| 摘要 |
The invention provides a lamp driver circuit for discharge lamps, in particular fluorescent lamps. An inverter (12) receiving DC provides a high frequency AC output. A resonant circuit includes a capacitor (C25) connected across the lamp (13) and a ballast inductor (L2) in series with them. A control arrangement (15, 16) causes the inverter (12) to operate at a frequency above the resonant frequency of the lamp when initially switched on. It is then caused to sweep down in frequency towards the resonance frequency so that the lamp strikes as a result of the magnified voltage applied to it. After the lamp has struck the frequency drops to a suitable running frequency. If the lamp strikes a circuit (L25, 201, 17) controls the frequency to limit the lamp voltage. Another circuit (DCT1, 203, P1, 17 min ) controls the lamp frequency for dimming purposes. The circuit when operative at the initial higher frequency provides heating current through the filament before the lamp strikes since the capacitor (C25) shunts the lamp at such frequency. |
