Patent GB-791905-A (GB)
Title: Improvements in or relating to circuit arrangements for producing substantially constant currents
Inventor: RIDLER DESMOND SYDNEY
IPC: G11C19/04
Filed: 1954-12-31
Abstract: 791,905. Circuits employing bi-stable magnetic elements. STANDARD TELEPHONES & CABLES, Ltd. Dec. 31, 1954, No. 37787/54. Class 40 (4). When a core having a substantially rectangular hysteresis loop is in a remanent condition in one direction of magnetism and a voltage is applied to an input winding in such a direction as to drive the core towards saturation in the other direction, the current through the winding inherently remains at a substantially constant and limited value during the time in which the core is changing its magnetic condition along the vertical portion of the hysteresis loop. As soon as the saturation condition is reached, an immediate increase in current takes place. The limited current period may be repeated by resetting the core, either by the use of a further winding or by reversing the voltage, control being effected over an electronic circuit. By connecting a load to an output winding on the core, a constant load current having an amplitude determined by the load and of limited duration is obtained which has the effect of increasing the transient input current. A constant current load transient is also obtained when the core is reset, but since its direction is reversed, suppression by a half-wave rectifier may be necessary. The amplitudes of the load and input currents may be limited to a constant value, whatever the value of the load, by connecting a winding of a second core 8, Fig. 4, in series with the input winding of the first core 9. In this case the second core has a rectangular hysteresis loop but this requirement in the first core is not essential. The second core has either fewer turns or an increased core length so that the changeover current of core 8 is higher than that of core 9. Core 8 also has a smaller crosssection so that it has the shorter switching time of the two cores. The load current produced during changeover of the cores is then limited, in the primary circuit, by the changeover current of core 8, the voltage being removed before this core saturates. For a constant load current it is essential that the load resistance does not exceed a critical value, Fig. 5 (not shown). A suggested application for the circuit is the formation of a pulse of definite amplitude from a master pulse of longer duration. In an alternative arrangement, Fig. 6, three cores 10, 11, 12 having different rectangular hysteresis characteristics produce a series of three staggered pulses which may have different amplitudes. Such an arrangement may be used as a distributer or to provide certain types of pattern movement for shifting registers and counters. The cores are arranged with their input windings in series and are selected such that an applied voltage causes one core to take a constant transient current which is below that needed to commence flux changeover in any of the other cores. When flux transition of the first core terminates, the current increases sufficiently to commence transition in a second core. Similarly, after a further time interval, a further increase in current triggers a third core. Thus a stepped input current pattern is obtained as shown in upper part of Fig. 7, while the individual output windings each produce a pulse in a different time position as shown in the lower part of the same Figure. The cores 10, 11, 12 may have non-rectangular characteristics, in which case a current-limiting core of rectangular characteristic and longer changeover time is connected in series. In a modification, the three cores can be arranged to commence changeover at the same value of current, and saturate at different times, so as to produce three output pulses commencing at the same time and of different lengths.