WO2016197263A1

WO2016197263A1 - Power efficient led drivers

Info

Publication number: WO2016197263A1
Application number: PCT/CN2015/000401
Authority: WO
Inventors: Hezhang Chu; Ho Yin LEE
Original assignee: Abbeydorney Holdings Ltd.
Priority date: 2015-06-12
Filing date: 2015-06-12
Publication date: 2016-12-15

Abstract

Method and system for driving LED lighting application (200) provide a driving circuit(202) that can power an array of LEDs(204) in a more efficient manner. The disclosed driving circuit(202) achieves higher power efficiency by maintaining the LED forward voltage and current at or near the minimum level needed to turn on the LED. In some embodiments, this entails providing the LEDs with a forward voltage and current that are within an initial nonlinear region (102) of the LED current-voltage curve (100). A greater number of LEDs may then be deployed to compensate for potentially less lumen output as a result of operating the LEDs at or near their turn-on point. Such an arrangement produces substantially the same lumen output as existing LED lighting application (200) while consuming less power and generating less heat, thereby increasing power efficiency.

Description

POWER EFFICIENT LED DRIVERS

Inventor (s) : Hezhang CHU and Ho Yin LEE

FIELD OF THE INVENTION

The disclosed embodiments relate generally to methods and systems for driving solid-state lighting devices, such as light emitting diodes (LEDs) , and particularly to a more power efficient method and system for driving such lighting devices.

BACKGROUND OF THE INVENTION

An LED emits light when a voltage exceeding the LED “turn-on” or forward voltage is applied across the LED to allow current to flow through the LED. The current flowing through the LED, or forward current, must be a constant or DC current and therefore LED lighting applications employ a driving circuit to convert AC line voltage to DC current to drive the LED. Within the LED, a significant portion of the current—as much as 70 percent according to some estimates—is converted to heat while only a small fraction is converted to light. The heat must be removed or otherwise dissipated in some way to prevent the LED from becoming too hot, which can lower its efficiency and also shorten the life of the LED. Compounding this heat problem, existing LED drivers are generally designed to over drive the LED so as to maximize the amount of light from the LED. The over driving increases the forward current well beyond the LED minimum “turn-on” point, which not only exacerbates the heat dissipation problem, but also results in wasted power, as the amount of light from the LED, typically measured in lumen (Lm) , does not increase linearly with increasing current.

Thus, a need exists for an improved driving circuit in LED lighting applications and other similar lighting applications, and particularly for a more power efficient driving circuit in such lighting applications.

SUMMARY OF THE DISCLOSED EMBODIMENTS

The disclosed embodiments are directed to a method and system for driving LED lighting applications and other similar lighting applications. The method and system provide a driving circuit that can drive an array of LEDs in a more power efficient manner compared to existing driving circuits. The disclosed driving circuit achieves higher power efficiency by carefullymanaging the forward voltage andcurrent of the LEDs. In particular, rather than over driving the LEDs to try and maximize lumen output, the disclosed driving circuit is designed to maintain the forward voltage andcurrent at or near the minimum level needed to turn on the LEDs. In some embodiments, this entails providing the LEDs with a forward voltage and current that are within an initial nonlinear region of the LED current-voltage curve. A greater number of LEDs may then be deployed to compensate for potentially lower lumen output resulting from operating the LEDs at or near their turn-on point. The use of a forward voltage andcurrent that are at or near the LED turn-on point together with a greater number of LEDs allows the disclosed LED lighting applicationsand other similar lighting applications to produce substantially the same lumen output as existing LED lighting applications while consuming less power and generating less heat, thereby increasing power efficiency.

In general, in one aspect, the disclosed embodiments are directed to a driving circuit for driving an array of LEDs. The driving circuit comprises, among other things, an AC/DC voltage converter configured to receive an AC voltage and output a DC voltage, and a DC/DC current converter connected to the AC/DC voltage converter and configured to receive the DC voltage from the AC/DC voltage converter and output a DC current. The driving circuit further comprises a voltage and current regulator connected to the DC/DC current converter and configured to receive the DC current from the DC/DC current converter and output a forward voltage and current to the array of LEDs. The voltage and current regulator is further configured to maintain the forward voltage and current to the array of LEDs within an initial nonlinear region of a current-voltage curve for an LED in the array of LEDs.

