CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, U.S. Provisional Patent Application No. 63/069,875, filed August 25, 2020, the contents of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

[0002] The invention relates to linear lighting with onboard control of light output, and more specifically, to methods and apparatus for onboard control of light output.

BACKGROUND

[0003] Linear lighting is a class of lighting based on light-emitting diodes (LEDs) in which an elongate, narrow printed circuit board (PCB) is populated with a plurality of LED light engines, typically spaced from one another at a regular pitch or spacing. In much of the linear lighting on the market, the LED light engines are surfacemounted on the PCB, along with other components. The PCB itself may be either rigid or flexible. If the PCB is flexible, strips of flexible PCB of defined lengths may be joined together at their ends to form strips of flexible linear lighting of arbitrary length.

[0004] Combined with an appropriate power supply, linear lighting may be considered a luminaire (i.e., a finished light fixture) in its own right. It may also be used as a raw material for the manufacture of other, more complex, luminaires.

[0005] The most popular form of linear lighting is flexible, cuttable linear lighting. In this form of linear lighting, a flexible PCB is divided into repeating blocks at defined cut points. Each repeating block is a self-contained lighting circuit that will light if connected to power. The cut points allow a manufacturer or an installer to choose the desired length of linear lighting by cutting the flexible PCB at the desired cut point and connecting the resulting length of linear lighting to power.

[0006] The convention in the linear lighting industry has been to keep the PCB, and the circuit components mounted on the PCB, as simple as possible. This has both cost and technical rationales. Simply put, more complexity in a PCB lighting circuit often means more cost. Beyond cost, more components mounted on the PCB often means more points at which the linear lighting could fail, a problem exacerbated by the flexibility of a flexible PCB.

[0007] However, the simplicity of a typical strip of linear lighting creates its own problem: a typical strip of linear lighting can only emit one type of light. A manufacturer or distributor may thus need to stock dozens of different varieties of linear lighting, each variety with a different light output level, correlated color temperature, or other characteristic. Just as one example, for a single line of linear lighting, a manufacturer might stock seven different color temperatures of linear lighting in three different light output levels, for each of two potential input voltages, resulting in 42 different varieties of linear lighting in that product line. This represents an enormous investment of resources, and can be difficult for manufacturers, distributors, retailers, and everyone else in the supply chain.

BRIEF SUMMARY

[0008] One aspect of the invention relates to linear lighting for which the light output is selectable among two or more predetermined options using onboard circuitry. In one embodiment of a strip of linear lighting according to this aspect of the invention, the onboard input-side power circuit for the linear lighting has multiple branches, each one connected to a separate solder pad, with one solder pad serving as a common anode or cathode for all branches. Typically, one branch of the input-side power circuit directs all power applied to its solder pad directly to the LED light engines, as would be done in a conventional strip of linear lighting. The other branches of the input-side power circuit have components in them that moderate or control the effective light output of the LED light engines. For example, each circuit branch that offers a reduced light output may include a pulse-width modulation (PWM) oscillator circuit that reduces the duty cycle of the LED light engines. A working embodiment may have, e.g., one circuit branch that produces 100% of rated light output, one circuit branch that produces 50% of rated light output, and one circuit branch that produces 25% of rated light output.

[0009] In linear lighting that is arranged as a series of identical repeating blocks, the PWM oscillator circuits may be arranged in each repeating block such that a PWM signal created by the first PWM oscillator in the strip of linear lighting will bypass the remaining PWM oscillator circuits. For example, each PWM oscillator may be arranged electrically in parallel with the main conductor that carries power for that circuit branch. PWM oscillators typically have, or can be configured to have, a high impedance to AC signals. Therefore, the AC PWM signal generated by the first PWM oscillator on the strip of linear lighting is much more likely to flow through the main conductor and bypass subsequent PWM oscillators than it is to flow through the subsequent PWM oscillators.

