GB660861A - Improvements in and relating to non-linear amplifiers - Google Patents

Abstract

660,861. Magnetic amplifiers. BRITISH THOMSON-HOUSTON CO., Ltd. May 3,1949 [May 7, 1948], No. 11777/49. Class 40 (iv). Relates to magnetic amplifiers designed to produce second harmonic output voltages or signals in response to direct current input signals. In one arrangement a pushpull output is provided together with elimination of second harmonic voltages from the signal circuit. In Fig. 1 series-connected reactor windings 2, 3 around the outer limbs of a three-limb core 1 are connected directly across the A.C. supply 4 and in parallel with a centre-tapped resistor 6 to form a bridge circuit with output taken from terminals 7, 8 connected respectively to a point between the windings 2, 3 and to the centre tap on resistor 6. The latter is precision adjusted to effect bridge balance and eliminate the fundamental frequency component of voltage between output terminals 7, 8. With D.C. applied to signal winding 5 on the centre limb of core 1 the respective flux densities in the top and bottom portions of core 1 reach their maxima during opposite half-cycles of the applied A.C. and this produces a second harmonic output voltage between terminals 7, 8. The theory underlying the action is explained with the aid of a hysteresis curve and current and flux wave forms, Fig. 4 (not shown). Fig. 1 is defective in that second harmonic voltages are induced in the signal circuit and this same defect occurs in another arrangement, Fig. 2 (not shown), wherein the basic element in Fig. 1 is duplicated to provide a push-pull output. If in Figs. 1 or 2 the impedance of the A.C. input circuit is low a choke or filter should be in series therewith. Fig. 3 is similarly a combination of two Fig. 1 basic elements but in this case the design is such that second harmonic voltages cancel out in the signal circuit. In Fig. 3 a phase-shifting network comprising resistors 16, 17 and capacitors 18, 19 provides current through the primary of transformer 20 which is 90 degrees out of phase with the A.C. applied to reactor windings 2, 3 on the first core 1. The secondary of transformer 20 is connected to the reactor windings 12, 13 on the second core 11 so that the fundamental frequency components of flux in cores 1 and 11 are 90 degrees apart to provide voltages 180 degrees out of phase between terminals 7, 8 and 8, 15, respectively. The second harmonic components are also 180 degrees out of phase in the two oppositely wound signal windings 5, 14 so that no second harmonic voltage is induced in the signal circuit. The centre tapped resistors 6, 21 provide means whereby the fundamental frequency components of voltage between terminals 7, 8 and 15, 8, respectively, may be balanced out independently. In all the arrangements an adjustable resistor 9 and capacitor 10 in series between the tap and one end of resistor 6 eliminates from the output any quadrature component of voltage at the fundamental frequency. In Fig. 3 duplication is necessary with tapped resistor 21 similarly associated with resistor/ capacitor combination 22, 23.