In general, in another aspect, the disclosed embodiments are directed to aLED lighting application. The LEDs lighting application comprises, among other things, an array of LEDs, and a driving circuit connected to the array of LEDs and configured to provide a forward voltage and current to the array of LEDs. The driving circuit maintains the forward voltage and current to the array of LEDs within an initial nonlinear region of a current-voltage curve for an LED in the array of LEDs. The array of LEDs is arranged in one or more strings of LEDs, each string of LEDs composed of one or more LED packages connected in series to one another, each LED package containing a plurality of individual LEDs connected in series to one another.

In general, in yet another aspect, the disclosed embodiments are directed to a method of driving an array of LEDs. The method comprises, among other things, receiving an AC voltage, converting the AC voltage to a DC current, using the DC current to generate a forward voltage and current, and providing the forward voltage and current to the array of LEDs. The forward voltage and current provided to the array of LEDs are maintained within an initial nonlinear region of a current-voltage curve for an LED in the array of LEDs.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the disclosed embodiments will become apparent upon reading the following detailed description and upon reference to the drawings, wherein:

FIG. 1A is a current-voltage curve showing the forward voltage and current usedby the power efficient driving circuit disclosed herein to drive an LED according to some embodiments；

FIG. 1B is a luminosity-current curve showing the forward current usedby the power efficient driving circuit disclosed herein to drive an LED and the resulting relative luminous intensity from the LED according to some embodiments；

FIG. 2 is a block diagram of the power efficient driving circuit disclosed herein according to some embodiments；

FIG. 3 is circuit diagram for the power efficient driving circuit disclosed herein according to some embodiments； and

FIGS. 4A-4D illustrate exemplary layers of a printed circuit board for the power efficient driving circuit disclosed herein according to some embodiments.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

As an initial matter, it will be appreciated that the development of an actual, real commercial application incorporating aspects of the disclosed embodiments will require many implementation specific decisions to achieve the developer’s ultimate goal for the commercial embodiment. Such implementation specific decisions may include, and likely are not limited to, compliance with system related, business related, government related and other constraints, which may vary by specific implementation, location and from time to time. While a developer’s efforts might be complex and time consuming in an absolute sense, such efforts would nevertheless be a routine undertaking for those of skill in this art having the benefit of this disclosure.

It should also be understood that the embodiments disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Thus, the use of a singular term, such as, but not limited to, “a” and the like, is not intended as limiting of the number of items. Similarly, any relational terms, such as, but not limited to, “top, ” “bottom, ” “left, ” “right, ” “upper, ” “lower, ” “down, ” “up, ” “side, ” and the like, used in the written description are for clarity in specific reference to the drawings and are not intended to limit the scope of the invention.

As alluded to above, rather than over driving LEDs to try and maximize lumen output, the driving circuit disclosed herein is designed to maintain the LED forward voltage and current at or near (e.g., within 10 percent) the minimum level needed to turn on the LED. An example of a current-voltage curve 100 showing the forward voltage and current for a typical LED can be seen in FIG. 1A, though not necessarily drawn to scale. An example ofluminosity-current curve 110 showing the forward current and corresponding relative luminous intensity for the LEDcan be seen in FIG. 1B, again not necessarily drawn to scale. The shape and location of these

curves

100 and 110 may of course vary depending on operating temperature, diode size, diode material, manufacturing process, number of diodes per package, and several other factors. An example of an LED with similar current-voltage and luminosity-current curves as those in FIGS. 1A and 1B is component number HL-A-2835H431W-S1-08-HR1 from Guangzhou Hongli Opto-Electronic Co., Ltd., of Huadong Town, Huadu Dist., Guangzhou, China.

