Importance

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Abstract

A power supply circuit for a vacuum fluorescent display includes a boosting coil, input terminal, switching transistor, PWM control circuit, boosting circuit, first filament terminal, and second filament terminal. The boosting coil is provided in a current path to generate an induced voltage in accordance with a change in current flowing therein. The input terminal receives a DC voltage to be applied to one terminal of the boosting coil. The switching transistor is provided between the other terminal of the boosting coil and a ground line. The PWM control circuit periodically turns on/off the switching transistor. The boosting circuit generates a boosted voltage on the basis of an induced voltage generated at the other terminal of the boosting coil when the switching transistor is switched from ON to OFF. The first terminal is connected to the node between the other terminal of the boosting coil and the switching transistor. A DC voltage lower than the induced voltage generated at the other terminal of the boosting coil is applied to the second terminal.

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First Claim