LT3384B - Circuit arrangement for protecting electronic subcriber line circuits - Google Patents

Abstract

Electronic subscriber line interface circuits, SLIC, (SLIC1 ... SLICn) are particularly susceptible to, and their function is particularly jeopardised by, overvoltages which occur primarily as a result of the effects of lightning on the subscriber connection lines (Ltg1 ... Ltgn). To protect against overvoltages, circuit arrangements with expensive special components and/or expensive additional circuits are known. The object of the invention is to indicate a protective circuit arrangement with low-cost components which guarantees common protection of a plurality of subscriber line interface circuits (SLIC1 ... SLICn). For this purpose, a conventional mains thyristor (Th) is used according to the invention whose gate control voltage (UG) or cathode voltage (UK) is compared by means of a comparator (K) with a reference voltage (UV) in the blocked state and, in the event of overvoltage, in the through-connected state. In the event of overvoltage, the comparator output voltage causes the subscriber line interface circuits (SLIC1 ... SLICn) to be isolated via a control input (IST) so that the current level falls below the level of the holding current of the thyristor (Th) and the latter reverts to the blocked state following the absence of the overvoltage. <IMAGE>

Description

The invention relates to the field of telephone communications, namely to power line protection circuits, and can be used in electronic subscriber circuits, where the electronic subscriber circuit inputs need to be protected against surges. This type of surge occurs, for example, when lightning strikes a subscriber line. The subscriber circuits connected to these lines, which are increasingly provided with integrated switching circuits, so-called Subscriber Line Interface Circuits (SLICs), are particularly susceptible to overvoltages that can interfere with their functionality.

It is known that in the case of power circuits with a commonly grounded positive voltage pole of the power supply, the positive over-voltage of the subscriber line through the diodes and the negative over-voltages through the diodes and the operating thyristor are directed to the mass.

The known circuitry requires thyristors capable of holding high blocking currents so that in the event of an overvoltage, the conducting state of the thyristor is separated from the current flowing in the subscriber circuit and, at the same time, independent of external overvoltage. However, this high blocking current requires a large current to control the gate of the protective thyristor. In order to reduce the effect of the gate current on the circuit diagram implemented according to German patent DD 281331 A7, the thyristor tuning is performed via an additional transistor circuit.

A circuit diagram for protecting transverse position circuits of subscriber lines is known in which the need for a special protective thyristor control current is reduced by an auxiliary thyristor connected in front of the gate electrode input (see European Patent EP 0247319 JV). In practice, the need for high control current often occurs when multiple subscriber lines are subjected to surges caused by lightning; in this case, the control voltage source is particularly heavily loaded.

Expensive special circuit kits or costly auxiliary circuits must be used to protect the subscriber circuits against surges by known circuit diagrams.

The object of the invention is to provide a protective circuit which can be realized by using cheap, commercially available circuit elements and which at the same time ensure the protection of several subscription circuits.

This object is achieved by a circuit diagram for the protection of subscriber lines against overvoltages, the respective wires of which at least one diode and thyristor located between the diodes form an earth circuit between the subscriber line wire and the mass when the overvoltage occurs. , a thyristor input is connected to a comparator first input, the second input of which is connected to a reference voltage source, and the comparator output is connected to a control input of at least one subscriber circuit.

The essence of the invention is that when an overvoltage occurs, an overvoltage thyristor is activated, which switches off the current flowing through the protected subscriber circuits through a comparator. For this purpose, a control circuit is required in the subscription circuit, but in the case of a monolithic integral, its installation does not entail significant costs. This prevents a large blocking current from flowing from the subscription circuit to the thyristor. In the event of a surge, the thyristor closes automatically and the subscriber circuits continue to operate. Turning on said thyristor has not only a technical advantage, i.e. the low power of the tuning current, but also the cost advantages of having a high volume of production and a simple semiconductor manufacturing technique. By utilizing the circuit diagram of the present invention, multiple subscriber circuits can be protected by a single protection circuit.

