GB1427336A - Electrical ignition systems in gas burning appliances - Google Patents

Abstract

1427336 Ignition circuits BRITISH GAS CORP 25 Oct 1973 [26 Oct 1972] 49436/72 Headings F4F and F4T A gas burning appliance has an ignition system of the hot wire type comprising a capacitor 12 which is arranged to discharge through the igniter filament 9 so heat the filament for gas ignition, means for connection to an electrical power source 1 for charging the capacitor, and a switch for controlling when the capacitor discharges. The filament 9 is preferably of molybdenum disilicide. In the embodiment of Fig. 1 the connection means comprises a mains transformer 2 and bridge rectifier 5 connected across the capacitor 12 and providing D.C. current for charging the capacitor. Rectifier 5 is also connected across a further capacitor 13 connected through a glow discharge tube 15 to a thyristor 10. Closure of switch 4 causes capacitors 12, 13 to charge at rates determined by resistances 7 and 14 respectively. At a predetermined potential tube 15 arcs and capacitor 13 discharges to trigger thyristor 10 to conducting state. Capacitor 12 then discharges through filament 9 in a high energy pulse. Inductance 8 is such that after discharge of capacitor 12 the current in the circuit is below the holding current of thyristor 10 so that the ignition cycle is repeated as long as switch 4 is closed. In a modification means is provided whereby the ignition cycle is non-repetitive. In a further modification a normally open mechanical switch is provided in series with the capacitor 12 and filament 9 and is closed to discharge the capacitor through the filament.