In the graph of FIG. 1A, the horizontal axis represents voltage (V) and the vertical axis represents current (I) . As the curve 100 shows, current does not begin to flow, and hence the LED does not turn on or emitlight, until the forward voltage reaches approximately 2.6 V. Once the forward voltage reaches about 2.6 V and the LED turns on, current begins flowing through the LED and increases quickly with increasing voltage. The increase in forward current is largely linear, but there is a small region of the curve 100 up to about 60 mA, generally indicated at 102, where the current increase is largely nonlinearfor this particular curve. In accordance with the disclosed embodiments, the driving circuit disclosed herein is designed to drive the LED using a forward voltage and current that are within this initial nonlinear region 102 of the curve 100. Such a forward voltage and currentin the nonlinear region 102 are considered to beat or near the minimum level needed to turn on the LED for purposes of the present disclosure. On the other hand, driving the LED with a forward voltage and current that areoutside the initial nonlinear region 102 of the curve 100 is considered to be over driving the LED for purposes of the present disclosure.

The relative luminous intensity resulting from driving the LED using the above-referenced forward voltage and current is indicated by the region 112 on the curve 110 in FIG. 1B, where the horizontal axis represents current and the vertical axis represents relatively luminous intensity. As can be seen, the relative luminous intensity increases relatively linearly with increasing forward current up to about 60 mA or about 1.0 candela (cd) for this particular curve 110. This linear region of the curve 110 is generally indicated at 112in FIG. 1B. Beyond this linear region 112, the luminous intensity does not necessarily increase linearly with forward current such that each subsequent increase in forward current may result in a progressively smaller increase in luminous intensity, potentially due to the greater heat generated as a result of the higher current affecting the LED. The nonlinear increase generally holds true whether for luminous intensity, luminous flux, luminous power, lumen output, or other measures of light from the LEDs. On the other hand, the amount of light from the LEDs does increase generally linearly with each additional LED. Thus, by leveraging the linear region 112 of the curve 110, the disclosed driving circuit can produce substantially the same number of lumens (e.g., within 10 percent) as existing applications, but using less power and generating less heat than existing applications, by driving a greater number of LEDs using a smaller forward voltage and current.

Referring next to FIG. 2, an exemplary LED lighting application 200 having adriving circuit 202in accordance with the disclosed is shown. The LED lighting application 200 may be any lighting application in which thedriving circuit 202 is used to drive or otherwise provide power to an array of LEDs 204. Examples of such lighting applications may include standard A-style omnidirectional LED lights, LED flood lights, LED tube lights, and similar lighting applications having various wattage ratings for both indoor and outdoor uses.

In the example of FIG. 2, the driving circuit 202 drives the array of LEDs 204 by converting an AC input voltage into a relatively constant DC output current and providing that current to the LEDs. Thedriving circuit 202 may incorporate a number of functional components that are depicted as discrete blocks in FIG. 2, including an AC/DC voltage converter 212 and a DC/DC current converter 214 connected downstream to the AC/DC voltage converter 212. An AC power source, typically a 120 V AC mains, provides power to the driving circuit 202. When connected to the driving circuit 202, AC voltage from the 120 V AC mains is converted by the AC/DC voltage converter 212 into a DC voltage that is provided to the DC/DC current converter 214. The DC voltage is then converted by DC/DC current converter 214 to a relatively constant DC current that is fed to the array of LEDs 204.

In accordance with the disclosed embodiments, the driving circuit 202 is configured to provide a forward voltage and current that are at or near the minimum level needed to drive or otherwise cause the array of LEDs 204 to turn on and emit light. To this end, the driving circuit 202 may further incorporate a voltage and current regulator 216 designed to control or otherwise limit the forward voltage and current provided to the array of LEDs 204. Specifically, the voltage and current regulator 216 may be configured to ensure that the driving circuit 202 provides only the minimum forward voltage and current needed, as discussed above, to drive the array of LEDs 204. A greater number of LEDs may then be deployed with the driving circuit 202 to make up for any deficiency in lumens outputted by the LEDs as a result of the voltage and current regulator 216limiting the voltage and current to the LEDs.

