FIELD OF INVENTION:
[001] The present subject matter described herein, relates to the technical field of LED drivers. The present subject matter, in particularly, relates to a single stage high power factor LED driver offering constant current to the LED bank with voltage limit function. The single stage LED driver is able to maintain constant current to the LED load for wide range of output voltage as well as wide range of input voltage with good Power Factor > 0.98 and Total Harmonic Distortion < 10%.
BACKGROUND AND PRIOR ART AND PROBLEM IN PRIOR ART:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] Demand of LED lights has increased nowadays due to their long life span and energy saving. LEDs requires a specialized device called LED driver to operate. LED drivers are similar to ballasts for fluorescent lamp or transformers for low voltage bulbs. LED drivers provide LEDs with the electricity they require to function and perform at their best. The main two purpose of LED drivers are:
• LEDs are designed to run on low voltage 2.8-3.3V each, by a direct current electricity. However, most places supply higher voltage (120-277V), alternating current electricity is available. An LED driver rectifies higher voltage, alternating current to low voltage, direct current.
• LED drivers also protect LEDs from voltage or current fluctuations. A change in voltage could cause a change in the current being supplied to the LEDs. LED light output is proportional to its current supply, and LEDs are rated to operate within a certain current range (measured in amps). Therefore, too much or too little current can

cause light output to vary or degrade faster due to higher temperatures within the LED.
[004] Summarizing, the LED drivers convert higher voltage, alternating current to direct current. They also keep the voltage and current flowing through an LED circuit at its rated level.
[005] Power factor describes how efficiently an LED driver is maintaining the input current sinusoidal and in-phase to grid AC voltage. It is calculated by dividing the active power being used by the driver (wattage) divided by the product of the input voltage times the current going in (volts x amps). The range for power factor is a decimal between 0 and 1. The closer to 1 the power factor is the less current harmonics is generated by the driver in the grid. A good power factor is 0.9 or above.
[006] For power factor correction, Buck Power Factor Correction (figure la) is used in consumer lighting industries, as LED bank is set at lower voltage level and input AC is stepped down with switching controlled to provide required current to low voltage LED from high voltage AC line. This topology provides power factor > 0.9 and Total Harmonic Distortion < 20%. Which is good enough for consumer application.
[007] For better results, Boost PFC (figure lb) Front End is used. It boosts the output voltage higher than peak of max input AC voltage and modulate the converter duty in relation to input instantaneous voltage to make input current follow the shape of input voltage. This topology provides the most optimum power factor > 0.98 and the Total Harmonic Distortion is controlled within 10%. While the input parameter is good but the output voltage is high and hence the second stage converter is used to reduce down the voltage required to the LED and maintain the LED current as PFC controller provides constant voltage not the constant current.
[008] Nowadays Flyback PFC (figure lc) is widely used as they provide the single stage conversion with good input parameters and voltage conversion for

low voltage LED driver. Further, in market, customized controller ICs are available which controls modulation in such a way that LED is also driven in constant current mode. This kind of converter topology have been widely used in professional LED lighting Application where requirement of Total Harmonic Distortion is strictly below 10%. One of the drawbacks of the Flyback PFC is overheating of the power converter during driving of the power LED. Also, the efficiency of this kind of topology is poor due to power loss of Flyback converter.
[009] Chinese Patent CN106028557B discloses a high power factor low total harmonic distortion constant current LED driver circuit comprising: a constant current driving circuit body, the constant current driving circuit connected to a peripheral circuit body; and an input capacitor discharge control module, an input capacitor discharge the control module is connected constant current drive circuit body, for controlling the peripheral circuits discharging an input capacitance so that an input voltage is changed to follow the peripheral circuit changes the voltage of an AC power the peripheral circuits and reduce the time in the valley of the input voltage. The present invention is low in total harmonic distortion power factor constant current LED driver circuit having the input current while maintaining the average value proportional to the input voltage in a fixed relationship to minimize or even eliminate the AC power supply voltage rises into the trough and during the input capacitance caused by distortion effects, dynamic adjustment to follow the input voltage AC power supply voltage into the valley, but not for a long time in a deep valley, a substantial increase in PF, the advantage of reducing the TFID.
[0010] United States patent US9774245B1 discloses a PFC switching power conversion circuit providing low TFID, including: a bridge rectifier for providing an input voltage according to an AC voltage; an electromagnetic interference filtering circuit for providing a line voltage according to the input voltage; a switching power converter for converting the line voltage to an output voltage or current under a control of a driving voltage, the driving voltage causing a switching current to flow through a main inductor; and a controller for receiving

