| 摘要 |
A ballast circuit for energizing a lamp includes an inductive element couple d to an input terminal and a capacitive element coupled to the inductive eleme nt in parallel with the lamp. In one embodiment, the capacitive element include s a plurality of capacitors each of which is coupled in series with a switch t o control the total capacitance provided by the capacitors. By controlling the total capacitance, the intensity of light emitted by the lamp can be selecte d. In another embodiment, a switching element is coupled across one of the capacitors for providing a selected capacitance to the circuit for controlli ng the lamp light intensity. In a further embodiment, a transformer has a first winding coupled in series with the capacitive element with the inductive impedance of the first winding being controlled via a second transformer winding coupled to a control circuit. In another embodiment, a ballast circu it includes a transformer for introducing a series current into the circuit for subsequent detection by a detection circuit. This arrangement can be used to send a data signal from one point in the circuit to another which can be use d to determine a lamp light intensity level.
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