Patent GB-625238-A (GB)
Title: High-voltage power-supply system
IPC: H04N3/18
Filed: 1947-07-07
Abstract: 625,238. Converting. HAZELTINE CORPORATION. July 7, 1947, No. 17893. Convention date, July 1, 1946. [Class 38 (ii)] [Also in Groups XL (a) and XL (b)] A system for developing a high unidirectional voltage for a television receiver, comprises discharge type apparatus in which primary electrons, emitted from a first cathode, bombard an auxiliary cathode which emits secondary electrons, these being collected by a collector cathode, the potential of which, periodically at least, is maintained positive relative to the first cathode, but low compared with the average potential of the auxiliary cathode and a high alternating voltage is applied between the auxiliary and collector electrodes, so that during those periods the potential of the auxiliary cathode is between those of the other electrodes, and the A.C. is rectified to develop the high direct voltage. A voltage is applied to the auxiliary cathode 33 of a valve 30, which is the sum of the positive high direct voltage output at terminal 53 and a high alternating voltage, generated by a class C oscillating valve 40, in a winding 41 of a transformer, of which other windings 42a and 43 serve as anode inductor and feed back to the grid circuit respectively. The frequency of oscillation is determined by a condenser 39, across winding 41, or the natural capacitance of the winding. Fig. 2a shows curves for that half period in which the voltage I of auxiliary cathode 33 falls to a value between the voltage J of collector 34, which is the sum of constant voltage D of source B and the alternating voltage generated in transformer winding 42b, and voltage L of cathode 31 determined by the self-biassing of valve 30 by resistance 72 and condenser 73 in the cathode circuit. The voltage K of control electrode 32 is the sum of bias voltage E<SP>1</SP> from the biassing resistance 44 and condenser 45 in the grid circuit of valve 40, and alternating voltage developed in winding 43 at tap 50. Current H (Fig. 2c) flows in the grid circuit when the grid potential C (Fig. 26) exceeds the cut-off voltage F. When the potentials of electrodes 32 and 34 rise sufficiently, primary electrons, i.e. current M in Fig. 2c, from cathode 31 bombard auxiliary cathode 33, secondary electrons from which, i.e. current N, are collected by electrode 34, shielded from cathode 31 by control electrode 32. Current P, the difference between M and N flows as a rectified current in the rectifying circuit in which cathodes 33, 34 act as rectifier, windings 41, 42 as A.C. source, and condenser 55 and resistors 51, 52 as load, whereby high voltage direct positive potential appears at 53, 54 connected to second and first anodes respectively of the cathode-ray tube 17. A good self-regulating characteristic results from the depression of curve I with increase in load, whereby the duration and value of secondary current N and of rectified current P are in-. creased. For smoothing, the ratio of the capacity of condenser 55 to the natural capacitance of the upper terminal of winding 41 to earth is equal to the voltage ratio of winding 41 to winding portion 42a. When source B has a sufficiently high voltage Q, collector electrode 34 needs no A.C., and control electrode 32 may receive direct volts only or enhanced alternating volts by connecting it to the lower or upper end of winding 43. Tap 48 of resistor 44 may provide a bias for the brilliancy control electrode of tube 17. In a modification, Fig. 3 (not shown), a single valve unites the functions of both valves 40, 30. It has similar electrodes 31, 33, 34 and two other electrodes 61, 62 which serve as grid and anode respectively of the oscillator system. As shown in Fig. 4, electrode 62 is formed of turns of relatively coarse wire aligned with those of collector 34 and spaced midway between those of control electrode 61 from which they are spaced by a distance smaller than the winding pitch. Thus the oscillator efficiency is increased by the lowered resistance of the electron path to electrode 62 which acts as a screen to shield collector electrode 34 from the electron flow from cathode 31 and to reduce that flow to electrode 33 to a suitable value.