Patent Application
20170339765
The present application relates to an apparatus for providing intelligence to a lighting system, and more particularly, to an apparatus for providing ALS strobe architecture for a lighting system.
Over the years lighting system technology has advanced manifold. Energy conservation in lighting systems plays a vital role in generating effective illumination, besides being cost effective. Without compromising on ambience, visual comforts and aesthetics, it is also a requisite to integrate light system-designs with economics and environment.
Of late, different light sources have come up and been replaced by improved variants. Prominent among them have been incandescent lamps, gas-discharge bulbs, fluorescent lamps and light emitting diodes, to name a few. Certain factors like life-span of the light source, light distribution, light diffusion, sensitivity to temperature and humidity and operational cost are crucial in determining reliability of lighting systems.
Light emitting diodes lamps are more energy efficient as compared to other conventional source of lighting. A trend of replacing conventional lamp with the LED retrofit lamp is getting more and more popular.
Since energy conservation and management of electrical power is a growing concern with regard to both cost and environmental impact, the LED retrofit lamp technology therefore requires further improvement. Therefore, a system is required that enables the user to harvest substantial portion of energy from the existing LED lamp circuit and to provide intelligence built-in features for controlling the wastage of energy.
Environment responsive intelligence in LED retrofits may further enhance energy management by drastically reducing wasteful consumption. Public spaces can be monitored on the basis of specific environmental stimuli like occupancy and time-clocks, so as to yield optimum light. This can bring significant improvement in user comfort and energy savings in commercial and industrial applications.
The preferred embodiment of the invention will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the invention, wherein like designation denote like element and in which:
In a first aspect of the present invention, a LED lighting system with built-in intelligence is provided. The LED lighting system comprising a power converter to control the dimming of an LED array in response to feedback received from one or more monitoring sensors; a bridge rectifier to convert AC power coming from an external source to DC power for the power converter and; a series combination of a first capacitor and a DIAC connected parallel at the input terminal of the bridge rectifier; a second capacitor connected in parallel to the series combination of the first capacitor and the DIAC, said second capacitor is present between the external source and the series combination of the first capacitor and the DIAC. The controlling unit dims off the LED array on receiving instructions from said one or more monitoring sensor while the LED lighting system draws a little power. The first capacitor has a rating of 50-300 nF and the second capacitor has a rating of 1-10 nF. The power converter may be any of a buck/boost converter, a flyback converter or single-ended primary-inductor converter (SEPIC), a linear converter or a resonant converter.
In another aspect of the present invention, a LED lighting system with built-in intelligence is provided. The LED lighting system comprising: an LED array having one or more light emitting diodes; a power converter for providing power to the LED array in a normal operating state; a capacitor placed in parallel with the LED array to prevent ripple current from flowing to the LED array; a controller to receive a request from an ambient light sensor for measuring ambient light parameters, said controller on receiving the request generate a strobe signal; a first field effect transistor connected in series at positive end of the LED array and a second field effect transistor connected in series with the capacitor; wherein when a request from the ambient light sensor is made, the microcontroller sends strobe signal to the first field effect transistor and the second field effect transistor to turn off the power supply to the LED array and the capacitor. The LED lighting system further comprising a third field effect transistor connected in series with a second end of the LED array which get asserted by the strobe signal. The LED lighting system further comprising a fourth field effect transistor connected in series with a second end of the capacitor which get asserted by the strobe signal. The strobe signal is generated for activating the ambient light sensing state to monitor the ambient light condition by switching off the LED array. The power converter for converting the DC voltage into a constant current output is a buck convert, a flyback converter or single-ended primary-inductor converter (SEPIC), a linear converter or a resonant converter.
In another aspect of the present invention, a LED lighting system with built-in intelligence is provided. The LED lighting system comprising an LED array having one or more light emitting diodes and a large capacitor placed in parallel to the LED array; a power converter to supply power to the LED array through an inductor and a charge pump circuit, said charge pump circuit comprises a first capacitor and a second capacitor, a filed effect transistor having a source terminal connected to the power converter for receiving the constant current output, a drain terminal connected to the LED array and a gate terminal connected to the charge pump circuit at a node present between the first capacitor and the second capacitor; a voltage source connected to the node between the first capacitor and the second capacitor; a second FET connected in parallel to the second capacitor to receive a strobe signal generated by a controller on a request made by an ambient light sensor for measuring ambient light parameters; wherein during the normal operating mode, the drain gate of the first FET is at higher voltage than the source voltage and the LED array is in ON state and when the request is made by ambient light sensor the controller turn ON the second FET which pulls down the voltage at the gate terminal of the first FET which turns off the LED array. The large capacitor placed in parallel to the LED array has a rating of 10 uF to 100 uF. The first field effect transistor remains open during normal operating state and the LED array remain ON. The power is a buck convert, a flyback converter or single-ended primary-inductor converter (SEPIC), a linear converter or a resonant converter. The first FET and the second FET is a MOSFET. The power converter further comprises a means that can be asserted by a pulse width modulating signal to switch off the supply to the LED array. The strobe signal is of 50 us to 150 us.
