| 摘要 |
<p>A ballast (10) for powering a gas discharge lamp includes a lamp-out detection circuit (300) that quickly responds to a lamp-out condition. Lamp-out detection circuit (300) receives a portion of the lamp current and provides a detection voltage. The detection voltage remains at a first average level while the lamp is conducting current in a normal manner, but quickly decreases below a second level if the lamp ceases to conduct current. In a preferred embodiment, ballast (10) includes an inverter (100) and a resonant circuit (210,220) that are normally operated at a high frequency. The detection voltage is coupled to an enable input (112) of an inverter drive circuit (110), and the inverter (100) is either shut off or operated in a low-power mode within less than ten high frequency cycles after occurrence of a lamp-out condition.</p> |
