Patent GB-917756-A (GB)
Title: Improvements in or relating to control circuit arrangements for supplying substantially flat topped voltage pulses
IPC: H02M3/04
Filed: 1959-02-17
Abstract: 917,756. Transistor bi-stable generating and gating circuits. SIEMENS-SCHUCKERTWERKE A.G. Feb. 17, 1959 [Feb. 17, 1958], No. 5527/59. Class 40 (6). [Also in Group XXXV] A trigger circuit comprises two reciprocallycoupled transistors, the emitter-base bias voltage for one transistor being derived jointly from a potentiometer chain connected across the collector-emitter supply source and from a Zener diode, the arrangement being such that this transistor only conducts when the supply voltage exceeds a predetermined value, the other transistor then being rendered non-conducting owing to the reciprocal coupling. By modifying the circuit so that the voltage across the potentiometer chain includes a component whose value depends upon whether or not the second transistor is conducting, the circuit may be rendered self-oscillatory. In Fig. 1, the emitterbase voltage for transistor 3 is derived from potentiometer chain 6, 7, 8 connected across the input terminals 1, 2 for the circuit power supply, the potential across resistor 6 being opposed by that developed across Zener diode 5 so that a sufficient potential is derived to cause transistor 3 to conduct only when the potential difference between terminals 1 and 2 exceeds a certain minimum value. A second transistor 9 whose emitter is given a permanent negative bias by a potentiometer chain 11, 12, 13 is biased off when transistor 3 conducts owing to the connection to its base from the collector of transistor 3. However, when transistor 3 ceases conducting the potential at its collector goes more negative, thus permitting the transistor 9 to conduct; this sends the potential at the junction of resistors 7 and 8 and hence that at the base of transistor 3 more positive, thus cutting transistor 3 further off by regenerative action. The circuit may be used to generate a rectangular output waveform between the terminals 14, 15 by superimposing a suitable sinusoidal variation upon the steady voltage applied to the terminals 1, 2. Fig. 2 shows the circuit modified so as to be self-oscillatory so that a rectangular waveform output is produced with a steady input voltage applied to terminals 1, 2. In this arrangement the resistor 6 is returned to a tapping point on the resistor 11, a capacitor 16 being connected between the tapping point and input terminal 1. When the circuit is switched on transistor 3 is initially non-conducting while transistor 9 conducts. The current flowing through transistor 9 causes the potential difference across capacitor 16 to build up until transistor 3 conducts, when owing to the regenerative coupling it is maintained conducting and transistor 9 is switchedoff. Capacitor 16 now discharges until transistor 3 is switched off again, transistor 9 then being rendered conducting and the capacitor 16 charging once more through the transistor 9. A smoothing capacitor 17 is provided to prevent false operation of the circuit due to variation in voltage applied to terminals 1, 2. The circuits may form part of a voltage regulator (see Group XXXV) in which the output voltage developed between terminals 14 and 15 is used to control the magnitude of the input voltage applied between terminals 1 and 2 and constituting the output voltage of a powersupply source. Oscillator WR, Fig. 5. Assuming transistor 65 of reciprocally coupled pair 65, 66 is conducting base current flows until capacitor 71 becomes sufficiently charged to prevent further conduction. Transistor 65 then ceases conducting and by reciprocal action transistor 66 commences conducting so charging up capacitor 72. Capacitor 71 meanwhile discharges through the diode 67, the emitter-collector path of transistor 66 and the right-hand portion of the primary winding of transformer 73 so that when capacitor 72 becomes fully charged and transistor 66 can no longer conduct, transistor 65 is able to conduct once more, capacitor 72 then discharging through diode 68 and the emitter-collector path of transistor 65. Transistor gating circuit. The output of the oscillator WR is applied to the full wave rectifier circuit 77, 78 through a gating circuit comprising a transistor 9 which when conductive allows diodes 75, 76 to conduct in alternate half-cycles of the generated oscillation thereby exciting the transformer 74 in alternate half-cycles in the two halves of its primary winding. When the transistor 9 is non-conducting no current can flow owing to the diodes 75 and 76 being opposed.