[0010] Other aspects, features, and advantages of the invention will be set forth in the description that follows.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0011] The invention will be described with respect to the following drawing figures, in which like numerals represent like features throughout the description, and in which:

[0012] FIG. 1 is a perspective view of a strip of linear lighting with selectable light output according to one embodiment of the invention;

[0013] FIG. 2 is a circuit diagram of one embodiment of a lighting circuit for the linear lighting of FIG. 1;

[0014] FIG. 3 is a perspective view similar to the view of FIG. 1, illustrating power connection for full light output;

[0015] FIG. 4 is a perspective view similar to the view of FIG. 1, illustrating power connection for 75% light output;

[0016] FIG. 5 is a perspective view similar to the view of FIG. 1, illustrating power connection for 50% light output;

[0017] FIG. 6 is a schematic illustration of a PWM oscillator that may be used in embodiments of the invention; and

[0018] FIG. 7 is a schematic illustration of another type of PWM oscillator that may be used in embodiments of the invention.

DETAILED DESCRIPTION

[0019] FIG. l is a perspective view of a strip of linear lighting, generally indicated at 10, according to one embodiment of the invention. The strip of linear lighting 10 includes an elongate, narrow printed circuit board (PCB) 12 on which a number of LED light engines 14 are mounted. [0020] As the term is used here, “light engine” refers to an element in which one or more light-emitting diodes (LEDs) are packaged, along with wires and other structures, such as electrical contacts, that are needed to connect the light engine to a PCB. LED light engines may emit a single color of light, or they may include red- green-blue (RGBs) that, together, are capable of emitting a variety of different colors depending on the input voltages. If the light engine is intended to emit “white” light, it may be a so-called “blue pump” light engine in which a light engine containing one or more blue-emitting LEDs (e.g., InGaN LEDs) is covered with a phosphor, a chemical compound that absorbs the emitted blue light and re-emits either a broader or a different spectrum of wavelengths. In the illustrated embodiment, the light engines are surfacemount devices (SMDs) soldered to the PCB 12, although other types of light engines may be used. The particular type of light engine is not critical, and other types of light engines may be used.

[0021] In the illustrated embodiment, the PCB 12 is divided into two repeating blocks 16 that are electrically in series with one another. Each repeating block 16 is a complete lighting circuit; separated from other repeating blocks 16, its LED light engines 14 will function when it is connected to power. The repeating blocks 16 can be separated from one another at a cut point 18, which is indicated by a line printed on the upper face of the PCB 12 in FIG. 1. In other embodiments, there may be no line indicating the position of the cut point 18. In yet other embodiments, there may be a “cut area” defined between two repeating blocks 16 that belongs to neither of them.

[0022] A strip of linear lighting 10 may include any number of repeating blocks 16. As was noted briefly above, during manufacture, shorter strips of linear lighting 10 may be connected together, usually at overlapping solder joints, to form a longer, continuous strip of linear lighting 10. Two repeating blocks 16 are shown in FIG. 1 merely for exemplary purposes.

[0023] Each repeating block 16 of FIG. 1 includes three LED light engines 14, although in other embodiments, there may be more or fewer LED light engines 14 in each repeating block, depending on the forward voltages of the LED light engines 14, the input voltage for which the strip of linear lighting 10 is designed, and other factors. In addition to the LED light engines 14, each repeating block 16 includes other elements. [0024] More specifically, PCB 12 contains contacts, solder pads, and conductors necessary to create an electrical circuit for the linear lighting 10. To make a functional strip of linear lighting 10, other components may be mounted on the PCB 12. For example, in a typical power circuit for LED light engines, the current flow to the LED light engines 14 is controlled. This may be done in the power supply (i.e., in the driver), or it may be done by adding components to the PCB 12 to manage current flow. Linear lighting that is designed to be used with an external driver that controls the current flow is called “constant current” linear lighting. Linear lighting that is designed to control the current flow using its own circuits is often referred to as “constant voltage” linear lighting. Constant-current linear lighting is often used when the length of the linear lighting is known in advance; constant-voltage linear lighting is more versatile and more easily used in situations where the length, and resulting current draw, is unknown or is likely to vary from one installation to the next.

[0025] In general, linear lighting may accept either alternating current (AC) or direct current (DC) power at either high voltage or low voltage. While the definition of “low voltage” varies according to the authority one consults, for purposes of this description, voltages under about 50V will be considered to be low voltage. Much of this description will assume that the linear lighting 10 is of the constant voltage variety and accepts low-voltage DC power, although constant-current linear lighting may be made according to embodiments of the invention. Because the linear lighting 10 is constant voltage, each repeating block 16 includes a current control component 20 to control the current to which the LED light engines 14 are exposed. The current control component 20 may be a passive component, like a surface-mounted resistor, or it may be an active component, like a current-control integrated circuit. Additionally, although one current control component 20 per repeating block 16 is shown in the view of FIG. 1, each repeating block 16 may have any number of current control components 20, and may combine passive and active components if necessary or desirable.

