CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] This patent application claims the benefit of priority from Sri Lanka Patent Application 19052 filed on October 25, 2016 entitled "Energy Efficient Smart LED Lamp", the entire contents of which are included herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates in general to an energy efficient light emitting diode (LED) lamp and more specifically to an energy efficient LED driver circuit for a LED lamp.

BACKGROUND OF THE INVENTION

[0003] LED based lighting applications (also referred to as LED units, comprising one or more light emitting diodes (LEDs)) require a regulated direct current for optimum use and are designed to run on low voltage (12-24V), direct current (DC) electricity. Normally power supplied by the electrical mains from the electricity grid contain a higher voltage (120- 277V), alternating current (AC) electricity and the drivers are used to supply power to LEDs by converting this higher voltage AC to the low voltage DC.

[0004] Generally, the LED drivers are designed to take high input voltage tolerance with an input range between 90V to 295V DC to accommodate different jurisdictions. However, under normal circumstances the grid supply voltage does not fluctuate this much and most of the time the tolerance of the input voltage by the driver is in a range of about 5% of the voltage of the rated grid supply.

[0005] In a grid supply with a voltage of 230V as the rated grid supply, e.g. Europe, the normal tolerance of the voltage by the driver is in the range between 218.5V AC to 241.5V AC. Between this range LEDs will illuminate at the brightness specified by the manufacture. Even when supplied with a voltage of or about 218.5V (minimal threshold) the driver operates efficiently and the LEDs will illuminate at the brightness specified by the manufacturer. At the minimal threshold the LEDs will illuminate without flicker. The energy provided by the grid over and above the minimal threshold (if the grid supply is 230V the additional energy is 230V - 218.V) is additional energy not required to power the LED unit. The waste of this energy is a drawback of the driver. [0006] LEDs are about 50 times efficient than incandescent bulbs in consuming energy which is beneficial today due to energy being an expensive commodity. Accordingly, developing an efficient and energy saving LED lighting system that reduces the use of grid power, saves resources and is economical is beneficial.

[0007] Several approaches have been made to improve the efficiency of the current in the LED drivers. Some of those approaches are briefly described below.

[0008] One approach includes a high efficiency dimmable LED driver for low power lighting applications and provides an improved pulse width modulation dimming technique for regulating the LED current and brightness. Under universal input voltage operation, high efficiency and high power factor can be achieved by a coupled inductor single-ended primary inductance converter power factor correction (PFC) converter with a simple commercial transition-mode PFC controller.

[0009] In another approach, a sensing resistor is used to provide feedback for LED-current regulation. This method adds an IR drop at the output branch, and limits power efficiency as LED-current is large and keeps increasing. In this approach, a power-efficient LED-current sensing circuit is proposed. The circuit does not use any sensing resistor but extracts LED current information from the output capacitor of the driver. The sensing circuit is implemented in a Buck-boost LED driver and has been fabricated in AMS 0.35 mum CMOS technology.

[0010] A further approach includes an efficient driver circuit for LED lamps with a dimming feature. The driver consists of a flyback converter in series with the dc-link. By processing partial power of the driver circuit for current regulation, the loss produced by power conversion can be reduced. The dimming feature is accomplished by means of current amplitude modulation (AM) or double pulse-width modulation (DPWM).

[001 1 ] Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

SUMMARY OF THE INVENTION

[0012] Major embodiments of the invention include an energy saving LED driver comprising an LED driver circuit which supplies from an external power source sufficient energy to a step down driver to provide an output current to illuminate an LED unit at its specified brightness and extracts energy not required by the step down driver. A charging and a discharging circuit which directs the extracted energy to an energy storage device. The energy is stored in the energy storage device is supplied to a step up driver to provide the output current to illuminate the LED unit. A switching and controlling unit that in response to the level of energy in the energy storage device, switches power between the external power source and the energy storage device to illuminate the LED unit, and to provide a uniform supply of energy to the energy storage device.

