Patent Application
20090296391
The present invention relates to light emitting diode (LED) lighting systems, and more specifically, to high power LED lamps.
Light emitting diodes (LEDs) have been available since the early 1960's in various forms, and are now widely used in various applications. The relatively high efficacy of LEDs (in lumens per Watt) is the primary reason for their popularity. Tremendous power savings are possible when LED signals are used to replace traditional incandescent signals of similar luminous output.
An LED is an electronic element, which can radiate light when applying electric power. The lighting principle of LED is translating electric power to light energy, that is, doping a minute amount of carriers into a conjunction of p side, or anode, and n side, or cathode, (p-n junction) and continuously combining the minute amount of carriers with a major amount of carriers to form a LED. As in other diodes, current can flow easily from the p side to the n side, but not in the reverse direction. Charge-carriers—electrons and holes—can flow into the p-n junction from electrodes with different voltages. When an electron meets a hole, it can fall into a lower energy level, and can release energy in the form of a photon.
Because of the various advantages of LEDs, they are widely used in the illumination of electronic devices or lamps. Further, in order to increase the illuminating range and intensity thereof, a plurality of LEDs are usually combined to form a LED lamp set. However, with the increase in the number of LEDs and the subsequent development of high-power LEDs, the heat generated by the operation of the LEDs is inevitably increasing. Therefore, it is an important issue for those skilled in this art to provide a heat-dissipating structure for LED lamps.
One aspect of LED technology that is not satisfactorily resolved is the application of LEDs in high temperature environments. LED lamps exhibit a substantial light output sensitivity to temperature, and in fact are permanently degraded by excessive temperature. Recent experiments with a wide variety of LEDs suggest an exponential relationship of life versus operating temperature. The well known Arhenius function is an approximate model for LED degradation: D varies according to tekT, where D is the degradation, t is time, e the base of natural logarithms, k an activation constant, and T the absolute temperature in degrees Kelvin. Recent developments in LED technology have extended the maximum recommended operating temperature to 85° C. These devices exhibit typical (half brightness) lives on the order of 100,000 hours at 25° C. However, degradation at or above 85° C. is very rapid as the LEDs degrade exponentially with increases in temperature. While such high temperatures might seem unusual for an LED operating environment, they are actually quite common.
To overcome the heat buildup within an LED system, manufacturers will often incorporate heat dissipation structures and systems within the LED package itself. However, the conventional heat-dissipating structures and systems can be bulky, unnecessarily complicated and/or ineffective. The lack of effective means to control overheating also limits the amount of drive energies that can be used to drive LEDs and therefore limits LEDs' use in high power lighting applications.
The present invention provides numerous improvements addressing a number of described drawbacks inherent in prior approaches and others. It will be appreciated, however, that the invention is also amendable to other like applications.
One aspect of the present invention provides a LED lamp assembly with one or more LEDs and LED drive circuits that can provide soft start pulses to drive the LEDs. This advance is significant in that it can provide a steady light source useful for a variety of applications while allowing the LEDs (or a group of the LEDs) to emit high power light intermittently, thereby reducing the heat generated by the LED lamp assembly. Additionally, with this arrangement, there can be more time for heat transfer from the LEDs, thus allowing for greater drive energies to be used, which can result in higher power of the light emitted by the LED lamp assembly. This is particularly useful for applications that can be benefited by a high power light source without compromising the service life of the LEDs.
In one embodiment, the LED lamp assembly comprises a plurality of LEDs and a circuit that provides soft start pulses for driving the LEDs. In another embodiment, the circuit comprises a pulse generator for generating pulses, and a field effect transistor for switching current flow in response to pluses generated by the pulse generator for driving the LEDs. In one specific embodiment, the field effect transistor is optically switched and has a relative slow response time to pulses generated by the pulse generator.
