Patent ID: 8115420
Filing Date: 2012-02-14
Classification: H05B

Abstract:
1. A filament power supply circuit of a vacuum fluorescent display, comprising: an integration circuit connected to a signal input terminal which receives a pulse signal having a magnitude corresponding to a DC power supply voltage; a comparison circuit which is connected to said integration circuit, compares an output voltage from said integration circuit with a reference voltage, and outputs a result; a first filament cathode connection terminal which is connected to one terminal of a filament cathode of a vacuum fluorescent display and applies the DC power supply voltage to said one terminal of the filament cathode, the vacuum fluorescent display including the filament cathode, an anode spaced apart from the filament cathode and having a fluorescent material applied, and an evacuated container that accommodates the filament cathode and the anode; a second filament cathode connection terminal which is connected to the other terminal of the filament cathode to ground said other terminal of the filament cathode via a capacitive element; and a three-terminal element including a first terminal, a second terminal, and a third terminal, the first terminal being connected to said first filament cathode connection terminal, the second terminal being grounded, and the third terminal receiving an output from said comparison circuit so that a path between the first terminal and the second terminal is switched in accordance with the output from said comparison circuit.