GB924281A - Improvements relating to relays and other electrical switches - Google Patents

Abstract

924,281. Arc-suppressing in switches. M.L. AVIATION CO. Ltd. Nov. 3, 1961 [Oct. 17, 1960], No. 35508/60. Class 38 (5). An arc-suppressing arrangement for an electromagnetic relay or other switch comprises a transistor 6 having its emitter-collector path connected across the switch contacts 2 and its base connected to means which on the opening of the contacts apply a potential to the base to cause the transistor to conduct momentarily. As applied to a relay, Fig. 1, the means for applying the potential to the base comprises a coil 7 inductively related to the operating coil 1 of the relay. The coil 7 may be wound on the coil 1, or on the same former as the coil 1, or on a ferrite core provided with spring clips for fixing it to the coil 1. In the last case the ferrite core, the transistor and any associated components may be potted. Fig. 3 shows an arrangement in which a toggle or limit switch 2 is provided with a permanent magnet 13 which is moved relative to a fixed magnetic part 12 when the switch is opened so as to induce a current in a coil 11 and so render the transistor 6 conductive momentarily. In both arrangements a capacitor 9 may prolong the period in which the bias potential is applied to the base. Also a simple rectifying diode 8 may be connected in circuit with the base, though a bridge rectifier may be used if it is desired that the transistor should also conduct momentarily on closing the switch. In a further arrangement, a capacitor may serve as the means for applying the potential to the base, Fig. 4 (not shown). Reference is also made to the use of a single transistor in conjunction with a number of relays or other switches.