The present invention relates generally to Light Emitting Diode “LED” lighting systems and more particularly LED lighting systems suitably adapted for airfield lighting (e.g. runway, taxiway and obstruction lights)
Airport edge lighting has been in existence for many years utilizing incandescent lighting technology. Conventional designs that utilize incandescent lights have higher power requirements, lower efficiency, and low lamp life which needs frequent, costly relamping by maintenance professionals.
Some airfield-lighting manufacturers are using more efficient devices such as LEDs where the LEDs are arranged in multiple rings shining outward. Optics of some sort are then used to concentrate the light in the vertical and horizontal directions to meet Federal Aviation Administration (FAA) specifications.
LEDs are current driven devices. A regulated DC current flows through each LED when the LED is conducting. There are two primary concerns with a pure DC power source. First, a field insulation resistance fault may degrade faster (corona or arc welder effect) and second, dimming.
Dimming is usually accomplished by reducing DC current, however LEDs are not reliable when operating at lower current levels. For example, LEDs available from Philips Lumileds Lighting Company, 370 West Trimble Road, San Jose, Calif., 95131 USA, Phone: (408) 964-2900, are on a die that contains many individual LED structures. If enough current is not provided, the current is not evenly distributed across the die, causing uneven illumination. Operation below 100 mA becomes extremely sporadic, and the LEDs may fail to light at all. Also, luminous flux output between devices is extremely uneven.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
In accordance with an aspect of the present invention, there is disclosed herein a system and method that contemplates operating an LED at its characterized current (e.g. 400 mA, 1600 mA) for any luminous intensity. A Pulse Width Modulation (PWM) is employed, wherein the pulse width of the pulse width modulated signal is used to control the luminous intensity of the LED. Optionally, the LED can be biased to reduce the intensity of the pulses used to operate the LED.
In accordance with an aspect of the present invention, there is disclosed herein an apparatus comprising a light emitting diode and control logic coupled to the light emitting diode. The control logic is configured to operate the light emitting diode with a pulse width modulated signal having an associated pulse width. The control logic achieves a desired level of luminous intensity from the light emitting diode by adjusting the pulse width of the pulse width modulated signal. “Logic”, as used herein, includes but is not limited to hardware, firmware, software and/or combinations of each to perform a function(s) or an action(s), and/or to cause a function or action from another component. For example, based on a desired application or need, logic may include a software controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), a programmable/programmed logic device, memory device containing instructions, or the like, or combinational logic embodied in hardware. Logic may also be fully embodied as software.
In accordance with an aspect of the present invention, there is disclosed herein an apparatus comprising a light emitting diode and means for operating the light emitting diode coupled to the light emitting diode. The means for operating the light emitting diode is configured to operate the light emitting diode with a pulse width modulated signal having an associated pulse width, achieving a desired level of light intensity from the light emitting diode by adjusting the pulse width of the pulse width modulated signal.
In accordance with an aspect of the present invention, there is described herein a method, comprising applying a pulse width modulated signal having an associated pulse width to a light emitting diode. The pulse width of the pulse width modulated signal is adjusted to achieve a desired luminous intensity from the light emitting diode.
Still other objects of the present invention will become readily apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of at least one of the best modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modifications in various obvious aspects all without departing from the invention. Accordingly, the drawing and descriptions will be regarded as illustrative in nature and not as restrictive.
The accompanying drawings incorporated in and forming a part of the specification, illustrates several aspects of the present invention, and together with the description serve to explain the principles of the invention.
Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than limitations, of the present invention. In accordance with an aspect of the present invention, there is disclosed herein a system and method that contemplates operating an LED at its characterized current (e.g. 400 mA, 1600 mA) for any luminous intensity. A Pulse Width Modulation (PWM) is employed, wherein the pulse width of the pulse width modulated signal is used to control the luminous intensity of the LED. Optionally, the LED can be biased to reduce the intensity of the pulses used to operate the LED.
Referring to
PWM circuit 104 provides pulses to LED 102 to operate LED 102. Control logic 106 controls the width of the pulse sent by PWM circuit 104 to achieve a desired luminous intensity, while operating LED 102 at its characterized current. For example, referring to
A benefit of employing PWM is that PWM helps quench series circuit faults since the power goes to zero volts, reducing galvanic deterioration. Also, since current and voltage levels are lower, cable insulation will last longer. In addition, improved LED life can be achieved because the LED cools off in between pulses, resulting in a lower junction temperature (Tj).
The rise time and fall time of the pulse width modulated signal may also be varied to reduce standing waves.
A problem with narrow pulses is that standing waves can be produced. In accordance with an aspect of the present invention, LED 102 can be biased. Biasing LED 102 can be useful to reduce standing waves by reducing the magnitude of pulses applied to LED 102. For example, referring to
Control logic 106 may suitably comprise a polarity reversing circuit. Reversing the polarity of the current can be useful to mitigate galvanic deterioration.
