Patent GB-1503546-A (GB)
Title: Power supply system for operational amplifiers and other circuit components
IPC: H02H9/02
Filed: 1975-06-10
Abstract: 1503546 Controlling aircraft BOEING CO 10 June 1975 [16 Sept 1974 7 Oct 1974] 24873/75 Heading B7G [Also in Division H2] A power supply system for operational amplifiers and other circuit components used in an analog control system employing a plurality of a signal channels, comprises first and second separate D.C. power supplies, both having output terminals which are respectively positive and negative with respect to a point of common potential, diodes poled to conduct current in one direction connecting each of the positive terminals to terminals in all of the channels for connection to a source of positive potential, and diodes poled to conduct current in the opposite direction connecting each of the negative terminals to terminals in all of the channels for connection to a source of negative potential, wherein the diodes are connected so as to prevent a short in one power supply from draining current from the other power supply. The invention may be used in control systems for aircraft or hydrofoils employing redundancy for safety purposes. Fig. 2 shows the application of the invention to a conventional control system for the port and starboard flaps 42, 44, 46, 48 of the aft foils 41 of a hydrofoil craft, the control system including derivative amplifiers 54, 58, 64 respectively supplying servo elements 56, 60 and 66, 70 and being connected to power supply leads 76, 78. To prevent an unstable craft condition produced by failure of the supply to the operational amplifiers and other circuit elements in any two of the amplifiers 54, 58, 64, their supply leads 76, 78 are connected through respective pairs of diodes 80, 84 and 82, 86 to separate D.C. power supplies 72, 74, whereby the parallel connection ensures continuity of supply should either supply 72 or 74 fail and the diodes prevent a power drain from one supply (e.g. 72) should a short-circuit occur on the other (74). Supply failure actuates a warning device 88, 90. Each supply 72, 74 may comprise an A.C. source feeding a centre-tapped transformer whose output is rectified and filtered, Fig. 1 (not shown). Alternatively a similar supply as shown in Fig. 3 may be used to prevent power supply faults causing mal-operation of the control system and an unstable craft condition. To this end, the transformer 16 of the A.C. and filtered D.C. system comprising members 10, 12, 16, 20, 22, 24, 28, 30, 32, 36, 38, has a saturable core whereby a short-circuit between either terminal 26, 34 and earth, causing saturation of the transformer and the voltage of that terminal to fall, also causes the voltage of the other terminal to fall simultaneously, so that an operational amplifier 40 supplied from terminals 26, 34 will not be driven hard over. Subsequent removal of the short-circuit or similar fault allows the voltages at terminals 26, 34 to simultaneously return to normal. If the voltage at terminal 26 or 34 exceeds a predetermined value, a Zener diode 92 or 94 breaks down to cause saturation of the transformer and reduction of the voltage across its secondary winding 18.