Patent Application
20150264755
The present disclosure relates to a lighting control of light-emitting diode (LED)-based lighting devices, and more particularly to a system and a method for LED-based lighting devices that require dimmability and correlated color temperature (CCT) tunability.
Solid-state lighting from semiconductor LED light sources has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (with no hazardous materials used), higher efficiency, smaller size, and longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. Meanwhile, as LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt LED-based lighting for their illumination applications. In this trend, more energy saving with a dimming control, more efficient CCT tunability, more environmental protection, and more aesthetic perception in lighting quality have become especially important and need to be well addressed.
The relationship between actual dimming and perceived dimming is not linear but logarithmic by nature because the human eye responds to low light levels by enlarging the pupil, allowing more light to enter the eye. This response results in a difference between measured and perceived light levels. For example, a lamp that is dimmed to 10% of its maximum measured light output is perceived as being dimmed to only 32%. Similarly, a lamp dimmed to 25% is perceived to be at 50%. Taking advantage of such differences, the use of a dimmer on LED-based lamps can save even more energy than actual dimming itself. Besides, reduced electrical consumption can further prolong life expectancy of the LED-based lamps and reduce maintenance or replacement costs.
A conventional wall-mount dimmer uses a leading-edge phase angle, trailing-edge phase angle, or phase cut to control a power delivering to a lighting device. Whereas such a dimmer seems to provide energy efficiency and is driving consumers to replace standard incandescent lamps with LED-based retrofit lamps, consumers often find that the performance they expect is not being achieved, at least when the solid-state lighting (SSL) products are used with existing TRIAC or phase-cut dimmers. Dimmer compatibility with LED-based lighting devices is a main issue. Basically, the wall-mount TRIAC dimmers are not so designed for LED loads that the existing residential wiring infrastructure can limit their capabilities for modern lighting controls. Furthermore, there are no industry standards that specifically guide LED dimming performance, and as such, a number of undesirable results may occur when one uses a dimmable LED-based lamp with an incandescent dimmer, such as reduced dimming range, flickering or strobing of the lamp, and inconsistent performance based on the number and classification of lamps being controlled by one incandescent dimmer. Moreover, a recent IEEE report raised a health concern due to invisible flicker at frequencies below 165 Hz including seizures, headaches, migraines, impaired ocular motor control, and impaired visual performance, etc.
Most of the existing residential and commercial electrical dimming infrastructures are single channel wall dimmers, which are crucial to serve the market with high quality solutions and to solve the various challenges to come. Furthermore, power factor of an electrical appliance refers simply to the degree to which the voltage potential and electric current draw required by the electrical appliance are in-phase for each half-cycle of the sinusoidal AC waveform. In fact, the current waveform should be in phase with AC voltage waveform to have a maximum power delivered to the load resulting in a unity power factor as in a purely resistive circuit. Conventional dimmers themselves have a major effect on power factor for all kinds of loads—capacitive, inductive, non-linear, and even linear and resistive, because such dimmers typically cut voltage phase over the current peak as required by the load, causing imbalance and harmonic distortion on the AC line. Poor power factor is rarely noticed by residential end-users because their utility companies usually pay the price by spending money on hardware and additional power to correct for this imbalance throughout their distribution systems. However, commercial users may either pay additional surcharges for low power factor or improve it at their own cost. For example, if their loads are highly inductive, they may have to install capacitor switch banks to compensate for this power loss.
A conventional driver employed to drive an LED-based lamp basically uses a switch-mode power supply (SMPS) and is considered to be nonlinear with reactive loads, which requires power factor correction (PFC) to reduce non-sinusoidal current distortion and excess energy at harmonics of the line frequency of the voltage. The EU standard EN61000-3-2 regulates harmonic contents and basic PFC criteria for all such switch-mode power supplies. Passive PFC in drivers/power supplies adopted in LED-based lamps usually involve adding capacitors, resistors and steering diodes in a valley-fill circuit. However, the power factor improvement using such a passive PFC circuit is limited. Active PFC involves redistributing the current over the voltage half-cycle waveform. The key is how to improve load regulation without adversely affecting the power factor or to make the load look like a linear resistor. Today, a conventional LED driver employing active PFC typically uses an energy transfer element that includes a flyback transformer to store energy which then directly provides LED current to an LED load. Although simple and low-cost, such a single-stage driver configuration provides so limited functionalities that can barely meet market demands. For example, market needs an external LED driver which can flexibly control one to several LED-based lighting devices in a luminaire. When part of lighting devices are removed from the luminaire for maintenance or replacement, an overall rated current can flow into the remaining LED-based lighting devices, resulting in excessive driving current for LED-based light sources. Market also needs an LED driver which can provide two or three sets of electric current to two or three types of LED-based light sources in order to control CCT of an LED lighting device that comprises such two or three types of LED-based light sources. The conventional LED driver can only provide single channel current control and thus fails to meet these market requirements.
