GB610511A - A thermionic saw-tooth wave generator - Google Patents

Abstract

610,511. Saw-tooth generating circuits. TRIGGS, W. W. (Farnsworth Television & Radio Corporation). Jan. 16, 1945, No. 1313. [Class 40 (vi)] In a blocking oscillator the frequency of oscillation is varied without affecting the amplitude by conjointly varying the internal resistance of the valve (e.g. by means of a variable resistor in the cathode circuit) and the amount of feed-back. Fig. 5 shows valve 10 arranged in a blocking oscillator circuit. A constant rate of change of anode current in inductance 19 produces constant anode and grid voltages 40, 41, as shown in Fig. 2. Initially, the screen grid receives most of the current and thereafter suffers a corresponding decrease as the anode current builds up so that the screen grid voltage starts at a low value and rises substantially linearly as at 39 in Fig. 2. The cathode voltage includes an initial step corresponding to the flow of screen grid current through cathode resistors 16, 46, 52, and then has a linear rise 38 corresponding to the flow of anode current. When regeneration occurs, the cathode returns rapidly to zero potential 45, the screen returns to battery voltage 44 and the grid experiences a large negative swing 43. The grid and cathode voltages are combined to remove the stepped portion of the cathode wave-form and give a true saw-tooth output 46. The frequency is changed from one value to another by means of switch 53 which removes the short across resistor 52 in the cathode circuit and decreases the amount of winding 54 in the grid circuit. A network 28, 29 is inserted to reduce non-linearity in the current wave-form which output 46 produces in the inductive load 27 and the network elements may be variable to give a control of amplitude in the output. Large positive pulses appearing at the anode may be rectified by diode 33 and applied as a high voltage supply for a cathoderay tube. If required, negative synchronizing pulses may be applied to terminal 30. In Fig. 6 (not shown), the linearising network 28, 29 is eliminated and an auxiliary winding on coil 22 is coupled to a. resistance capacity network in the grid circuit of the valve.