Design considerations for implementating low-cost integrated LED drivers for lighting applications

LEDs have advantages and disadvantages when compared with other light sources such as incandescent or fluorescent lamps. The most significant advantages are fast turn-on, lower heat generation, lower power consumption, higher operating life, and high resistance to shock/vibration. Some of the limitations are the narrow viewing angle, near monochromatic light, limited wavelength selection, and the fact that LEDs require electronic drive circuits for operation.

Figure 1
LEDs need to be driven properly to ensure optimal performance and long life, and designing and implementing an effective driver is key to obtain all the benefits of LEDs. The driver's implementation must be cost effective, which is not usually achieved with discrete components but can be realized with integrated solutions.

LEDs, regardless of color, have an extremely long lifetime (often 100K hours), whenever their current and temperature limits are not exceeded. LEDs must be operated within the manufacturer's specified limits of both current and diode junction temperature in order to obtain maximum life.

Figure 1 shows a typical I-V curve for an LED. This graph in particular makes reference to the high-current LED technology recently introduced by Lumileds. The maximum forward current varies with the different type, style, and manufacturer of LEDs. Lumileds has specified the maximum forward currents at 30 mA, 75 mA, 150 mA, 350 mA, and 700 mA for differently constructed LEDs. The higher current devices have special thermally designed packages to transfer the heat to a heat sink. The same rules can apply to devices having other current ratings by simply scaling down the current and power designs.

Driving LEDs using discrete components

There are several methods to drive LEDs with discrete components. Figure 2 illustrates one of the simplest using a resistor in series with the supply voltage to limit the current. This type of methodology is simple and cheap but has several weaknesses. The most significant is that since there is not current control device, the variations in the input voltage will change the average current to the LEDs, which results in poor illumination quality and sometimes even in the degradation or total damage of the LEDs for high line-voltage conditions.

Figure 2
To better illustrate the problem, calculations of the current supplied to the LEDs will be made based on the circuit shown in figure 1. The normal ac line can fluctuate by 10 percent and therefore the transformer output can vary between 10.8 Vac and 13.2 Vac whenever the normal secondary voltage is 12.0 Vac. Based on this, the LED's current calculation for low, normal, and high voltage ac line is made through the following formula:

ILED = [(Vin x sq.root 2) – (3 x VLED)] / R1

Assuming that the characteristics of the LEDs are If = 350mA and Vf = 3.5V, then the resulting value for ILED for each of the voltage line conditions is as follows:

- Low line: 238 mA
- Normal line: 323 mA
- High line: 408 mA

As it can be seen, the change of the LED's current is higher than ±25% for a ±10% variation in the ac line. In the low line case, this variation causes the LEDs to dim while for the high line case it may potentially damage them due to the overheating caused by the high current. This explains why this type of drive circuit is not recommended, nor often used, because they degrade the LED's quality and life time.

Figure 3
Another common LED driver method using discrete components is made through a linear regulator (ON Semiconductor MC7805, MC7809 or similar), and a series medium power resistor (usually 1W or bigger). Figure 3 shows this concept. The LED's current is set by the regulated output voltage of the linear regulator and the value of the resistor R1.

Assuming that the characteristics of the LEDs are If = 350mA and Vf = 3.5V, then the resulting resistor value is as follows:
R1 = (Vout - VLEDs) / ILEDs = (9V - 7V) / 0.350A = 5.7 ohms

The power dissipation in R1 is given by:
P = I2 x R = (0.350)2 x 5.7 = 0.7 Watts

The current regulation is mostly dependent on the regulator's performance and should be expected to be good since most voltage regulators provide a good percentage of line and load regulation, usually lower than ±5%.

Although this type of concept provides good current regulation to the LEDs, it may not be optimum for applications where cost is critical, and either for those requiring enable or electronic dimming functions.

Integrated LED drivers

Integrated LED drivers provide a constant current source and are designed to replace discrete solutions for driving LEDs in ac or dc voltage applications. An integrated driver eliminates the need for individual components by combining them into a single small surface mount package (SO-8), which results in a significant reduction of both system cost and board space.

Figure 4
This device provides a regulated dc current to a LED array, from an ac or dc input. It can drive arrays of series or parallel-series LEDs for a wide range of applications. It has a low voltage overhead (1.4V) to facilitate its usage in low voltage applications. Its current regulating principle is made through the generation of an internal constant reference voltage (0.7V) across an external low power resistor (Rext), which sets the current independently of the input voltage supplied.