The drawing shows an electrical protection diagram.

The invention of the circuit is exemplified in more detail

In the drawing, bl _n is illustrated with the two subscriber-owned subscriber lines 2, 2 _n described below, which consist of wires 3, 4. Other subscriber circuits and subscriber lines are not shown, but may be connected as shown by the connection scheme of the protective circuit. . Subscriber line 2, two voltages _is positive during the first diodes 5, _n 5 and to the second diode 6, _N 6 are connected to mass. A protection circuit to each subscriber line 2, 2 _n, respectively connected to the third diode 7, 7 _n and the fourth diode 8, 8 _n, as well as the thyristor 9, the gate electrode terminals connected to the comparator 10 a first input as well as through a resistor 11 connected to a control voltage U _ST source 12.

In the uninitiated state, the thyristor 9 is closed, the gate operating voltage U _G , e.g., -100 V at the first input of comparator 10, is greater in magnitude than the reference voltage U _v , e.g., -5V at the second input of comparator 10 and comparator 10. the output which is connected to the control input 13 of each of the subscriber circuits 1, l _n is inactive. Instead of the gate control voltage U _G, the cathodic voltage U _{K of the} thyristor 9 can be applied to the first input of the comparator. The latch control voltage U _G is fed from the control voltage U _ST source 12 via a resistor 11 to a thyristor 9.

If negative overvoltages greater than the gate-holding voltage U _G , e.g., 100 V, occur in the subscriber line or subscriber lines 2 ... 2 _n , a thyristor 9 is triggered and together with the third and fourth diodes 7, 8; _N 7, _n 8 consisted of a low connected to the weight circuit. Then, the gate-operated Voltage U _G and the cathodic voltage U _{K have} values U _{G of} about -IV and U _{K of} about -IV and are smaller in magnitude than the reference voltage U _v supplied to the second input of comparator 10. In this case, the comparator 10 output signal is generated, which in each subscriber circuit 1 ... _n l Management Introduction 13 disconnects said circuit power, that is all, without exception, on attached abonementinėse chains of ... the current _is essentially lost. In the event of a negative surge, the subscriber circuits 1.. . l _n can only give a small current, thus the magnitude of the blocking current of the thyristor 9 is unavailable and the thyristor 9 closes. At the same time, the gate control voltage U _G , or the cathodic voltage U _K at the first input of comparator 10, becomes more negative than the reference voltage U _v at the second input of comparator 10, i.e. IU _G I> IU _V I; and in this case, the output signal of the comparator 10, via the control input 13 of each of the subscription circuits 1 ... ln, reconnects the power to the subscription circuits. Due to the very small blocking current flowing through the thyristor 9 when disconnecting the power supply of the subscriber circuits 1 ... ln, it is possible to use inexpensive network thyristors with sufficient current reserve in the proposed circuitry. Until now, the small current blocking the thyristors of the network was the reason that prevented them from being used as protective thyristors for the purpose described.

Claims (3)

DEFINITION OF INVENTION 1. A protective circuit for electronic subscriber circuits, protection of subscriber lines (2 ... 2n) against overvoltages, the respective conductors (3,4) of which are at least one diode (7,8,7n, 8n) and between diodes (7,8, The thyristor (9n) in the 7n, 8n) forms an earth circuit between the wire (3,4) of the subscriber line (2 ... 2n) and the mass, characterized in that the thyristor (9) gates the electrode input through the resistor (11). ) is connected to the control voltage U _ST source (12), the thyristor (9) input is connected to the first input of the comparator (10), the second input is connected to the reference voltage U _v source and the output of the comparator (10) is connected to at least one circuit (l ... ln) control inlet (13). 2. A protective circuit as claimed in claim 1, characterized in that the gate electrode input of the thyristor (9) is connected to the first input of the comparator (10). 3. A protective circuit as claimed in claim 1, characterized in that the cathode of the thyristor (9) is connected to the first input of the comparator (10).