| 摘要 |
An improved ballast circuit (49) for use with a compact fluorescent lamp includes an EMI filter (44), a rectifier and a voltage amplification stage (48), an active resonant circuit (52), a dimming circuit (56), and a power factor correction stage (52) which is connected to a lamp load (60). In one embodiment, the ballast circuit operates in cooperation with a three way switch (1) to adjust the light output of the lamp to three discrete levels corresponding to each setting of the three way switch (1). In another embodiment, the ballast circuit (49) includes a feedback capacitor (C9) which provides a feedback path (55) for a portion of the high frequency current to the rectifier and voltage amplification stage (48). In still another embodiment, the ballast circuit is configured to accept input from a triac or an SCR device (71). In all of the embodiments, the dimming circuit (56) works with the active resonant circuit (52) to vary the amount of power that is supplied to the lamp load (60). Further, the ballast circuit embodiments automatically limit the voltage buildup in the lamp filaments (A, B) at the end of their lifetime to prevent catastrophic failure of fluorescent and compact fluorescent lamps. |
