| 摘要 |
PURPOSE:To detect a broken filament in either case that a bulb is on or off by discriminating a voltage across a detecting resistance by means of a comparator through a current flowing the detecting resistance when the bulb is on and detecting the broken filament through voltage detection when the bulb is off. CONSTITUTION:For example, when flicker signals are input to the gate G of a field effect transistor(FET) 3 so that the input of the FET 3 is at an H level, the FET 3 is ON to light on a bulb 1 and if the bulb 1 is in a normal condition the drain D-side point A of the FET 3 is at a L level and the output terminal B of a comparator 4 is at an H level, and when the gate G of the FET 3 is at a L level the FET 3 is OFF to light off the bulb 1 but the drain D-side point A of the FET 3 is at an H level, so that output signals are obtained in both cases. When the broken filament of the bulb 1 occurs, both of the drain D-side point A of the FET 3 and the output-side point B of the comparator 4 are at an L level regardless of the condition of the FET 3, so that output signals are not obtained in both cases. It is thus possible to detect the broken filament in either case that the bulb is on or off. |