Used as an early fluorescent dimming system and still used today, 0-10 V dimming has been employed to become one of reliable LED dimming control protocols although it is one of the earliest and simplest electronic lighting control signaling systems. A 0-10 V dimmer does not cut AC voltage for introducing phases and thus keep the AC voltage waveform intact. However, to control a dimming level of a lighting device using such a 0-10 V dimmer, one needs to have two extra low-voltage wires separately connected to the lighting device to be dimmed in addition to the power lines from the AC mains. This is so called 4-wire low voltage 0-10 VDC dimming. The low voltage control wires are polarity sensitive, and so accuracy is critical in wiring. This increases the wiring difficulty and installation cost, especially for the existing residential and commercial infrastructures that have two or three power wires in a wall-mount electrical box.
In today's lighting applications, CCT tuning is important. Although consumers demand a CCT tunable lamp that can tune from warm-white at 2,700 K, via sun-white and natural-white at 4,100 K, to cool-white at 6,200±300 K in general lighting to help improve the atmosphere in their working, exhibiting, or living areas, there have been very few such lighting products in luminaire markets. Manufacturers can generally make an LED-based lighting device using two kinds of phosphor coated white LEDs, one cool white and the other warm white, to mix light emissions with different ratios to come up with desired CCTs. However, the approach needs a proper LED driver to provide two sets of electric current with a proper ratio to the cool white and the warm while LEDs such as to emit a light emission with desired CCTs. A conventional driver apparently cannot meet such requirements.
The present disclosure relates to a lighting control of LED-based lighting devices that adopt a command scheme to control multiple LED-based lighting devices that require dimmability and CCT tunability. As mentioned in the description of related art, the best solution to avoiding wiring difficulty associated with 4-wire low voltage 0-10 VDC dimming control is to incorporate dimming control signals into the power line in the dimming mode and to remove dimming control signals from the power line in the normal mode. In this case, AC voltage in the power line remains intact in most of operating time, thus providing an acceptable power factor. To control an LED-based lighting device with dimmability and CCT tunability, one needs to have a dimming and CCT tuning controller comprising power input terminals, a voltage sensing circuit, a dimming input, a CCT tuning input, a modulator, an AC current return controller, and a dimming and CCT signal generator that generates control signals to control the modulator and the AC current return controller. The dimming and CCT tuning controller can generate dimming and CCT tuning commands according to signals received from a dimming input and a CCT tuning input, which involves multiplexing dimming and CCT tuning signals and modulating the multiplexed dimming and CCT tuning signal portion in the AC voltage to deliver to the LED-based lighting device. In the LED-based lighting device, a demodulator needs to recover the dimming and CCT tuning signal portion and to generate pulse-width modulation (PWM) control signals to control at least two sets of drive current provided for two types of LED-based light sources in the lighting device to change dimming levels and to tune CCT of the lighting device.
Without introducing AC voltage waveform distortion that happens in an AC phase control dimming and affects the power quality, the dimming and the CCT tuning commands are sent in a dimming and CCT tuning mode but not resent in a normal mode unless there are signal changes. In the dimming and CCT tuning mode, a time-division multiplexing is used in the dimming and CCT tuning controller to multiplex the dimming and the CCT tuning signals with a command initiation signal in the first three cycles of the voltage in AC mains to form a complete command that includes the dimming and the CCT tuning signal portion and the command initiation signal. In the normal mode, however, the dimming and CCT tuning controller sends a regular AC voltage to the lighting device to maintain its dimming level and CCT.
