GB1289118A - - Google Patents

Abstract

1289118 Starting discharge lamps GENERAL ELECTRIC CO Ltd 12 Oct 1970 [10 Oct 1969] 49916/69 Heading H2H A starting circuit for an electric discharge lamp comprises a voltage transformer, a charging circuit including resistance and capacitance which in use in adapted to be charged by a power supply for the lamp, and a discharge circuit responsive to the voltage developed across the capacitance to discharge same into the primary of the transformer when that voltage attains a predetermined value. In the embodiment shown, a lamp and an A.C. or D.C. supply is in use placed across terminals 2, 3, and in operation, capacitor C 1 is charged via a diode D 1 until the reverse potential across Z 1 is sufficient to cause breakdown and trigger SCR 1 causing C 1 to discharge into the primary of the transformer T 1 , the high voltage pulse generated in the secondary being sufficient to start the lamp. The time constant of the R-C circuit is preferably greater than the frequency of the supply e.g. 1 second. In the event of the lamp failing to ignite, a protective system is incorporated, the resistor R 2 being a thermistor and arranged to be thermally connected to R 1 , whereby, after operation of the circuit for a particular time preferably in the range 1-5 minutes, the resistance of R 2 will fall to a value whereby the breakdown voltage of Z 1 across C 1 is not attached. In a modification, Fig. 5 (not shown), such protective features are provided by a second capacitor (C 3 ) in parallel with a resistance (R 10 ) of the potential divider, the capacitor being in the emitter-base circuit of a normally non-conducting transistor (X 1 ) and in parallel with a further Zener diode (Z 3 ) connected to the emitter. In use, in the event of lamp failure, the capacitor (C 3 ) is charged to the reverse breakdown voltage of the diode (Z 3 ) to render the transistor (X 1 ) conducting to allow discharge of the capacitor C 1 through collector resistance (R 12 ). Several alternative embodiments are mentioned: the diode Z 1 may be replaced by a resistance arrangement or other breakdown diode: the rectifier SCR 1 may be replaced by a two terminal breakdown device.