| 摘要 |
PURPOSE:To wire easily and determine a lamp life correctly even when a plural fluorescent lamps are used by providing a detection circuit to detect a current through a filament power supply, and obtaining a filament breakage detection signal from this detection circuit. CONSTITUTION:A constant voltage is supplied from a filament power supply to each filament of fluorescent lamps 2a, 2b, so a predetermined current flows through it constantly, and thermoelectrons are generated taking this filament for an electrode. A current detecting circuit 5 detects that at least one point is broken for the filaments connected with an output of the filament power supply 3 by reduction of an input current to the power supply 3, and it outputs a breakage signal S. When this signal S is given to a base of a transistor Q6, the transistor Q6 gets off, and a transistor Q5 also gets off. A power is thus prevented from being supplied to a high voltage generating circuit 4, and action of a circuit 4 is stopped. |
