Ballast circuit for controlled regulation of high pressure sodium lamp - measures instantaneous current to control colour temp. by current level and pulse rate

摘要

A high pressure natrium lamp (V) is coupled to a starter circuit (IV) that connects to a bridge rectifier having four solid state switches (III). A regulator circuit (VI) provides gating pulses (G1-G4) for the bridge. The bridge receives voltage pulses (H) from a converter (II) and rectifier network (I). The pulses have a controlled mark to space ratio. The converter is controlled by the regulator, the clock pulses being provided by a generator (VII). A comparator (VIII) compares the measured instantaneous current with upper and lower levels to effect control. The change in mark to space ratio (delta D) in comparison with the change in current (delta I) is such that delta D/delta I is less than zero. ADVANTAGE - Allows control of colour temp. by limited change in current.