Abstract: A backlight display system having a display screen illuminated directly by high intensity daylight lamps and illuminated indirectly by lower intensity nightlight lamps positioned to reflect their light off the daylight lamps and onto the display screen. The backlight display system includes intensity gradient filters and/or distribution lenses to enhance the uniformity of reflected nightlight, a brightness enhancement filter/diffuser disposed before the display screen, and optical filtering positioned between the illumination sources and the display screen. Photosensor controlled intensity feedback is used to provide smooth continuous dimming transition from a wide range of maximum to minimum intensity. The system also provides a third monochromatic nightlight lamp array for "class A" Night Vision Imaging System (NVIS) compatibility and an override switch to assure that lighting restrictions needed for night-vision are maintained.

Abstract: A system wherein light from a fluorescent lamp is dimmed by modulating the pulse-width of current pulses. A current-command signal is applied to a lamp driver in response to a voltage-level corresponding to a given, selectable level of desired lamp brightness. The lamp driver operates as a flyback AC power source that advantageously uses a FET switch to decouple the lamp and a resonant bridge, with the current-sampling process. The circuit samples only the inductor current while the FET switch is active. Because the sample is decoupled from the lamp and bridge, this sampling provides particularly tight control of the regulation process needed to control the incoming noise and transients that affect the power supplied to the lamps. The lamp driver a can also operate as a synchronously-driven resonant forward converter that senses the current actually supplied to the lamp and responds to changes in the fluorescent lamp's condition since the lamp is coupled to the circuit.

Abstract: Various video signals provide horizontal sync pulses for generating a horizontal drive signal only during a horizontal sync portion and part of the vertical sync portion of a video signal. The invention generates a horizontal drive signal in the absence of horizontal sync pulses through the use of a phase locked loop (PLL) connected in feedback to horizontal counter logic. The counter logic receives pulses from the phase locked loop and at a predetermined count generates a horizontal drive signal. During the horizontal sync portion of the video drive signal, the frequency of the phase locked loop is determined by a time difference between a second signal derived directly from a horizontal sync pulse and a first signal generated by a predetermined count. The horizontal drive signal is thus synchronized to the horizontal sync pulses.

Abstract: A processor controlled fluorescent lamp dimmer circuit is shown for use in an aircraft display system utilizing a fluorescent lamp in the backlight system of individual LCD display devices. By use of a processor control dimming circuit in control over each LCD display, greater flexibility, e.g., as by adjustment in software parameters, is made possible in the operation of a dimmer control circuit. The dimmer control circuit reacts to such conditions as ambient light within the aircraft cockpit, fluorescent lamp light energy output, and fluorescent lamp temperature to provide substantially consistent actual and perceived luminance on the LCD display as a function of such detected conditions. Furthermore, the processor control achieves the desired luminance without over-driving, and therefore deteriorating, the lamps. As a result, the pilot of the aircraft enjoys a more reliable and consistent LCD display and need not be distracted by variation in luminance of the LCD display in operation of the aircraft.