[0013] In further embodiments, the energy not required by the step down driver is extracted by a step down transformer.

[0014] In other embodiments, the charging and discharging circuit comprises a rectifier to convert AC current to DC current.

[0015] In some embodiments, the charging and discharging circuit comprises a current sensor.

[0016] In further embodiments, the charging and discharging circuit comprises a field effect transistor (FET) to provide a continuous supply of energy to charge the energy storage device.

[0017] In some embodiments, the FET comprises a p-channel FET.

[0018] In some embodiments, the charging and discharging circuit comprises a step up driver.

[0019] In other embodiments, the switching and controlling unit comprises an integrated circuit (IC) to control the switching of power from the external power source to the energy storage device and vice versa.

[0020] In some embodiments, the IC comprises of a microcontroller

[0021 ] In further embodiments, comprising a manual switch to switch power between the external power source and the energy in the energy storage device.

[0022] A second major embodiment of the invention includes a method of improving the energy efficiency of an LED unit. The method comprises the steps of determining sufficient energy required for a driver to operate efficiently and a LED device to illuminate at its specified brightness. Supplying from an external power source the sufficient energy to the driver and the LED device. Extracting excess energy not required for the driver in the process of regulating the power from the external power source in supplying sufficient energy to the LED device. Storing the excess energy in an energy storage device. Detecting the level of energy stored in the energy storage device. Reusing the energy in the energy storage device upon detecting the energy stored in the energy storage device has reached a first predetermined threshold sufficient to illuminate the LED unit. Stepping up the voltage and the current in the energy discharged from the energy storage device to the level sufficient to illuminate the LED device. Supplying the stepped up current to the LED device and switching off the power from the external power source. Switching off the current provided by the energy storage device upon the energy level in the energy storage device falling to a second determined threshold and switching to the external power source.

[0023] In further embodiments, the switching from the external power source to the energy storage device is performed manually.

[0024] The present invention relates to developing an efficient energy saving LED lighting system that reduces the use and waste of energy (e.g. grid power).

[0025] In general, the invention relates to extracting of the energy provided by an external power source over and above the minimal threshold (i.e. if the grid supply is 230V, which is an example of an external power supply, and the minimal threshold is 218V then the remaining additional energy not required to drive the LEDs is 230V - 218.V and similarly in a grid supply with 1 10V the minimal threshold required to power the LEDs could be determined) or energy not required or used (wasted energy) by the driver in providing an output to power the LEDs, without reducing the brightness of the LEDs or causing flicker. The extracted energy is stored in an energy storage device. The energy stored in the energy storage device is re used to power the LEDs whilst power in the external power source is not drawn to drive the LEDs. In this way energy in the external power supply is saved when energy in the energy storage device is used to power the LEDs.

[0026] This invention is achieved by utilizing an LED driver circuit, a charging and discharging circuit, a switching and controlling unit connected together.

[0027] A LED driver circuit is used to supply from the external power source the minimal sufficient energy to the step down driver to provide an output current to illuminate the LED unit at its specified brightness and to extract the energy not required by the step down driver.

[0028] A charging and a discharging circuit is used to direct the extracted energy to an energy storage device, supply the energy stored in the energy storage device to a step up driver to provide an output current to illuminate the LED unit.

[0029] A switching and controlling unit is used to switch power automatically between the external power source and an energy storage device to illuminate the LED unit, depending on the level of energy in the energy storage device and to provide a uniform supply of energy to the energy storage device. [0030] The controlling and switching unit further comprises a manual switch to switch power from the external power source to the energy storage device, depending on the level of energy stored in the energy storage device.