Note in the embodiment of FIG. 2 that the voltage and current regulator 216 is being shown as operationally external to the DC/DC current converter 214 for illustrative purposesonly. In other implementations, the voltage and current regulator 216 may instead be operationally internal to the DC/DC current converter 214, for example, as part of a highly integrated circuit, without departing from the scope of the disclosed embodiments. Similarly, it should be noted throughout FIG. 2 and other figures described herein that although a number of discrete blocks may be shown, those having ordinary skill in the art will understand that any block may be divided into two more constituent blocks, and any two or more blocks may be combined into a single block, without departing from the scope of the disclosed embodiments.

As can be seen in FIG. 2, the array of LEDs 204 may be arranged in one or more strings of LEDs 206, each string 206 being composed of one or more LED packages 208, labeled ED1, ED2, …EDn, connected in series to one another. In addition, each LED package 208 may contain one or more individual LEDs 210 that may also be connected in series to one another. The number of individual LEDs 210 in each LED package 208 may vary and may be selected based on, among other things, the lumen output needed for the lighting application, number of LED packages the lighting application can feasibly physically house, heat dissipation capacity, acceptable power consumption level, and other factors. The voltage and current regulator 216 may then be adjusted or otherwise fine-tuned as needed based on the total number of individual LEDs 210 to ensure the driving circuit 202 provides only the minimum forward voltage and current needed to drive the LEDs, as discussed above.

As one example of the above LED driving strategy, it has been found that a 4 W A-style lightbulb application requiring a target lumen output near 450 Lm may need around 90 individual LEDs 210 to achieve the target lumen output. These 90 individual LEDs 210 may be arranged in any manner known to those having ordinary skill in the artthat is feasible for the specific requirements of the LED lighting application. Thus, for example, one stringof 30 series-connected LED packages 208 may be used, each LED package 208 containing three series-connected individual LEDs 210. In another example, one string of 45 series-connected LED packages 208 may be used, each LED package 208 containing two individual LEDs 210. It is also possible to use LED packages 208 with only a single individual LED 210 and then select the number of LED packages 208 and/or the number of strings of LEDs 206 as needed. For example, a single string of 90 series-connected LED packages 208, each package containing a single LED 210 may be used. The target lumen output may then be achieved by adjusting or fine-tuning the voltage and current regulator 216to ensure that the driving circuit 202 providesonly theminimumforward voltage and currentneeded, as discussed above, which may be about 249 V and about 12 mA, respectively, for this particular example.

As another example, it has been observed that a 7 W A-style lightbulb application requiring a target lumen output near 850 Lm may need roughly 140 individual LEDs to achieve the target lumen output. As before, these 140 individual LEDs 210 may be arranged in any manner known to those having ordinary skill in the artthat is feasible for the specific requirements of the LED lighting application. There may be, for example, two parallel strings of 35 series-connected LED packages 208, each LED package 208 containing two series-connected individual LEDs 210. Alternatively, there may be four parallel strings of 35 series-connected LED packages 208, each LED package 208 containing one individual LED 210. The target lumen output may then be achieved by adjusting or fine-tuning the voltage and current regulator 216so the driving circuit 202 provides only the minimum forward voltage and current needed, as discussed above, which may be about 188 V and about 30 mA, respectively, for this particular example.

In the foregoing examples, it is also possible for the voltage and current regulator 216 to be adjusted such that the driving circuit 202 drives the LEDs well beyond the minimum forward voltage and current in the event such over driving should ever be needed.

A specific implementation of the 7 W A-style lightbulb application discussed above is depicted in FIG. 3 according to the disclosed embodiments. The specific implementation shown here generally follows the high-level implementation shown in FIG. 2 insofar as an LED lighting application 300 includes a driving circuit 302 connected to an array of LEDs 304. The array of LEDs 304 is composed of two parallel strings of LEDs 306, each string 306 having 35 series-connected LED packages 308, labeled ED1, ED2, …ED35, each LED package containing two series-connected individual LEDs310 for a total of 140 LEDs. Connection of the array of LEDs 304 to the driving circuit 302 may be accomplished via terminals or similar connection pointslabeled as JLED in FIG. 3. The driving circuit 302 itself is composed of a combination of discrete and integrated circuit components connected as shown and having the values listed in Table 1 below. An AC/DC voltage converter is indicated generally at 312 and a DC/DC current converter is generally indicated at 314. As before, an AC power source, typically a 120 V AC mains, provides power to the driving circuit.

