Lamp ignition detection circuit

摘要

A circuit for detecting the ignition of a fluorescent lamp at any dim position by comparing the phase of the current flowing through the lamp resonant output stage to a predetermined reference phase value. When the phase of the current is coincident with the predetermined reference phase, lamp ignition has occurred and the circuit automatically "closes the loop" so that the lamp power can be regulated (via phase control) to a user designated setting. The phase of the lamp resonant circuit current is measured in the present invention by detecting the zero-crossing of the inductor current as measured across a resistor disposed in the lamp resonant circuit. The only way for the phase of the inductor current to reach the reference phase is if the lamp ignites (provided the frequency is above the resonance frequency and is ramping smoothly from a high frequency down to the ignition frequency). The circuit is designed to wait approximately 10 cycles to avoid closing the loop before the lamp has struck.