[0031 ] In general, the methodology used to implement the invention is by determining the minimal threshold of energy adequate to the driver to operate efficiently and give out an input current to the LEDs to illuminate at its specified brightness. Thereafter, a method is used to supply from the external power source the determined sufficient energy to the driver, and to extract the energy supplied over and above the minimal threshold. The extracted energy is directed to an energy storage device and is stored. Thereafter, the level of energy stored in the energy storage device is detected and the energy in the energy storage device is re used to illuminate the LED unit when the energy stored reaches a determined threshold. A method is used to step up the voltage and the current in the energy discharged from the energy storage device to the level sufficient to illuminate the LEDs and supply the stepped up current to the LEDs and simultaneously switching off the power from the external power source. Further, a method is used to switch off the current provided by the energy storage device upon the energy level in the energy storage device falling to a determined threshold and to switch to the external power source. In addition, a manual switch is incorporated to manually perform switching from the external power source to the energy stored in the energy storage device and vice versa depending on the energy in the energy storage device is above/ below Dead of discharge of the energy storage device.

[0032] The energy efficient LED driver according to the present invention thus enables the powering of the LEDs by an energy saving device which stores energy wasted when powering the LED driver using the energy supplied by an external power source.

[0033] A better understanding of the present invention could be obtained with reference to the detailed description below in conjunction with the following drawings.

[0034] Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] An exemplary embodiment of the present invention is illustrated by way of example in the accompanying drawings in which like reference numbers indicate the same or similar elements and in which: [0036] Figure 1 is a diagrammatic representation of an exemplary saving driver circuit within which the present invention may be deployed; and

[0037] Figure 2 is a graphical presentation of the charging and discharging versus time, of the Lithium Ion battery used in the embodiment of the invention.

DETAILED DESCRIPTION

[0038] In an embodiment of the present invention with reference to Figure 1, a Driver 10 with a step down power of 230V-36V is connected to a LED unit 20. The LED unit 20 used in an embodiment of the invention is a 24 W LED lamp. The Driver 10 is connected to a grid supplying 230V as the rated power supply, which is the external power source used in the embodiment. A step down transformer 30 is connected to the L wire between the Driver 10 and the grid supply. The current drawn by the step down transformer 30 is 0.106 A (Primary) and 0.6 A (Secondary). A Signal Relay 40 is connected to the N and L wires of the grid supply which gives a signal to a Relay Switch 100 when the driver 10 is connected to the grid supply. The step down transformer 30 is configured in such a way that it extracts the excess power not required by the driver 10 to provide an input current to the LED unit 20. The excess energy extracted by the step down transformer 30 is directed through the charging and discharging circuit towards a 12V lithium ion rechargeable battery 50. The lithium ion rechargeable battery 50 constitutes an energy storage device. Many other types of energy storage devices may be used consistent with the spirit of the invention.

[0039] Between the step down transformer 30 and the lithium ion rechargeable battery 50 are, a rectifier 60, to convert alternative current (AC) to direct current (DC), an ACS 712 current sensor (Sensor) 70 and a field effect transistor (FET) 80, for example a p-channel FET 80. The Sensor 70 is employed to sense the charging current and the FET 80 is used to provide the energy storage device 50, with a uniform charging current. The energy storage device is connected to a second driver 90 which steps up the current discharged from the energy storage device 50, from 12 V to 36 V Between the energy storage device 50 and the second Driver 90 is a second Relay Switch 110 which disconnects the power supply from the energy storage device 50 to the second driver 90 if the voltage in the energy storage device 50 drops below a threshold such as 7.5 V and switches on the connection when the voltage in the energy storage device 50 is charged (generally up to 13.5V). The second driver 90 is connected to the LED unit 20 and when relay switch 110 is switched on the LED unit 20 will be powered by the energy stored in the energy storage device 50, (at which time the grid power supply will be disconnected).

[0040] The Switching and Controlling Unit comprises a microcontroller integrated circuit (IC) 120, for example an AT EGA 328P microcontroller IC, which is programmed to control a second Signal Relay 130, and a third Signal Relay 140, and a Signal FET 150, which controls the functioning of the embodiment of the invention. The Sensor 70 provides an input of the charging current of the energy storage device, to the IC 120 to determine its value. The IC 120 is powered by the energy storage device which power is controlled by a 5 V regulator 160. In parallel to the 5V Regulator 160, a Voltage Divider 170 is connected between the energy storage device 50 and the IC 120, which provides a reading of the voltage of the energy storage device 50 to the IC 120. The Relay Switch 100 is connected between the energy storage device 50 and the 5V Regulator 160 and a manual switch 180 is connected to the circuit in parallel to the Relay Switch 100.

