Patent GB-586519-A (GB)
Title: Improvements in frequency changers
IPC: H03B19/03
Filed: 1944-05-03
Abstract: 586,519. Frequency-changing. AUTOMATIC ELECTRIC LABORATORIES, Inc. May 3, 1944, No. 8312. Convention date, May 6, 1943. [Class 38 (ii)] A frequency reducing system which generates current of a frequency which is a sub-harmonic of the frequency of the input, has an auxiliary circuit having capacitive reactance in which are produced oscillations different in frequency from both the input and sub-harmonic frequencies, but mutually self-exciting with the latter. Various circuits are described in which* several modulating effects are utilized, these being especially the conversion to a subharmonic frequency as disclosed in U.S.A. Specification 1,633,481 and also Specification 470,128, and the method for producing selfstarting oscillations in two circuits which share the power at two frequencies related to each other and to the input frequency as described in U.S.A. Specifications 1,656,195 and 1,884,845. Fig. 1 shows a bridge formed by four similar inductances 17, 18, 19, 20 which are magnetically biassed from a D.C. source 11. An input circuit comprising a source 10 and capacitor 12 connected to opposite terminals 13, 14 of the bridge forms one oscillating circuit which supplies a load 24 connected across the capacitor with a current which is a sub-harmonic preferably <1>/3 or <1>/5 of the input frequency. The output from bridge terminals 15, 16 to a load 23 connected across a capacitor 22 in series with an inductance 21 is then of a frequency <2>/3 or <4>/5 of the source frequency. Oscillations in the two circuits supplying loads 23, 24 interact and are self-starting as described above, the power from source 10 dividing between the two loads and being able to flow in either direction between the loads results in great stability even if one load is omitted. Various modifications of the Fig. 1 circuit are disclosed. In one, the two load frequencies are 1/5 and 2/5 of the source frequency and the necessary starting transient is provided by the' opening of relay contacts which initially shortcircuit inductance 18, Fig. 2 (not shown). In another modification, a capacitor in parallel with a series connected capacitor and inductance are connected across the output terminals 15, 16 for self starting, Fig. 3 (not shown). In a further modification the D.C. biassing current is supplied to the bridge from the input side in which is connected a further inductance, while a capacitor is connected across the inductance in series with load 23 in the output circuit. This is suitable for supplying frequencies “ and # of the input frequency to loads 24, 23 respectively, Fig. 4 (not shown). As the bridge is balanced, inductances 17, 19 and 18, 20 may be wound in pairs on two common cores. Load 23 may be supplied through a transformer for varying its voltage, Fig. 5 (not shown). The circuit of Fig. 6 shows another arrangement of balanced inductances 29, 30, 33, 34 on cores 25, 26 biassed by D.C. through coils 31, 32 from a rectifying bridge 37 supplied from source 10 through a transformer 39. Capacitor 22 and inductance 21 form the oscillating output circuit supplying load 23 through transformer action between windings 31, 33 and 32, 34 of inductances 25, 26, while load 24 is substantially supplied from the input circuit through windings 29, 35 and 30, 36. A secondary winding 42 on transformer 39 is used to balance out the input frequency component from load 24. In the Specification as open to inspection under Sect. 91, a circuit is described with reference to Fig. 4 (Cancelled) in which unbiassed saturable inductances are used, whereby loads 23, 24 may receive power from source 10 at frequencies respectively <1>/5 and <3>/5 of the input frequency. When starting relay 44 operates to open its contacts, it connects a saturable inductance 48 in series with the input winding 55 of an inductance which together with winding 56 acts as an auto-transformer to step up the voltage across capacitors 53, 54 in series with linear inductances 49, 51 which also act as transformer primaries. The input circuit contains both <1>/5 and <3>/5 harmonics which are supplied to loads 24, 23 through secondaries 57, 58, the unwanted harmonic being balanced out of each load circuit by oppositely induced harmonics in coils 52, 50. This subject-matter does not appear in the Specification as accepted.