and processing at least one feedback signal from the switching power converter to generate the driving voltage in a constant on-time manner, the controller including an off-time detector and a timer, the off-time detector being used to detect decreasing periods of the switching current to determine respective off-time periods, and the timer being used to set a minimum limit on the respective off-time periods.
[0011] United States patent US8884541B2 disclose an illustrative LED driver circuit which includes dimming control of the LED lamp. The circuit uses flyback converter topology, a power factor correction (PFC) primary side controller, a secondary side controller that includes current control and voltage control regulation, and a dimming control circuit. The dimming control circuit includes a selectable dimming control signal added together with a sensed current output signal to provide a control signal supplied to the secondary controller for output current control.
[0012] United States patent US9048750B2 disclose a power active buck power factor correction device, comprising: a AC source; a rectifying device coupled to the AC source for receiving and rectifying the AC source so as to generate an input voltage; a first converting device coupled to the assistance device for receiving, transmitting, converting and storing energy; a load coupled to the first converting device; and an assistance device coupled to the first converting device for generating an assistance voltage. Specifically, the polarity of the assistance voltage is same with the input voltage, but is contrary to an output voltage, so that the first converting device may continue to work and receive an input current under the input voltage is smaller than the output voltage while the discontinue time of the input current is getting shorter so as to obtain the perfected power factor correction effect.
[0013] United States patent US9190899B2 disclose a power circuit for protecting against high pulse load current and inrush current. The power circuit comprises a buck-boost module and a PFC controller operatively coupled with the buck-boost module. The PFC controller is configured to receive an input voltage feedback, an

output voltage feedback, and a current feedback, and is configured to utilize one of an Integral Gain Compensation (IGC) and an Integral Value Compensation (IVC) to control the high pulse load current and inrush current in the power circuit.
[0014] None of the cited prior art disclose a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function. The LED driver uses only single stage boost PFC controller as LED driver controller with modification in feedback method which does not involve any extra active circuit.
[0015] The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
OBJECTS OF THE INVENTION:
[0016] It is therefore the object of the present subject matter to overcome the aforementioned and other drawbacks in prior method/product/apparatus.
[0017] The principal objective of the present subject matter is to develop a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function.
[0018] Another object of the present subject matter is to develop a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function, having power factor > 0.98.
[0019] Another object of the present subject matter is to develop a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function, having Total Harmonic Distortion < 10%.
[0020] Another object of the present subject matter is to develop a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function, without involving any extra active circuit.

[0021] Yet another object of the present subject matter is to develop a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function, having simple electronic circuit.
[0022] Yet another object of the present subject matter is to develop a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function, which can be fit with LED in a single one sided Printed Circuit Board.
[0023] Yet another object of the present subject matter is to develop a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function, having higher power efficiency.
[0024] Still yet another object of the present invention is to a single stage high power factor LED driver, offering Constant Current to the LED bank with voltage limit function, having lower cost than LED driver currently available in market.
[0025] These and other objects and advantages of the present subject matter will be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION:
[0026] Solution to one or more drawbacks of existing LED driver, and additional advantages are provided through the present single stage high power factor LED driver as disclosed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0027] A single stage high power factor LED driver offering constant current to LED bank, the driver comprises a rectifier connected to an AC input and giving a rectified DC output, an inductor (LI) having its input terminal coupled to the DC output from the rectifier, an integrated circuit configured to control a switch, wherein the integrated circuit primarily having an input terminal, a ground

terminal, a feedback terminal, and an output terminal giving control gate drive signal to a switch, an enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) configured to perform switching operation, wherein the switching operation is controlled by the control gate drive signal, a rectifier diode having its first terminal coupled to the output terminal of the inductor (LI), a capacitor (C2) coupled to the output terminal of the diode to hold output DC voltage given to the LED bank, and a hybrid feedback circuit connected parallel to the capacitor (C2), wherein the hybrid feedback circuit gives a hybrid feedback signal to the feedback terminal of the integrated circuit.
[0028] In an aspect, the hybrid feedback circuit comprises a current feedback circuit, and a zener breakdown based voltage feedback circuit.
[0029] In an aspect, the hybrid feedback circuit gives a hybrid feedback signal dominated by the current sense signal (I sense) from the current feedback circuit when the output voltage is lower than zener breakdown voltage to control the constant current output of the driver.
[0030] In an aspect, the hybrid feedback circuit gives a hybrid feedback signal dominated by the voltage feedback signal (V sense) from the zener breakdown based voltage feedback circuit, when the output voltage exceeds the zener breakdown voltage to limit the voltage output of the driver.
[0031] In an aspect, the current feedback circuit is coupled, in series, to the zener breakdown based voltage feedback circuit via a resistor (R5).
[0032] In an aspect, the current feedback circuit comprises a plurality of resistors in parallel with each other, coupled to the LED Bank in series.
[0033] In an aspect, the zener breakdown based voltage feedback circuit comprises a plurality of zener diode in series with each other, coupled with the capacitor (C2) in parallel.
[0034] In an aspect, the integrated circuit generate the control gate drive signal by sensing the mains rectified signal and hybrid feedback signal.

