News Column

Patent Issued for Method and Apparatus for Controlling Dimming Levels of LEDs

January 29, 2014

By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Clauberg, Bernd (Schaumburg, IL); Greischar, Richard (Oak Park, IL); Shrotriya, Ameya (Schaumburg, IL), filed on August 18, 2010, was published online on January 14, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8629619 is assigned to Koninklijke Philips N.V. (Eindhoven, NL).

The following quote was obtained by the news editors from the background information supplied by the inventors: "Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Pat. Nos. 6,016,038 and 6,211,626, incorporated herein by reference.

"Significant advances have been made in manufacturing of LEDs emitting white light. Currently, white light LEDs are commercially available which generate more than 100 lumens per watt. This is comparable to the performance of fluorescent and HID lamps. In addition, these LEDs offer other advantages such as longer operating life, shock/vibration resistance and design flexibility because of their small size. As a result, white light LEDs are gaining acceptance as a replacement for traditional incandescent sources, compact fluorescent and HID for illumination applications such as signage, accenting, and pathway lighting, downlighting, parking lot and roadway lighting. The white LEDs can be used alone or in conjunction with colored LEDs for a particular effect.

"The electrical characteristics of LEDs are such that small changes in the voltage applied to the LED lamp will cause appreciable current changes. In addition, ambient temperature changes will also result in LED current changes by changing the forward drop across the LEDs. Furthermore, the lumen output of LEDs depends on the LED current. The existing electrical power supplies for LED light sources are designed to precisely regulate the LED current to prevent luminous intensity variations due to input AC voltage variations and ambient temperature. Operation of LED lamps at excessive forward current for a long period can cause unacceptable luminous intensity variations and even catastrophic failure. In addition, current electrical power supplies do not minimize power consumption to maximize energy savings.

"It is often desirable to provide a dimming capability to LEDs and lighting fixtures employing LEDs. Known ways of dimming LEDs include pulse-width modulation (PWM) 'chopping' of the current waveform and analog reduction of the amplitude of the current waveform. Unfortunately, using known analog amplitude reduction and PWM dimming it is difficult to obtain good efficiency and good performance over an entire dimming range of 0% light output (no light output) to 100% light output(full light output). Many known high efficiency LED drivers use a switch mode converter to regulate the current to the LED's. To achieve 'deep dimming', (e.g., dimming to less than 5% and up to 30%), PWM pulsing of the LED current is typically used to ensure proper operation of the LED's. With a current source output, PWM dimming requires a shunt switch that shunts the LED current during the 'off' pulses of the PWM cycle. As such, relatively high losses are realized in the main converter and the shunt switch because the current to the LEDs is at a comparatively high level, even though only a portion is of the current is being delivered. Accordingly, known shunt switches and their methods of use are comparatively inefficient in LED applications involving dimming. In addition, the efficiency (Im/W) of LED's us comparatively high at lower drive currents, and as a result known PWM dimming methods are less efficient than known analog dimming methods. However, analog dimming also has some disadvantages at low dim levels. For example, if the LED current is less than approximately 5% and as great as 30% of the full output rating, light levels might not be uniform between different LEDs, color shifts can occur, and at very low current levels efficiencies of the LED's are also comparatively poor. In addition, the driver electronics become more difficult as the current levels drop below 1%, offset voltages and electrical noise in the current sensing circuitry become a major concern. At dim levels below 0.1% these issues make analog dimming undesirable.

"Thus, there is a need in the art to provide dimming of LEDs that overcomes at least the drawbacks of known dimming methods described above."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "The present disclosure is directed to inventive methods and apparatuses for controlling dimming levels. Applicants have recognized and appreciated that it would be beneficial to provide more efficient dimming of LEDs over the entire dim range of 0% to 100% dimming in a manner that overcomes certain shortcomings in analog and pulse width modulation (PWM) dimming. Applicants have further recognized and appreciated that it would be beneficial to provide analog dimming to a certain dimming level, and to provide PWM dimming for dimming to below a certain dimming level.

"In accordance with one aspect, the present disclosure focuses on a dimming circuit for an LED comprises a current controller configured to receive a dimming input provide a pulse width modulation signal (PWM) and a reference voltage. The dimming circuit also comprises a current converter configured to provide an output current; and a shunt switch connected to the controller and to the current converter and between the current controller and the LEDs, wherein the shunt switch is non-conducting when the dimming input is more than a threshold level.

