Patent GB-583497-A (GB)
Title: Improvements in frequency changers
IPC: H01F38/04
Filed: 1944-05-06
Abstract: 583,497. Frequency changing. AUTOMATIC ELECTRIC LABORATORIES, Inc. May 6, 1944, No. 8617. Convention date, May 6, 1943. [Class 38 (ii)] A self-starting frequency reducing system produces currents of a frequency which is an even subharmonic of the input frequency in a capacitor in series with an inductance biassed by a direct current, the load being connected across either the inductance or the capacitor. In the arrangement shown in Fig. 1, an inductance 13 is magnetically biassed from a D.C. source 11 in series with a filter inductance 12 having an air gap in the core to prevent saturation, and the circuit characteristics upon connection of an A.C. source 10 in series with a capacitor 14 across inductance 13 are such that oscillations of a frequency which is an even subharmonic, preferably a half, of the input frequency appear in the circuit and a current of this frequency is taken by load LD connected across the condenser. Stabilization of the oscillations may be effected by a suitable value of inductance 12 or by cutting an air gap in the core of inductance 13. Regulation may be improved by an automatic phase change between input and output. In a modification, the D.C. biassing current which flows through a second winding of the biassed inductance, and the load current which is supplied from the main circuit through a transformer, the primary of which acts as an autotransformer to supply higher voltage to the capacitor, are both isolated from the input circuit, Fig. 2 (not shown). In a further modification, the D.C. source 11 of Fig. 1 is replaced by a half-wave rectifier through which mainly passes the subharmonic current, and the load LD is isolated from the input by being fed from a second winding on the non-linear inductance, Fig. 3 (not shown). An additional regulating effect may be obtained, in that as the subharmonic voltage rises the biassing current increases the saturation of inductance 13 which tends to reduce the voltage, and vice versa, but a disadvantage is that the effect may reverse when the load is heavy, Fig. 3 (not shown). Fig. 4 shows a modification in which subharmonic oscillations are generated in an inductance 22 and capacitor 14 in series across an A.C. source 10, and in which the biassing current comes from a full-wave rectifier bridge 20 supplied from secondary 18 of a transformer 19 fed from source 10. Load LD receives subharmonic current from a secondary winding 24 on inductance 22 and harmonics of the input frequency are balanced out of the load circuit by oppositely phased voltage derived from a secondary winding 17 of the transformer 19. Inductance 12 passes subharmonic current and acts as a stabilizing unit giving good regulation, whereby the volts may remain constant or rise with increase in load. Regulation is also obtained by phase change as in the other modifications. A heavy load stops the oscillations which restart automatically as the load impedance increases. A condenser 21 reduces the peak inverse rectifier voltage and determines the value of subharmonic current passing through the bridge and thereby the regulation characteristics. Saturable inductance 26 and capacitor 27 may, be connected in parallel in the circuit to provide a small percentage of higher harmonics if these are wanted, e.g. as audible ringing tone in a telephone system where the subharmonic supply is used as a telephone ringing voltage.