A universal dimming topology is provided for an electronic ballast having an inverter providing an output current across first and second output branches for driving a light source in accordance with a dimming control input signal. A filament voltage control block modulates first and second filament heating switches to provide filament heating voltage across first and second connection terminals associated with the output branches. During a preheat operating mode a control block disables the inverter and provides pulse width modulated control signals to the filament voltage control block to modulate the filament heating switches at a predetermined frequency. During a normal operating mode the control block enables the inverter and provides pulse width modulated control signals to the filament voltage control block to modulate the filament heating switches in accordance with a duty ratio based on a detected output current.