The voltage sensing circuit is connected to the power input terminals which receive an AC power for sensing voltage peaks of the AC mains in the dimming and CCT tuning mode to provide synchronization information for the dimming and CCT tuning signals to be successfully modulated and delivered to the lighting device. The dimming and CCT tuning signal generator generates two sets of control signals, one in the dimming and CCT tuning mode and the other in the normal mode. Each set of the control signals comprises two control signals, controls signal 1 sent to the AC current return controller and controls signal 2 sent to the modulator. In the dimming and CCT tuning mode, the controls signal 1 is sent to disable the AC current return controller in the positive half cycle while the controls signal 2 is sent to turn the modulator on and off according to the dimming and CCT tuning signals. In this way, the dimming and the CCT tuning signals are modulated in the AC voltage to form a dimming and CCT tuning output power to deliver to the LED-based lighting device. After the three cycles in the dimming and CCT tuning mode, if users perform no dimming and CCT tuning adjustment, the dimming and CCT tuning controller enters the normal mode. In the normal mode, the controls signal 1 is sent to enable the AC current return controller in the positive half cycles while the controls signal 2 is sent to disable the modulator; no dimming and CCT tuning signals are modulated and sent, thus a regular AC power being delivered to the LED-based lighting device. As the time for performing a dimming and CCT tuning adjustment is within three cycles of the AC mains or 3/60 seconds, AC voltage distortion can be ignored in a long term perspective, thus maintaining a power factor which is only determined by the LED driver used to drive the LED-based light sources in the LED-based lighting device.
A dimming and CCT tuning lighting system comprises the foregoing dimming and CCT tuning controller and at least one lighting device. The at least one lighting device comprises a demodulator, a dimming and CCT tuning controllable driver comprising a power supply section and an LED driving section further comprising at least two LED driving circuits, a dimming and CCT tuning control circuit, and at least two types of LED-based light sources. The power supply section, connecting to the output terminals of the dimming and CCT tuning controller, receives and converts a regular AC power or the dimming and CCT tuning output power into a DC power supplying the dimming and CCT tuning control circuit and the at least two LED driving circuits which then drive at least two types of LED-based light sources to emit light. The demodulator receives the dimming and CCT tuning output power and extracts a dimming and CCT tuning signal portion in the dimming and CCT tuning output power. Based on the recovered dimming and CCT tuning signal portion, the dimming and CCT tuning control circuit generates PWM control signals to send to the at least two LED driving circuits to change at least two sets of time-averaged driving current to drive the at least two types of LED-based light sources to emit a resultant light with a desired dimming level and CCT. In the normal mode, the demodulator receives the regular AC power, and the dimming and CCT tuning control circuit sends PWM control signals to LED driving circuits simply to maintain the original time-averaged driving current to drive the LED-based light sources with an unchanged the dimming level and the CCT.
The present disclosure provides a method in the dimming and CCT tuning lighting system that comprises the dimming and CCT tuning controller used for multiplexing and modulating dimming and CCT tuning signals in the voltage of the AC mains in the dimming and CCT tuning mode. A modulated dimming and CCT tuning output power is delivered to multiple LED-based lighting devices to change their dimming levels and CCTs. The method comprises: (1) the dimming and CCT tuning controller determines if receiving a user signal to perform a dimming and CCT tuning adjustment; (2) if the dimming and CCT tuning controller is not instructed to perform the dimming and CCT tuning adjustment, the dimming and CCT tuning controller executes a normal process in a normal mode, in which the AC power is delivered to the multiple lighting devices to maintain their luminance and CCTs; (3) if the dimming and CCT tuning controller is instructed to perform the dimming and CCT tuning adjustment, the dimming and CCT tuning controller executes a dimming and CCT tuning process in a dimming and CCT tuning mode, in which the dimming and CCT tuning controller further performs: (a) controlling the AC current return controller and the modulator to modulate the first three cycles of AC power by turning on and off the power according to a pulse train of a dimming and CCT tuning signals so as to generate the dimming and CCT tuning output power having the dimming and the CCT tuning signal portion embedded therein; (b) delivering the dimming and CCT tuning output power to the multiple lighting devices to demodulate and recover the dimming and the CCT tuning signal portion, to receive AC power, and to perform the dimming and CCT tuning adjustment according to the recovered dimming and CCT tuning signal portion.
The lighting control according to the present disclosure may find applications in general lighting, signage, stage lighting, wall-washer, etc.
