Please refer to FIG. 1 which shows a traditional surge protector 1 available in market. The surge protector 1 includes a dielectric material 10, two conductive wires 12 and an insulating element 13. The dielectric material 10 is a plate made of polycrystalline semiconductor ceramic material which contains a vast amount of disorderly zinc oxide grains, and the boundaries between the zinc oxide grains and the other oxides form boundary layers where diode effects occur, so that the entire dielectric material is equivalent to an aggregate of a large number of diodes connected back to back. When the dielectric material is subjected to a low voltage, only a small reverse leak current flow through the dielectric material 10, but when a high voltage is applied to the dielectric material, the punch-through effect occurs, causing the large current of the high voltage to pass through the dielectric material 10. The reason why the dielectric material 10 is extensively used in making surge protectors lies in their non-linear current-voltage characteristic curves, in which electrical resistance is high under a low voltage and low under a high voltage. Two electrodes 11 are attached on two opposite sides of the dielectric material 10, respectively. Each of the two conductive wires 12 has an end fixed on the corresponding electrode 11 by welding, and other end defined as a pin 121 to electrically connect the traditional surge protector 1 to the power supply terminal of the electric device (not shown in FIG. 1). The insulating element 13 encloses the dielectric material 10, the electrodes 11 and the conductive wires 12, and only the pins 121 are exposed out of the insulating element 13.
Please refer back to FIG. 1. In the traditional surge protector 1, the fixed connection regions between the dielectric material 10 and the conductive wires 12 withstanding an extremely high voltage and current tends to cause breakage of the physical connections. Moreover, because of the extremely high voltage and current that the dielectric material 10 has to withstand per unit area, a strong transient overvoltage may pass through the dielectric materials 10 and form through holes in the resistors of the dielectric material 10 such that an even larger current runs through the resistors in an instant, causing high heat or fire by electric arc. Please refer to FIG. 2. In view of the aforesaid shortcomings of the traditional surge protector 1, the manufacturer connects a fuse 3 with a power supply pin of a power supply terminal Vi of the electric device 2 in series when the traditional surge protector 1 is connected between the power supply terminal Vi and a circuit of the electric device 2 in parallel, so that a fuse element of the fuse 3 can be melted under the large current run therethrough in an instant and the occurred high temperature to form a cut-off state in a condition that the breakages are occurred at the fixed connection regions between the dielectric material 10 and the conductive wires 12, or the through holes are formed in the resistors of the dielectric material 10, thereby avoiding the fire occurred by continuous power supply and protecting the electric device from damage. However, the fuse 3 not only increases manufacturing cost and design complexity, but also occupies the space for circuits, and it is a main reason why the relevant circuit cannot be designed more compact.
Please refer to FIG. 3. Some manufacturers extra install a thermal fuse 14 in the traditional surge protector 1 shown in the FIG. 1. An end 141 of the thermal fuse 14 is welded and fixed on the electrode 11. The thermal fuse 14, the dielectric material 10, the electrodes 11 and the conductive wires 12 are enclosed by the insulating element 13, and only the pins 121 and other end 142 of the thermal fuse 14 are exposed out of the insulating element 13, so that the thermal fuse 14 can be in cut-off state when sensing the temperature of the electrode 11 exceeding a predetermined threshold value, and then drive the power supply terminal to stop supplying power. However, the thermal fuse 14 not only increases the cost and volume of the surge protector, but also occupies more space for the circuit. In addition, an entire circuit of the electric device must be redesigned to timely stop supplying power according to the cut-off state of the thermal fuse 14, so the entire circuit becomes more complicated.