| 摘要 |
1,185,909. Transistor circuits; radio signalling. PYE Ltd. 21 Nov., 1968 [30 Nov., 1967], No. 54685/67. Headings H3T and H4L. [Also in Division G3] An arrangement for reducing the power taken from the battery supply to a radio receiver in the absence of a signal and including a semiconductor switch device for rendering the D.C. path to the receiver alternately conductive and non-conductive, the device being maintained in the ON position on receipt of a signal, is characterized in that the semi-conductor switch device also acts as a series stabilizing element of a constant voltage supply forming the power supply to the receiver. The arrangement comprises a Schmitt trigger pair TR1, TR2, a multivibrator TR3, TR4 controlling switching transistors TR6, TR7 and an auxiliary control transistor TR5. In the multivibrator transistors TR3, TR4 are coupled by means of resistor R11 and back-coupled via emitter reactors R10, R12 and capacitor C, R10 being made small to obtain a short ON period. Transistor TR3 is given a stabilized bias by means of resistors R8, R9 which are equal to resistors R11, R10 respectively, and diode D1 which is of like material to transistor TR3. The collector load of transistor TR4 comprises diodes D2, D3 the constant voltage drop across which in the ON position biases transistor TR6 conductive. The resulting constant current supplied to Zener diode D5 provides a bias for transistor TR7 which renders it conductive, this transistor and the Zener diode then forming a constant voltage supply to terminal D to which the radio receiver is connected. In the OFF position of the multivibrator transistor TR4 is non- conductive, transistor TR6 biased non-conductive so no current passes to Zener diode D5 and transistor TR7 is biased non-conductive. The arrangement may be held in ON position upon receipt of a signal, which is caused to lower the potential of point E and so render transistor TR3 permanently non-conductive. Alternatively a positive potential may be applied to the point F to render transistor TR5-which derives a positive emitter bias from potentiometer R15, R16-conductive and draw current through diodes D2, D3 independently of the position of the multivibrator. If, in this arrangement a short-circuit should occur between output terminal D and earth, diode D4 becomes conductive, clamping to earth the base potential of transistor TR5, which becomes non-conductive. The circuit then reverts to multivibrator operation whereby excessive continuous current through transistor TR7 is prevented. The positive potential at point F may be derived from the collector of transistor TR1, lowering of the base potential of which causes switching to continuous operation. This hold voltage may be arranged to persist, to cover pauses in a signal by connecting a capacitor between terminal F and earth and including a diode in the connection between terminal F and collector of transistor TR1. Capacitor CD is provided to prevent unwanted RF effects |
