JPH0799903B2 - Voltage surge protection circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a voltage surge protection circuit for protecting a home device from a voltage surge caused by a lightning strike.

(Prior Art) Currently, office telephones, button telephones, and the like are widely used, and a plurality of office lines are efficiently used in telephones. It is also possible to talk between extension telephones. The home appliances used for these have been conventionally used in the same building, but are often installed in another building such as an office building or a factory building. If the home equipment is installed in the same building, it would have been sufficient to provide lightning protection between the central office line and the facility in the office, but if it is a separate building, the wiring between the home equipment will be outside, so here It is necessary to take measures against lightning.

Fig. 2 shows the outline of the equipment arrangement in the home.
Main equipment ME and telephones TEL ₁ and TEL ₂ are installed in the factory, and telephone TEL ₃ is installed in the factory building 2. A plurality of these telephones are installed as needed. 3 is the main device ME and telephone
This is an outdoor line that connects to TEL _3, and is overhead wired. Fig. 3 shows the interface circuit of the main unit,
Is a power supply terminal for communication, T is a transformer, T ₀ is a voice signal input terminal, Q ₁ and Q ₂ are transistors, C _{1 to} C ₃ are capacitors, and R _{1 to} R are
₅ is a resistor, T ₁ and T ₂ are main device side terminals, T ₃ and T ₄ are telephone side terminals 3 are outdoor lines. The telephone TEL ₃ is connected to the telephone terminals T ₃ and T ₄ , but it is not shown.

(Problems to be Solved by the Invention) In the conventional arrangement and circuit shown in FIG. 2, when a lightning strike occurs on the outdoor line 3 and a voltage surge occurs, the transistors Q ₁ , Q _2, etc. mounted on the interface circuit are generated. Is directly damaged by a voltage surge of several tens of KV. Further, there is a problem that other parts and devices are damaged.

In order to solve the above problems, it is an object of the present invention to provide a voltage surge protection circuit of a four-terminal circuit in which a surge absorbing constant voltage element and a diode are combined.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention has an input terminal and an output terminal of a four-terminal circuit having a pair of input terminals on the main device side and an output terminal on the lightning surge intrusion side, respectively. Insert a diode so that they will be in opposite directions, and insert two surge absorbing constant voltage elements in series between the output terminals,
A gist of a voltage surge protection circuit is characterized in that a connection point of the surge absorbing constant voltage element is grounded.

(Operation) The present invention has an effect of grounding a voltage surge caused by lightning through the surge absorbing constant voltage element and protecting various parts by the diode reverse direction voltage.

(Examples) Examples of the present invention will be described below with reference to the drawings. It is needless to say that the embodiment is merely an example, and changes or improvements can be made without departing from the spirit of the present invention.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 1 is a diagram showing two extension circuits. In the figure, ME ₁ M
E ₂ is the main device, A, B, are call power terminals, T ₁ , T ₂ are transformers,
T ₀₁ and T ₀₂ are voice signal input terminals, Q ₁₁ and to Q ₂₂ are transistors, T ₁₃ and to T ₂₄ are telephone side terminals, 3 is an outdoor line, and the call current is the same as the conventional power source terminal A for call. , B respectively, via transistors Q ₁₁ , Q ₁₂ and Q ₂₁ , Q ₂₂ , respectively,
Audio signals are supplied from audio signal input terminals T ₀₁ and T ₀₂ via transformers T ₁ and T ₂ , respectively. U ₁ and U ₂ are the voltage surge protection circuits of the present invention, and are composed of a four-terminal circuit consisting of the input terminals on the main device side of TI ₁₁ and TI ₁₂ and the output terminals on the lightning surge intrusion side of T 0 ₁₁ and T 0 _12. Then, a series circuit of surge absorbing constant voltage elements MOV ₁₁ and MOV ₁₂ is connected to the output terminals T0 ₁₁ and T0 ₁₂ side, the connection terminal TE ₁ is connected to the ground E, and the input terminal TI ₁₁ and the output terminal Diodes D ₁₁ and D ₁₂ are inserted and connected between the terminal T 0 ₁₁ and between the input terminal TI ₁₂ and the output terminal T 0 ₁₂ so as to be in opposite directions to the input and the output, respectively.

In such a configuration, when there is a lightning strike on the outdoor line 3, the voltage surge caused by the lightning strike is a constant voltage element for surge absorption MOV ₁₁ , MOV.
It flows to the ground E through V ₁₂ . However, when the surge absorbing constant voltage elements MOV ₁₁ and MOV _{12 are} used as the protection circuit,
High voltage is generated at the main device side terminals T ₁₁ and T ₁₂ due to operation delay of the surge absorbing constant voltage elements MOV ₁₁ and MOV ₁₂ and imbalance of various components. Therefore, this high voltage is applied to the diodes D ₁₁ and D
The reverse withstand voltage of ₁₂ causes the burden, and finally the surge absorbing constant voltage elements MOV ₁₁ and MOV ₁₂ cause the current to flow to the ground E. In this way, other components including the transistors Q ₁₁ and Q ₁₂ of the interface circuit are protected from the voltage surge caused by lightning strike.

When a surge absorbing constant voltage element is used, only a few KV of voltage surge can be protected, while a diode together can protect against a few tens of KV of voltage surge.

(Effect of the Invention) As described above, the present invention provides a mutual connection between each input terminal and output terminal of a four-terminal circuit having a pair of input terminals on the main device side and an output terminal on the lightning surge intrusion side. By inserting a diode so that it is in the reverse direction, and inserting two surge absorbing constant voltage elements in series between the output terminals and grounding the connection point of the surge absorbing constant voltage element, It is possible to provide a protection circuit against several tens of KV voltage surges with a simple circuit configuration using few parts and inexpensive components.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a schematic diagram for explaining the arrangement of home appliances, and FIG. 3 is a diagram showing an interface circuit of the main device. U ₁ , U ₂ …… Voltage surge protection circuit TI ₁₁ , TI ₁₂ …… Input terminal T0 ₁₁ , T0 ₁₂ …… Output terminal MOV ₁₁ , MOV ₁₂ …… Surge absorption constant voltage element D ₁₁ , D ₁₂ …… Diode

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shinichi Shinohara 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Toru Matsushima 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. (56) Reference JP-A-63-73826 (JP, A)

Claims (1)

[Claims] 1. A diode is provided between each input terminal and output terminal of a four-terminal circuit having a pair of input terminals on the main device side and an output terminal on the lightning surge intrusion side so that they are in opposite directions. A voltage surge protection circuit characterized in that, in addition to being inserted, two surge absorbing constant voltage elements are inserted in series between output terminals, and a connection point of the surge absorbing constant voltage elements is grounded.