Patent Application
20140125248
The present inventive subject matter relates to lighting apparatus and methods and, more particularly, to solid-state lighting apparatus and methods.
Solid-state lighting arrays are used for a number of lighting applications. For example, solid-state lighting panels including arrays of solid-state light emitting devices have been used as direct illumination sources in architectural and/or accent lighting. A solid-state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs), which may include inorganic LEDs, which may include semiconductor layers forming p-n junctions and/or organic LEDs (OLEDs), which may include organic light emission layers.
Solid-state lighting devices are also used in lighting fixtures, such as incandescent bulb replacement applications, task lighting, recessed light fixtures and the like. For example, Cree, Inc. produces a variety of recessed downlights, such as the LR-6 and CR-6, which use LEDs for illumination. Solid-state lighting panels are also commonly used as backlights for small liquid crystal display (LCD) screens, such as LCD display screens used in portable electronic devices, and for larger displays, such as LCD television displays.
LEDs can be dimmed using, for example, linear dimming or pulse-width modulated (PWM) dimming, In a typical LED lighting apparatus, a microcontroller generates a PWM signal that is provided to a driver circuit that controls current passing through one or more LEDs. By varying the duty cycle of the PWM signal, the average current of the LEDs is proportionally changed, and the brightness of the LEDs varies accordingly. The PWM dimming control generally exhibits low appreciable color shift, and thus is widely used.
Some conventional microcontroller-based dimming controllers implement linear dimming. Typically, the microcontroller samples a dimming control signal (e.g., from a commercial dimmer) and generates a PWM signal with its duty cycle varying with the dimming control signal. The PWM signal may be filtered with a low-pass filter, producing a DC voltage that is used to control a power stage of the driver circuit to adjust the LED current.
Some embodiments provide an apparatus including a driver circuit configured to control a current through at least one LED responsive to a control signal. The apparatus further includes a modulated oscillator circuit configured to generate and modulate an oscillating signal responsive to a dimming signal and to generate the control signal responsive to the modulated oscillating signal.
The modulated oscillator circuit may be configured to pulse width modulate the oscillating signal responsive to the dimming signal. The driver circuit may be configured to control the current through the at least one LED responsive to the pulse-width modulated oscillating signal. In further embodiments, the modulated oscillator circuit may include a filter configured to generate a voltage from the pulse-width modulated oscillating signal and the control signal may include the voltage.
In some embodiments, the modulated oscillator circuit may include a sawtooth generator circuit configured to generate a sawtooth signal and a comparator configured to generate the pulse width modulated oscillating signal based on a comparison of the dimming signal to the sawtooth signal.
According to additional embodiments, the modulated oscillator circuit may be configured to amplitude modulate the oscillating signal responsive to the dimming signal. In some embodiments, the modulated oscillator circuit may include a forward converter configured to generate a voltage responsive to the dimming signal and the control signal comprises the voltage.
In some embodiments, the modulated oscillator circuit may be configured to galvanically isolate the control signal from the dimming signal. For example, the modulated oscillator circuit may be configured to galvanically isolate the control signal from the dimming signal using an opto-isolator or a transformer.
In some embodiments, the driver circuit comprises an AC/DC converter, a DC/DC converter or a buck converter configured to control the current through the at least one LED responsive to the control signal. The dimming signal may include a voltage signal, such as a dimming signal produced by a commercial dimmer or occupancy sensor.
Further embodiments provide apparatus as described above coupled to at least one LED.
Additional embodiments provide methods of controlling a lighting apparatus. The methods include modulating an oscillating signal responsive to a dimming signal and controlling a current through at least one LED responsive to the modulated oscillating signal. Modulating an oscillating signal responsive to a dimming signal may include pulse width modulating the oscillating signal responsive to the dimming signal. Controlling a current through at least one LED responsive to the modulated oscillating signal may include filtering the pulse-width modulated signal to generate an voltage and controlling the current through the at least one LED responsive to the voltage. Pulse width modulating the oscillating signal responsive to the dimming signal may include comparing a sawtooth signal to the dimming signal to generate the pulse width modulated oscillating signal.
In further embodiments, modulating an oscillating signal responsive to a dimming signal may include amplitude modulating the oscillating signal responsive to the dimming signal. Controlling a current through at least one LED responsive to the modulated oscillating signal may include generating a control signal from the modulated oscillating signal and controlling the current through the at least one LED responsive to the control signal, wherein the control signal is galvanically isolated from the dimming signal.
The accompanying drawings, which are included to provide a further understanding of the inventive subject matter and are incorporated in and constitute a part of this application, illustrate certain embodiment(s) of the inventive subject matter. In the drawings:
Embodiments of the present inventive subject matter now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the inventive subject matter are shown. This inventive subject matter may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive subject matter to those skilled in the art. Like numbers refer to like elements throughout.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present inventive subject matter. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. It will be further understood that elements “coupled in series” or “serially connected” may be directly coupled or may be coupled via intervening elements.
It will be understood that when an element or layer is referred to as being “on” another element or layer, the element or layer can be directly on another element or layer or intervening elements or layers may also be present. In contrast, when an element is referred to as being “directly on” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Spatially relative terms, such as “below”, “beneath”, “lower”, “above”, “upper”, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. Throughout the specification, like reference numerals in the drawings denote like elements.
