GB1485166A - Ballast circuit for a gaseous discharge lamp - Google Patents

Abstract

1485166 Supply circuits for discharge lamps GENERAL ELECTRIC CO 30 Oct 1974 [2 Nov 1973] 47006/74 Heading H2H In order to avoid large variations in the light output from a fluorescent lamp due to increases in the ambient temperature around the lamp apparatus a capacitive circuit 7 is provided, the capacitance of which decreases with an increase in ambient temperature. The impedance of the circuit 7 thus increases to decrease the power dissipation of the lamp with a resulting decrease in the ambient temperature. The combination of the decrease in lamp power dissipation and decrease in ambient temperature allows the light output of the lamp to remain nearly constant. The circuit 7 may comprise a capacitor 19 in parallel with a capacitor 22 and a thermistor 21 in series. An increase in temperature causes the thermistor 21 to effectively remove the capacitor 22 from the parallel circuit. In alternative embodiments the circuit 7 may include a bimetal switch or a triac controlled by a thermistor for removing the capacitor 22 from circuit. Furthermore the capacitor 22 may be of the kind having capacitance variable with temperature or may be placed in series with the capacitor 19. Lastly the circuit 7 may comprise only a capacitor having capacitance variable with temperature. The lamp apparatus may include two lamps 9, 10, having filamentary electrodes 12, 13, 17, 18 heatable from windings 6, 14, 15 of a transformer 4 having a primary winding 3 and a secondary winding 5. Capacitor 16 is provided for starting purposes and the capacitor 19 will provide power factor correction.