GB769186A - Improvements in or relating to magnetic amplifiers - Google Patents

Abstract

769,186. Magnetic amplifiers. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. May 27, 1955 [June 8, 1954], No. 15356/55. Class 40 (4). In a magnetic amplifier in which the level of magnetization of a saturable core is set in one direction by a control circuit and is subsequently taken back to saturation by a firing circuit, the firing circuit includes a transistor 26 connected with windings 24 and 28 such that when current flows through coil 24 from a D.C. source 22, winding 28 holds transistor 26 conductive, but when saturation is reached no further voltage is induced in coil 28 and transistor 26 ceases to conduct. Conduction through the transistor 26 is initiated by a pulse applied to terminals 36, the pulse being of greater magnitude than the bias 62 which normally holds the transistor unconducting. The control circuit may simply comprise a winding 40 to which an input signal is applied, but as shown it includes a transistor 60 and a winding 70 to break the circuit of the winding 40 during the interval when transistor 60 conducts. This is effected by winding 70 in which a voltage is induced to overcome the bias of 72 and prevent transistor 60 conducting. A load 12 is connected to a winding 44 which may alternatively be connected in series or parallel with winding 24. The period during which the control voltage sets the core 16 may be of longer duration than the period during which the transistor 26 is caused to conduct. In consequence the power output at the load 12 during a firing period will be greater than the power input during a setting period. The control coil 40 may be dispensed with and the control voltage can be applied directly across the coil 24. If the control voltage is allowed to take the core 16 from saturation in one direction to saturation in the other direction, the sudden increase in current in the control winding on reaching saturation may be utilized to set the transistor 26 in the firing circuit conducting. As shown in Fig. 4, the transistors 26 and 60 may be held alternately conducting and non-conducting by voltages in windings 86 and 88 of a transformer, the primary winding 84 of which is fed with an alternating voltage having a square waveform.