In the following detailed description of embodiments of the invention, numerous specific details are set forth in order to provide a thorough understanding of the embodiment of invention. However, it will be obvious to a person skilled in art that the embodiments of invention may be practiced with or without these specific details. In other instances, well known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the invention.
Furthermore, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art, without parting from the spirit and scope of the invention.
The present invention provides a lighting system with built-in intelligence feature to allow it to dim itself in response to autonomous or external stimuli and to harvest power for the internal and external circuit. The lighting system comprises a LED lamp driven by a ballast and a controlling unit that imparts built-in intelligence system to the LED lamp. The circuit of the lighting system comprises a LED lamp having an array of light emitting diodes, wherein one set of the series diodes is left on and the power is harvested, in parallel from the set of series diode. A field effect transistor (FET) is wired in parallel with a portion of the light emitting diode array; the field effect transistor controls the forward voltage of the LED lamp. The Field Effect Transistor, when turned off, exposes the full light emitting diode array and the maximum forward voltage to the LED lamp. Similarly, field effect transistor, when turned on, short circuits many of the light emitting diodes and reduces the forward voltage and the power drawn from the ballast.
The embodiments of the present invention comprise a controlling apparatus with an 8 bit micro controller, a power conditioning circuitry such as a Low Dropout Regulator (LDO) to regulate power to the peripheral interface controller (Microcontroller unit) and an external interface.
In an embodiment of the invention, the controlling unit 103 may enable additional functionality to the LED lamp 102 such as power reduction for thermal management, top trimming at factory via the controlling unit 103, and top trimming in field via circuit switching or other stimulus. Furthermore, a single controlling unit 103 can control a plurality of LED lamps 102. The lamp may be circuit switched via the controlling unit 103, in addition to being locally controlled. The controlling unit 103 further comprises a means for sensing the ambient parameters such as an occupancy sensor or a photo sensor. The controlling unit 103 further comprises a modem that allows control at a higher level or may comprise of a combination of the sensors and the modem.
The controlling unit 103 is further connected to an external monitoring device such as an occupancy sensor or a photo sensor. The controlling unit 103 receives the input from the monitoring device and controls the dimming of the LED lamp 102. The occupancy sensor is a lighting control device that detects occupancy of a space by people and turns the lights on or off automatically, using infrared or ultrasonic technology. The energy saved by the occupancy sensors provides automatic control over lighting and complies with the building's codes.
In an embodiment of the present invention the controlling unit 103 harvests a small amount of DC power from the constant current supplied by the non-dimmable ballast 101. The harvested power is then used to drive the external and internal electronics of the controlling unit 103 as well as the monitoring device. Thus, there is no need of providing extra power to the controlling unit 103.
In another aspect of the present invention, the controlling unit 103 further comprises a means to control the forward voltage to the LED lamp 102 that enables the dimming of LED lamp 102 in response to external stimuli.
The controlling unit 103 contains a power harvesting means 203 that harvest the power simultaneously from the LED lamp 102. The LED lamp 102 contains a series of LED array 308 that always remains in an ON position; a circuit is extended parallel from the LED strings from where power is drawn to the power harvesting means 203 in the controlling unit 103 using the micro USB cable 104 and the connection interface 208. The power harvesting means 203 in the controlling unit 103 stores the power and uses it for driving the internal components of the controlling unit 103 as well as for feeding power to the monitoring sensors 209. The use of power harvesting means 203 eliminates the need of extra source of power for driving the controlling unit 103.
In an embodiment of the present invention, the connection interface 208 is connected to the LED lamp 102 through the cable 104 which is class 2 type. The cable 104 comprises a micro USB cable, RJ11, RJ14, RJ21, RJ45, RJ48 or other known class 2 type cables.
The field effect transistors 204 and 207 present in the controlling unit 103 control the forward voltage to the LED lamp 102. The field effect transistors 204 and 207 are circuited in parallel with the portion of LED array 308. Turning the field effect transistors 204 and 207 off exposes the full LED array 308 and thus maximum forward voltage to the LED lamp 102. On turning the field effect transistors 204 and 207 ON, many of the LEDs get short circuits thereby reducing the forward voltage and power drawn from non-dimmable ballast 101.
The dimming control 205 in the controlling unit 103 controls the illumination intensity of LED lamp 102. The microcontroller 202 receives the input from monitoring sensors 209 and on receiving the input instructs the dimming control 205 to control the output to the LED lamp 102.
