Patent GB-842219-A (GB)
Title: Improvements in or relating to transistor circuits
IPC: H03B5/12
Filed: 1957-08-21
Abstract: 842,219. Transistor oscillating and amplifying circuits. COLE Ltd., E. K., COX, V. J., and YARROW, C. J. Nov. 20, 1958 [Aug. 21, 1957], No. 26354/57. Class 40(6). A transistor circuit which develops a sinusoidal oscillation across the winding of a tuned transformer, either by selfoscillation or on the application of an input signal of suitable amplitude and frequency thereto, comprises a pair of alternately-conducting transistors each conducting in alternate half-cycles of the sinusoidal oscillation and so connected that the current supplying the transistors flows in alternate half-cycles in opposite directions through a tuned winding of the transformer, a choke coil being provided and so connected that the said current flows in the same direction therethrough in alternate halfcycles. The transistors are alternately in a non-conducting and bottomed condition; the choke ensures that switching from one condition to the other occurs at instants when the current through the conducting transistor has fallen to zero. In a first embodiment illustrated in the drawing accompanying the Provisional Specification, a selfoscillatory circuit comprises a transformer having a centre-tapped tuned winding W 1 connected between the collector electrodes of transistors A, B. The direct-current supply to the transistor is connected to the centre tap of winding W1 through a series choke L. A resistor R is connected from the same terminal of the power supply to the centre-tap of feedback winding W2. the value of the resistor being such as to permit sufficient base current to flow therethrough to ensure that one of the transistors is. always bottomed. In a second embodiment, Fig. 1, the choke Ll is connected as shown between alternately conducting transistors T1, T2. The tuned winding Wl is connected between a centre-tap on the choke L1 and a centre-tap on the power supply, or, as shown, to a capacitor C2 across which is developed a voltage equal to half that of the power supply. The circuits of feedback windings W2, W3 are coupled together by a bifilar choke L2 which acts to maintain the sum of the baseelectrode currents flowing constant and assists the change-over from one transistor to the other. In a further embodiment, Fig. 2, the sum of the voltages across windings Wl and W3 equals the voltage across W2. The coupling between the feedback circuits of the two transistors which maintains the sum of the base currents equal is provided by capacitor C3. In a final embodiment, Fig. 3, transistors Tl and T4 conduct simultaneously and in alternation with transistors T2 and T3. Thus the current path between the supply terminals and including choke L1 is completed in alternate half-cycles through transistors Tl and T4 and through transistors T2 and T3 respectively, current flowing through the winding W1 in different directions in the two cases. Bifilar choke L3 maintains the sum of the base currents in transistors T3 and T4 constant while choke L2 performs the same function for transistors Tl and T2. The circuits described above may all be modified so as to be externally driven, the feedback windings being replaced by windings on a transformer supplied from an alternating-current source of appropriate amplitude and frequency.