| 摘要 |
<p>A protection method (10) and protection circuit (500) for protecting an inverter (300) in an electronic preheat ballast (100) for powering fluorescent lamps (900). The protection circuit (500) comprises a frequency shift circuit (600), a latch circuit (700), a current source network (520), a current sensing circuit (510), and a DC supply capacitance (502). The protection method (10) includes the steps of: (a) providing a filament preheat period by initially setting the inverter drive frequency at a first frequency; (b) shifting the drive frequency to a second frequency for igniting and operating the lamps; (c) changing the drive frequency back to the first frequency in response to a lamp fault; and (d) providing, upon correction of the lamp fault, a filament preheat period prior to attempting to ignite and operate the lamps.</p> |
