GB894185A - Improvements in and relating to magnetic amplifiers of the flux-reset type - Google Patents

Abstract

894,185. Magnetic amplifiers. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Nov. 10, 1958 [Nov. 13, 1957], No. 35411/57. Class 40 (9). In a two-stage full-wave magnetic amplifier secondary windings on a transformer 1 during any given half-cycle supply excitation for a load winding 9 or 9<SP>1</SP> of the first stage while supplying excitation for a control winding 7<SP>1</SP> or 7 of the second stage, current in both windings passing through a rectifier 3 common to both circuits. As shown in Fig. 7, the transformer 1 feeds four secondary windings 2a<SP>1</SP>, 2a<SP>11</SP>, 2b<SP>1</SP> and 2b<SP>11</SP>. During a half-cycle in which the windings 2a<SP>1</SP>, 2a<SP>11</SP>, are positive with respect to the centre tap CT, current flows over rectifier 5, resistor 4, and rectifier 3, to CT. Current also flows in reverse through rectifier 3 through control winding 71 and rectifier 8<SP>1</SP> and in parallel through load winding 9<SP>1</SP> and rectifier 10<SP>1</SP>. When load winding 9<SP>1</SP> becomes low impedance after an interval determined by control current in winding 11 of the first stage, control winding 7<SP>1</SP> of the second stage is short-circuited and current flows solely through rectifiers 3 and 10<SP>1</SP> and load winding 9<SP>1</SP>. Since the saturation time of winding 9<SP>1</SP> governs the reset time of winding 7<SP>1</SP> the input to the first stage governs the output to load L in the following halfcycle. During a half-cycle in which windings 2b<SP>1</SP>, 2b<SP>11</SP>, are positive with respect to CT winding 7 is reset for as long as it takes winding 9 to saturate, rectifier 3 being opened to reverse conduction by current over rectifier 6. Secondary windings 2a<SP>11</SP> and 2b<SP>11</SP> may be omitted, rectifiers 5 and 6 being connected in common with rectifiers 8, 10 and 8<SP>1</SP>, 10<SP>1</SP>, provided windings 9 and 9<SP>1</SP> are given a higher current rating. To block back coupling between the windings 9 and 9<SP>1</SP> through control winding 11 when the control source has a low impedance, a bias voltage is connected into the idle half of the inter-stage coupling during each halfcycle. As shown in Fig. 8, this is achieved by use of two rectifiers 31 and 3<SP>11</SP> with alternating off-centre taps CT1 and CT2. Alternatively, a rectified bias voltage may be generated across a resistor in series with rectifier 3 of Fig. 7 or separate such bias resistors may be included in series with each rectifier 10 and 10<SP>1</SP> (see Figs. 10 and 11, not shown). To provide an improved resetting current waveform the resistor 4 is preferably given some inductance.