Patent GB-786462-A (GB)
Title: Improvements relating to magnetic amplifiers
IPC: H03F9/04
Filed: 1955-11-10
Abstract: 786,462. Magnetic amplifiers. SPERRY RAND CORPORATION. Nov. 10, 1955 [Nov. 22, 1954], No. 32192/55. Class 40 (4). In a magnetic amplifier in which autoself-excited transductors are connected in a bridge circuit and establish a half-wave rectified output in a load in response to an alternating or a direct current control signal, the control windings are electrically isolated from the signal source during the alternate half-cycle periods of A.C. energization in which load currents flow through the output power windings of the transductors. As shown in Fig. 1, the arms of the bridge may comprise reactor windings A, A<SP>1</SP>, B, B<SP>1</SP>, each associated with a self-exciting rectifier 10-13, magnetic coupling being provided between respective winding pairs A, A<SP>1</SP> and B, B<SP>1</SP>. A fixed bias is provided by windings 19, 20 which are energized over rectifiers 21, 22 from the A.C. energizing supply. In operation, a control signal in windings 17, 18 causes the two cores each associated with a pair of output power windings to saturate at different times in the half-cycle periods during which the power windings are conductive. Between these successive saturation times, a resultant current pulse passes through a load 14, and an unbalanced voltage pulse is induced by the unsaturated core into the control winding circuit. The effect on the controlling source of the induced unbalanced voltage is neutralized by isolating the control source from the control windings during those half-cycles when the output power windings are energized, and the cores of the transductors as a result are acted upon alternately by the energizing supply and the control signal in the manner of a resetting type amplifier. The polarity of a D.C. control signal or the phase of an A.C. signal synchronized with the energizing supply determines the direction of resultant current in the load. In Fig. 1, the control source isolation is effected by a gate comprising oppositely directed rectifiers 26, 27 and high value resistors 29, 30, the gate being opened only during alternate half-cycles of an A.C. reference signal 31 which has a larger amplitude than the control signal and is synchronized with the energizing supply. A resistor 28 and rectifier 33 are also provided and reduce the amplitude of the reference signal acting on the rectifiers 26, 27 in the inoperative half-cycles. In a modification, Fig. 3, the gate comprises transistors 41, 42 which are associated over a transformer 43 with a reference signal obtained directly from the energizing supply. An alternative embodiment, Fig. 4, relates to the use of a full-wave rectifying bridge gate comprising rectifiers 58-61, a high resistance 62 being incorporated in the reference signal circuit. In this Figure the amplifier has two auto-self-excited windings A, B only and the bridge is completed by resistors 51, 53. An alternative amplifier is shown in Fig. 5 which makes use of a centretapped transformer 71 for applying a resultant current to, a load 74. In this arrangement gating is effected by a synchronously-operated relay 80 which is polarized by a rectifier 79. In the final embodiment, Fig. 6, a pair of autoself-excited windings form a bridge with a centre-tapped transformer 94 the primary 95 of which is connected to the A.C. supply. The gating arrangement in this example comprises a commutator 101 driven by a synchronous motor 102. Specification 782,032 is referred to.