Protective circuit arrangement for electronic subscriber line interface circuits

摘要

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>