| 摘要 |
A gas discharge lamp 4 is driven by a high frequency pulse train formed by combining a first pulse train with a second pulse train. The two pulse trains may be generated by respective inverters with input drive signals P0, P1 and output transformers T0, T1 having secondaries TP30, TP40 and TP31, TP41 connected in series with one another across the lamp 4. The circuit has a high power factor and may be used for driving a lamp at a steady power, but is particularly intended for dimming metal halide or sodium vapour lamps, or especially fluorescent lamps. A digitized dimming control signal causes the phase of drive signal P0 to be shifted relative to drive signal P1, signals P0 and P1 being in phase for 100% light output and 180 degrees out of phase for 0% light output (Fig.2), so that the outputs from transformers T0, T1 combine to drive the lamp with pulses having a width dependent on the dimming level (Fig.5). Secondaries TP10, TP20 and TP11, TP21 provide high frequency lamp filament heating currents which remain steady irrespective of the dimming level. The circuit may be used to dim a 2.44 m (8 feet) long fluorescent lamp to less than 1% of full light output. |
