Starting and operating circuit for gas discharge lamp

摘要

Starting and operating power is provided to a gas discharge lamp by a circuit which includes a constant-voltage current-limiting ferroresonant transformer connected to an AC source and having high and low voltage output terminals. A full-wave rectifying bridge is selectively connectable to either the high or low voltage output terminals by relay control means which includes a choke coil connected in series with the lamp and a magnet reed. On starting of the lamp the magnetic flux of the choke coil operates the reed for shifting to the low voltage condition, and on extinguishing of the lamp the collapse of the choke coil flux operates the reed for shifting to the normal high voltage condition. A transient high voltage starting pulse is applied to the lamp across a spark gap by a pulse generating starting circuit in which a capacitor, charged from the DC output, is discharged through a self-commutating SCR and an ignition transformer. The transient pulse is effectively blocked from the DC supply by the choke coil and two diodes. Capacitive discharge means is also provided for maintaining operating voltage to the lamp during the switching of the power supply. For higher power applications there is provided an alternative AC supply circuit utilizing two constant-voltage current-limiting ferroresonant transformers, the control means switching the transformers between series and parallel connection for high and low voltage output, respectively.