The dimming control 205 then sends instruction to the field effect transistors 204 and 207 to reduce the forward voltage to LED lamp 102.
In another embodiment of the present invention, the forward voltage to the LED lamp 102 is controlled by placing a series of FET connected in parallel to the LED array. On receiving an input from the dimming control 205, the microcontroller 202 decides the number of FETs to remain in ON position. Each FET in the series is having an extra LED connected to the series. Depending on the instructions received from the microcontroller 202, the FETs in series turn ON additional LEDs thus regulating the forward voltage to the LED lamp 102.
In an embodiment of the present invention, the lighting system further comprises a thermistor 201 that monitors the temperature of the LED lamp circuit 102. The thermistor 201 may be present in the LED lamp 102 or it may be in the controlling unit 103. In case of overheating, the thermistor 201 senses the temperature and sends the feedback to the microcontroller 202. The microcontroller 202 then instructs the field effect transistors 204 and 207 to regulate the forward voltage in the event of the overheating of circuit.
In another embodiment of the present invention the controlling unit 103 further comprises a communication means 206 such as a modem or a radio frequency means. The communication means 206 is connected to the microcontroller 202. The user can send his instructions to the microcontroller 202 using the communication means 206.
In an embodiment, the present invention provides a LED lighting system with a controlling unit connected to an ambient light sensor (ALS). The ambient light sensor (ALS) can be disposed at different positions around the LED lighting system such as inward or outward of the optical cavity. The ambient light sensor (ALS) is designed to measure the ambient light coming back into the lamp when the LEDs are in OFF state. When the intensity of light is to be measured in ambient light sensing state, the LED lighting system are turned OFF for a small interval of time such that flickering of LEDs is not perceivable with human eyes. This can be done by controlling the power to the LEDs in the LED lighting system.
In order to prevent ripple current entering into the LED array, a filter capacitor 508 is placed in parallel to the LED array 514, which filters the DC rippled voltage into the smooth DC output voltage to drive the LED array 514. The filter capacitor 508 is sized large enough to operate on both the switching frequency of FET 502 as well as the frequency of line input.
The filter capacitor 508 and the LED array 514 have a discharging time constant (τ) that defines an exponential current decay of the filter capacitor 508 across the LED array 514. The ALS sampling event is affected by long time constant between the filter capacitor and LEDs. If the LEDs do not turn completely OFF within the required short amount of time the residual LED light washes out ambient light that leads to prevent proper ALS detection. On the other hand, to ensure the LEDs are OFF on a PWM cycle requires waiting too long causing a visual glitch in the LED output. In order to shut the LEDs off rapidly with a minimized ripple, various mechanisms can be implemented such as the filter capacitor could be reduced in size to reduce the time constant of current decay to the LEDs; the LED string itself could be interrupted with a FET and the like. However, these mechanisms do not provide an optimal solution for minimizing ripple current and turning ON and OFF the LED array rapidly so that the visual glitches do not appear.
During the operation, when a pulse width modulating signal is de-asserted, switching of the FET 502 stops, and capacitor 508 starts discharging through the LED array. Time constant (τ) to the capacitor 508 through LEDs is chosen to be much larger than the switching frequency of FET 502 to minimize current ripple. For instance, for 100 kHz, an increase of 10-40 ms is typical resulting in a current ripple of 5%. Unless PWM frequency is greater than 5τ, LEDs will never turn off. The time constant (τ) is desired to be five times of the switching frequency of FET 502 in order to adequately filter ripple.
While working with a LED array and a capacitor, to filter a 40 kHz switching frequency having time period of 25 us, the time constant (τ) is desired to be greater than 125 us in order to get 10% ripple. Thus, the 40 kHz switching frequency requires a filter capacitor of approximately 470 nf. Similarly, to filter a 60 Hz line input with a rectified period of 8.3 ms, the time constant (τ) is desired to be greater than 41 ms in order to get 10% ripple. Thus, the 60 Hz line frequency requires a filter capacitor of approximately 150 uf.
For ambient light sensor to work, the requirement of the power system present in the lighting system is to be able to turn off the LEDs for a period of approximately 100 us, letting the ambient light sensor (ALS) stabilize and strobe it and then turn the LEDs on. One of the methods is to interrupt the LEDs array with a FET present either at the high end of LED arrays or at the low end of LED array. The FET present at the end of LED arrays can be asserted by a microcontroller on receiving feedback from the ambient light sensor. The FET will then stop supply of power to LED array and the LEDs get turn off for the desired duration of time. However, the power converter will continue to charge the capacitor to VBoost.