[0026] The linear lighting 10 of FIG. 1 has a light output that is selectable from among two or more predetermined options using onboard circuitry. Thus, in addition to current control components 20, the PCB 12 includes a number of light output controllers 22, 24. These light output controllers 22, 24 define the light output of the LED light engines 14, as will be described below in more detail. A set of four solder pads 28, 30, 32, 34 allow for connection to power as will also be described below in more detail. The solder pads 28, 30, 32, 34 may be soldered to or attached to power via a connector.

[0027] FIG. 2 is circuit diagram of the strip of linear lighting 10 of FIG. 1. As was described briefly above, in addition to the basic circuits and components used in most LED lighting circuits, the strip of linear lighting 10 is adapted to provide different levels of light output depending on which solder pads 28, 30, 32, 34 are connected to power.

[0028] More specifically, the input-side of the circuit of the strip of linear lighting 10 has three branches. For convenience, the circuit branches are labeled A, B, and C in the diagram of FIG. 2. Each branch begins with one of the solder pads 28, 30, 32. As will be described below in more detail, each branch of the circuit includes different components that create a predetermined light output level for the linear lighting 10.

[0029] There are many different ways of reducing the light output of an LED light engine 14. For example, a large resistor or a voltage divider in the circuit can reduce the voltage received by the LED light engines 14, and thus, their light output. In some cases, these types of passive components may be used, with each branch of the circuit having a different resistance, for example. However, as those of skill in the art will understand, techniques like increased resistance and voltage division tend to be inefficient and wasteful of power.

[0030] Because LEDs are solid-state components able to respond very quickly to changes in voltage, one of the most common techniques for reducing their light output is pulse-width modulation (PWM). In PWM schemes, the “duty cycle” of the LED light engines 14 is modified by rapidly switching them on and off, which creates a reduction in the effective light level that is emitted. For example, the duty cycle may be modified to 75%, meaning that the LED light engines 14 are off 25% of the time. PWM is typically created by powering the LED light engines 14 with an oscillating signal whose amplitude is sufficient to turn the LED light engines 14 on and off (or, at least, to significantly reduce their light output) and whose period is suitable for producing the desired duty cycle. The oscillating signal is often a square wave, but could be a sinusoid or another form of oscillating signal. The frequency of the PWM switching is high enough that the switching is imperceptible to the human eye, typically at least in the kilohertz range, and possibly in the megahertz range. In deciding the appropriate PWM switching frequency, one should take into account the type of LED light engine 14. For example, although an LED itself may be able to switch on and off very rapidly, if the LED light engine 14 includes a phosphor, its response time may be slower.

[0031] Circuit Branch A provides full light output, i.e., 100% duty cycle. (Here, the term “light output” is intended to be synonymous with the more technical term “luminous flux.”) Solder pad 28 provides a positive terminal (i.e., a cathode) for power connection to Circuit Branch A. As shown in the circuit diagram, power applied to solder pad 28 flows directly to the LED light engines 14. Circuit Branch A is thus similar to a typical lighting circuit.

[0032] Solder pad 30 is part of Circuit Branch B and solder pad 32 is a part of Circuit Branch C. In each of Circuit Branches B and C, the incoming DC power flows through a PWM oscillator circuit 22, 24, which serves as the light output controller 22, 24 described above. The PWM oscillator circuits 22, 24 are configured to produce different duty cycles. In the example of FIG. 2, Circuit Branch B, connected to solder pad 30, includes a PWM oscillator circuit 22 that is configured to produce a 50% duty cycle; Circuit Branch C, connected to solder pad 32, includes a PWM oscillator circuit 24 that is configured to produce a 25% duty cycle.

[0033] Thus, when either of the solder pads 30, 32 connected to a PWM oscillator circuit 22, 24 is provided with power, the incoming DC voltage is modified by the PWM oscillator circuit 22, 24 to produce the desired duty cycle and consequent light output. This allows the manufacturer or an installer to choose the effective light output of the strip of linear lighting 10 at the time the finish manufacturing or installation steps are completed. Moreover, while this description focuses on soldering, a solderless connector may be used.