Embodiments of the inventive subject matter are described herein with reference to plan and perspective illustrations that are schematic illustrations of idealized embodiments of the inventive subject matter. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, the inventive subject matter should not be construed as limited to the particular shapes of objects illustrated herein, but should include deviations in shapes that result, for example, from manufacturing. Thus, the objects illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the inventive subject matter.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present inventive subject matter. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this present inventive subject matter belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The term “plurality” is used herein to refer to two or more of the referenced item.
The expression “lighting apparatus”, as used herein, is not limited, except that it indicates that the device is capable of emitting light. That is, a lighting apparatus can be a device which illuminates an area or volume, e.g., a structure, a swimming pool or spa, a room, a warehouse, an indicator, a road, a parking lot, a vehicle, signage, e.g., road signs, a billboard, a ship, a toy, a mirror, a vessel, an electronic device, a boat, an aircraft, a stadium, a computer, a remote audio device, a remote video device, a cell phone, a tree, a window, an LCD display, a cave, a tunnel, a yard, a lamppost, or a device or array of devices that illuminate an enclosure, or a device that is used for edge or back-lighting (e.g., back light poster, signage, LCD displays), bulb replacements (e.g., for replacing AC incandescent lights, low voltage lights, fluorescent lights, etc.), lights used for outdoor lighting, lights used for security lighting, lights used for exterior residential lighting (wall mounts, post/column mounts), ceiling fixtures/wall sconces, under cabinet lighting, lamps (floor and/or table and/or desk), landscape lighting, track lighting, task lighting, specialty lighting, ceiling fan lighting, archival/art display lighting, high vibration/impact lighting, work lights, etc., mirrors/vanity lighting, or any other light emitting device. The present inventive subject matter may further relate to an illuminated enclosure (the volume of which can be illuminated uniformly or non-uniformly), comprising an enclosed space and at least one lighting apparatus according to the present inventive subject matter, wherein the lighting apparatus illuminates at least a portion of the enclosed space (uniformly or non-uniformly).
According to further embodiments, a modulated oscillator circuit may provide a control signal in the form of a voltage derived from a PWM signal.
The sawtooth signal is provided to a first input of a second comparator U2 via a resistor R15. A second input of the second comparator U2 receives the dimming signal VDIM. The second comparator U2 produces the PWM control signal 605 responsive to a comparison of the sawtooth signal to the dimming signal VDIM. The dimming signal VDIM may be received, for example, from a voltage source or a 0-10V commercially available dimmer.
An example of an LED lighting apparatus 800 powered by a two-stage driver with a modulated oscillator circuit according to some embodiments is shown in
A boost power factor correction (PFC) circuit 820 is coupled to the output of the rectifier 815. The PFC circuit 820 includes an inductor LPFC and a transistor Q1, which is controlled by a PFC controller 825. The PFC circuit 820 also includes a bias capacitor CBIAS, an output capacitor CB and diodes D5 and D8.
A resonant type DC/DC converter 830 is coupled to the output of the PFC circuit 820. The DC/DC controller 820 includes transistor switches Q2 and Q3, a resonant capacitor Cr, a resonant inductor Lr, a transformer T1, diodes D6 and D7, and an output capacitor COUT. The DC/DC converter 830 is an LLC resonant converter, with zero-voltage turn-on of the transistor switches Q2 and Q3, and zero-current turn-off of the diodes D6 and D7 when the operating frequency is lower than the resonant frequency determined by Lr and Cr. An LLC converter can provide high efficiency and low EMI (Electro-magnetic Interference). The DC/DC converter 830 is coupled to a string 10 of LEDs, producing an output voltage V0 and current iLED. The DC/DC converter 830 is controlled by a DC/DC controller 835, which drives the transistors Q2 and Q3. The DC/DC converter 830 can have other configurations, such as a flyback (voltage step down or up) converter or a buck (voltage step-down) converter.
A transistor switch Q4 serves as a protection switch. When there is a short circuit or over current, or an over-voltage of the output, the transistor Q4 is turned off to protect the driver circuit and the LED load. A resistor Rs senses the LED current, and the DC/DC controller 835 uses the sensed current signal to provide current regulation of the LED load 10 and protect the DC/DC converter 830 during fault conditions.
A dimming controller 840 provides a current control signal 845 to the DC/DC controller 835, which responsively controls the DC/DC converter 830 to control the LED current iLED. The dimming controller 840 generates the current control signal 845 responsive to the dimming signal DIM+/DIM− generated by the occupancy sensor 805. The dimming controller 840 may be a modulated oscillator circuit similar, for example, to the circuits of
Such a dimming controller may also be connected to user-controlled dimmer, such as a commercial 0-10V dimmer. The LED current hence the LED brightness is adjusted based on the voltage appearing between DIM+and DIM−. For example, the LED current may be at a maximum level that provides full brightness when the voltage between DIM+ and DIM− is 10 V, whereas the LED current is half the maximum preset current and the brightness is half the full brightness when the voltage between DIM+ and DIM− is 5 V.
In the drawings and specification, there have been disclosed typical embodiments of the inventive subject matter and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the inventive subject matter being set forth in the following claims.