"In accordance with another aspect, the present disclosure focuses on a dimming circuit for an LED comprises a controller configured to receive a dimming input provide a pulse width modulation signal (PWM) and a reference voltage. The dimming circuit also comprises a current converter configured to provide an output current; and a buck converter connected between the LEDs and current converter, wherein the buck converter comprises a shunt switch that is non-conducting when the dimming input is less than a threshold level.

"As used herein for purposes of the present disclosure, the term 'LED' should be understood to include any electroluminescent diode or other type of carrier injection/junction-based system that is capable of generating radiation in response to an electric signal. Thus, the term LED includes, but is not limited to, various semiconductor-based structures that emit light in response to current, light emitting polymers, organic light emitting diodes (OLEDs), electroluminescent strips, and the like. In particular, the term LED refers to light emitting diodes of all types (including semi-conductor and organic light emitting diodes) that may be configured to generate radiation in one or more of the infrared spectrum, ultraviolet spectrum, and various portions of the visible spectrum (generally including radiation wavelengths from approximately 400 nanometers to approximately 700 nanometers). Some examples of LEDs include, but are not limited to, various types of infrared LEDs, ultraviolet LEDs, red LEDs, blue LEDs, green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white LEDs (discussed further below). It also should be appreciated that LEDs may be configured and/or controlled to generate radiation having various bandwidths (e.g., full widths at half maximum, or FWHM) for a given spectrum (e.g., narrow bandwidth, broad bandwidth), and a variety of dominant wavelengths within a given general color categorization.

"For example, one implementation of an LED configured to generate essentially white light (e.g., a white LED) may include a number of dies which respectively emit different spectra of electroluminescence that, in combination, mix to form essentially white light. In another implementation, a white light LED may be associated with a phosphor material that converts electroluminescence having a first spectrum to a different second spectrum. In one example of this implementation, electroluminescence having a relatively short wavelength and narrow bandwidth spectrum 'pumps' the phosphor material, which in turn radiates longer wavelength radiation having a somewhat broader spectrum.

"It should also be understood that the term LED does not limit the physical and/or electrical package type of an LED. For example, as discussed above, an LED may refer to a single light emitting device having multiple dies that are configured to respectively emit different spectra of radiation (e.g., that may or may not be individually controllable). Also, an LED may be associated with a phosphor that is considered as an integral part of the LED (e.g., some types of white LEDs). In general, the term LED may refer to packaged LEDs, non-packaged LEDs, surface mount LEDs, chip-on-board LEDs, T-package mount LEDs, radial package LEDs, power package LEDs, LEDs including some type of encasement and/or optical element (e.g., a diffusing lens), etc.

"The term 'light source' should be understood to refer to any one or more of a variety of radiation sources, including, but not limited to, LED-based sources (including one or more LEDs as defined above), incandescent sources (e.g., filament lamps, halogen lamps), fluorescent sources, phosphorescent sources, high-intensity discharge sources (e.g., sodium vapor, mercury vapor, and metal halide lamps), lasers, other types of electroluminescent sources, pyro-luminescent sources (e.g., flames), candle-luminescent sources (e.g., gas mantles, carbon arc radiation sources), photo-luminescent sources (e.g., gaseous discharge sources), cathode luminescent sources using electronic satiation, galvano-luminescent sources, crystallo-luminescent sources, kine-luminescent sources, thermo-luminescent sources, triboluminescent sources, sonoluminescent sources, radioluminescent sources, and luminescent polymers.

"A given light source may be configured to generate electromagnetic radiation within the visible spectrum, outside the visible spectrum, or a combination of both. Hence, the terms 'light' and 'radiation' are used interchangeably herein. Additionally, a light source may include as an integral component one or more filters (e.g., color filters), lenses, or other optical components. Also, it should be understood that light sources may be configured for a variety of applications, including, but not limited to, indication, display, and/or illumination. An 'illumination source' is a light source that is particularly configured to generate radiation having a sufficient intensity to effectively illuminate an interior or exterior space. In this context, 'sufficient intensity' refers to sufficient radiant power in the visible spectrum generated in the space or environment (the unit 'lumens' often is employed to represent the total light output from a light source in all directions, in terms of radiant power or 'luminous flux') to provide ambient illumination (i.e., light that may be perceived indirectly and that may be, for example, reflected off of one or more of a variety of intervening surfaces before being perceived in whole or in part).

