Abstract: A voltage regulator circuit provides an economical approach for maintaining the RMS filament voltage of vacuum fluorescent tubes within an acceptable voltage range during input supply voltage variations. The regulator circuit includes substantially identical upper and lower clipper circuits which clip the AC voltage of a step-down transformer secondary. The supply voltage is allowed to vary so that the secondary voltage is outside of the acceptable range of voltage defined by substantially identical voltage reference circuits. Each of the voltage reference circuits is coupled to its respective clipper circuit and to the center tap of the secondary winding of the transformer so that the regulator circuit and the clipped output voltage are symmetrical about the center tap. Th regulator circuit is simple and power-efficient while keeping the filament voltage within the acceptable range of voltages.

Abstract: An interface circuit for reading data to a programmable message display is provided wherein input power is reduced through sampling techniques and circuit complexity is reduced through multiplexing. Stable operation is providing in the presence of noise when the interface circuit is coupled to a device, such as a programmable controller. The circuit includes a plurality of input circuits which receive and condition a like plurality of parallel input data signals. A reference signal generating circuit is responsive to control signals from a microprocessor of the display to provide reference signals. A like plurality of comparator circuits are coupled to their responsive input circuits and to the reference signal generating circuit. Different banks of the comparator circuits sequentially compare the conditioned input signals with the reference signals. Isolation circuits are coupled to the outputs of the comparator circuits.