GB779024A - Improvements in or relating to circuit arrangements for controlling gas- or vapour-filled discharge tubes - Google Patents

Abstract

779,024. Rectifying. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Feb. 11, 1955 [Feb. 13, 1954], No. 4152/55. Class 38 (2). The instant of ignition of a gas- or vapourfilled valve 8 through which a load 9 is supplied with D.C. from a source of A.C. 10, is controlled by varying its grid-cathode voltage which is the sum of an alternating voltage from transformer 7 and the voltage drop across resistor 5 which is in the anode-cathode circuit of a hard valve 1 in series with a battery 6. Conductivity of valve 1 is controlled by variation, e.g. by a high-speed circuit breaker, of the unidirectional voltage of source 4 which is connected in series opposition to a battery 2 and in series with a source 3 of alternating voltage. With zero voltage of source 4, valve 1 carries saturation anode current and the consequent voltage drop a, b, c, d, Fig. 4, added to voltage 22 of source 7 gives a resultant cathode voltage 23 to valve 8 which, being less than the required value 20 does not fire valve 8. When voltage 4 increases, the voltage across resistor 5 becomes e, f, g, h, Fig. 5, and the resultant grid voltage 24 rises above valve 20 at point 25 to fire valve 8 at instant 26 in the positive halves of the anodecathode voltage wave 16. As voltage 4 increases, the instant of firing advances. The trailing edge of the firing peak follows closely the voltage 22 which leads the anode-cathode voltage 16 by 30 degrees so that when the latter reverses the grid of valve 8 is negative and danger of back fire is reduced. Voltage from source 3 leads voltage 22 from source 7 by 45 degrees. In a three-phase circuit, Figs. 7, 9 (not shown), the danger of back firing before ignition of the incoming phase may be reduced by arranging an R.C. circuit in the grid circuit of valve 8, Fig. 8 (not shown), whereby the phase of voltage 22 is altered and a negative direct voltage is added to it.