Arrangement of an over-voltage protection circuit

#The present invention relates to an arrangement of the components in a circuit, in order to prevent the electronic components in the circuit from being damaged by an over-voltage. The arrangement is especially suitable for high electric power devices requiring a high voltage processing operation or usually having to be installed outdoors so as to protect the component elements thereof.

#Previously, the practice of preventing over-voltage damage was usually conducted using a photo coupler (such as photo-transistor coupler and photo-thyristor coupler etc.) as a coupling element between an input terminal and an output terminal of an electronic circuit for the purpose of isolating the input terminal and the output terminal. Generally, the breakdown voltage of the optimal photo coupler recognized in the art is approximately up to 5,000 VAC. Therefore, devices having such couplers are free of any problems as long as the over-voltage thereof does not exceed 5,000 VAC. However, once a high voltage over 5,000 VAC appears across the input and the output terminals of the circuit, the high voltage will go from the input (or output) side to the output (or input) side through the photo-thyristor and the electronic elements of the circuit. In such case, the photo-thyristor and the electronic elements will be damaged, and the entire printed circuit board may even be burned out. It is clear that over-voltage protection between the input terminal and the output terminal of a circuit is of vital importance. In view of the fact that the maximum breakdown voltage of existing photo-couplers is no more than 5,000 VAC, the present invention develops a specific circuit arrangement based on a series of experiments.

#One object of the present invention is to provide a circuit arrangement which is capable of protecting the electronic elements between the input side and the output side of a circuit from being damaged by electric-strike or over-voltage, as well as having the effect of keeping the input side isolated from the output side of the circuit. The object is achieved by a specific arrangement of copper foils or conductive wires which themselves may be ones of composed elements of the circuit or additional elements on the inner side of both input terminal and output terminal, so that when an over-voltage occurs, the over-voltage will first go through the conductive wires to a ground or a low voltage side. In this way, the electronic elements in the circuit will be protected from damage from the over-voltage.

#FIG. 1 shows a first embodiment of the present invention in the application as an over-voltage protection device in a printed circuit board;

#FIG. 2 shows, a second embodiment of the present invention in the application as an over-voltage protection device in a transformer; and

#FIG. 3 shows a perspective view of a photo-electric box of the present invention.

#FIG. 1 illustrates an embodiment of the present invention wherein a printed circuit board with the arrangement of the present invention is disclosed. The printed circuit board includes an input side 11, an output side 10 and a number of electronic elements (not shown in the Figure) and an additional photo-coupler 6 for preventing the board from damage from over-voltage. According to the present invention, four copper foils 15, 14 and 13, 12 are used which extend respectively to the photo-coupler 6 from an upper input end 1 and an lower input end 2 on the input side 11 and an upper output end 4 and an lower output end 3 on the output side 10. In addition, two burst absorbers 16 and 8 are connected respectively between the upper input end 1 and the lower input end 2, and the upper output end 4 and the lower output end 3 for absorbing unnecessary burst waves on the input and output sides when an over-voltage occurs. It should be noted that the copper foils 15 and 14 respectively extending from the upper input end 1 and lower input end 2 form an enclosure 504 and the enclosure has a gap 505 between one end of each of the copper foil 15 and 14 for serving as a first buffer space when the circuit is subject to an over-voltage or an electric strike. Similarly, the copper foils 13 and 12 extending respectively from the upper output end 4 and the lower output end 3 also form an enclosure 502 and the enclosure 502 has a gap 503 between one end of each of the copper foil 13 and 12 for serving as a second buffer space. The enclosures 504 and 502 are divided by a separated space 501, which is used for isolating the input side from the output side. The electronic elements of the printed circuit board are installed in the enclosures 504 and 502.

#The photo coupler 6 is a conventional coupler with an input terminal 601 thereof being placed in the enclosure 504 and an output terminal 602 thereof being placed in the enclosure 502. The other portions of the photo coupler except for the input and output terminals 601 and 602 are installed in the separated space 501. As shown in FIG. 1, the distance of the separated space 501 should be suitable to accommodate the portion of the body of the photo coupler 6, excluding the input terminal 601 and the output terminal 602.

#The arrangement in accordance with the present invention may also be applicable for providing over-voltage protection in transformers, as shown in the second embodiment illustrated in FIG. 2. The transformer shown in FIG. 2 comprises a primary winding 11' and a secondary winding 10' with burst absorbers 16' and 8' connected respectively between upper and lower input ends 1' and 2' of the primary winding and upper and lower output ends 3' and 4' of the secondary winding of the transformer for absorbing abnormal voltage. Two copper foils 15' and 14' extend from an upper and a lower input ends 1' and 2' of the primary winding 11' respectively to a center part of the two windings 11' and 10' to form a first enclosure 504' with a gap 503' provided between the ends of the two foils 15' and 14'. Similarly, two copper foils 13' and 12' extend from an upper and a lower output ends 4' and 3' of the secondary winding 10' of the transformer respectively toward the center part of the two windings to form a second enclosure 502' with a gap 505' provided between ends of the two copper foils 13' and 14'. As mentioned above, the gaps 503' and 505' are used as buffer spaces when an over-voltage or electric-strike occurs. In addition, the enclosures 504' and 502' are separated by a separated space 501' used for isolating the primary winding 11' from the secondary winding 10'. The wider the separated space 501' is, the higher the voltage it can withstand.