[0034] In the circuit of FIG. 2, solder pad 34 serves as a common negative terminal (i.e., a common anode) for all of the circuit branches. However, in some cases, the various circuit branches may share a common cathode, instead of a common anode.

[0035] Although the strip of linear lighting 10 has four circuit branches, which range from 100% to 25% of full light output, more or fewer circuit branches may be provided in other embodiments. The only potential limitation is that the respective solder pads 28, 30, 32, 34 should be large enough to connect to. Moreover, while these components are referred to as “solder pads” in accordance with industry conventions, they are electrical contacts, and they may be used to make any type of electrical connection. For example, instead of a soldered joint, clip-on or push-on connectors may be used.

[0036] One consideration when including elements like the PWM oscillator circuits 22, 24 in linear lighting with repeating blocks 16 is the effect of these elements on subsequent repeating blocks 16 of the strip of linear lighting 10. The first PWM oscillator circuit 22, 24 to encounter a DC voltage will introduce the desired oscillation into that voltage. The circuit of FIG. 2 is arranged such that PWM oscillator circuits 22, 24 in subsequent repeating blocks are likely to have little effect on the already- oscillating voltage signal.

[0037] Specifically, in the circuit of FIG. 2, each PWM oscillator circuit 22, 24 is actually arranged electrically in parallel with the main conductive trace for the circuit branch. PWM oscillators are designed to receive DC signals and typically have a high impedance to AC signals; therefore, in subsequent repeating blocks 16, after an oscillation has been introduced, current is more likely to flow through the lower- impedance circuit path without a PWM oscillator circuit than to flow through the parallel branch with the high-impedance PWM oscillator circuit 22, 24.

[0038] In the above description, and in the diagram of FIG. 2, the PWM oscillator circuits 22, 24 are shown as simple “black box” components. In an actual implementation, each of the PWM oscillator circuits 22, 24 would likely comprise at least several components. An integrated circuit (IC) oscillator would typically lie at the center of that circuit. The IC oscillator may be a simple oscillator, such as a 555 timer IC, or it may be a more complex form of oscillator. Although the PWM oscillators 22, 24 are shown in the circuit diagram of FIG. 2 as receiving the full voltage (and current) that is flowing through the circuit, some actual IC oscillators are not capable of accepting the level of voltage or current used to power a strip of linear lighting 10. Therefore, the circuit around the IC oscillator would typically provide appropriate input voltage and current for the IC oscillator. The output of the IC oscillator would typically be applied to the gate of a transistor or transistors to control the flow of current and create the PWM oscillation in the higher-power branch of the circuit. In addition to those circuit elements, additional resistors, capacitors, diodes, and other elements may be used for various purposes in a PWM oscillator circuit 22, 24. For example, additional passive or active components may define the duty cycle and other performance characteristics of the IC oscillator. In essence, the PWM oscillators 22, 24 may be the same or similar except for those components used to set the duty cycle. [0039] In many embodiments, the PWM oscillator circuit 22, 24 may comprise a specialized surface-mount technology (SMT) IC LED driver with PWM dimming capability. These types of IC LED drivers typically serve as a current source for the LED light engines 14, which may reduce or eliminate the need for passive circuit elements, like resistors, to set the current in the circuit. In other words, in some embodiments, an IC LED driver serving as a part of a PWM oscillator circuit 22, 24 may also serve the purpose of the current control element 20 described above. Many IC LED drivers of this type also accept the full voltage used to drive LED light engines 14, e.g., 12V or 24V. A typical IC LED driver takes an input to set the duty cycle of the LED light engines 14 connected to it. That input may be either a DC voltage or an oscillating signal, e.g., a square wave. The nature of the input to the IC LED driver will often determine the other components in the circuit. If the duty cycle input to the IC LED driver is a DC voltage, then the other components of the PWM oscillator circuit 22, 24 may be, for example, a buck converter, a voltage divider, or another element that can take the input voltage and downconvert or divide it to create an appropriate input. If the duty cycle input to the IC LED driver is a square wave or another type of oscillating signal, the other components of the PWM oscillator circuit 22, 24 would produce that signal.

