FI79427B - KOPPLINGSANORDNING FOER OEVERSPAENNINGSSKYDD VID ANSLUTNINGSKOPPLINGAR. - Google Patents

Abstract

1. A circuit arrangement for surge voltage protection of interface circuits (SLIC 1 to SLIC 3) constructed of semiconductor components and connected in groups to a supply voltage source to connect two-wire, analogue subscriber connection lines (TL) to telephone exchanges, where the circuit arrangement contains, in respect of each interface circuit, a diode bridge whose diodes (D1 to D4) are normally biased in the blocking direction by the supply voltage and which has one diagonal connected to the two wires of the subscriber connection line (TL) in question and its other diagonal connected to the supply voltage via at least one blocking element (Da, L) which assumes the blocked state when a surge voltage occurs and is common to a plurality of interface circuits, and where the circuit arrangement likewise contains by-pass circuit elements (C, V) common to a group of interface circuits via which leakage currents are diverted from the last-mentioned bridge diagonal to a circuit point which carries reference potential on the occurrence of a surge voltage, characterised in that by-pass circuit elements (C, V) are used which flatten and/or limit voltage swings occurring on the occurrence of surge voltages across the bridge diagonal to which they are connected.

Description

and 79427

Switchgear for overvoltage protection of connection connections

The invention relates to a switching device for overvoltage protection which is used in connection with connection connections made of semiconductor elements and which are connected in groups to a supply voltage source and are intended for connecting two-wire analog subscriber lines to telephone exchanges.

Connections of this type, comprising e.g. reception transmission amplifiers, devices for digital-to-analog conversion and analog-to-digital conversion, and reception and transmission filters, are exposed to the effects of the environment, which can be reached through the subscriber lines connected to them, for example in the form of lightning strikes. Known measures for overvoltage protection in such connection circuits are to use diode bridges whose diodes are biased by the distribution voltage normally in the blocking direction and are reversed in the presence of overvoltages, and thus become conductive. The use of shut-off elements through which the distribution voltage is applied to the second diagonal of these diode bridges and which are mapped so that they switch to the closed state in the event of overvoltages prevents the subscriber line , to other components connected to the distribution line.

In a known case, said charge is conducted via bypass elements to a switching point in the reference potential, for example to the body mass. These switching elements are in a known case thyristor elements which, for reasons of cost and space, are arranged only individually in a group, i.e. bridge connections between the two common connection points of the second diagonal in each case and the connection point leading to the reference potential.

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When overvoltages occur in such a switching device on a given subscriber line, the diodes of its bridge connection and also said bypass elements become conductive, this causes that connection to be effectively protected, but also to operation is disrupted.

It is therefore an object of the present invention to avoid such interference in the connection connections in question directly in a protective circuit of the type mentioned above.

According to the invention, this object is solved by using bypass switching elements which smooth and / or limit the voltage fluctuations formed in the bridge diagonals connected to them in the event of overvoltages, i. stabilizing auxiliary voltages.

Said stabilization of the potentials, which means that they have regularly achieved only a small overvoltage by the end of only a short-term overvoltage load, eliminates the effect on other terminals not directly exposed to overvoltage in the group, so that there can be no incorrect operation of the coupling devices. response.

According to other embodiments of the invention, the bypass switching elements can be implemented according to practical needs in the form of a capacitor, zener diode or varistor, or by means of a parallel connection of a capacitor and a zener diode or varistor, as well as in the form of a suitable voltage-stabilizing semiconductor circuit.

In the example assumed in the figure, three connection connection fields SLIC 1 to SLIC 3 are assembled into one group, which in each case operate to connect the subscriber connection line TL to a relay station not shown here. Since the subscriber connection lines 3 79427 are two-wire lines for transmitting analog signals, such connection connections must assume the existence of a digital transmission station in which the switching takes place in four conductors, e.g. an apparatus for analog-to-digital conversion or counter to digital-to-analog conversion, and receiving or receiving, transmission filters and forks for a two-wire / four-wire shift arranged thereon. Furthermore, as part of these connection connections, the receivers include a transmission amplifier, a switching device for loop assignment and possibly means for paging power supply and inspection. Most of these components are formed using semiconductor elements that must be shielded from voltages that may enter them through the subscriber line.