[0041 ] Switching and Controlling Unit controls the functioning of the embodiment of the invention in such a way that when power is supplied from the grid, the Signal Relay 40 sends a signal to the Relay Switch 100, which switches on and provides a connection between energy storage device 50 to the IC 120. IC 120 receives input from the Sensor 70 of the charging current and an input of the voltage of the energy storage device 50 is provided by the Voltage Divider 170. The IC 120, in the event the energy storage device 50 is charged, controls the second Signal Relay 130, which sends a signal to the third Relay Switch 190 to disconnect the grid supply, and the third Signal Relay 140 provides a signal to the second Relay Switch 1 10 to switch on the power supply from the energy storage device 50 to the second Driver 90. When the energy level in the energy storage device 50 drops below 7.5V, input of the voltage is measured by the Voltage Divider 170 and the IC 120, through the second Signal Relay 130 and the third Signal Relay 140 provides respectively, a signal to the third Relay Switch 190 to switch on the power from the grid supply, and simultaneously a signal to the second Relay Switch 1 10 to disconnect supply from the energy storage device 50 to the second Driver 90.

[0042] When the third Relay Switch 190 is switched on the grid supplies power to drive the LED unit 20 (through Driver 10) and the energy not required to drive the LED unit is extracted by the step down transformer and is supplied to charge the energy storage device. The IC 120 is provided an input of the charging current by the Sensor 70. Normally the charging current drops when the energy storage device is being charged and the IC 120 through Signal FET 150 controls the FET 80 to provide a uniform current to the energy storage device till it is charged. At which point the Voltage Divider 170 measures the voltage of the energy storage device 50 and the IC 120 using the said measurement of the voltage through the second Signal Relay 130 and the third Signal Relay 140 provide signal respectively to the third Relay Switch 190 to switch off the grid power and the second Relay Switch 1 10 to connect the circuit and provide energy stored in the energy storage device 50 to the second Driver 90 to power the LED unit 20.

[0043] In the event of a discontinuation of the grid supply the Switching and Controlling Unit may not operate but the energy storage device 50 has a sufficient level of energy stored to power the LED unit 20. Accordingly, the stored energy could be used to light the LED unit 20 by employing a manual switch which connects power between the energy storage device 50 and LED unit 20 either directly or via the IC 120.

[0044] The second Driver 90 steps up 12V current provided by the energy storage device 50 to 36V as output to light the LED unit 20.

[0045] The current provided from the step down transformer 30 to the energy storage device 50 is nominally 15 V and 1 ampere (amp).

[0046] The embodiment of the invention has been tested and according to this test results it will take about 6 hours to charge the 12V lithium ion rechargeable battery 50 and 2 hours to discharge the battery 50. When the lamp is turned on, it will run through the grid supply for about six hours and if the said battery 50 is fully discharged and the said battery 50 will be charging during that time. Thereafter, when the said battery 50 is fully charged it will power the LED unit for a period of about two hours. This two hour period will be the energy saving period of the LEDs. In the present embodiment of the invention the energy saving is estimated at 25% [(21 (2+6)) x 100]. Figure 2 provides a graphical presentation of the test data obtained in testing the embodiment of the invention set out above. This value can be improved with some modifications such as installing a more efficient battery pack and improving the control circuitry.

[0047] According to the theoretical calculation this method is capable of saving 30% of energy in lighting. The energy efficiency that could be obtained in an embodiment of the invention may be from 20% to nearly 30% depending on the circuitry used.

[0048] All these and other variations or modification to the embodiment are considered to be within the sphere and scope of the present invention as defined by the claims appended hereto.