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.