[0035] In an aspect, the control gate drive signal is given to the gate terminal of the enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) in the form of Pulse-width modulation signal.
[0036] In an aspect, the LED bank is connected in parallel to the output of single stage high power factor LED driver.
[0037] In an aspect, the various signals received or given by the integrated circuits are in the form of voltages or currents or a mixture of voltages and currents.
[0038] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0040] Fig. la illustrates a graphical representation of Buck Power Factor Correction LED driver according to prior art;
[0041] Fig. lb illustrates a graphical representation of Boost Power Factor Correction LED driver according to prior art;
[0042] Fig. lc illustrates a graphical representation of Flyback Power Factor Correction LED driver according to prior art;

[0043] Fig. 2 illustrates a graphical representation of a single stage high power factor LED driver, offering Constant Current and Constant Voltage to the LED according to one of the embodiment of present subject matter; and
[0044] Fig. 3 illustrates V-I characteristics of a single stage high power factor LED drive, offering Constant Current and Constant Voltage to the LED according to one of the embodiment of present subject matter.
[0045] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0046] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[0047] The terms "comprises", "comprising", or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that a device, system, assembly that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in a system or device proceeded by "comprises... a" does not, without more constraints, preclude the existence of other elements or additional elements in the system or device.
[0048] Referring to figure 2 illustrating a graphical representation of a single stage high power factor LED driver 200, offering Constant Current to the LED bank 204 with voltage limit function according to one of the embodiment of

present subject matter. As illustrated in figure 2, the single stage high power factor LED driver 200 comprises a rectifier 201, an integrated circuit 202, an enhancement metal oxide semiconductor field effect transistor (MOSFET) 203, a capacitor C2, an inductor LI, a diode Dl and a hybrid feedback circuit.
[0049] The rectifier 201 is coupled to an AC input and provide a rectified DC output. The inductor LI has its input terminal coupled to the DC output from the rectifier 201 and its output terminal coupled to the input terminal of the diode Dl. The integrated circuit 202 is configured to control the switching operation of the enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 203.
[0050] The integrated circuit 202 primarily has an input terminal VIN to receive main rectified signal, a ground terminal connected to the ground, a feedback terminal FB receiving a hybrid feedback signal from the hybrid feedback circuit and an output terminal giving control gate drive signal to the enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 203 for controlling switching operations.
[0051] The capacitor C2 is coupled to the output terminal of the inductor LI. The capacitor C2, holds the output DC voltage given to the LED bank 204, and is connected in parallel with the hybrid feedback circuit. The hybrid feedback circuit includes a current feedback circuit 205 and a zener breakdown based voltage feedback circuit 206. The current feedback circuit 205 has a plurality of resistors R4, R6 coupled in parallel with each other. The plurality of resistors R4, R6 is coupled to the LED bank 204 in series. These plurality of resistors R4, R6 are coupled to the zener breakdown based voltage feedback circuit 206 via a resistor R5. The zener breakdown based voltage feedback circuit 206 has a plurality of zener diodes D4, D5 coupled in series with each other. The current feedback circuit 205 together with the zener breakdown based voltage feedback circuit 206 generates a hybrid feedback signal. This hybrid feedback signal is received by the integrated circuit 202 in feedback terminal FB.
[0052] The hybrid feedback signal is a hybrid of current (I sense) and voltage (V sense) signal. The current (I sense) part of the hybrid signal, from the current

feedback circuit 205, dominates in the hybrid signal when the output voltage is lower than zener breakdown voltage. Similarly, the voltage (V sense) part of the hybrid signal, form the zener breakdown based voltage feedback circuit 206, dominates in the hybrid signal when the output voltage exceeds the zener breakdown voltage.
[0053] The integrated circuit 202 generates the control gate drive signal by sensing the main rectified signal and hybrid feedback signal. The control gate drive signal is generated in the form of pulse-width modulated signal and accordingly drive the switching state of the enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 203. The control gate drive signal is received on the gate terminal of the enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 203.
WORKING OF THE SINGLE STAGE HIGH POWER FACTOR LED DRIVER
[0054] The enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 203 switches rapidly between two states based on the control gate drive signal. The first state occurs when the enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 203 is closed. In this state, the inductor LI is energized and the current of inductor LI increases with applied voltage at the input. At the same time the diode Dl becomes reversed bias.
[0055] The second state follows the first state when the enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 203 is open. In this state, the inductor LI de-energizes as it supplies energy to the LED bank 204 by boosting the voltage higher than the input peak voltage and for recharging the capacitor C2. The diode Dl is forward biased in this case and provide no resistance to the inductor LI current, supplied to the LED bank 204 and for recharging the capacitor C2.
[0056] The cycling back and forth between the two states is done rapidly and in the manner that both maintains a constant output current and controls the average