Component	Description
Component	Description	F1	Fuse 1A 125VAC
DB1	Diode Bridge Rectifier	F1	Fuse 1A 125VAC
DB1	Diode Bridge Rectifier	RV1	Varistor 275VAC
R1/R2	Resistor 10K	RV1	Varistor 275VAC
R1/R2	Resistor 10K	R3	Resistor 220K
R4	Resistor 750K	R3	Resistor 220K
R4	Resistor 750K	R5	Resistor 3.3K
R6/R8/R10	Resistor 510K	R5	Resistor 3.3K
R6/R8/R10	Resistor 510K	R7	Resistor 10K
R9	Resistor 10ohms	R7	Resistor 10K
R9	Resistor 10ohms	L/N Line	Wire #26AWG 150℃ 3KV
LED–	Wire #26AWG 150℃ 3KV	L/N Line	Wire #26AWG 150℃ 3KV
LED–	Wire #26AWG 150℃ 3KV	LED+	Wire #26AWG 150℃ 3KV
C1	Capacitor 47nF 500V	LED+	Wire #26AWG 150℃ 3KV
C1	Capacitor 47nF 500V	C4/C5	Capacitor 1uF 50V
C2	Capacitor 10nF 1000V	C4/C5	Capacitor 1uF 50V
C2	Capacitor 10nF 1000V	C3	Capacitor 0.1 uF 250VDC
C6	Capacitor 2.2uF 400V	C3	Capacitor 0.1 uF 250VDC
C6	Capacitor 2.2uF 400V	D3	Diode Schottky 60V 1A

Component	Description
Component	Description	D4	Diode General Purpose 85V 200MA
VR2	Diode Zener 100V 310MW	D4	Diode General Purpose 85V 200MA
VR2	Diode Zener 100V 310MW	VR3	Diode Zener 13V 150MW
Q1	Transistor General Purpose PNP 80V 0.5A	VR3	Diode Zener 13V 150MW
Q1	Transistor General Purpose PNP 80V 0.5A	Q2	Transistor MOSFET P-Channel 300V 210MA
D1/D2	Diode General Purpose 400V 1A	Q2	Transistor MOSFET P-Channel 300V 210MA
D1/D2	Diode General Purpose 400V 1A	PCB	29.0mm x 17.5mm x1.6mm Copper 2-layer
IC1	Constant Current LED Driver	PCB	29.0mm x 17.5mm x1.6mm Copper 2-layer
IC1	Constant Current LED Driver	L2	Inductor 3.3mH 140mA
L3	Inductor 680uH 250mA	L2	Inductor 3.3mH 140mA
L3	Inductor 680uH 250mA	T1	Transformer 880uH

TABLE 1

In general operation, AC voltage from the AC main, typically 120 V at 60 Hz, is converted to DC voltage by a full-wave rectifier composed of diode bridge DB1, varistor RV1, and an inductive network made of resistors R1, R2, inductors L2, L3, and capacitors C1, C2, C3, connected as shown. A fuse F1 provides overcurrent protection for the LED lighting application 300. The rectified and filtered input voltage is applied to one end of the primary winding of transformer T1. Diode D3 is used to protect the integrated circuit IC1 from negative ringing (drain voltage below source voltage) when the power MOSFET Q2 is off and the input voltage is below the reflected output voltage. Transistor Q1, Zener diode VR3, and resistors R7, R8 help improve the efficiency of the driving circuit. A constant current driver IC1, which may bepart number LNK457DG from Power Integrations, Inc., of San Jose, California, USA, provides the forward voltage and current that drive the array of LEDs 304. The constant current driver IC1 is powered from its BYPASS pin (Pin 2) via a decoupling capacitor C5. Resistors R4, R6 and Zener diode VR2 regulate the voltage across IC1.