A bridge connection consisting of four diodes is provided for each connection connection. The second diagonals of these bridge connections (in the bridge connection for SLIC 1 are the connection points of diodes D1 and D3 or vast, diodes D2 and D4) are connected to all three connection connections to the common distribution line V11 and V12. The diodes are biased at this distribution voltage normally ... in the blocking direction. Other diagonals of bridge connections (ie

in the case of said bridge connection of the connection connection SLIC 1, the diodes D3 and D4 or resp. D1 and D2) are connected to one conductor of the subscriber line in question.

’: The supply voltage is supplied to the distribution lines V11 and V12 via individual shut-off elements, in this case the series switching of diodes Dal and Da2, which is normally used in the discharge direction and controlled in the event of overvoltages, and the inductive switching elements L1 and L2.

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The switching device further likewise comprises group-specific bypass elements which connect the end points of the bridge diagonals in the distribution lines V11, V12 to the switching point conducting the reference potential, preferably to the body mass. In the case shown, these bypass elements consist in each case of a parallel connection of a capacitor C and a varistor V, i.e. a voltage-stabilizing resistor.

For example, when a lightning strike causes one of the subscriber interface lines TL to overvoltage, depending on the polarity of this voltage, two diodes of that diode bridge become conductive, so that the charge on the subscriber line due to this overvoltage can flow through the bypass elements C / V. Due to the switching characteristics of the bypass elements, on the one hand, there is a low-ohmic path for the bypass current, but on the other hand it is ensured that the voltage in these bridge diagonals rises only relatively little, so it cannot reach the maximum value due to the short duration. This is due to the capacitor C on the one hand, but also to the stabilizing effect of the varistor on the other hand. The DC voltage potential at these switching points therefore changes only so little that other non-direct overvoltage connection circuits, which are also at these switching points, cannot have an undesired effect which results in an incorrect response.

In principle, a correspondingly dimensioned capacitor alone would also suffice as a bypass element, which, however, should then have a large capacitance, depending on the conditions. In the shown parallel connection of the capacitor and the varistor, one capacitor with a small capacitance is sufficient. Instead of a varistor, a zener diode or a semiconductor circuit having a corresponding current voltage characteristic can also be used, depending on the conditions, it is sufficient to use a zener diode or a varistor or such a semiconductor circuit without an additional capacitor.

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In such an overvoltage effect, the diodes Da of the closing elements change to a closed state, so that the effects on other groups of connection connections or other parts of the switching center connected to the supply power supply are excluded.

Claims (7)

1. Surge protection coupling device when using interfaces (SLIC 1 - SLIC 3), which are constructed with semiconductor elements and which are connected in groups to a supply voltage source and which are intended for connection of two-pronged analogue subscriber lines (TL) to television switches, which for each interface have a diode bridge with diodes (D1-D4), which are normally biased by the supply voltage in the blocking direction, whereby one bridge diagonal is connected between the two trees in the corresponding subscriber line and where the supply voltage is connected over the other bridge a blocking element common to several interfaces (Da, L), which in case of an overvoltage transfers to a blocked state, and wherein the diverter element (C, V), which is also common to a group of interfaces, through which the conducting currents from the latter bridge diagonals in the event of an overvoltage are brought to a circuit point with reference potential, characterized in that the diverter elements (C, V) are used, which upon occurrence of overvoltages, there are arranged to flatten and / or limit voltage peaks at the bridge diagonals associated with them. Device according to claim 1, characterized in that the diverter elements are capacitors (C). Device according to claim 1, characterized in that the diverter elements are zener diodes.