GB968531A - Arrangement for controlling the brightness of direct current operated illuminating or signalling lamps for example in aircraft - Google Patents

Abstract

968,531. Supply circuits for incandescent lamps. K. DIEHL. Nov. 22, 1962, No. 44112/62. Heading H2H. [Also in Division H3] A system enabling the brightness of a plurality of lamps to be controlled comprises switching means the ratio of the ON to OFF times of which can be varied so that the average current through the lamps can be controlled according to the degree of brightness required. A potentiometer P and switches S 4 , S 5 are operated by a single control knob, the initial movement of which closes switch 5 and places the slider of potentiometer P at the left-hand end so placing all the potentiometer resistance in series with resistor R 3 and transistor T 2 . Transister T 2 thus remains non-conductive for a period considerably longer than transistor T 1 and hence the conductive periods of amplifying transistor T 3 and power transistor T 4 is short compared to the non-conductive periods thereof. With switches S 1 -S 3 closed, the average current supplied to lamps L 1 -L 3 over transistor T 4 will thus be small and the lamps will thus burn with minimum brilliancy. Further rotation of the control knob will move the slider of the potentiometer P to the right, thus altering the portions of its resistance which are in series with transistors T 1 , T 2 to alter their relative conducting periods so that the conductive period of the transistor T 4 becomes increasingly longer relatively to the non-conducting period and thus the brilliancy of the lamps L 1 -L 3 increases. When the slider of the potentiometer P reaches the right hand end of the potentiometer resistance the switch S 4 is simultaneously closed thereby connecting the lamps directly to the supply U B , the lamps then burning at full brilliancy. A relay circuit (see Fig. 7) is provided to give an indication of failure of the system or of the supply. The relay circuit is connected across the emitter-collector path of transistor T 4 such that as transistor T 4 becomes operative a transistor T 5 becomes intermittently conductive to charge a condenser C 3 . When sufficient charge exists on this condenser a transistor T 6 becomes conductive and remains conductive to energize the relay coil R. Failure of either the system or the supply will cause the transistor T 6 , after condenser C 3 has discharged, to assume its non-conductive state to deenergize the relay coil R to provide an indication of failure.