Patent GB-578135-A (GB)
Title: Improvements relating to thermionic generators for producing scanning and like voltages
IPC: H03K3/04
Filed: 1944-04-19
Abstract: 578,135. Saw-tooth generators; square-wave generators. COSSOR, Ltd., A. C., and WILLIAMS, B. C. FLEMING-. April 19, 1944, No. 7268. [Class 40 (v)] In a saw-tooth and square-wave generator of the type in which the grid of a valve is fed from the anode over a differentiating network, a rectifier is connected between an electrode and a triggering source so that the electrode is isolated from the source throughout the period of the anode sweep. In the quiescent state, the control grid of valve V1 is maintained at earth potential due to a diode D2, the total cathode current passing to the screen grid, the suppressor grid being biassed off so that no anode circuit flows. The anode potential is maintained constant at the potential of the slider of potentiometer R 1 due .to diode D1 conducting. The anode of diode D3 is biassed negatively with respect to the cathode to avoid unwanted triggering due to extraneous sources. Upon a positive triggering pulse being applied over condenser C3, it charges to increase the bias throughout the sweep. The pulse raises the potential of the screen grid and due to the coupling condenser C2 also that of the suppressor grid, thus causing anode current to flow and the screen grid current to fall, in turn raising further the screen and suppressor grid potentials. This process continues extremely rapidly until a state is reached in which the anode potential has fallen slightly and due to the coupling condenser C1 also the grid potential, and the screen grid has taken up a considerably higher potential than previously and the suppressor grid has risen to the cathode potential, being held there by diode D4. Due to resistance R3 being connected to the H.T. supply, the control grid potential tends to rise while the anode potential makes a linear sweep downward. Condenser C1 discharges in a similar manner to that which would occur if it were connected to G times the potential over G times the resistance R3. The anode potential continues to fall to a low value, when the screen grid current begins to increase and the potential to fall, thereby lowering the suppressor grid potential, thus causing a further increase of the screen grid current until the anode current falls to zero. The anode potential rises exponentially as the condenser C1 charges through resistance R4 and diode D2. The control grid potential rises due to the coupling condenser C1, but is held by diode D2 at earth potential, the cycle then being completed. The square-wave may be taken from the screen grid and the saw-tooth from the anode, To trigger the circuit with negative pulses, the pulse is applied to the anode over condenser C5 and diode D5 biassed by battery B or, alternatively, positive pulses may be applied over condenser C6 and resistance R12 biassed more negatively than the lower end of resistance R2. The diodes D3, D5 and D6 may be dispensed with and the pulse applied to diode D1, with a resistance inserted between the cathode and the slider of potentiometer R1, provided no standing bias is required for avoiding unwanted triggering. By reducing the bias on the suppressor grid, the circuit becomes free running, but may still be synchronized with an appropriate positive or negative pulse over condensers C3, C6 or C5.