| 摘要 |
<p>A ballast (104) to power a lamp (106) includes two switches, each to selectively connect the ballast (104) to respective high voltage terminals, each having two states (ON and OFF). The ballast (104) also includes a converter circuit (130) that provides a voltage to energize the lamp (106), and a detector circuit (132). The detector circuit (132) includes two inputs, each coupled to a respective switch; two resistors, each coupled to a respective input; two outputs, each connected to the converter circuit (130); a transistor network; and a capacitor (C4). One output provides the converter circuit (130) with power, and is connected to the input via the resistors. The other provides the converter circuit (130) with a control signal, indicating a voltage level so as to power the lamp (106) to a particular light level, depending on the switches' states. The transistor network detects a differential voltage between the inputs, generating the control signal as a result. The capacitor (C4) smoothes the control signal.</p> |
