Filament detection circuit

A ballast comprising:

• a driver circuit to generate an oscillating current signal;
• a filament heating circuit to heat filaments of at least one lamp connected to the ballast, wherein the filament heating circuit comprises:
• a heating transformer having a primary winding and a secondary winding, each adapted to conduct current, wherein the primary winding is connected to the driver circuit and the secondary winding is coupled to the primary winding and adapted to be connected to the at least one lamp;
• and
• a switching circuit connected to the primary winding, wherein the switching circuit has a duty cycle to control the current signal provided from the driver circuit to the primary winding to heat the at least one lamp;
• a current detector circuit connected to the switching circuit to detect a particular parameter of the current conducted by the primary winding, wherein the particular parameter is indicative of a total number of particular lamp filaments connected to the ballast;
• and
• a control circuit connected to the current detector circuit and to the driver circuit, wherein the control circuit is configured to generate and transmit an output signal to the driver circuit based on the particular parameter detected by the current detector circuit.