| 摘要 |
PROBLEM TO BE SOLVED: To prevent an adverse effect on an AM radio unit mounted on a vehicle and the like, by cutting high frequency components of AC voltage output from a transformer and generating a rounded AC voltage waveform. SOLUTION: A waveform shaping circuit 6 is provided with a resistor 18 for low pass filtering with its one end connected to one end of a secondary coil 11 which constitutes a transformer 5 and the other end connected to an output terminal 17, a resistor 20 for low pass filtering with its one end connected to the other end of the secondary coil 11 and the other end connected to an output terminal 19, and a capacitor 21 for low pass filtering connected between the other ends of the resistors 18, 20. High frequency components of AC voltage outputted from the secondary coil 11 are cut and a rounded AC voltage waveform is generated and then is supplied as filament voltage Vf to a fluorescent character display tube. By this method, radiant noise can be remarkably reduced. |