The LED lighting system illustrated in
When the ambient light sensor (ALS) has collected data, the LED lighting system will resume to normal state and the high end FET or low end FET is turned back on, the capacitor starts discharging resulting in a large surge of current through the LEDs. To avoid the flow of surge current through LEDs, a set of FETs is required that disconnect both the capacitor as well as LED array from the power converter.
In another embodiment of the present invention, the power architecture can be a buck/boost converter, a flyback converter, a SEPIC converter, a linear converter or a resonant converter.
In normal operating state, the FET 808 is in conducting state and the power controller 806 receives continuous power supply. The power controller 806 operates the LED array 514 at high voltage with a large filtering capacitor 810 to minimize ripple current. When an ambient light sensing event is desired, a microcontroller dims the power controller 806 to zero to stop it from switching by driving a pulse width modulating signal high. Simultaneously it asserts a 100 us strobe signal for 100 us through a first FET 810. The first FET 810 conducts the current to the gate terminal of a second FET 812 which opens up the second FET 812 and turns the LEDs off almost instantly without requiring the large capacitor to discharge. The 100 us strobe signal is ground references and voltage translation from the 100 us strobe signal is made to the second FET through a charge pump circuit operating off the switching power supply. The charge pump circuit comprises a first capacitor 814 and a second capacitor 816.
In another embodiment of the present invention, the power architecture performed in two states: normal operating state and ALS sampling event. During the normal operation Vdd 818 is charged to a few volts. When the FET 820 present in the power converter 806 turns off, the left side of the first capacitor 814 rises to LED operating voltage, which pulls the right side of the first capacitor 814 to LED operating voltage+Vdd. The LED operating voltage+Vdd is conducted through a diode and charges the gate of second FET 812. At this time, the source of the second FET 812 stays at LED operating voltage, which turns ON the LED 514.
During the ALS sampling event, a strobe signal is generated by the microcontroller which turns ON the first FET 810, which in turn pulls down the gate of second FET 812 and turns the second FET 812 off. When the ALS sampling event is over, the gate voltage of the second FET 812 quickly recovers and turns the second FET 812 On, which turns ON the LED array 514.
During the dimming off state, only the sensors and modems are drawing power and hence the LED lighting system draws a little standby power. In one embodiment, the present invention provides an input circuit for the LED lighting system designed in such a manner that the LED lighting system and the ballast to which the LED lighting system is connected remains stable during the low power.
In an embodiment of present invention, the LED lighting system 900 can be operated with different external sources such as, but not limited to, 120/277V line input, 60 Hz magnetic ballast, high frequency electronic ballast having frequency 40-60 kHz and low frequency electronic ballast having frequency 20-25 kHz.
In an embodiment of present invention, the LED lighting system 900 is compatible to dim off the LED array 514 while keeping the plurality of monitoring sensors and the communication means 206 awake, satisfying the ballast operational requirement and drawing as little standby power or “Vampire power” as possible.
When the external source is a line voltage, the power coming to the input terminals 902 is a constant voltage source. On receiving feedback from the plurality of microsensors the controlling unit 103 dims off the power to the LED array 514 and only the plurality of micro sensors 916 and the communication units are using the current power. Since, the external source is a constant voltage source therefore; in this case, LED lighting system can draw as little current as required and thus minimizing the vampire power. In this case, the power will not flow from the first capacitor 912 and the second capacitor 908, and power directly passes through the bridge rectifier 910 where it is rectified and passes through the power converter 920.
In an embodiment of the present invention the LED lighting system 900 can be operated with a magnetic ballast. During the magnetic ballast operation, the input power is supplied to the rectifier circuit directly without passing through the first capacitor 912 and the large second capacitor 908. The rectified power is fed to the LED array through the switching converters.
In another embodiment of the present invention the LED lighting system 900 is compatible to operate with a high frequency electronic ballast in a dim-off condition. In case of the high frequency electronic ballast, current passes through the first capacitor 912 in order to convert ballast constant current input to 100V constant voltage output. Further, the 100V constant voltage is rectified using rectifier circuit and supplied to the LED array through the switching power converter.
In another embodiment of the present invention the LED lighting system 900 can be operated with a low frequency electronic ballast. During low frequency electronic ballast operation, the current passing the capacitor 912 is converted into a very high voltage causing DIAC 906 to close. The remaining current of the DIAC is being passed through the larger second capacitor 908 in order to create a constant voltage of 100V. Then, the 100V constant voltage is rectified and passes through the switching power supplies to glow the LED array 514.
The invention finds lightening application in various areas like indoor light, outdoor light and various other decoration or ornamental light, power reduction for thermal management. The lighting system has ability to harvest a small amount of DC power from the constant current AC ballast to drive internal and external electronics.
This application is a continuation-in-part of U.S. application Ser. No. 14/147,607 filed on Jan. 6, 2014, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14147607 | Jan 2014 | US |
| Child | 15669122 | US |
