Vacuum tube fluorescent displays (VFDs) are a common display in consumer electronics. Widely used in video recorders, car radios, microwave ovens, etc. Unlike liquid crystal displays (LCDs), VFDs have a high brightness and a clear contrast, which can easily support display units of different colors. This technology is related to cathode ray and cathode tube. Unlike LCD, most VFDs can work effectively below zero, making them ideal for outdoor equipment in cold climates.
The VFD contains three basic electrodes, a cathode filament, an anode (phosphorescent material) and a grid, and a high vacuum glass envelope. The cathode is composed of a tungsten wire, an alkaline earth metal oxide coating (emission electron). The gate is a wire for controlling and transmitting electrons emitted by the cathode. The anode is the electrode and is plated with a phosphorescent material for displaying characters, diagrams or symbols. The electrons emitted by the cathode accelerate under the forward voltage between the gate and the anode, and after striking the anode, the electrons excite the phosphor to emit light. The desired brightness template can be obtained by controlling the positive or negative pressure of the grid and anode. The anode and gate require a DC regulated voltage to prevent the display from flickering. In order to drive large VFDs, the cathode requires an AC drive to avoid brightness variations, such as different brightness levels appearing on both sides of the display. Operating frequencies in the 20" 200 kHz range are recommended to avoid audible noise and flicker.