The accompanying drawings are included to aid further understanding of the present disclosure, and are incorporated in and constitute a part of the present disclosure. The drawings illustrate a select number of embodiments of the present disclosure and, together with the detailed description below, serve to explain the principles of the present disclosure. It is appreciable that the drawings are not necessarily in scale as some components may be shown to be out of proportion than the size in actual implementation in order to clearly illustrate the concept of the present disclosure.
When users perform either a dimming or a CCT tuning adjustment at either the dimming input 110 or the CCT tuning input 111, the dimming and CCT tuning signal generator 114 senses either a dimming or a CCT tuning signal change and then generates a first set of control signals in first three cycles. The first set of control signals comprises the control signal 1 sent to the AC current return controller 115 and the control signal 2 sent to the modulator 116, both in synchronization with the peaks of the AC mains with clock information provided by the voltage sensing circuit 113.
After the three cycles, if users do not perform a dimming and CCT tuning adjustment at the dimming and the CCT tuning inputs 110 and 111, the dimming and CCT tuning signal generator 114 senses no dimming and CCT tuning signal changes from the dimming input 110 and the CCT tuning input 111 and then generates a second set of control signals in a way that the control signal 1 is always at a high level in the positive half cycles and at a low level in the negative half cycles, and the control signal 2 is always at a low level, as shown from the fourth cycle in
The control signal 2 in the dimming and CCT tuning mode may have a most common line codes such as a return-to-zero (RZ) format that comprises a high level and a low level, a Universal Asynchronous Receiver/Transmitter (UART) format with the high level representing “1” and the low level representing “0”, or any other pulse modulation formats as long as “1” and “0” can be distinguished. Comprising a microcontroller, the dimming and CCT tuning signal generator 114 may have built-in specific lighting settings for different times of the day and may use daylight to offset the amount of electric lighting needed to properly light a space, in order to reduce energy consumption. This can be accomplished by using lighting control systems adopting photo-sensors to reduce luminance of lighting devices in response to changing daylight availability. When a specific time arrives, the dimming and CCT tuning signal generator 114 automatically generates a dimming and CCT tuning output power to achieve automatic luminance and CCT tuning adjustments, such as lighting with higher luminance and lower CCT at night or lighting with lower luminance and higher CCT in the daytime. In the present disclosure, the dimming and CCT tuning signal generator 114 generates the dimming and CCT tuning control signals according to the dimming and the CCT tuning inputs 110 and 111. The dimming and the CCT tuning inputs 110 and 111 may be locally or remotely controlled by users. For example, the dimming and the CCT tuning inputs 110 and 111 may be replaced by a receiver to receive an external dimming and a CCT tuning signals from a remote transmitter. In this case, the dimming and the CCT tuning inputs 110 and 111 may be in other forms than the potentiometer/variable resistor as shown in
In the dimming and CCT tuning mode, users may adjust a dimming level and a CCT up or down. For example, an original light level is at 100% maximum luminance, and adjusting a dimming level up means making the light level less than 100% of its maximum luminance. The minimum luminance is 0%. An original light is at a CCT of 2,700K (warm white), and adjusting a CCT up means increasing the CCT of the light to be greater than 2,700K. In general lighting applications, CCT can vary from 2,700K (warm white) to 5,700K (cool white). Users can adjust CCT of a lighting device within this range to change a room atmosphere for their working or living requirements. Furthermore, since the dimming and CCT tuning controller 100 has built-in dimming and CCT tuning commands configured for different schedules, the present disclosure can automatically generate dimming and CCT tuning control signals upon configured schedules without having to receive users' adjustment signals through the dimming and the CCT tuning inputs.
Not like a conventional TRIAC dimming system in which the phase angle information is continuously sent whether or not a dimming change is needed, the present disclosure uses a command scheme in which the dimming and CCT tuning signal is sent but not resent unless there is a change. As mentioned above, in the dimming and CCT tuning mode, a command initiation signal, a dimming signal, and a CCT tuning signal are embedded respectively in three cycles of the AC mains. The initiation cycle used to identify a start of a dimming and CCT tuning command is vital for the dimming and CCT tuning signal portion to be demodulated and recovered in the multiple LED-based lighting devices 200 controlled by the dimming and CCT tuning controller 100. In the first positive half cycle, a typical pulse train at a frequency several times higher than 60 Hz with 0 degree phase shift is sent to the modulator 116 for initiating the dimming and CCT command, providing not only timing information but also phase information of the pulse train for successfully setting up the dimming signal and the CCT tuning signal in the second and the third positive half cycles.
