GB1468979A - Emergency electricity control device - Google Patents

Abstract

1468979 Emergency lighting systems THORN ELECTRICAL INDUSTRIES Ltd 4 July 1975 [6 Aug 1974] 34649/74 Heading H2H A system for controlling an emergency lighting system which comprises separate emergency lights is provided with means to prevent energization of the emergency lights when the normal A.C. supply is present but which has been switched from the main lights by a lighting control switch to deenergize the main lights. A main lighting system 14 is energized from a normal A.C. supply 10L, 10N by the closure of a main control switch 12. At the same time a transformer 40 in a control circuit 20 is energized, the output of the transformer, by way of diodes 44C, 44D, maintaining an emergency battery 30 charged. The remaining diodes 44A, 44B provide a negative hold off bias signal at a terminal 24 which forms one control terminal of an inverter 28. A voltage is developed at a point 54 by means of a pair of zener diodes 42 and this voltage is effective to render a transistor 50 conductive thereby the positive terminal of the battery 30 is connected to terminal 26 forming a second control signal for the inverter 28. With both the negative hold off bias signal and the enabling bias signal applied to the inverter 28 operation of the inverter 28 is inhibited and the emergency lights 32 remain unenergized. If the mains supply 10 fails with the switch 12 closed the negative hold off bias at terminal 24 disappears and direct current from the battery 30 flows through a circuit including the emitter base junction of the transistor 50, diode 52, winding 36 of the transformer 40, switch 12 and resistor 60. Transistor 50 is thus held conductive so that the battery still supplies an enabling signal to the terminal 26. With this signal and the absence of a hold off bias signal the inverter 28, which is supplied by the battery 30, functions to cause the emergency lights 32 to be energized. Should however the switch 12 be open no enabling signal at the terminal 26 can be developed. Functioning of the control circuit 20 is dependent on no D.C. circuit existing across any of the main lighting units 14. If such a circuit does exist, the lights 14 must be connected to terminals 62 so as to be in series with a switch which may be a thyristor 64 or a relay, the coil of the relay being connected across the diode bridge 44.