Patent attributes
Light sources (1) such as retrofit light emitting diode tubes comprise light circuits (11) with light emitting diodes (12) and feeding electrodes (13, 14), terminals (21-24) for exchanging signals with ballasts (2, 3) or supplies (4, 5), and filament circuits (31, 41) for coupling the terminals (21-24) and the feeding electrodes (13, 14). The filament circuits (31, 41) comprise switch circuits (32) and trigger circuits (33) for in response to presences of frequencies in the signals bringing the switch circuits (32) into conducting modes to introduce relatively low impedances in the filament circuits (31, 41). In non-conducting modes the switch circuits (32) introduce relatively large impedances. This way, in case the light source (1) is connected to a high-frequency ballast (2), the switch circuit (32) is triggered and the light source (1) is normally activated. In case the light source (1) is connected to mains (4) or an external direct-current driver (5) or an electro-magnetic ballast (3), the switch circuit (32) is not triggered, and the light source (1) is not activated and protected against damage.
