Patent Application
20140001344
The present invention relates generally to night vision devices, and more particularly, to night vision devices with switched mode power supplies.
Night vision devices are optical instruments that allow images to be produced in levels of light approaching total darkness. Such devices are commonly used by the military and law enforcement agencies. Night vision devices amplify light to form images, and allow a user to easily see through the darkness. These devices usually refer to a complete unit including an image intensifier tube and a power supply. The image intensifier tube absorbs the surrounding light, converts the light into electronic patterns, changes them into light discernible by a user, and transmits the light to a photosensitive screen. There are several generations of image intensifier tubes.
An image intensifier tube comprises different components. For example, an image intensifier tube usually includes a micro-channel plate (MCP), which is a planar component used for detection of particles, e.g., electrons or ions, and impinging radiation, e.g., ultraviolet radiation and X-rays. An MCP intensifies single particles or photons by the multiplication of electrons via secondary emission. In addition, an image intensifier tube also includes a screen which displays the output of the image intensifier tube. Phosphor is commonly used on the inside surface of the screen to produce the image. Different phosphors are used on the inside surface of the screen of different image intensifier tubes. Further, an image intensifier tube includes a photocathode, which is a negatively charged electrode that emits electrons when struck by a quantum of light. Optionally, a plain metallic cathode is coated with specialized coating that increases the photoelectric effect. As a result, photocathodes of different intensifier tubes have different coatings as well as different photocathode materials.
Night vision devices require high voltage power supplies that transform low direct circuit (DC) voltage to one or different levels of high DC voltages depending on the voltage requirements of various components of a night vision device. One battery or more 1.5V to 3V batteries are typically used to power the device. Typically, two N-cell or two “AA” batteries are used. Power supplies convert the battery voltage to a high DC voltage, e.g. 5000V, to power the image intensifier tube. Different components of the image intensifier tube may require different levels of high DC voltages. Current generations of night vision device power supplies utilize oscillators, combined with high voltage transformers and voltage multipliers, to produce high voltage DC output to light the image intensifier tube. Sinusoidal oscillators produce input to voltage multipliers, which boost and rectify the signal, and subsequently produce high DC voltages to power the night vision device. However, this solution is physically large and all the output voltages move together rather than independently. Additionally, analog oscillators are sensitive to temperature and part tolerance, and thus are difficult to build consistently in volume.
Further, because different night vision devices comprise different components that may have different voltage requirements, transformers are then application-customized because the requisite turns-ratio may vary for different night vision devices. Because a night vision device's screen resolution can be adjusted by altering the photocathode voltage (even for night vision devices using the same screen), different transformers are needed for powering different night vision devices operating the same screen at different resolutions. As a result, conventional solutions are extremely expensive. Moreover, transformers are inefficient, have high losses, and generate heat. Often, transformers are implicated as the point of failure in product returns.
In addition, night vision tube power supplies deliver Nanoampere(nA) scale currents to the tube, which needs to be sensed in order to provide control. In current designs, this output current is either estimated, or sensed directly using resistors and operational amplifiers (OpAmps.) Nevertheless, the estimation is ineffective and sensing using resistors and OpAmps adds to the overall cost and complexity of power supplies for night vision devices.
Embodiments of the present invention are directed toward a switched mode design of night vision tube power supplies. By utilizing a switched mode design, low cost commercially available inductors replace transformers to generate the high voltage pulses needed for the voltage multipliers. The topology is physically smaller and has a lower cost as it accommodates all needs of different night vision devices comprising different image intensifier tubes.
According to various embodiments of the present invention, separate switching circuits generate the photocathode voltage, the MCP voltage, and the screen voltage. Output voltages of the switching circuits vary from 0V to the maximum output, and thus capable of accommodating various voltage needs of different image intensifier tubes of different night vision devices.
According to one embodiment of the present invention, a night vision device comprises an image intensifier tube and a switching power supply which comprises a first switching system generating a photocathode voltage and comprising a first switch for turning on and off a first input voltage in response to a first instruction signal; a second switching system generating a micro-channel plate (MCP) voltage and comprising a second switch for turning on and off a second input voltage in response to a second instruction signal; a third switching system generating a screen voltage and comprising a third switch turning on and off a third input voltage in response to a third instruction signal; and a drive voltage regulator converting a battery voltage to the first input voltage, the second input voltage, and the third input voltage.
Other features and aspects of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features in accordance with embodiments of the invention. The summary is not intended to limit the scope of the invention, which is defined solely by the claims attached hereto.
