US 20070069663 A1
A solid-state light engine comprised of light emitting diodes (LEDs) configured into a bridge rectifier with a current limiting module coupled to the LED bridge rectifier. The light engine may be packaged for high temperature operation. Optionally, the LEDs comprise wavelength-converting phosphors with a persistence that is a multiple of the peak to peak current period, to smooth and mask ripple frequency pulsation of emitted light.
1. A solid state light engine comprising:
an LED bridge rectifier; and
a current limiting module electrically connected to the rectified output of the LED bridge rectifier;
wherein the LED bridge rectifier comprises a plurality of LEDs configured to rectify an AC power signal and emit light, and the current limiting module limits the current passing through the LEDs in the LED bridge rectifier.
2. The light engine of
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8. The solid-state light engine of
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13. A solid state light engine comprising an LED bridge rectifier, wherein the LED bridge rectifier comprises four bridge legs, each bridge leg having at least two LEDs.
14. The solid state light engine of
15. The solid state light engine of
16. The solid state light engine of
17. A solid state light engine comprising an LED bridge rectifier having a plurality of LED dice, wherein the LED bridge rectifier is packaged for high temperature operation.
18. The solid state light engine of
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This application claims the benefit of U.S. Provisional Patent Application No. 60/685,680, filed May 27, 2005, the entire disclosure of which is hereby incorporated by reference herein.
1. Field of the Invention
Embodiments of the invention relate to a solid-state light engine that is directly compatible with alternating current (AC) input power, without the need for a separate rectification module, but that can also alternatively be powered by direct current (DC) input power.
2. Related Art
In many lighting applications, solid-state light engines are superior to conventional incandescent lamps. Beneficially, solid-state light engines can, in certain circumstances, achieve an almost 20% improvement in efficiency and an extended lifetime (e.g. exceeding 50,000 hours) as compared to incandescent lamps.
Traditional solid-state light engines are powered by a direct current or pulsating direct current drive. As such, to drive the light engine using an AC power source, the AC input line must first be conditioned. Power-conditioning commonly involves the rectification of AC input power, typically achieved by inserting rectifier diodes in a bridge configuration, as well as a means of limiting current, such as a series resistance or reactance in the power path. However, the addition of such electronic components into the power path may increase manufacturing costs and complexity, and can cause a decrease in the lifetime (or time to failure) of the light engine, and can decrease efficiency due to power loss.
To avoid the performance-related issues caused by the insertion of power conditioning elements into the power path, some standard solid-state light engines are powered directly from the AC line. However, the direct AC powering of a light engine causes the light output to pulsate at the frequency of the AC power source, typically in the range of 50 to 60 Hz. This line frequency pulsation can produce eye fatigue or annoyance when viewed, even in cases where the engine is viewed for a short period of time.
Accordingly, there is a need for a solid state light engine that is directly compatible with an AC input power source, which does not exhibit the deleterious pulsation effects generated by a direct AC powering arrangement, and/or which does not require the use of separate power conditioning or rectification circuitry.
Embodiments of the invention satisfy these and other needs. Embodiments of the invention relate to a solid state bridge rectifier light engine arrangement that may be powered directly by an AC input line, without the need for further power conditioning. Although full-wave bridge rectifiers are known in the art, they utilize non-light emitting diodes, and are used to convert AC current to DC current for use as a power source for external electronic components, not to produce useful illumination. Similarly, although the use of LEDs for illumination is known in the art, LEDs are typically powered by a DC power source. The present invention advantageously uses LEDs in a novel way by configuring them into a bridge rectifier to produce useful light directly from an AC power source without the need for separate rectification or other conditioning of the input power.
More specifically, embodiments of the invention provide for a solid state light engine arrangement that includes a full wave bridge rectifier configuration of light emitting diodes (LEDs) directly compatible with an AC power input, which may advantageously also be connected to a current limiting element. An added benefit to this configuration is that the light engine may be constructed with two sets of terminals for connection to a power source, so that the user has the option of powering the light engine by either AC power or the more traditional DC power, depending on the terminals to which the user connects the power source.
Embodiments of the invention can also include a solid-state LED bridge rectifier circuit advantageously using phosphors to further smooth any frequency pulsation or ripple of light emitted from the light engine. The LED bridge rectifier can include one or more LEDs configured such that the LED bridge rectifier receives and rectifies an AC power signal and emits light. The current limiting module can be used to protect the LEDs by limiting the current passing through the LEDs within the LED bridge rectifier. The LEDs can emit any of a number of colors of light, depending on the type of LED used. Advantageously, LEDs that emit of blue and/or ultraviolet wavelength emissions can be used, in combination with wavelength converting phosphors known in the art, to create light that is perceived as white light by a user. See, for example, U.S. Pat. No. 5,998,925 to Shimizu. The converting phosphor can be particles of Cerium activated Yttrium Aluminum Garnet (YAG:Ce) or Europium activated Barium Orthosilicates (BOSE).
The turn-on and turn-off time for typical LEDs is in the tens to one hundred nanosecond range. With this response time, LEDs will virtually follow the low frequency AC waveform without delay. According to an aspect of an embodiment of the invention, through rectification, the light pulsation or ripple frequency will typically be increased to approximately twice the frequency of the input AC line current (e.g., 100 to 120 Hz). This frequency doubling has the advantageous effect of speeding up the light pulsation to a frequency beyond what is typically perceptible to human observers, thus making it more appealing for use in standard lighting applications than would an LED array powered directly from AC current that was not configured into a bridge rectifier. In addition, the frequency doubling that occurs in the LED bridge rectifier configuration results in a shortening of the time duration between current peaks to about 10 ms for a 50 Hz line and about 8 ms for a 60 Hz line. The shortened peak to peak period, together with the advantageous use of phosphors having a persistence of 5 to 10 times that duration, masks the light pulsation or flicker, allowing it to be smoothed and integrated into a nearly continuous white light output. Phosphors having a longer or shorter persistence may also be used advantageously.
