Patent GB-1531279-A (GB)
Title: Electric supply system for providing uninterrupted power to a load
IPC: H02H7/122
Filed: 1975-12-19
Abstract: 1531279 Power supplies GENERAL ELECTRIC CO 19 Dec 1975 [24 Dec 1974 (5)] 52122/75 Headings H2F and H2H An electric power supply system for providing an uninterrupted supply to a load comprises a plurality of power supplies, such as 10, 12 having their outputs connected in parallel to provide a common output voltage VOP, VON for the load, each of the power supplies comprising an inverter 28 having the input thereto controllable by switching means driven by signals B1, B2 in accordance with a desired output thereof, means being provided to generate a current limiting signal so as to sense when the current input to the inverter reaches a predetermined magnitude and which signal is effective to turn off the inverter 28 by control of the drive signals B1, B2. The system output voltage VOP, VON is developed from an unregulated D.C. input INP, INN, by way of the inverter 28, which includes a transformer T1, and a rectifier filter device 30. The inverter 28 is of the pulse width modulated type when the the primary winding of the transformer T1 centre tapped and connected to the D.C. input by way of a current shunt 31, the current flowing alternately in the two halves of the primary winding by the control of transistors receiving signals B1, B2 from a base driver circuit 72. A "crowbar" type circuit 40 is operative to short circuit the output of the rectifier 30 should the output voltage VOP, VON exceed a predetermined maximum. The output voltage of the inverter 28 is compared with a reference voltage developed in a reference regulator and isolator 56 by a high voltage cut-off and isolator circuit 44, a signal appearing on line 46 to a high voltage shut-off latch circuit 48 whenever the inverter output voltage exceeds the reference voltage. The circuit 56 also provides a feedback signal on a line 60 to a feedback circuit 78, which signal is proportional to the difference between the reference voltage and the output voltage VOP. A circuit 64 monitors high and low values of the output voltage VOP, a light-emitting diode being lit to indicate power is present and the output voltage is within limits and an alarm 99 sounding if the output voltage is high. A pulse generator oscillator 66 produces steering signals LOGA; LOGB signals to the base driver circuit 72 whereby to control the inverter 28, and at the same time produces further signals which are fed to the base driver circuit 72, the feedback circuit 78 and a current limit regulator 76. A fast current limit circuit 36 is operative to sense the current flowing in the primary winding of transformer T1 by means of the current shunt 31 and is effective by way of the base driver circuit to turn off the inverter 28 whenever the current in the shunt exceeds a predetermined value. The circuit 36 also provides signals representing the actual value of, and a reference value for, the inverter output current to the current limit regulator circuit 76 the latter circuit being effective to hold the output current constant at a maximum allowable value when the current reaches this value whilst simultaneously allowing the output voltage to decrease. The high voltage shut off latch circuit 48 turns off the inverter 28 whenever the output voltage VOP exceeds a predetermined level and also senses whether the output is present, from another supply, when the inverter 28 is first turned on. A turn off circuit 91 receives a current representing signal from the first current limit circuit 36 and acts to turn off the inverter 28 in an overcurrent condition. A start-up circuit 93 operates to turn on the inverter 28 whenever the inverter is turned off, the circuits 91, 93 acting in a cyclic-manner to turn off-turn on the inverter 28 until the overcurrent condition has disappeared. The circuits 91, 93 together with the circuit 48 act in a similar manner should the output voltage VOP be in an overvoltage condition. A second inverter 22 of the oscillating saturable core type produces various output voltages which are used to power the various circuits of the system 10. The inverter circuits 22, 28 are illustrated in Figs. 15, 16 respectively (not shown).