Patent GB-1123183-A (GB)
Title: Electric power control circuits
IPC: H02M3/315
Filed: 1965-08-23
Abstract: 1,123,183. D. C. converting. GENERAL ELECTRIC CO., 23 Aug., 1965 [14 Sept., 1964], No. 36147/65. Heading H2F. A circuit for supplying a controllable D.C. voltage to a load in accordance with the mark-to-space ratio of current flowing through a controllable device comprises an autotransformer in series with the device across a D.C. source, means for initiating conduction of the device in accordance with a control signal which is independent of the load voltage, and similarly directed rectifiers connecting tappings on the transformer to a common load terminal. As shown in Fig. 1 a silicon controlled rectifier 11 is connected to one end of an autotransformer winding 12 and a tapping 17 is connected to the negative supply line. Rectifiers 25, 28, are connected to tappings on either side of tapping 17. These are connected so as to apply to the load the voltages appearing when the flux changes due to the conduction and non-conduction of rectifier 11. A capacitor/saturable inductor commutation circuit 22 is provided for this rectifier. A diode 33 limits the voltage at the other end of the transformer winding to the supply voltage. Fig. 2 (not shown) discloses an arrangement wherein a transistor replaces the S.C.R. and the tappings 31, 17, 32 are not symmetrically disposed. Fig. 3 (not shown) discloses a step-up arrangement wherein the diodes 25, 28 are connected to the ends of the winding and the rectifier 11 and diode 33 to the tappings. The rectifier 11 in this circuit is a " gate-turn-off " S.C.R. A breakdown device is included in the gate circuit and this conducts at a predetermined voltage to cause a capacitor to discharge reversely through the cathode gate circuit of the rectifier to shut this off. Fig. 4 (not shown) discloses an arrangement similar to that of Fig. 3, but in which the controlled rectifier has both turn on and turn off electrodes and is connected to the negative supply line. Fig. 5 (not shown) discloses an arrangement similar to Fig. 1 but in which the connections of the diodes 25, 28 and tapping 17 are reversed with respect to the load. Two operational modes are possible: (a) low voltage/high current in which the " on " to " off " ratio of the rectifier is small and the operation is as described above; (b) high voltage/low current in which the " on " to " off " ratio is high and the transformer core operates near saturation. The commutation circuit includes a further controlled rectifier and L.C. circuit and a diode. In this and in later embodiments the " on " to " off " ratio may be altered by varying the frequency whilst maintaining a fixed " on " period. Fig. 6 (not shown) discloses a transistor controlled arrangement with only one rectifying diode which operates on the " on" stroke. The second diode carries the current flow due to the inductive load circuit during the " off " period. With a high " on " to " off " ratio the rectifier operates substantially as an on/off switch between the source and the load i.e. low voltage/high current conditions. With a small " on #to " off" time normal high voltage/low current conditions occur. Fig. 7 (not shown) discloses a push pull arrangement using transistors. Fig. 8 (not shown) discloses a push pull arrangement operable like Fig. 5, in two modes, and utilizing d.v./d.t. fired S.C.R.'s. These operate with an open circuited gate and the Specification discloses the circuitry necessary to provide the firing pulses. Fig. 9 (not shown) discloses a push pull variation of Fig. 6, operable in the aforesaid modes. Fig. 10 (not shown) discloses a further push pull transistor arrangement wherein under low frequency conditions a high voltage/ low current mode obtains. If however the on to off ratio is increased by increasing the frequency overlapping rectifier operation occurs and the arrangement acts as a chopper giving a high voltage/high current output. Fig. 11 shows a further push pull arrangement. With switch 84 open and at low frequency the arrangement operates in a low voltage/ high current mode. With increasing frequency the voltage rises until with overlap a high voltage/high current mode obtains. The switch 84 may then be opened when the supply to the load takes place through a rectifier 85 acting as a chopper, in which case diode 86 serves as a coasting diode for the inductive load. Fig. 12 (not shown) discloses an arrangement similar to Fig. 11, in which the separate third rectifier 84 is dispensed with, the rectifiers 11, 11<SP>1</SP> and associated switches being used instead.