The light engine arrangement according to certain embodiments of the invention can be used as a solid-state replacement for conventional Edison-base incandescent lamps or as a replacement for low-voltage halogen lamps or other low voltage lamps. Advantageously, since no additional electronic components need be inserted into the power path, the increased useful life offered by the solid state light engine need not be compromised.
The invention can be understood from the detailed description of exemplary embodiments presented below, considered in conjunction with the attached drawings, of which:
to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale.
Embodiments of the invention are directed to a solid state light engine producing white or near white light that is constructed by using LEDs that emit blue or ultraviolet wavelength emission which stimulates a phosphor, or some mixture of phosphors, that emit light in the green, yellow and/or red wavelengths. The combination of all these wavelengths is perceived as white light by the human eye. If one were to look at just a monochrome color LED driven with an AC source, one would see the pulsation of the light at the 50 Hz or 60 Hz frequencies. Even if the pulsation is above the detectable threshold to 100 Hz or 120 Hz, the pulsation can still be detected when the light interacts with objects or images moving or pulsating at close to the LED pulse rate or harmonics of that rate. This is, at the least, annoying and, at worst, potentially dangerous. Strobing light could possibly make moving or spinning objects appear to be not moving at all. An example of this is a fluorescent light source flickering at line frequency illuminating strobe marks on a turntable.
With reference to
With reference to
The reverse voltage seen by each leg 110, 120, 130, 140 of the bridge module 100 is represented by the following equation:
Since typical LEDs do not have the capacity to withstand high reverse voltages, the number of LEDs in the array can be chosen to limit the reverse voltage on each LED to a safe (i.e., not damaging to the LEDs) level, as would be known to one of skill in the art, as informed by the present disclosure. In addition, because individual LEDs may exhibit differing leakage current levels under the same reverse voltage, in some embodiments, a shunt resistance or reactance network can be used to assure the total reverse voltage is distributed equally, as illustrated in
With reference to
The phosphors can be disposed within a packaged LED array in several ways. Typically, in packaged LED assemblies, each LED die is encapsulated in an epoxy or silicone to protect the die from the environment, and optionally to serve as an optical element that may focus or otherwise direct the emitted light. Phosphor particles may be utilized in the LED package in a number of ways. For example, as can be seen in
Alternatively, the phosphors particles 40 a may be dispersed in the encapsulant 44, or applied overlying the encapsulant 44, either directly applied in a layer 40 b to the outer surface of the encapsulant, or (not shown) in a second layer that may comprise an optical element.
As illustrated in
Where du, or duty factor, is the conduction time (τ) divided by the total period (T).
The resistor value (R) of resistor RL is determined by the following equation:
Alternative embodiments of the invention are depicted in FIGS. 7 to 11, each embodiment including a different exemplary current limiting module 200 for use in the solid state light engine arrangement of the invention. In all embodiments, the current limiting module 200 can be applied external to the light engine, or, alternatively, it may be integrated into the light engine package (i.e., LED bridge 100).
FIG.8 depicts a solid state light engine according to an embodiment of the present invention wherein the current limiting module 200 is configured such that the resistive element RL of
One having ordinary skill in the art will appreciate that alternative current limiting elements may be used in accordance with the solid-state light engine arrangement of embodiments of the invention.
According to an embodiment of the invention, the circuit pictured in
The above described LED bridge rectifier light engine can be manufactured using any method suitable for the assembly of LED arrays, including the use of pre-packaged LEDs mounted on conventional printed wiring boards with other components. Alternatively, the above described LED bridge rectifier light engine can be manufactured in pre-packaged integrated arrays where LED dice are mounted on thermally-conductive substrates for heat management and integrated with other components.
Preferably, the LED bridge rectifier light engine is made using packaging methods suitable for high temperature operation LED light engines. In a typical high temperature package, LED dice are mounted, directly or indirectly, on a metal substrate layer that serves as a heat spreader or sink. Alternatively, non-metallic materials with proper heat conduction and strength properties may be used instead of a metal layer. The circuit traces in a high temperature package may be embedded in or imposed on ceramic layers or contained in a conventional printed wiring board layer or layers overlying the metal layer. The LED dice may be electrically connected to the circuit traces through methods known in the art, including use of lead frames, bonding wires, or other known methods. Other electronic components may be mounted on the ceramic layers or printed wiring board, or mounted on the metal layer, directly or indirectly through an interposing element for electrical isolation or other advantageous purposes.
In a preferred embodiment, the LED bridge rectifier light engine can be fabricated using the packaging methods, including the low temperature co-fired ceramic-on-metal (LTCC-M) technique, described in U.S. Patent Application Publication No. 2006/0006405, Mazzochette, “Surface mountable light emitting diode assemblies packaged for high temperature operation,” published Jan. 12, 2006 (“Mazzochette”), the entire contents of which are hereby incorporated as if fully set forth at length herein. Although the description and diagrams in Mazzochette do not embody an LED bridge rectifier, one of skill in the art may readily adapt the disclosed packaging methods for use in the present invention.
It is to be understood that the exemplary embodiments are merely illustrative of the present invention. Many variations, modifications and improvements to the above-described embodiments will occur to those skilled in the art upon reading the foregoing description and viewing the Figures. It should be understood that all such variations, modifications and improvements have not been included herein for the sake of conciseness and readability, but are properly within, and are intended to be within, the scope of the invention and the following claims.