Patent GB-529383-A (GB)
Title: Improvements in or relating to thermionic valve circuits for the generation of saw tooth currents
IPC: H03K4/32
Filed: 1939-05-15
Abstract: 529,383. Valve generating circuits; television. WHITE, E. L. C. May 15, 1939, No. 14467. [Classes 40 (iii) and 40 (v)'] A circuit for generating a desired wave-form, particularly a circuit of the "resonant return" type for generating linear sawtooth currents for inductive loads, comprises a valve 6, the output circuit of which includes the inductive load 8, 9 and a second valve 13 effectively in shunt with the load, a control potential being applied to the grid of valve 13 to control the potential difference developed across the load to maintain the desired linearity of the current in the load. The valve 6 is of high impedance and is in the cathode and grid circuits of the valve 13, which thus acts as a cathode follower and causes the potential of the anode of valve 6 to follow the control potential applied to the grid of valve 13. This control potential may be substantially constant as in Fig. 1, or may be dependent on the anode current in the valve 6 as in Figs. 4, 5, or may be derived from the load as in Fig. 6. The wave form may be further improved by a negative feed-back from the anode of valve 13 to the grid of valve 6, e.g. by a condenser 17, Fig. 1, or 24, Fig. 5, or by a transformer 23, Fig. 4. A diode 28, Figs. 4, 6 may be inserted between the valves 6, 13 to protect the cathode heater insulation against the high positive potentials developed on the anode of valve 6 during the generation of the short-flank of the saw-tooth wave. In Fig. 1, when the valve 6 is rendered non-conducting by a negative synchronizing impulse 5, the current through the valve is suddenly decreased and the oscillatory circuit, formed by the coils 8 and their distributed capacity and other stray capacities, performs a half cycle of oscillation, generating the short flank of the wave. When the valve 6 is rendered non-conducting, its anode potential rises, causing valve 13 to become non- conductive. As soon as one half cycle of oscillation is complete, the potential of the anode of valve 6, and thus on the cathode of valve 13, is decreased to such a value that valve 13 again conducts, causing the oscillation to cease, and permitting valve 6 to commence generating a further flank of the saw-tooth wave. The duration of the synchronizing pulses should be equal to the duration of the short flank of the saw-tooth wave. In Fig. 4, a control potential of saw-tooth form applied to the grid of valve 13 is derived from the screen grid of valve 6 and is proportional to the anode current of valve 6. The potential thus developed across valve 13 is applied to the load 8, 9 to compensate for the effect ot the resistance of the load. In Fig. 5, the control potential applied to valve 13 is derived from the screen of valve 6, and in order to effect "keystone" modulation a frame-frequency saw-tooth component indicated at F is fed to the grid of valve 30, the anode of which is connected' via condenser 33 to the grid of valve 13. In order to correct slight " skewness " of the resulting scanned patch, a frame frequency component in opposite phase is supplied by valve 30 via resistance 37 to the grid of a valve 35, in parallel with valve 6. The synchronizing pulses are applied to the grid of a valve 38, the anode of which is connected to the grid of valve 6. In Fig. 6, the control potential applied to valve 13 is derived from the load circuit 8, 12, being applied to the grid of a valve 51. A constant potential is applied to the grid of a valve 50. associated with 51, the anode circuits of these valves being connected to the grid of valve 13. The grid of valve 50 may also have applied to it a frame frequency saw-tooth potential for " Keystone " modulation as in Fig. 5. Instead of utilizing synchronizing pulses as in Figs. 1, 4, 5, the valve 6 is controlled by a saw-tooth potential 55 derived from a blocking oscillator. Specifications 400,976 and 482,740 are referred to.