can not be detected. 
     SUMMARY OF THE INVENTION 
     Accordingly, the primary object of the present invention is to provide a circuit for indicating abnormality of a three-mode surge absorber and a multiple-end fuse. 
     To achieve above objects, the present invention provides a circuit for indicating abnormality of a three-mode surge absorber of a public electric power serially connected to an input end and an output end of a public power supply, the circuit for indicating abnormality of a three-mode surge absorber of a public electric power comprising: a first two-end fuse having a first end coupled to the line input end; a first surge absorbing device coupled to a second end of the first two-end fuse and the neutral input end for absorbing a surge between the line input end and the neutral input end; a second surge absorbing device coupled to the line input end and the neutral input end for absorbing a surge between the neutral input end and ground input end; an abnormal indication circuit coupled to the first surge absorbing device, the second surge absorbing device and the neutral input end for indicating abnormalities in three-mode of a public power supply; and a second two-end fuse having a first end coupled to the second surge absorbing device, and a second end coupled to the ground input end for preventing abnormalities of parts. By the aforesaid circuit, other than indicating the abnormality of the L-N, L-G, N-G surge absorbing devices, the present invention can prevent current leakage as destroys occurs in above modes. 
     The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various objects and advantages of the present invention will be more readily understood, from the following detailed description when read in conjunction with the appended drawing, wherein: 
     FIG. 1 shows the circuit for indicating abnormality of a surge absorber in the prior art; and 
     FIG. 2 shows the circuit for indicating abnormality of a three-mode surge absorber of a public electric power in the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2, the circuit diagram of the circuit for indicating abnormality of a three-mode surge absorber of a public electric power in the preferred embodiment of the present invention is illustrated. The circuit of the present invention includes a first two-end fuse F 1 , a first surge absorbing device  40 , a second surge absorbing device  50 , an abnormal indication circuit  60 , and a second two-end fuse F 2 . The first surge absorbing device  40  has a two-end temperature sensing fuse  401  and a metal oxide varistor  402 . The second surge absorbing device  50  includes a surge absorbing device  501 , the first end thereof is coupled to a line output end, and the second end is coupled to the abnormal indication circuit  60 . The first end of the second surge absorbing device  502  is coupled to a line input end, and the second end thereof is coupled to the abnormal indication circuit  60 . The two-end temperature sensing fuse  503  has a first end coupled to the second ends of the first and second surge absorbing devices  501  and  502 , and has a second end coupled to the first end of the second two-end fuse F 2 . 
     The abnormal indication circuit  60  has a diode D 3 . The anode thereof is coupled to a first surge absorbing device  40 . A second end of a first resistor R 1  is coupled to the cathode of the diode D 3 . A second resistor R 2  has a first end coupled to a second end of the first resistor R 2 , and the second surge absorbing device  50  (point A in FIG.  2 ). A first transistor Q 1  has a base coupled to the second end of the second resistor R 2 , and the emitter thereof is coupled to the ground input end. A third resistor R 3  has a first end coupled to the cathode of the diode D 3 . A fourth resistor R 4  has a first end coupled to the first resistor R 1 , the third resistor R 3 , and the cathode of the diode D 3 , and the second end thereof is coupled to the collector of the first transistor Q 1  (point B in FIG.  2 ). A fifth resistor R 5  has a first end coupled to a second end of the fourth resistor R 4  and the collector of the first transistor Q 1 . A second transistor Q 2  has a base coupled to a second end of the fifth resistor R 5 , and the collector thereof is coupled to the second end of the third resistor R 3 . A light emitting diode D 4  has a anode coupled to the emitter the second transistor Q 2 , and the cathode thereof is coupled to the neutral output end. A Zener diode Z 1  has a cathode coupled to the collector of the second transistor Q 2 , and the anode thereof is coupled to the neutral output end for supplying a rated voltage. 
     The circuit property for the circuit for indicating abnormality of a three-mode surge absorber of a public electric power according to the present invention may be analyzed by the following two modes (1) The transient/surge absorber is heated and then is destroyed gradually, and (2) The transient/surge absorber is subjected to a high voltage instantly and then is destroyed. In the following, the properties of these two modes are analyzed. 
     (1) The transient/surge absorber is heated and then is destroyed gradually. 
     a) L-N mode: the metal oxide varistor  402  is abnormal, and is heated, since it tightly resists against the two-end temperature sensing fuse  401 . Finally, the temperature of the metal oxide varistor  402  will burn-cut two-end temperature sensing fuse  401 . Therefore, the surge protection indicator D 4  has no current and then extinguishes. 
     b) L-G mode: the metal oxide varistor  502  has abnormality and then heat gradually, since it resists tightly against the two-end temperature sensing fuse  503 , when the two-end temperature sensing fuse  503  is burn-cut so that point A is in a floating condition. When the transistor is conductive, point B is grounded so that transistor Q 2  is turned off and the surge protection indicator D 4  extinguishes due to no current flowing therethrough. 
     c) N-G mode: The metal oxide varistor  501  has abnormality and heats gradually. Since it resists tightly against the two-end temperature sensing fuse  503 , when the two-end temperature sensing fuse  503  is burn-cut so that point A is in a floating condition. When the transistor is conductive, point B is grounded so that transistor Q 2  is turned off and the surge protection indicator D 4  extinguishes due to no current flowing therethrough. 
     (2) The transient/surge absorber is subjected to a high voltage instantly and then is destroyed. 
     a) L-N mode: When abnormality occurs, and high voltage retains, the metal oxide varistor  402  will short-circuit instantly. Since a large current flows into the fuse F 1  so that the fuse F 1  is heated instantly and then burn-cut. Other than cutting off the current path of the metal oxide varistor  402 , the path of the surge protection indicator D 4  is also cut off so that the surge protection indicator D 4  extinguishes. 
     b) L-G mode: When abnormality occurs, and high voltage retains, the metal oxide varistor  502  will short-circuit instantly. Since a large current flows into the fuses F 1  and F 2 , and thus in design, F 2  has a smaller current path (or F 2  has a small turn-off current than that of F 1 ), so that the fuse F 2  is heated instantly and then burn-cut. The current path of the metal oxide varistor  502  is cut off so that point A is in a floating condition and transistor Q 1  is conductive, point B is grounded so. that transistor Q 2  is turned off. The surge protection indicator D 4  extinguishes due to no current flowing therethrough. 
     c) N-G mode: When abnormality occurs, and high voltage retains, the metal oxide varistor  501  will short-circuit instantly. Since a large current flows into the fuse F 2 , so that the fuse F 2  is heated instantly and then burn-cut. The current path of the metal oxide varistor  503  is cut off so that point A is in a floating condition and transistor Q 1  is conductive, point B is grounded so that transistor Q 2  is turned off. The surge protection indicator D 4  extinguishes due to no current flowing therethrough. 
     In summary, other than indicating the abnormalities of the L-N, L-G, N-G surge absorbing devices, the circuit for indicating abnormality of a three-mode surge absorber of a public electric power according to the present invention assure that no leakage occurs as it is destroyed in all modes. Besides, herein, the metal oxide varistor is taken as an example of the first and second surge absorbing devices of the present invention, however, the surge absorbing device, such as a gas tube, a transient voltage suppressor or sidactor, etc. serves in the present invention. Especially, the three-end fuses  50  and  80  are not limited to a structure of three ends, it is only for the sake of convenience. 
     The present invention is thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.