ES345659A1 - Relay latching circuit - Google Patents

Abstract

Faults in a load 30, of the type requiring a fast power cut-off in the event of such faults, are sensed by current-sensing network 31 which provides a short pulse to transistor 13 to turn it on and hence operate fast acting relay 11 to cut-off the power to the load. Operation of relay 11 also supplies latching current through concontacts 11-1 and transistor 18 for transistor 13, maintaining transistor 13 conductive even after the cessation of the pulse from network 31 so that slow acting relay 12 eventually energizes to close contacts 12-1, thus latching the circuit, and also operating contacts 12-2 . . . 12-5, to cut the current to power-on indicator lamp 32, complete the circuit to fault indicator lamp 33, and to perform other switching operations. The circuit is reset by momentarily opening switch 14. In Fig. 4 (not shown), a number of latching circuits are connected in parallel, each circuit having a slow relay, but there being a single fast relay common to all circuits. When an input signal is received at any one circuit, the fast relay and consequently the slow relay of the one circuit are energized, and operation of all the other circuits is inhibited, the inputs of all these circuits being connected to the negative terminal of the battery through the conductive emitter-collector path of the transistor 13 of the one circuit.