GB917609A - Magnetic flux oscillators - Google Patents

Abstract

917,609. Transistor oscillator circuits. BENDIX ERICSSON U.K. Ltd. Nov. 3, 1961 [Nov. 23, 1960], No. 40213/60. Classes 40 (5) and 40 (6). An oscillator of the type comprising a transformer winding connected between the collector electrodes of two transistors which are rendered alternately conducting by switching windings on the transformer and in which a variable voltage is connected to the centre tap of the transformer so as to vary the oscillation frequency, has a resistor connected in the common emitter circuit of the transistors to limit the emitter-collector current. Fig. 2 shows an oscillator of the type in which feedback windings S1 and S2 cause transistors T1 and T2 to conduct alternately, the change-over of conduction occurring when the square-loop core saturates. The frequency of oscillation depends on the value of the voltage V1 and a more linear relation is obtained by connecting a resistor R in the common emitter circuit to limit the surge of transistor current when the core saturates. A further increase in linearity is obtained by the provision of clamping diodes D1 to D4 which maintain the emitter-base voltage of the conducting transistor close to zero. To still further linearize the relation between the control voltage and oscillator frequency an additional winding W (Fig. 3) of the transformer may provide a voltage dependent on the rate of change of current in the transformer primary and this may be rectified at X and compared in amplifier A with the control voltage VC to provide a modified control voltage. A capacitor C1 may be provided to prevent operation by unwanted impulses. Fig. 4 shows a practical embodiment of Fig. 3 in which the basic oscillator comprises transistors T1, T2 and transformer windings M1, M2, S1, S2, output voltages being taken from transistors TO1 TO2 coupled to the bases of the oscillator transistors. The transformer has further output windings W1 and W2 and feedback windings S1 and S2 which render transistors X1 and X2 alternately conducting so as to provide an output voltage in R4 dependent on the frequency of oscillation. This voltage is compared in amplifier A with the control voltage fed through R14 and R13 to the amplifier, and control of the oscillator frequency is effected from the output of amplifier A through a transistor TR. A rectifier D6 provides a bias for the transistors X1, X2, while a thermistor t mounted adjacent to the transformer core helps to maintain the oscillator frequency constant. A Zener diode D5 provides a stabilized bias voltage for clamping diodes D1 and D2. Fig. 5 shows a circuit having two input terminals i1 and i2 coupled to respective output terminals of Fig. 4 and which provides an output at 3 for each transition of the oscillator output waveform.