GB1449198A - Excitation control circuit for electromagnetic coil - Google Patents

Abstract

1449198 Operating circuits for electromagnetic actuators SQUARE D CO 7 Dec 1973 [21 Dec 1972] 56924/73 Heading H3T An electromagnetic actuator is energised by a high voltage rectifier bridge until the armature engages the magnet wherupon the supply to the bridge is switched off and energisation is continued from a lower voltage rectifier bridge. When current is supplied to the transformer Fig. IT current flows through contacts SW to the gate of triac TR2 so that TR1 conducts and a rectifier bridge 10 is energised. Current is also supplied via transformer Fig. 2T to a rectifying bridge 11 so that a constant current transistor switch T1 T2 conducts to complete the operating path across bridge 10 for a relay coil 30. When its armature 29 has nearly reached the core, switch SW of the relay opens, breaking the control current circuit of triac TR2 so that after a delay provided by a capacitor C1 sufficient to allow the armature to complete its movement, the supply to rectifier 10 is switched off. Operation is thereafter maintained from the lower voltage rectifier 11 via a diode 13 which previously had blocked the higher voltage from the lower voltage rectifier bridge. When the supply to the transformer Fig. IT is broken the energisation is removed and the back emf renders a Zener diode D4 conducting so that the energy dissipates quickly through transistor T2 and T1. The Zener diode alternatively could be connected across transistor T1 or the circuit provided by the transistors could be replaced by a direct connection.