Patent GB-915393-A (GB)
Title: Improvements in or relating to sine-wave generators
IPC: H02M5/293
Filed: 1959-05-28
Abstract: 915,393. Inverter oscillator circuits. INTRON INTERNATIONAL Inc. May 28, 1959 [May 28, 1958], No. 18173/59. Classes 40 (5) and 40 (6). An oscillator comprises a switch device connected in a primary circuit to a power source and a secondary circuit coupled to the primary circuit and including a series circuit in series with a parallel circuit, both tuned to the oscillation frequency, a feedback path being provided between the parallel circuit and the switch to open the latter when the primary current is zero. Fig. 4 shows an oscillator comprising two transistors 415<SP>1</SP>, 415<SP>11</SP> arranged in push-pull and supplied with D.C. or a lowfrequency A.C. 413 of frequency not equal to that of the oscillation frequency. The output of the transistors is fed through a transformer 410 to a series circuit 416, 417 and a parallel circuit 418, 421, both tuned to the oscillation frequency, the coil 721 being coupled to the load L and to the oscillator feed-back windings 422B<SP>1</SP> and 422B<SP>11</SP>. The series circuit 416, 417 ensures that though a sine-wave current flows to the output circuit the voltage at the collector electrode is of square waveform so that the collector voltage polarity changes occur when the current is zero. The transistor can be of junction or point contact type, or other solid state element such as a double-base diode, controlled rectifiers magneto-resistive devices. Alternatively, thermionic valves or electromagnetic relays can be used (Fig. 1, not shown). In addition the transistors could be in the common emitter, common base or common collector configuration and Fig. 3 (not shown), illustrates a common collector arrangement in which the load is connected directly across the parallel tuned circuit and feedback is provided to the emitters from capacitors connected to opposite ends of the load. The feedback may have both sine wave and square wave components if the feedback windings are coupled both to transformer 410 and 420 (Fig. 5, not shown). Three phase operations may be obtained by providing three oscillators with appropriate phase changes in the feedback paths from one output circuit to the input circuits of the oscillators (Fig. 6, not shown). In a further three-phase embodiment (Fig. 7, not shown), the two transformers each have a common core for the three oscillators and a single series tuned circuit which is connected in the neutral lead between the transformers. In addition, where the three-phase feedback is not automatically available, for example as a result of the output being used in a threephase motor, the feedback circuits may be connected to a common parallel tuned circuit through appropriate phase-shifting networks. Fig. 2 shows a " single ended " embodiment using a thermionic valve. The parallel tuned circuit 318, 321 is isolated from the load by a resistor 324 and a phase-adjusting inductance 326. Tuned transmission lines may replace the tuned circuits and the technique is illustrated by a system embodiment of the invention with a UHF generator feeds an amplifier 1315 (not in accordance with the invention (Fig. 3, not shown)) in which a UHF generator feeds an effectively parallel tuned output cavity resonator through a circuit comprising a quarter wave line operating as the series tuned circuit. It is also stated that amplitude regulation and frequency stabilizing networks incorporating breakdown devices such as Zener diodes or glow tubes may be incorporated in the embodiments. In addition, self-starting of the oscillator circuits may be assisted by replacing the biasing batteries by a combination of resistance and capacitance.