AN-E-1901a Operating Parameters for Vacuum Fluorescent Displays - FUTABA America - #1

This Application Note AN-E-1901A describes cautions to be exercised when operating VFD's properly. To avoid occurrence of problems in quality, full understanding of all the items listed below is required prior to using VFD's in designing and assembling process.

1. ELECTRICAL OPERATING CONDITION 1.1 Filament Voltage

(1) The life of VFD's depend considerably upon the cathode temperature. The filament voltage is properly applied within the rating to achieve uniform luminance. Brightness should never be adjusted by changing the filament voltage.

(2) When a VFD designed for AC filament voltage has DC filament voltage applied, a brightness gradient will be caused horizontally between the digits. Thus, only VFD's specially designed for DC filament voltage should be used in such case.

(3) The value of the filament voltage shall be set so that the effective r.m.s. value may co­incide with the rating; even when the waveform is different from a sine wave.

(4) The cut-off bias (Ek) should be applied to the center tap provided in the filament trans­former; or a neutral point in the filament circuit.

(1) The correlation of brightness to voltage is much larger than that of the anode and grid voltages, approximately 2.5 powers. Therefore, set the voltage in order to obtain the brightness.

(2) The operating voltage should be set referring to the operating range chart "Du-eb-ec". Set the value according to the duty cycle within the maximum rating.

(3) The required brightness varies depending on the operating environment (ambient bright­ness). The operating condition should correspond to the operating environment.

(4) In case of drawing cut-off bias (Ek) from one power source, the voltage determined by adding Ek to the value eb-ec set in the item (2) above is required as a power supply voltage.

(5) When the brightness is adjusted by changing the anode and grid voltages, luminous non-uniformity can occur if operated at the minimum rating or less.

Adjusting brightness by changing the duty cycle is preferred.

(6)