It should be appreciated that signals 302, 304, 306, 404, 502, 504, 506 of
As illustrated in signal 602, the difference between the positive peak 612 and negative peak 614 of the signal is the operating current (e.g. 400 mA as shown) for LED 102. Because AC PWM signals constantly change polarity, this helps quench series circuit faults and reduces galvanic deterioration.
As was illustrated in
Control logic 204 suitably comprises several circuits for controlling the operation of LED 202. A pulse width modulation circuit (PWM) 206 provides the pulses to LED 202. As already described herein (see e.g.
As illustrated, LED 202 is inside housing 216. A heating element 218 is provided in housing 206 for cold weather operation. Heating circuit 220 controls the operation of heating element 218. Heating circuit 220 can employ a thermostat or other control mechanism for controlling the heating of housing 216 by heating element 218.
An aspect of circuit 200 illustrated in
Referring to
DCR 902 DC PWM signals as described herein to operate LEDs 904. LEDs 904 are operated at their characterized current and pulse width of the PWM signal sent by DCR 902 is varied to achieve the desired luminous intensity from LEDs 904. As already described herein (see
DCR 902 also provides power for operating heater elements 906. Heater elements 906 can be thermostatically controlled. A thermostat can be disposed with heating element 906 inside housing 908 or can be disposed at DCR 902.
Aspects of circuits 800, 900 in
As already described herein (see
An aspect of an alternating DC PWM is that it can allow more fixtures per regulator 1002. Furthermore, transformers 1006 match the load of LEDs 1002 to regulator 1002. This allows the use of regulators that are universal and interchangeable as well as fixtures that are interchangeable with the appropriate transformer. Furthermore, lower gauge wire can be employed in circuit 1000. For example, a 4 amp regulator producing 2 KW would be operating at 500V, enabling 600V wiring to be employed.
The invention is related to the use of computer system 1100 for controlling a LED using pulse width modulation. According to one embodiment of the invention, controlling a LED using pulse width modulation is provided by computer system 1100 in response to processor 1104 executing one or more sequences of one or more instructions contained in main memory 1106. Such instructions may be read into main memory 1106 from another computer-readable medium, such as storage device 1110. Execution of the sequence of instructions contained in main memory 1106 causes processor 1104 to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory 1106. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software. Processor 1104 sends signals to PWM 1112 via bus 1102 to control the operation of PWM 1112. PWM 1112 is responsive to the signals from processor 1104 to vary pulse width, biasing and/or shape of pulses produced by PWM 1112.
The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to processor 1104 for execution. Such a medium may take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include for example optical or magnetic disks, such as storage device 1110. Volatile media include dynamic memory such as main memory 1106. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus 1102. Transmission media can also take the form of acoustic or light waves such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include for example floppy disk, a flexible disk, hard disk, magnetic cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASHPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.
Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to processor 1104 for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system 1100 can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus 1102 can receive the data carried in the infrared signal and place the data on bus 1102. Bus 1102 carries the data to main memory 1106 from which processor 1104 retrieves and executes the instructions. The instructions received by main memory 1106 may optionally be stored on storage device 1110 either before or after execution by processor 1104.
Computer system 1100 also includes a communication interface 1118 coupled to bus 1102. Communication interface 1118 can provide a two-way data communication to an external or remote sight (not shown) using network link 1120. For example, an external device can be employed to control when the lighting system operates and the intensity. The external device can communicate and send commands to computer system 1100 via communication interface 1118. Communication interface 1118 can employ any suitable communication technique. For example, communication interface 1118 may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface 1118 may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface 1118 sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information. Computer system 1100 can send messages and receive data, including program codes, through the network(s), network link 1120, and communication interface 1118. The received code may be executed by processor 1104 as it is received, and/or stored in storage device 1110, or other non-volatile storage for later execution. In this manner, computer system 1100 may obtain application code in the form of a carrier wave.
In view of the foregoing structural and functional features described above, a methodology in accordance with various aspects of the present invention will be better appreciated with reference to
At 1204, a PWM signal is generated for turning the diode on. In accordance with an aspect of the present invention, the duration of the pulse of the PWM is varied to achieve the desired luminous intensity from the LED. Longer pulse widths are used for higher intensity illumination and shorter pulse widths are used for dimmer intensities (see for example
At 206, either one of the rise time or the fall time, or both, of the PWM signal is adjusted. Decreasing the slope (or conversely increasing the amount of time) of the rising and/or falling edges of the PWM signal can mitigate the impact of standing waves. The slope (or amount of time) of the rising and falling edges of the PWM signal can be selected to be proportional with the pulse width. For example, the rising and/or falling edges of the PWM signal can be set to about 5-10% of the pulse width (see for example
At 1208, the PWM signal is applied to the LED. This causes the LED to conduct and emit light during the time period the pulse is at or above the conducting (ON) threshold of the LED.
What has been described above includes exemplary implementations of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.
This application claims the benefit of priority of U.S. Provisional Application No. 60/679,601, filed on May 10, 2005.
Number | Date | Country | |
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60679601 | May 2005 | US |