Direct current power source for an electric discharge lamp

A power supply for an electric discharge lamp comprising, in combination,

• a source of a direct current potential,
• at least one semiconductor device having a control electrode and a transconductive path, said transconductive path being serially connected with said lamp across said source,
• a fixed ballast resistance connected in parallel with said transconductive path,
• circuit means for establishing a threshold current level, and
• means responsive to the magnitude of current flowing through said lamp for applying a control signal to said control electrode to maintain said transconductive path in a substantially non-conductive state as said lamp is heated immediately following ignition until lamp current decreases to said threshold current level, and for thereafter increasing the conductivity of said transconductive path in response to further decreases in lamp current below said threshold current level.

A power supply for an electric discharge vapor lamp comprising, in combination,

• a source of a direct-current potential,
• a resistive semiconductor ballast circuit connected in series with said lamp across said source,
• means for establishing a threshold current level,
• means for increasing the conductivity of said ballast circuit whenever the magnitude of current flowing through said lamp decreases below said threshold current level, and
• means for decreasing said threshold current level in response to increases in the magnitude of voltage across said lamp.