Filament power supply circuit for vacuum fluorescent display

摘要

In a filament power supply circuit of a vacuum fluorescent display, an integration circuit is connected to a signal input terminal which receives a pulse signal having a magnitude corresponding to a DC power supply voltage. A comparison circuit compares an output voltage from the integration circuit with a reference voltage, and outputs a result. A first filament cathode connection terminal is connected to one terminal of the filament cathode of a vacuum fluorescent display and applies the DC power supply voltage to the one terminal. A second filament cathode connection terminal is connected to the other terminal of the filament cathode to ground the other terminal via a capacitive element. A three-terminal element includes first, second, and third terminals. The first terminal is connected to the first filament cathode connection terminal. The second terminal is grounded. The third terminal receives the output from the comparison circuit so that the path between the first terminal and the second terminal is switched in accordance with it.