GB536153A - Improvements in periodic wave generators particularly applicable for use in television - Google Patents

Abstract

536,153. Valve generating circuits. HAZELTINE CORPORATION. Jan. 15, 1940, No. 880. Convention date, Feb. 13, 1939. [Class 40 (v)] A wave generator supplying saw-tooth current to an inductive load comprises two valves 31, 32 reversely connected to the load circuit 39, 40, 21 and so controlled that the current from valve 31 increases. during trace intervals whereas that from valve 32 decreases. The grid of valve 32 is used as the output electrode, and this grid and the electrode 22 (normally the anode) are connected across condenser 41 which is in series with resistance 42 across the primary 39 of the output transformer, the arrangement being such that the valve 32 acts as a negative resistance across the load circuit during the trace period, but has no effect during the retrace period. The current taken by the valve 32 decreases as that from valve 31 increases, thereby increasing the current in the load circuit, and improving its wave-form. Valve 31 is a screen-grid valve of high amplification, whilst the reversed triode 32 may have an amplification factor about or below unity. During trace intervals the internal resistance of the valve 32 is less than the impedance of the load circuit, and the time constant of the circuit comprising the inductance of the load circuit and the resistance of valve 32 is of the same order as the period of the trace interval. The valve 31 is operated to cut-off during retrace intervals by a driver valve 30 fed by synchronizing pulses, the resistance-capacity combination 33, 34 supplying a negative pulse followed by a slowlyrising wave-form, as shown in Fig. 2e. A feedback circuit from anode of valve 31 to the grid of valve 30 may be provided, Fig. 4 (not shown), so that the valve 31 is essentially an oscillator controlled by the synchronizing pulses, rather than an amplifier driven by these pulses. In a further modification, the two-coil transformer 39, 40 is replaced by an auto-transformer 391, 401, Fig. 5, and feed-back coils 66, 67 perform the function of valves 30 in Fig. 1. Condensers and resistances prevent undesired feed back into the source 20 of synchronizing signals, damp out transient high-frequency oscillations, &c.