Another aspect according to the present invention provides improved heat dissipating method and system for the LED lamp assembly. In one embodiment, the LEDs are disposed on a substrate comprising an elongated structure (e.g., polygonal tubular structure). In another embodiment, the elongated structure comprises an outer surface, an inner surface, and a bore extending in the direction of the longitudinal axis of the elongated structure defining the inner surface. In yet another embodiment, the LEDs are disposed along the outer surface of the elongated structure and are thermally coupled with the elongated structure, which can dissipate heat from the LEDs. In one specific embodiment, the LEDs maintain electrical insulation from the elongated structure.
In one embodiment, the elongated structure further comprises a cover above the LEDs. In another embodiment, the cover forms a hermetic seal covering the plurality of LEDs. This allows the LED lamp assembly to be used or placed in or around liquid, ice or both, which can allow for even greater heat dissipation of the LEDs.
Other advantages of the present invention will become apparent as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying illustrative drawings.
To aid in understanding the following detailed description of the present invention, the terms and phrases used herein shall have the following, non-limiting, definitions:
As used herein, “circuit” means at least either a single component or a multiplicity of components, either active and/or passive, that are coupled together to provide a desired function.
The wavelengths of light emitted from LEDs 23 and LEDs 21 can be infrared, visible, ultraviolet or combinations thereof, and can depend on the composition and condition of the semiconducting material used. LEDs 21 and LEDs 23 can comprise a variety of semiconductor materials, including: aluminum gallium arsenide (red and infrared), aluminum gallium phosphide (green), aluminum gallium indium phosphide (orange-red, orange, yellow, green), gallium arsenide phosphide (red, orange-red, orange, yellow), gallium phosphide (red, yellow, green), gallium nitride (green, blue, white), indium gallium nitride (450 nm-470 nm—near ultraviolet, blue, bluish-green), silicon carbide (blue), silicon (blue), sapphire (blue), zinc selenide (blue), diamond (ultraviolet), and aluminium nitride, aluminium gallium nitride, and aluminium gallium indium nitride (near to far ultraviolet).
The range of wavelengths of light emitted from LEDs 21 can be different from the range of wavelengths of light emitted from LEDs 23 and a feature of the present invention allows the generation of a third range of wavelengths of light that is a combination of the two provided by LEDs 21 and LEDs 23. The combination of the wavelengths can be controlled by the magnitude and duration of the voltage potential applied to the LEDs. As such, one or more of LEDs 21 and LEDs 23 can emit light simultaneously, alternatively or independently from each other.
LEDs 21 and LEDs 23 can be coupled in a manner that allows currents alternatively flow through LEDs 21 and LEDs 23, so that they can emit light when properly forwardly biased. In one specific embodiment, LEDs 21 and LEDs 23 can be driven by an opposite polarity current on a drive circuit so that, when voltage is applied, the current is allowed to flow through only one type of LEDs, so that light is emitted only from the LEDs through which the current flows. In another specific embodiment, LEDs 21 and LEDs 23 can be driven by more than one drive circuit (e.g., two) that allow them to emit light when properly forwardly biased.
Still referring to
LED lamp assembly 100 can comprise a reflector (not shown) for redirecting light emissions. However, the lamp assembly can be used without a reflector, e.g., for omni-directional light emissions.
In this specific embodiment, an external dimension of LED lamp assembly 100 is 48 inches in length and 0.625 inches in diameter. However, the dimension is for illustration purposes only and is not intended to limit the scope of the present invention.
As shown in
In the embodiment shown in
Voltage regulator 42 can maintain a substantially constant voltage level (e.g., 5 VAC), which can be communicated with pulse generator 44. Pulse generator 44 can generate pulses having widths or durations ranging from minutes to under one picosecond. In one embodiment, pulse generator 44 can generate voltage pulses.
Pulse generator 44 can communicate with output regulator 46, which can output electric power (e.g., from source power unit 40) for driving one or more LEDs. Output regulator 46 can comprise a field effect transistor that can function as a switch in response to pulses generated by pulse generator 44, thereby regulating the electric power outputted by output regulator 46. In one embodiment, output regulator 46 can comprise a field effect transistor that is optically (e.g., LED) switched and has a relatively slow response time (e.g., in the range of 0.1 to 20 microseconds) to voltage changes. The results of this circuit combination can output a regulated, steady lower voltage, which can provide soft start pulses for driving LEDs without overshoot. This output can be communicated to LEDs through one or more resistors, which can further enhance the soft start of the drive pulses.