This operating principle makes it very simple to design LED circuits around the NUD4001 device. Nevertheless, there are certain design considerations such as the maximum device's power dissipation (1.13 Watts), operating ambient temperature range, device's voltage overhead and LED's array configuration that have to be taken into account before implementing this integrated driver. Figure 4 shows a typical application utilizing the NUD4001 device to drive three high-intensity white LEDs (If = 350mA and Vf = 3.5V).

The typical current regulation performance of the NUD4001 device for the circuit of figure 4 using a Rext = 2.2 ohms is shown in figure 5. At 25°C, the change of the LED's current is only 1% for an increment of 15% in the input voltage. The regulation ratings are obtained from the data shown in figure 5:

Figure 5
For Vin = 12 Vdc, Iout = 328 mA
For Vin = 13.8 Vdc, Iout = 331 mA

Similar regulation values are obtained at low and elevated temperatures. However, it is important to note that at low temperature, the LED's current is shifted by a factor of 5% while at elevated temperature it is lowered by a factor of 11%. These values are also obtained from the data shown in figure 5:

For Ta = 0°C and Vin = 12.5Vdc, Iout = 344 mA
For Ta = 25°C and Vin = 12.5Vdc, Iout =329 mA
For Ta = 85°C and Vin = 12.5Vdc, Iout =291 mA

This type of behavior is ideal and usually desired by LED manufacturers. This is because at high ambient temperatures the junction temperature in the LEDs increases but the reduction in current cancels this effect. At low temperatures the current may be increased by a small percentage (usually no higher than 10%) since the LED's junction temperature is colder.

PWM and enable functions

Pulse width modulation (PWM) and enable functions are very important for some LED applications, especially for those where color mixing and dimming is required. Implementing these functions into discrete LED drivers is complex and increases the system cost significantly. Most integrated LED drivers (such as the NUD4001 device) offer a PWM/enable function that is used for dimming and color mixing applications.

Figure 6
Figure 6 shows how to implement a PWM/enable function on the NUD4001 device. This is made by simply adding an external small signal NPN transistor connected between pin 4 and ground. The same small signal transistor can be used for an enable function for conditioning applications.

The function of Rext2 is to pull up the pin 4 of the device when the PWM signal in the base of the NPN transistor is low. The average current applied to the LED is directly dependent on the duty cycle (Iavg =Ipeak x duty cycle). And the LED's light intensity is directly dependent on the average current I(avg) applied. In the case of figure 6, the current is set to be 350 mA at 100% duty cycle and therefore, it proportionally decreases for narrower duty cycles. The PWM circuit is good for frequencies up to 10 kHz.

The same type of configuration is used for the enable function. The only difference is the way that the base of the NPN transistor is driven.


Series resistor methods: Use of these methods to drive LEDs is not recommended nor often used because they basically eliminate the valuable features of LEDs, and sometimes even cause total damage to the devices.

Linear regulators: Although the concept of linear regulators provides good current regulation for LED circuits, it may not still be optimum for applications where cost is critical, and either for those applications requiring enable or electronic dimming functions.

Integrated LED drivers: If implemented correctly, integrated drivers offer a low-cost current regulation solution for different LED circuits of ac/dc voltage. Design considerations such as the device's power dissipation, breakdown voltage and maximum current capability have to be taken into account before implementation in application circuits.

The enable and PWM features, as well as the low cost implementation, are usually determines the use of an integrated LED driver rather than a discrete solution in LED lighting applications.


Cree Inc

Leads the LED industry in performance, brightness and reliability with its XLamp LED family, enabling the lighting industry with efficient, environmentally-friendly LEDs that produce beau...

Zierick Manufacturing Corp

Offers innovative solutions for interconnect applications. Specializes in wire-to-board and board-to-board applications. Provides surface mount and thru-hole products while further reduci...

InnoLight sp zoo

EU located lighting manufacturer for LED GU10 5W 600lm CRI>80 reflector, great performance, and LED E27 5W 380lm classic traditional appearance.

eldoLED America Inc

Designs and manufactures drive solutions for LED based lighting systems. Our technologies empower our customers to deliver the promise of LED lighting.