When users adjust a dimming level at the dimming input 110, the dimming and CCT tuning signal generator 114 senses not only a change of dimming level but its sign, plus (up) or minus (down). This can be achieved by a phase modulation of the pulse train. If it is down, say, an increased voltage at the dimming input 110, the dimming and CCT tuning signal generator 114 generates a pulse train with a phase shift 90 degrees backward (phase lag) for the second positive half cycle in the control signal 2 used to turn the modulator 116 on and off; if it is up, the pulse train shifts forward by 90 degrees (phase lead). Similarly for CCT tuning, when users adjust a CCT level at the CCT tuning input 111, the dimming and CCT tuning signal generator 114 senses not only a change of CCT but its sign, plus (up) or minus (down). If it is down, say, an increased voltage at the CCT tuning input 111, the dimming and CCT tuning signal generator 114 generates a pulse train with a phase shift 90 degrees backward (phase lag) for the third positive half cycle in the control signal 2; if it is up, the pulse train shifts forward by 90 degrees (phase lead). If only a dimming level change is sensed by the dimming and CCT tuning signal generator 114, then the pulse train generated in the third positive half cycle in the control signal 2 has no phase shift.
In
In
The dimming and CCT tuning demodulator 500 taps a signal from a high potential output of the bridge rectifier 303 of which two inputs are directly connected to the power and signal input terminals 301. If the dimming and CCT tuning signal portion exists in the dimming and CCT tuning output power, then the dimming and CCT tuning demodulator 500 demodulates and converts such signal portion into original pulse trains. In
An input terminal of the dimming and CCT tuning control circuit 600 is connected to the dimming and CCT tuning demodulator 500, and output terminals are connected to the LED driving circuit section 400. The dimming and CCT tuning control circuit 600 comprises an analog-to-digital converter (ADC) 601 to convert analog data into digital ones, a flash memory 602 to store the dimming and CCT tuning signal portion demodulated by the dimming and CCT tuning demodulator 500 and digitized by ADC 601, a processor 603 to generate pulse-width modulated (PWM) control signals according to the dimming and CCT tuning signal portion and to send at least two control signals respectively to the at least two LED driving circuits 401 and 402 so that the LED driving circuit section 400 can drive the at least two types of LED-based light sources 701 and 702 to emit light with a desired luminance and a CCT. Furthermore, the flash memory 602 in the dimming and CCT tuning control circuit 600 may also store a lighting status of the at least two types of LED-based light sources 701 and 702 and even an address of the lighting device 201. Once receiving dimming and CCT tuning signal portion demodulated by the dimming and CCT tuning demodulator 500, the dimming and CCT tuning control circuit 600 increases or decreases the duty cycle of the PWM signals coupled to the PWM inputs of the at least two LED driving circuits 401 and 402 such that the two sets of driving current provided to the two types of LED-based light sources 701 and 702 can change accordingly. Based on magnitude of the currents and their ratio, a resultant light emitting from the two types of LED-based light sources 701 and 702 can emit light with a desired luminance or a CCT. Whereas the address may be stored in the flash memory 602, the command initiation signal in the dimming and CCT tuning signal cluster may contain such address information to call a specific lighting device to respond with a desired luminance or a CCT.
In the dimming and CCT tuning mode, there are eight possible dimming and CCT tuning commands which can be embedded in the AC voltage waveform as the dimming and CCT tuning output power is sent from the dimming and CCT tuning controller 100 to the multiple LED-based lighting devices 200.
In
In
Although for illustration purpose, the control signal sent to the modulator in the dimming and CCT tuning mode is within the first three cycles of AC voltage. The particular number of cycles used is a matter of design choices and depend on how fast the system should respond.
Whereas preferred embodiments of the present disclosure have been shown and described, it will be realized that alterations, modifications, and improvements may be made thereto without departing from the scope of the following claims. Accordingly, the foregoing description and attached drawings are by way of example only, and are not intended to be limiting.