In one embodiment according to the present invention, a second drive circuit with differently or oppositely timed pulses to drive a second group of LEDs, as illustrated by
As shown in
In one embodiment, drive circuits 400 and 500 can provide differently or oppositely timed pulse voltage of opposite polarity for driving one or more LEDs, so that, for example, when drive circuit 400 provides a positive voltage, drive circuit 500 provides a negative voltage, to drive the one or more LEDs. The timing of the pulses provided by drive circuit 400 and drive circuit 500 can be controlled by field effect transistors in the circuits (e.g., in output regulator 46 and 46a, respectively), so that they do not overlap (e.g., as shown in
Still referring to
This feature is a significant advance from prior art in that it can provide a steady light source useful for a variety of applications while allowing the LEDs (or a group of the LEDs) to emit high power light intermittently, thereby reducing the heat generated by the LED lamp assembly. Additionally, with this arrangement, there can be more time for heat transfer from the LEDs, thus allowing for greater drive energies to be used, which can result in higher power of the light emitted by the LED lamp assembly.
The invention is illustrated by the following non-limiting Examples.
Field effect transistor 56 is optically or LED switched, which has a relatively slow response time (e.g., 5 microseconds or longer) to voltage changes. The results of this circuit combination can output a soft start potential to a much higher potential without overshoot for driving one or more LEDs, which allows for longer service life of the LEDs. Each LED can be connected with LED driver circuit 500 via resistors, further enhancing the soft start of the drive pulses.
Circuit 500 can comprise transorb D2 and zenor diode D3 coupled in parallel, which can regulate voltage output for protecting the LEDs from being reverse biased.
For driving LEDs alternatively, a 556-type dual timer pulse generator and separate 5-Amp regulators can be used to drive different groups of LEDs at different or opposite times.
For sets of three 395 nm LEDs the steady state voltage was not lower than 10.8 V outputting a drive current of 30 mA, which corresponds to 0.324 W power. For the LEDs used there was a steady low output of 9.72 lm per LED set, or 1166.4 lm for 120 sets.
The drive pulse voltage was 11.4 V and current was 240 mA, for 2.736 W of power. This provided 9849.6 lm for a pulse of less than one millisecond. The LED lamp can run with this configuration non-stop for more than eleven years. Steady state at this current, on the other hand, would substantially shorten the service life of the LEDs (e.g., to 100 hours or less).
Each set of three LW W5SN LEDs (typical efficiency: 30 lm/W (white)) provides 225 lm at 700 mA. At 3.6 V per LED the drive power would be (3×3.6 V)×700 mA=7.56 W. This means for 11 sets of the LEDs, 85 W input would provide about 2530 lm.
Each set of the LEDs is capable of being pulsed at 2500 mA for a driver power of 12.9 V×2500 mA=32.25 W. Eleven sets of the LEDs would provide 10,642 lm at a rate comparable to the steady state of 85 W, while providing an over four-fold increase in intensity.
The LEDs' response time is set by its approximate 100 pF capacitance. With a rise time of 200 ns and a fall time of 150 ns, its shortest time period is 350 ns for a pulse frequency compatibility of about 28.5 MHz. Being able to switch on and off rapidly allows for high power light bursts with low total energy consumption.
Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
The terms “a” and “an” and “the” and similar referents used in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
Certain embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations of these embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
In closing, it is to be understood that the embodiments of the invention disclosed herein are illustrative of the principles according to the present invention. Other modifications that may be employed are within the scope of the invention. Thus, by way of example, but not of limitation, alternative configurations according to the present invention may be utilized in accordance with the teachings herein. Accordingly, the present invention is not limited to that precisely as shown and described.
