| 摘要 |
A ballast ( 20 ) for powering one or more gas discharge lamps ( 70,72,74,76 ) comprises an inverter ( 200 ) and a lamp fault protection circuit ( 400 ). Inverter ( 200 ) has an operating frequency that is load-dependent. Lamp fault protection circuit ( 400 ) monitors an electrical signal within inverter ( 200 ). In response to a change in the fundamental frequency of the electrical signal, such as what occurs when a lamp is removed, when a lamp approaches the end of its operating life, or when an arcing condition occurs at one or more of the ballast output connections ( 302,304,306,308,310 ), lamp fault protection circuit ( 400 ) disables the inverter ( 200 ) for a predetermined shutdown period. Lamp fault protection circuit ( 400 ) also provides a restart function for periodically attempting to ignite and operate the lamps. Additionally, in response to a sustained fault condition, lamp fault protection circuit ( 400 ) increases the predetermined shutdown period so as to minimize any undesirable effects due to the restart function. Lamp fault protection circuit ( 400 ) is preferably realized using a suitable microcontroller integrated circuit ( 420 ) with associated discrete circuitry, and is especially well-suited for use in ballasts for powering multiple lamps via a current-fed self-oscillating inverter and an isolated parallel resonant output circuit. |
