| 摘要 |
938,007. Transistor oscillator circuits. ERICSSON TELEPHONES Ltd. Sept. 6, 1960 [June 6, 1959], No. 19423/59. Class 40 (6). Telephone ringing currents are generated in a circuit comprising two transistors and a transformer which in operation saturates and means are provided for eliminating transient voltages resulting from the switching action of the transistors. The oscillator shown in Fig. 2 is of the type in which current build-up is limited by saturation of the core of the transformer and in which oscillation is initiated by the circuit 25, 26 and 27. Transients are eliminated by the circuit 19, 20 and this circuit is so connected to the main on-off switch 30 that when the generator is switched off the elements 19, 20 are connected across respective halves of the transformer to prevent the generation of excessive oscillatory currents. In Fig. 3, switching transients are eliminated by capacitors 23 and 24. The supply voltage is excessive for the transistors used and accordingly a voltage dropping resistor is connected in the supply circuit. Diodes 36 and 37 limit the collector voltage swing. According to the Provisional Specification transient voltages can alternatively be eliminated by non-linear resistors connected between the collector electrodes. |
