GB889778A - Improvements relating to pulse generating circuits - Google Patents

Abstract

889,778. Valve and semi-conductor pulse circuits. FERRANTI Ltd. July 22, 1960 [July 28, 1959], No. 25786/59. Class 40(6). In a circuit for producing a pulse or train of pulses commencing at any desired part of each cycle of the alternating current supply A, a sawtooth oscillator is synchronized with the supply A and a second oscillator having a higher frequency is started when the combined value of the sawtooth waveform B and an adjustable direct current supply reaches a predetermined value. As shown in Fig. 1, waveform B is generated by charging capacitor 5 through resistor 3 until the voltage, when combined with the instantaneous voltage across diode 2 reaches the critical voltage of the silicon PNPN device 1, when capacitor 5 is discharged via devices 1, 2. When the voltage across capacitor 10, which is dependent on the sum of the adjustable voltage from the potentiometer 9 and the instantaneous value of waveform B, reaches the critical value of the PNPN device 7, capacitor 10 is discharged and executes higher frequency sawtooth oscillations until the end of the sawtooth stroke B. Waveforms C, D, E respectively show the effect of changing the voltage at the slider of potentiometer 9 from a low to a high value. The output may be fed via capacitor 14 to a controlled rectifier which is rendered conductive at the first cycle of the higher frequency sawtooth waveform. Gas discharge tubes may be used to replace the silicon devices 1, 7.