The present invention, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments of the invention. These drawings are provided to facilitate the reader's understanding of the invention and shall not be considered limiting of the breadth, scope, or applicability of the invention.
These figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the invention be limited only by the claims and the equivalents thereof.
The present invention, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments of the invention. These drawings are provided to facilitate the reader's understanding of the invention and shall not be considered limiting of the breadth, scope, or applicability of the invention.
The switched mode power supply 102 also includes a photocathode voltage circuit 106, a MCP voltage circuit 107, and a screen voltage circuit 108. In one embodiment, the photocathode voltage circuit 106, the MCP voltage circuit 107, and the screen voltage circuit 108 are all switching resonant circuits. The photocathode voltage (output of the photocathode voltage circuit 106) powers the photocathode 103; the MCP voltage (output of the MCP voltage circuit 107) powers the MCP 104; and the screen voltage (output of the screen voltage circuit 108) powers the screen 105. In one embodiment, either one or two AA batteries are used and the photocathode voltage, MCP voltage, and the screen voltage rise to maximums of −2100V, −1200V, and 4800V, respectively.
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The output photocathode voltage is continuously variable from 0V to the maximum voltage. The maximum voltage is determined by the number of multiplier stages. In one embodiment, a user may select the output photocathode voltage level or the resolution level which is adjusted by altering the photocathode. Higher resolution requires higher photocathode voltage level but draws more power from the battery. The photocathode voltage controller 501 may include a PWM generator.
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In one embodiment, the method may compare a feedback voltage to a reference voltage when generating the instruction signals. In another embodiment, the method may regulate the screen current to a fixed value by altering the instruction signal to alter the MCP voltage. In a further embodiment, the method may regulate the photocathode current to a fixed value by altering the instruction signal to control the gating duty cycle.
The terms “less than,” “less than or equal to,” “greater than,” and “greater than or equal to,” may be used herein to describe the relations between various objects or members of ordered sets or sequences; these terms will be understood to refer to any appropriate ordering relation applicable to the objects being ordered.
As used herein, the term “module” might describe a given unit of functionality that can be performed in accordance with one or more embodiments of the present invention. As used herein, a module might be implemented utilizing any form of hardware, software, or a combination thereof. For example, one or more processors, controllers, ASICs, PLAs, PALs, CPLDs, FPGAs, logical components, software routines or other mechanisms might be implemented to make up a module. In implementation, the various modules described herein might be implemented as discrete modules or the functions and features described can be shared in part or in total among one or more modules. In other words, as would be apparent to one of ordinary skill in the art after reading this description, the various features and functionality described herein may be implemented in any given application and can be implemented in one or more separate or shared modules in various combinations and permutations. Even though various features or elements of functionality may be individually described or claimed as separate modules, one of ordinary skill in the art will understand that these features and functionality can be shared among one or more common software and hardware elements, and such description shall not require or imply that separate hardware or software components are used to implement such features or functionality.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. Likewise, the various diagrams may depict an example architectural or other configuration for the invention, which is done to aid in understanding the features and functionality that can be included in the invention. The invention is not restricted to the illustrated example architectures or configurations, but the desired features can be implemented using a variety of alternative architectures and configurations. Indeed, it will be apparent to one of skill in the art how alternative functional, logical or physical partitioning and configurations can be implemented to implement the desired features of the present invention. Also, a multitude of different constituent module names other than those depicted herein can be applied to the various partitions. Additionally, with regard to flow diagrams, operational descriptions and method claims, the order in which the steps are presented herein shall not mandate that various embodiments be implemented to perform the recited functionality in the same order unless the context dictates otherwise.
Although the invention is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations, to one or more of the other embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments.
Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as meaning “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; the terms “a” or “an” should be read as meaning “at least one,” “one or more” or the like; and adjectives such as “conventional,” “traditional,” “normal,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future.
The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. The use of the term “module” does not imply that the components or functionality described or claimed as part of the module are all configured in a common package. Indeed, any or all of the various components of a module, whether control logic or other components, can be combined in a single package or separately maintained and can further be distributed in multiple groupings or packages or across multiple locations.
Additionally, the various embodiments set forth herein are described in terms of exemplary block diagrams, flow charts and other illustrations. As will become apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives can be implemented without confinement to the illustrated examples. For example, block diagrams and their accompanying description should not be construed as mandating a particular architecture or configuration.
