HID lamp driver with phase controlled resonant-mode ignition detection and fast transition to LFSW warm-up mode

The paper presents an integrated lamp ignition and ballast with a resonant ignition and fast transition to low-frequency square-wave mode for warm-up and steady-state operation. The circuit employs a soft-saturation core inductor in order to reduce size as well as to control Q factor. Phase control is used in the resonant mode to track the changing inductor value. Ignition detection is performed by monitoring the actual phase, and comparing it to the previous phase. A dramatic shift indicates a change in the lamp impedance, corresponding to lamp ignition. Current is controlled in order to stabilize the arc, and allows for manipulation of the current envelope during warm-up. During steady-state, an outer power loop controls overall lamp power. This ignition and startup differs from previous work in that the warm-up is conducted in the low-frequency square-wave mode, requiring a larger stable operating load resistance range, as lamp resistance varies during warm-up. Fast low-frequency square-wave transitions are obtained by use of a time-optimal control. Experimental tests demonstrate successful acoustic resonance free lamp operation of a 150 W high pressure sodium lamp.