"The term 'spectrum' should be understood to refer to any one or more frequencies (or wavelengths) of radiation produced by one or more light sources. Accordingly, the term 'spectrum' refers to frequencies (or wavelengths) not only in the visible range, but also frequencies (or wavelengths) in the infrared, ultraviolet, and other areas of the overall electromagnetic spectrum. Also, a given spectrum may have a relatively narrow bandwidth (e.g., a FWHM having essentially few frequency or wavelength components) or a relatively wide bandwidth (several frequency or wavelength components having various relative strengths). It should also be appreciated that a given spectrum may be the result of a mixing of two or more other spectra (e.g., mixing radiation respectively emitted from multiple light sources).

"For purposes of this disclosure, the term 'color' is used interchangeably with the term 'spectrum.' However, the term 'color' generally is used to refer primarily to a property of radiation that is perceivable by an observer (although this usage is not intended to limit the scope of this term). Accordingly, the terms 'different colors' implicitly refer to multiple spectra having different wavelength components and/or bandwidths. It also should be appreciated that the term 'color' may be used in connection with both white and non-white light.

"The term 'color temperature' generally is used herein in connection with white light, although this usage is not intended to limit the scope of this term. Color temperature essentially refers to a particular color content or shade (e.g., reddish, bluish) of white light. The color temperature of a given radiation sample conventionally is characterized according to the temperature in degrees Kelvin (K) of a black body radiator that radiates essentially the same spectrum as the radiation sample in question. Black body radiator color temperatures generally fall within a range of from approximately 700 degrees K (typically considered the first visible to the human eye) to over 10,000 degrees K; white light generally is perceived at color temperatures above 1500-2000 degrees K.

"The term 'lighting fixture' is used herein to refer to an implementation or arrangement of one or more lighting units in a particular form factor, assembly, or package. The term 'lighting unit' is used herein to refer to an apparatus including one or more light sources of same or different types. A given lighting unit may have any one of a variety of mounting arrangements for the light source(s), enclosure/housing arrangements and shapes, and/or electrical and mechanical connection configurations. Additionally, a given lighting unit optionally may be associated with (e.g., include, be coupled to and/or packaged together with) various other components (e.g., control circuitry) relating to the operation of the light source(s). An 'LED-based lighting unit' refers to a lighting unit that includes one or more LED-based light sources as discussed above, alone or in combination with other non LED-based light sources. A 'multi-channel' lighting unit refers to an LED-based or non LED-based lighting unit that includes at least two light sources configured to respectively generate different spectrums of radiation, wherein each different source spectrum may be referred to as a 'channel' of the multi-channel lighting unit.

"The term 'controller' is used herein generally to describe various apparatus relating to the operation of one or more light sources. A controller can be implemented in numerous ways (e.g., such as with dedicated hardware) to perform various functions discussed herein. A 'processor' is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform various functions discussed herein. A controller may be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

"The term 'user interface' as used herein refers to an interface between a human user or operator and one or more devices that enables communication between the user and the device(s). Examples of user interfaces that may be employed in various implementations of the present disclosure include, but are not limited to, switches, potentiometers, buttons, dials, sliders, a mouse, keyboard, keypad, various types of game controllers (e.g., joysticks), track balls, display screens, various types of graphical user interfaces (GUIs), touch screens, microphones and other types of sensors that may receive some form of human-generated stimulus and generate a signal in response thereto.

"It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein."

URL and more information on this patent, see: Clauberg, Bernd; Greischar, Richard; Shrotriya, Ameya. Method and Apparatus for Controlling Dimming Levels of LEDs. U.S. Patent Number 8629619, filed August 18, 2010, and published online on January 14, 2014. Patent URL:

Keywords for this news article include: Electronics, Electromagnet, Semiconductor, Microprocessors, Light-emitting Diode, Koninklijke Philips N.V..

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Source: Electronics Newsweekly

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