| 摘要 |
PROBLEM TO BE SOLVED: To provide a filament driving circuit which eliminates the need for arranging a transformer for each kind of a fluorescent character display tube and is easy to change a filament voltage. SOLUTION: A binary counter 1, a comparator circuit 2, a counter 3, an inverter 4, and AND circuits 5, 6 output pulse width modulated signals CTL1, CTL2 of duty ratios in accordance with set data D0-D5. The output circuits 8, 9 switches on-off a positive DC voltage Vfs supplied from a filament power source 7 according to the pulse width modulated signals CTL1 CTL2 and applies pulse-like output voltages F1, F2 to a filament 11a. When the output circuits 8, 9 are brought into an on-off state according to the pulse width modulated signals CTL1, CTL2, the terminal of the filament 11a is connected to a lower potential side.
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