An electronic circuit for dimming a fluorescent tube can be designed using this circuit diagram. The brightness of a fluorescent tube can not adjust as simple as that of an incandescent bulb because the tube starts only at a much higher voltage than the grid, then stays on mains voltage. The starting voltage level and it depends on the temperature of the tube.
High starting voltage is obtained by interrupting the current flowing through a coil shock. This is usually done by a starter, which also ensure a sufficient current through the filament of the tube. This electronic circuit starter replaces all functions, while allowing and regulating intensity.
During network voltage zero crossing, triac locks instantly, at which capacitor C3 load quickly, resulting in application across the tube, in-instantaneously, the voltage lags the current report. Capacitor C3 and shock coil form a resonant circuit that raises the instantaneous voltage across the tube at a great value, in which the tube starts.
As the grid voltage phase angle triac drive during which is greater, the greater will be the current through the filament, resulting in a lower starting voltage. Since the triac move a larger part of the current, the tube is reduced, so the tube will turn weaker.
When ordering ignition tube brightness control potentiometer, P1 must be put in the position of maximum brightness of the tube, to facilitate startup.
Used triac must have du / dt high value, otherwise during the zero voltage crossings, steep variations of the voltage will remain in the triac conduction.