Patent GB-767371-A (GB)
Title: Bistable state circuits
IPC: H03K3/49
Filed: 1955-02-02
Abstract: 767,371. Ferro-resonant circuits. NATIONAL CASH REGISTER CO. Feb. 2, 1955 [March 22, 1954], No. 3035/55. Class 40(4). Two ferro-resonant circuits Pa, Pb connected in parallel are separately associated with inductive loads and operate as a trigger-pair in response to a triggering pulse common to both circuits, the inductive loads causing the circuits to change to opposite stable current states by producing transient voltage changes each time the trigger pulse is applied. As shown in Fig. 1, the circuits Pa, Pb are series resonant and comprise saturable inductors L1, L2 and capacitors C1, C2 connected in parallel to a low-impedance alternating supply X through a common capacitor C3, a short-circuit path for direct currents being provided by a choke 7. Outputs are taken across the condensers C1, C2 and are applied to separate loads over rectifiers 17a, 17b and filters 18a, 18b, each comprising a series inductor 19a, 19b and shunt resistance and capacitance. The value of C3 is so chosen that only one of the ferro-resonant circuits at a time can operate in the stable series-resonance condition. When a trigger pulse is applied to inductor windings 14, 15 from terminal 8, the inductor in the offresonance circuit is also saturated and this circuit brought into series resonance. As both circuits are then resonant, an increased voltage drop is obtained across C3 with the result that the voltage across one condenser C1, C2 falls and across the other rises. The load currents change as a consequence, but due to the selfinduced voltages of the series inductors 19a, 19b, the transient conditions are prolonged. Since the current in the circuit formerly resonant is decreasing, the circuit is effectively damped during the transient condition and passes to the off-resonant state when the trigger pulse terminates. The other circuit then takes over the stable resonant condition. An essential requirement is that the pulse terminates before stabilization of the transient load-current conditions. In a modified arrangement, Fig. 4, the trigger pulse is applied directly to the ferroresonant circuits over non-linear resistors 26, 27, and the inductors L1, L2 are arranged with mutual inductance coupling in place of the capacitor C3. This coupling is arranged to have an opposing relationship when both circuits Pa, Pb take the same current, and as this condition is unstable one circuit will proceed to resonance and the other to the off-resonance states. When the trigger pulse is applied to the circuits,it is mainly effective over the non- linear resistor connected to the circuit in resonance. The impedance of this resistor is then sufficiently low to damp the resonant circuit and cause it to proceed to the offresonance state. On termination of the pulse, the transient conditions maintained by inductors 19a, 19b establish the trigger pair action as previously described. In a modification, Fig. 6 (not shown), the inductive load connected to each circuit is constituted by the control winding of a magnetic amplifier, and the series inductors 19a, 19b are omitted. A shortcircuited winding coupling both cores of inductors L1, L2 is also provided to enhance the mutual inductance.