[0040] One schematic diagram of a PWM oscillator circuit 22 can be found in FIG. 6. The PWM oscillator circuit 22 has main power lines 50, 52 that are electrically connected to, and receive power from, voltage and minus-return solder pads 30, 34 and their associated conductors, as shown in FIG. 2. As was described immediately above, this embodiment of the PWM oscillator circuit 22 uses an IC LED driver 54 that is adapted to operate with the operating voltage of the linear lighting 10 (e.g., 12 or 24 VDC). Thus, the power lines 50, 52 connect directly to the driver IC 54.

[0041] Within the PWM oscillator 22, branches 56, 58 of the main power lines 50, 52 supply a low voltage source 60. As was described above, the low voltage source 60 takes the full operating voltage (e.g., 12 or 24 VDC) and outputs a lower voltage of, e.g., 10V, 5V, 3.3V, 1.8V, etc. In this, it is assumed that there is at least one electronic component that does not operate at the full operating voltage of the linear lighting 10. The low voltage source 60 in this embodiment may be assumed to be a buck converter, but voltage dividers and other DC-DC conversion topologies may be used in other embodiments. In this embodiment, the low voltage source 60 supplies an oscillator 62, that in this case is a square wave generator 62, but may produce other types of oscillating signals in other embodiments. The output from the square wave generator 62 is sent to a designated input pin of the driver IC 54 to provide an indication of the desired duty cycle. The square wave generator 62 may have any topology - for example, it may be based on a generic op amp, or it may use a specialized timer or clock IC, like the 555 timer IC described above. If needed, an amplifier or conditioning circuit could be placed between the square wave generator 62 and the IC LED driver 54 to amplify or further condition the signal for use as input to the IC LED driver 54.

[0042] The PWM oscillator 22 shown in FIG. 6 assumes that the IC LED driver 54 takes an oscillating signal, such as a square wave, to set the duty cycle, and thus, the brightness, for the LED light engnies 14. However, as explained above, that may not be the case. Some IC LED drivers may take a DC voltage as an indication of the desired duty cycle. FIG. 7 is a schematic diagram of a PWM oscillator 100 illustrating this concept. In the PWM oscillator 100, power lines 102, 104 are connected to solder pads 106, 108 and their associated conductors to receive the full operating voltage of the linear lighting 10. That full operating voltage is supplied directly to the IC LED driver 110 by the power lines 102, 104. Branches 112, 114 from the main power lines 102, 104 bring the operating voltage to a low voltage source 116. The low voltage source 116 may have the same topology as the low voltage source 60 described above. However, there is a functional difference between the two low voltage sources 60, 116: instead of a “standard” low voltage to power other microelectronic elements or devices, the low voltage source 116 of the PWM oscillator 100 produces whatever voltage is necessary as input to the IC LED driver 110 to set the desired duty cycle for the LED light engines 14. That output voltage is provided via appropriate conductors 118, 120 to the IC LED driver 110.

[0043] In contrast to a typical PWM dimmer used in lighting circuits, which provides variable, user-selectable levels of dimming, the PWM oscillators 22, 24 of the linear lighting 10 offer one or more fixed, predetermined levels of light output other than 100% that are selectable at the time of finish manufacturing or installation and are usually not altered after that point. Of course, nothing prevents an installer or user from removing a power wire from one solder pad 28, 30, 32 and connecting it to another solder pad 28, 30, 32 to change the duty cycle and light output of the linear lighting 10. If more selectability or variability is desired, a strip of linear lighting 10 with a selectable light output could be paired with a connector that has a built-in switch to define which solder pads 28, 30, 32, 34 are connected. [0044] The fact that some embodiments of linear lighting 10 may use onboard PWM to offer specific light output levels does not foreclose the possibility of using such linear lighting 10 with a conventional PWM dimmer. If the linear lighting 10 is used with a PWM dimmer, the PWM dimmer would typically have a modulation frequency much higher than that of the onboard PWM oscillators 22, 24. The precise modulation frequencies are not critical. However, it may be helpful if both the onboard PWM oscillators 22, 24 and any external PWM dimmer have frequencies that are high enough to reduce or eliminate visible flicker. In some cases, frequencies may be chosen in accordance with IEEE 1789-2015 or other regulatory standards implemented in order to reduce or eliminate the deleterious effects of flicker on people.

[0045] While the invention has been described with respect to certain embodiments, the description is intended to be exemplary, rather than limiting. Modifications and changes may be made within the scope of the invention, which is defined by the appended claims.