In accordance with the disclosed embodiments, a voltage and current regulator 316 is connected to the feedback pin of the constant current driver IC1 to control the forward voltage and current to the array of LEDs 304. This voltage and current regulator 316 may then be adjusted or otherwise fine-tuned as needed for the specific implementation in which it is used. In the implementation of FIG. 3, the voltage and current regulator 316 is composed of resistors R5, R9, capacity C4, and diode D4, connected as shown and having the values listed in Table 1. It has been observed that these particular components R5, R9, C4, and D4 having the values listed in Table 1, when connected as shown in the 7 W A-style lightbulb application of FIG. 3, mayproduceperformance measures similar to those shown below in Table 2:

TABLE 2

As can be seen in the third row of Table 2, the driver efficiencyis about 90.08 percent and 90.81 percent, respectively, before and after the LED thermal has stabilized when a voltage and current regulator 316 as described above is connected to the 7 W A-style lightbulb application of FIG. 3. In contrast, for existing 7 W A-style lightbulb applicationsthat over drive the LEDs rather than minimize the forward voltage and current to the LEDs, the driver efficiency is significantly higher.

In addition, the particular design of the voltage and current regulator 316 shown here allows the driving circuit 302 to be used with another lighting application having a different array of LEDs 304 simply by adjusting or otherwise fine-tuning the voltage and current regulator 316 for the other lighting application without having to alter other components in the driving circuit 302. For example, resistor R9, by virtue of being connected between a feedback pin and a ground pin of the constant current driver IC1, acts as a limiting resistor that restricts the amount of forward current provided to the array of LEDs 304. Changing the value of limiting resistor R9 therefore changes the amount forward current that may be provided to the array of LEDs 304. By changing R9 from the 10 ohms listed in Table 1 to 23 ohms, the driving circuit 302 may be dropped in as a driving circuit for the4 W A-style lightbulb application discussed earlier. Table 3 below shows performance measures similar to those that may be obtained for the referenced 4 W A-style lightbulb application when driven by the driving circuit 302 in which resistor R9 has a value of 23 ohms:

TABLE 3

As the thirdrow of Table 3 shows, the lamp efficiency is about 89.35％and 91.85％, respectively, before and after the LED thermal has stabilized when R9 is replaced in the voltage and current regulator 316 as described above for the 4 W A-style lightbulb application. On the other hand, for existing 4 W A-style lightbulb lighting applications that over drive the LEDs, the lamp efficiency is substantially higher.

In the foregoing embodiments, although a particular design has been shown for the AC/DC voltage converter 312, the DC/DC current converter 314, and the voltage and current regulator 316, numerous equivalent alternative designs may be used without departing from the scope of the disclosed embodiments. For example, instead of a single resistor R9in the voltage and current regulator 316, two resistors having roughly the same value as R9 may be used, and the like. Moreover, specific circuit components have been included in the AC/DC voltage converter 312, the DC/DC current converter 314, and the voltage and current regulator 316 for illustrative purposes only, and one or more components may be added to or removed therefrom without departing from the scope of the disclosed embodiments. Therefore, the particular design for the AC/DC voltage converter 312, the DC/DC current converter 314, and the voltage and current regulator 316 shown above should be viewed as exemplary only and not exhaustive.

Turning now to FIGS. 4A to 4D, an exemplaryprinted circuit board (PCB) is shown that may be used for implementingthe driving circuit disclosed herein according to some embodiments. The PCB shown here may be a copper based PCB having at least a top overlay 400 (FIG. 4A) , a top trace layer 402 (FIG. 4B) , a bottom overlay 404 (FIG. 4C), and a bottom trace layer 406 (FIG. 4B) . The operation and interaction of the various layers is self-explanatory to those versed in the art and therefore a detailed explanation is omitted for economy of the disclosure. Suffice it to say, it is important that the impedance of the PCB be analyzed and factored into any design of the voltage and current regulator 316 and particularly the derivation of the value of limiting resistor R9. Other PCB layouts besides the one shown here may of course be used without departing from the scope of the disclosed embodiments.

While particular aspects, implementations, and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the scope of the disclosed embodiments as defined in the appended claims.

