Patent GB-772559-A (GB)
Title: Improvements in and relating to magnetic amplifiers
IPC: H03F9/04
Filed: 1955-04-19
Abstract: 772,559. Magnetic amplifiers. GENERAL ELECTRIC CO. April 19, 1955 [April 19, 1954], No. 11300/55. Class 40 (4). A half-wave magnetic amplifier is combined with a saturable inductor in such a way that for a half-wave input the saturable inductor delivers an output during the non-conducting halfcycles of the amplifier so that a full-wave output is produced.. In Fig. 1 a half-wave input is applied to winding 12 of the amplifier core 21 and an A.C. source is applied to terminals 18. A rectifier 16 in series with main winding 15 on core 21 ensures that core 21 and saturable inductor 13 are saturated when rectifier 16 ends a conducting and a non-conducting half-cycle respectively. The dimensions of core 21 and inductor 13 are such that neither can be saturated from an unmagnetized state by one half-cycle of the A.C. source. When 16 is not conducting the input to coil 12 withdraws core 21 from saturation and during the time 16 conducts core 21 fires at a firing angle dependent on the input, while inductor 13 is withdrawn from saturation until shunted by main winding 15 when core 21 fires. During the next half-cycle when 16 is not conducting inductor 13 fires with an angle equal to that at which core 21 fired in the preceding half-cycle. A full-wave alternating output is therefore produced across load 17 with inductor 13 supplying an inverted replica of the output supplied through main winding 15 in the preceding half-cycle. The output as above described is unsymmetrical, as when 16 conducts the load takes magnetizing current from both core 21 and inductor 13, while when 16 blocks main winding 15 magnetizing current of inductor 13 alone is passed. To balance the output a transformer 24, resistor 28 and rectifier 27 are arranged to draw a current in parallel with load 17, the average value of which equals the average value of the magnetizing current passed by main winding 15. In Fig. 6 a load 17 is shown connected across a bridge which produces a fullwave rectified output. The inductor 13 is set back from saturation during a conducting halfcycle of the rectifier 16 by means of current induced in a winding 35 on core 21. A feedback winding 33 in series with the load ensures that for maximum current output, despite back leakage across rectifier 34, core 13 can still be held saturated. Rectifiers 27 and 37 block the winding 35 when inductor 13 delivers output current. An arrangement analogous to that of Fig. 6 and using a centre-tapped transformer is also described (see Fig. 4, not shown). In Fig. 7 a centre-tapped transformer is shown with a load 17 to which a full-wave rectified output is delivered. The inductor 13 is set back from saturation by the application of a half-wave of current from a winding 46 on the transformer in series with the load 17 and a winding 45 on the inductor. Current is passed through winding 45 until core 21 fires when the output current delivered to the load backs off the voltage applied by transformer winding 46. So as not to draw induced current from the input windings 12 of the embodiments a current limiting arrangement such as high resistance 19 may be placed in the input circuit. Alternatively the input may be taken from the stage of half-wave pre-amplification shown in Fig. 2 which comprises a transformer 61 with a primary winding across the A.C. supply 18 and a secondary winding delivering a half-wave input to the input winding 12 under the control of saturable reactor 63. A rectifier 66 and resistor 65 bias the winding 12 to inhibit induced currents during half-cycles in which core 21 fires.