A discharge lamp lighting circuit facilitates carrying out re-ignition and addresses a problem than can arise due to an influence of a capacitor in an auxiliary lighting circuit. A driving voltage generating portion supplies an AC driving voltage to a discharge lamp to be a driving target. An auxiliary lighting circuit is provided on a terminal side of the discharge lamp. An auxiliary lighting capacitor, an auxiliary lighting resistor and a switch are provided in series between the terminal of the discharge lamp and a fixed voltage terminal. A control circuit controls a conducting state of the switch. The switch is brought into an ON state before the discharge lamp is turned ON, and is brought into an OFF state after the discharge lamp is turned ON.

Discharge lamp lighting circuit

An ambient light sensor produces a current signal that varies linearly with the level of ambient light. The current signal is multiplied by a user dimming preference to generate a brightness control signal that automatically compensates for ambient light variations in visual information display systems. The multiplying function provides noticeable user dimming control at relatively high ambient light levels.

Method and apparatus to control display brightness with ambient light correction

An illumination control circuit allows a user to set a desired brightness level and maintains the desired brightness level over temperature and life of a light source. The illumination control circuit uses a dual feedback loop with both optical and thermal feedbacks. The optical feedback loop controls power to the light source during normal operations. The thermal feedback loop overrides the optical feedback loop when the temperature of the light source becomes excessive.

Optical and temperature feedbacks to control display brightness

A switching power supply unit of the present invention a timing generating circuit ( 121 ) which receives a first control signal formed by a rectifier-transistor driving circuit ( 104 ), forms a second control signal based on the first control signal, and supplies the second control signal to a control electrode of the rectifier transistor ( 113 ). The first control signal is synchronized with the switching operation of a half-bridge circuit ( 102 ), and the second control signal exceeds a threshold voltage of a rectifier transistor ( 113 ) at a timing substantially equal to the timing that one edge of the first control signal is generated and falls below the threshold voltage of the rectifier transistor ( 113 ) at a timing earlier by predetermined time than the timing that the other edge of the first control signal is generated.

Switching power supply unit

A xenon arc searchlight or illumination system incorporates a high frequency/high efficiency electronic circuit that allows lamp ballasting and charging of the system battery to occur over a wide range of external DC power supplies. The tolerance to variations in the system battery voltage as well as external battery voltage are increased by providing logic control of the converter circuit through a programmed logic device. The intensity of the arc lamp is smoothly decreased or increased in a continuous manner from a maximum intensity to a minimum intensity beam. Ignition of the lamp at its minimum illumination levels is thereby permitted. The xenon arc lamp is uniquely oriented within the searchlight with respect to the reflector to provide the most concentrated and convergent field of illumination on which the lamp is capable, namely with the anode of the lamp turned away from the forward beam direction in the reflector. The resulting light beam is focused by relative movement of a reflector with respect to the lamp by advancing or retracting the reflector along its optical axis of symmetry on which the lamp is also aligned. The searchlight is designed so that the lamp, reflector and battery assemblies are easily field replaceable without tools. The lamp, ballast, battery and charger are provided in a single rugged package which can be sealed for field use. The searchlight is combined by an appropriate mounting adaptable with other optical detector devices such as cameras, binoculars and night vision telescopes. The beam output is similarly usable with a combination of filters to allow the most varied intensity and wavelengths for a particular application, such as smoke filled environments, surveillance employing near-infrared or infrared illumination, ultraviolet, underwater illumination or illumination with any color in the visible range.

Apparatus and method for operating a portable xenon arc searchlight

A ballast circuit for a high intensity discharge lamp (24) includes a boost converter (16), a boost controller (36), responsive to the boosted dc output voltage, for driving the boost converter (16) to maintain the boosted output voltage at a predetermined level; a buck converter (18); and a buck controller (38) for driving the buck converter to operate the lamp in a transition mode and maintaining the reduced dc output voltage at a preselected level for operating the lamp in a steady mode.

Lake Lau

Papers

Ballast circuit for high intensity discharge lamps