| 摘要 |
<p>The circuit has a first comparator (14) for producing a feedback error signal (E) that represents the difference between a reference signal (VR1) and a feedback signal. The state of a switch (16), controlled by a logic circuit (18), determines if the feedback signal is non-light (F1) or light (F2) feedback. The feedback error signal is fed to a power control circuit (12) that powers the discharge lamp (10). The non-light feedback is provided by a summing amplifier (20) with inputs from a feedback loop (22) and a designated input (24) that may include a special power profile, over time, of lamp warm-up. The light feedback is generated while the lamp is in operation. A phototransistor (26) senses the lamp light (10A) and the resultant current is converted to a voltage by an operational amplifier (28). A DAC (30) produces a current (F2') that is converted (34) to a voltage that acts as the light feedback source and as an input to a second comparator (38). The counter (32) calibrates lamp operation by adjusting gain in the DAC depending on the signal from the second comparator.</p> |