inductor LI current to follow the input voltage. The control gate drive signal is maintained so that the final current output is constant and final voltage output is limited within the safe value.
[0057] Referring to Figure 3 illustrating V-I characteristics of a single stage high power factor LED driver 200, offering Constant Current to the LED bank with voltage limit function according to one of the embodiment of present subject matter. It is evident from the V-I characteristics that present single stage high power factor LED driver 200 according to present subject matter is capable of limiting the voltage in the range 650V to 690V and limiting the current in the range of 20mA to 64mA. The voltage is limited to optimum condition even in no load condition.
[0058] The advantage of the single stage high power factor LED driver 200 is that it a simple circuit which leads to the reduced cost of the manufacturing. Further, the single stage high power factor LED driver 200 uses no additional active circuit requiring extra power supply to operate.
[0059] The performance of the single stage high power factor LED driver ensures good power factor > 0.98 and low Total Harmonic Distortion < 10%.
[0060] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such

introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."
[0061] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures

depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of "comprising" or "including" also contemplates embodiments that "consist essentially of or "consist of the recited feature.

WE CLAIM:
1.A single stage high power factor LED driver (200) with voltage limit, the
driver (200) comprises:
a rectifier (201) connected to an AC input and giving a rectified DC output;
an inductor (LI) having its input terminal coupled to the DC output from the rectifier (201);
an integrated circuit (202) configured to control a switch, wherein the integrated circuit (202) primarily having an input terminal VIN, a ground terminal, a feedback terminal FB, and an output terminal giving control gate drive signal to a switch;
an enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) (203) configured to perform switching operation, wherein the switching operation is controlled by the control gate drive signal;
a diode (Dl) having its first terminal coupled to the output terminal of the inductor (LI);
a capacitor (C2) coupled to the output terminal of the diode (Dl) to hold output DC voltage given to the LED bank (204); and
a hybrid feedback circuit connected parallel to the capacitor (C2), wherein the hybrid feedback circuit gives a hybrid feedback signal to the feedback terminal (FB) of the integrated circuit (202).
2. The single stage high power factor LED driver (200) as claimed in claim
1, wherein the hybrid feedback circuit comprises:
a current feedback circuit (205); and
a zener breakdown based voltage feedback circuit (206).

3. The single stage high power factor LED driver (200) as claimed in claim 2, wherein the hybrid feedback circuit gives a hybrid feedback signal dominated by the current sense signal (I sense) from the current feedback circuit (205) when the output voltage is lower than zener breakdown voltage to control the constant current output of the driver (200).
4. The single stage high power factor LED driver (200) as claimed in claim 2, wherein the hybrid feedback circuit gives a hybrid feedback signal dominated by the voltage feedback signal (V sense) from the zener breakdown based voltage feedback circuit (206), when the output voltage exceeds the zener breakdown voltage to limit the voltage output of the driver (200).
5. The single stage high power factor LED driver (200) as claimed in claim 2 wherein the current feedback circuit (205) is coupled, in series, to the zener breakdown based voltage feedback circuit (206) via a resistor (R5).
6. The single stage high power factor LED driver (200) as claimed in claim 2, wherein the current feedback circuit (205) comprises a plurality of resistors (R4, R6) in parallel with each other, coupled to the LED Bank (204) in series.
7. The single stage high power factor LED driver (200) as claimed in claim 2, wherein the zener breakdown based voltage feedback circuit (206) comprises a plurality of zener diode (D4, D5) in series with each other, coupled with the capacitor (C2) in parallel.
8. The single stage high power factor LED driver (200) as claimed in claim 1, wherein the integrated circuit (202) generate the control gate drive signal by sensing the mains rectified signal and hybrid feedback signal.
9. The single stage high power factor LED driver (200) as claimed in claim 8, wherein the control gate drive signal is given to the gate terminal of the enhancement Metal Oxide Semiconductor Field Effect Transistor (MOSFET) (203) in the form of Pulse-width modulation signal.

10. The single stage high power factor LED driver (200) as claimed in claim 1, wherein the LED bank (204) is connected in parallel to the output of the single stage LED driver (200).
11. The single stage high power factor LED driver (200) as claimed in claim 1, wherein the various signals received or given by the integrated circuit (202) are in the form of voltages or currents or a mixture of voltages and currents.