Claims

A driving circuit for driving an array of LEDs, comprising:

an AC/DC voltage converter configured to receive anAC voltage and output a DC voltage；

a DC/DC current converter connected to the AC/DC voltage converter and configured to receive the DC voltage from the AC/DC voltage converter and output a DC current； and

a voltage and current regulator connected to the DC/DC current converter and configured to receive the DC currentfrom the DC/DC current converter and output a forward voltage and current to the array of LEDs,

wherein the voltage and current regulator is further configured to maintain the forward voltage and current to the array of LEDs within an initial nonlinear region of a current-voltage curvefor an LED in the array of LEDs.
The driving circuit of claim 1, wherein theDC/DC current converter is a constant current driver and the voltage and current regulator includes a limiting resistor connected between a feedback pin and a ground pin of theconstant current driver.
The driving circuit of claim 1, wherein the limiting resistor has a resistance value that is specifically selected to restrict the forward current to the array of LEDs to within the initial nonlinear region of the current-voltage curve of the array of LEDs.
The driving circuit of claim 3, wherein the array of LEDs is configured for a 4 W lighting application and the limiting resistor is a 23 ohm resistor.
The driving circuit of claim 3, wherein the array of LEDs is configured for a 7 W lighting application and the limiting resistor is a 10 ohm resistor.
An LED lighting application, comprising:

an array of LEDs； and

a driving circuit connected to the array of LEDs and configured to provide a forward voltage and current to the array of LEDs, the driving circuit maintaining the forward voltage and current to the array of LEDs within an initial nonlinear region of a current-voltage curve for an LED in the array of LEDs；

wherein the array of LEDs is arranged in one or more strings of LEDs, each string of LEDs composed of one or more LED packages connected in series to one another, each LED package containing a plurality of individual LEDs connected in series to one another.
The LED lighting application of claim 6, wherein the LED lighting application is a 4 W lightbulb application and the array of LEDs is arrangedin one string of 30 series-connected LED packages.
The LED lighting application of claim 7, wherein each LED package contains three series-connected individual LEDs.
The LED lighting application of claim 6, wherein the LED lighting application is a 7 W lightbulb application and the array of LEDs is arrangedintwo parallel strings of 35 series-connected LED packages.
The LED lighting application of claim 9, wherein each LED package contains two series-connected individual LEDs.
The LED lighting application of claim 6, wherein the LED lighting application isone of: an A-style omnidirectional LED lightbulb, an LED flood light lightbulb, an LED tube light lightbulb.
A method of driving an array of LEDs, comprising:

receiving an AC voltage；

converting the AC voltage to a DC current；

using the DC current to generate a forward voltage and current； and

providing the forward voltage and current to the array of LEDs；

wherein the forward voltage and current provided to the array of LEDs are maintained within an initial nonlinear region of a current-voltage curve for an LED in the array of LEDs.
The method of claim 12, wherein theforward voltage and current are generated using a constant current driver, the constant current driverhaving a limiting resistor connected between a feedback pin and a ground pin of theconstant current driver.
The method of claim 13, wherein the limiting resistor has a resistance value that is specifically selected to restrict the forward current to the array of LEDs to within the initial nonlinear region of the current-voltage curve of the array of LEDs.
The method of claim 14, wherein the array of LEDs is configured for a 4 W lighting application and the limiting resistor is a 23 ohm resistor.
The method of claim 14, wherein the array of LEDs is configured for a 7 W lighting application and the limiting resistor is a 10 ohm resistor.
The method of claim 12, wherein the array of LEDs is arranged in one or more strings of LEDs, each string of LEDs composed of one or more LED packages connected in series to one another, each LED package containing a plurality of individual LEDs connected in series to one another.
The method of claim 15, wherein the array of LEDs is arrangedin one string of 30 series-connected LED packages.
The method of claim 18, wherein each LED package contains three series-connected individual LEDs.
The method of claim 16, wherein the array of LEDs is arrangedintwo parallel strings of 35 series-connected LED packages.
The method of claim 20, wherein each LED package contains two series-connected individual LEDs.