Patent GB-666574-A (GB)
Title: Improvements in the use of saturable magnetic chokes as discharge devices
IPC: H02M9/06
Filed: 1948-11-15
Abstract: 666,574. Changing wave-form. BRITISH THOMSON-HOUSTON CO., Ltd., and MELVILLE, W. S. Dec. 6, 1949 [Nov. 15, 1948], No. 29613/48. Class 38 (ii). A circuit for producing pulses of electrical energy in a load includes a multiple T-network of series inductances L1, L2, L3, and shunt capacitances C2, C3, the inductances having saturable cores and being so graded that the unsaturated value of each, other than that nearest the load-terminals, is substantially higher and the saturated value is substantially lower than the unsaturated value of the next inductance nearer the load, and a capacitor C1 connected to supply-terminals and adapted to be charged to supply energy to the circuit. When the voltage across capacitor C1 reaches a sufficient value, the reactor L1 becomes saturated and the charge is transferred to capacitor C2, this operation continuing to the end of the series when the charge is applied to the load. In each stage the time for transfer decreases, a sufficient number of stages being included to allow the saturated value of the final inductance to be negligible compared to the load in which the voltage is built up at an accelerated rate. In Fig. 1 the capacitance C3 is formed by a network having series inductance windings e and shunt capacitors c, The load may be the firing circuit of an ignition discharge valve, the network C3 being replaced by a single condenser. Unidirectional pulses may be supplied to the load by providing the inductance L1 with a biasing winding which is energized with direct current, alternatively direct current may be injected into the principal reactor winding through a suitable de-coupling circuit. The capacitor C1 may be charged from a source of sinusoidal voltage through an inductance of such value to afford a condition approaching resonance at the supply frequency, Fig. 3a (not shown). In Fig. 4 the capacitor Cl is charged through a saturable inductance L1 and the primary winding of a saturable-cored transformer T1, the secondary circuit of which includes capacitance C2 and the primary winding of a saturable cored transformer T2. The secondary circuit of transformer T2 includes network C3, a magnetron M being supplied from pulse transformer T3. The unsaturated primary inductance of transformer T1 is low compared to that of inductance L1 but high compared to its saturated value. The primary inductance of transformer T2 has an unsaturated value which is low compared to that of transformer T1 but high in relation to its saturated value. The transformers T1, T2, may be arranged to step up or down. The inductance L1 is preferably resonant with capacitor C1 at the supply frequency, and at voltage maximum on capacitor C1 the inductance L1 saturates, the capacitor discharging to charge capacitor C2. When the voltage on capacitor C2 is at a maximum, the core of transformer T2 saturates so that the network C3 is charged, and the load is energized when the network discharges. Fig. 5 (not shown), illustrates a circuit comprising a large number of stages each comprising a series saturable reactor and a parallel capacitor. In Fig. 6 (not shown), a four-stage circuit is used as a radar modulator, a step-up transformer giving the high voltage output required. A pulseshaping network of inductances and capacitances is connected across the load. Direct current bias may be applied to the cores of the saturable transformers or reactors to counter some of the effects of large line-directional flux impulses which occur during discharge through the windings. The cores of the inductances may be made of a material having a sharp magnetization characteristic, such as 50-50 cold-rolled nickel-iron. Specification 666,575 is referred to.