A filament driver circuit 33, interposed between a fluorescent lamp 30 and a phase controlled dimmer 32, comprises a transformer 38 having a primary winding 39 connected to the dimmer 32 and secondaries 40 connected to the lamp filaments, and a high pass filter which passes to the filaments only harmonic components of the output voltage from dimmer 32. The filter may be an active device, or may be formed by the primary 39 and a capacitor 41. A bleed device 43 discharges capacitor 41 before each firing cycle of the dimmer 32 and may be formed by a switched device or a resistor such as an incandescent lamp. Circuit components may be arranged so that secondaries 40 have an output that rises from 3 volts with the dimmer 32 at a maximum light setting, to 4.5 volts with dimmer 32 at a minimum light setting. The transformer 38 may have a further secondary (44), (Fig. 4) auto wound with primary 39 to provide an increased lamp starting voltage, a capacitor (45) acting effectively to open circuit secondary (44) when the lamp is operating.
|IPC||H05B 41/232,H05B 41/392|
|Publication status||Submitted - 30 Nov 1988|