Patent GB-798240-A (GB)
Title: Two-stage half-wave magnetic amplifier
IPC: H03F9/02
Filed: 1957-01-18
Abstract: 798,240. Magnetic amplifiers. SPERRY RAND CORPORATION. Jan. 18, 1957 [Feb. 2, 1956], No. 1892/57. Class 40 (4). A magnetic amplifier consists of first and second transductor stages both of the resetting type, the first stage comprising cores 6, 8 having control windings 5, 7 energized by A.C. or D.C. signals which influence the simultaneous halfwave outputs of power windings 11, 14 in opposite respects, while the second stage comprises cores 43, 44, the power windings 21b, 24b, 31, 33 of which are arranged in bridge connection and have portions 21a, 24a which function as control windings and are separately energized by the outputs of power windings 11, 14. As shown, full energizing voltage from an A.C. source is applied to the power windings 21b, 24b, 31, 33 of the second stage transductor over terminals 19, 20, and a reduced voltage derived from a potentiometer 17, 18 is applied to the power windings 11, 14 of the first stage. A still lower voltage developed across an adjustable potentiometer 28, 29 is applied to the first stage over an adjustable resistor 26 and rectifiers 12, 13, this voltage functioning to reset the cores 6, 8 during the alternate half-cycles when the rectifiers prevent current conduction through the power windings 11, 14. A resistance 47 adjustably connected to one of a number of tappings on each of the windings 11, 14 provides a positive feedback path for currents induced in winding portions 21a, 24a during the non-conducting periods of the first stage, the induced currents being established by load current through a power winding 21b or 24b depending on the operating asymmetry of the bridge circuit as determined by the control currents in the preceding half-cycle period. The second stage transductor cores 43, 44 are reset in alternate half-cycles by the control currents from the first stage in windings 21a; 24a, and the power windings are permitted to conduct by rectifiers 30, 32, 34, 35 in the remaining half-cycles. A difference in degree in the resetting of the individual cores 43, 44 by dissimilar control currents from the first stage in a preceding half-cycle causes one core to become saturated before the other during an output half-cycle, thereby unbalancing the bridge and establishing output current in a load 40 in a direction determined by the polarity or phase of the input signal in control windings 5 and 7. Output current terminates when the second core saturates and rebalances the bridge. A self-biasing circuit is provided by a low-pass filter comprising inductor 45 and resistor 46. The amplifier includes overall negative feedback which is taken from across the load, and is combined with a demodulating voltage from terminals 19, 20 in a stabilization circuit 50 before application to the control windings 5, 7 of the first stage over a variable resistor 55. The stabilization circuit is shown in greater detail in Fig. 6 and comprises a full-wave demodulator and a series combination of capacitance 57, resistance 58 and inductance 59 which prevents feedback when the input signal remains constant. Fig. 6 also shows the circuit connections for the amplifier to be utilized in controlling the direction of rotation of a twophase servomotor 60 having individual phases 40<SP>1</SP>, 61.