Cirrus Logic Inc

Cirrus Logic develops high-precision, analog and mixed-signal integrated circuits for a broad range of innovative customers across a variety of energy-related applications, including the ...


Established in 2002 as an ecommerce store for all your LED product needs.


Designer and manufacturer of custom and industry standard LED, DC-DC and AC-DC power supplies from 1W to 1600W. Cincon also designs and manufacturers lighting controllers, interfaces...

Illumination Machines

Illumination Machines designs custom optics, heat sinks, and remote phosphor systems for LED luminaires and lamps.

eldoLED BV

eldoLED is a world leader in the design and manufacture of intelligent drive solutions for LED based lighting systems. Our technologies empower our customers to deliver the promise of LED...

CSA Group

A global solutions provider of product testing and certification services for electrical, mechanical, plumbing, gas, medical and a variety of other products.

Energy Efficient Lighting

Energy Efficient Lighting offers total solutions to both conventional and more advanced LED lighting fixtures and LED retrofit kits for commercial and industrial applications.


48 companies worldwide, passionate about light and innovation, experts in developing LED lighting solutions for safe and comfortable environments with significant energy and cost savings,...

Guardian Industries

Guardian Industries Corp. is a leader in float glass, fabricated glass and high performance coated glass products. Guardian lighting solutions deliver optimal performance, flexibility and...

ELMA Electronic Inc

Provides standard and customized LED solutions. Elma's LED family offers consistent, reliable, and durable illuminating and indicating solutions.

LEDSAmerica Inc

LedsAmerica is a full line LED line company and has manufacturing in Iowa where T8 LED-O tubes and street lights are made together with PL, PARs, High Bay lights. MAx

Lumentra Inc

Provides NVLAP accredited optical (photometry, colorimetry, Lumen maintenance), thermal (mapping and transient analysis), electrical characterization services, product development, supply...


The LED, DC-DC and AC-DC power supplies from 1W - 1600W. Cincon’s lighting controllers, interfaces and devices incorporating DALI protocol. LED drivers from 25W - 150W with international ...


LTF, LLC is a U.S based solid-state lighting product development and manufacturing company with facilities located in both USA and China.

Marian Inc

Marian is a global company who supplies die cut and converted parts to the LED market. Materials include thermal pads, reflective, venting, gaskets, insulators, diffusers and more.

Colorimetry Research

Specializes in the field of optics, manufacturing, electronics and software enables us engineer products with the right balance of hardware and software.

Surface Mount Wire Gripper - Part Number 1301

The Zierick 1301 is designed to allow customers to easier terminate a stripped wire to a PCB. Wire sizes to 24 AWG. Terminal is UL Recognized.

Surface Mount Wire Gripper - Part Number 1262

The Zierick 1262 is designed to allow customers to easier terminate a stripped wire to a PCB. Wire sizes from 0.025" to 0.095". Terminal is UL Recognized.

Unlock new LED lighting solutions with Cree High Density LEDs

Cree® High Density LEDs deliver the industry’s highest optical control factor enabling lighting manufacturers to improve performance, cost and size of LED lighting—enabling never before p...

Cree CXA LED Array Family

Cree’s CXA LED Arrays are optimized to simplify design and lower system cost, delivering high lumen output and efficacy with a family of single, easy-to-use arrays.

Cree LED Modules

Cree LED modules deliver beautiful, consistent light, backed by a 5-year warranty. They offer a choice of dimming options, while reducing the lighting power load by 80%.

Cree XLamp® XP-L LEDs-the industry’s highest efficacy single-die LED.

Cree® XP-L LED is the first commercially available single-die LED to achieve up to 200LPW at 350mA. The XP-L enables 50% or more performance increase as a drop-in upgrade.

Cree XLamp® XM-L2 EasyWhite® LED

The first 5mmx5mm LED to enable color-consistent 50W halogen performance; the XM-L2 EasyWhite delivers 1,100 lumens and is optimized to replace halogen technology.

Surface Mount Insulation Piercing Terminals

Surface Mount Wire-to-Board terminals available for wire gauges ranging from 24 to 14 AWG. Parts can be terminated to allow daisy-chain applications. Eliminates difficulty with direct...

Super bright Injection LED modules

Housed by ABS material,covered by epoxy resin on surface with good insulation.Beautiful appearance.Waterproof.Anti-fire.Super bright 5050/3528 LED.12V voltage.Ideal light source for backl...

Flexible LED screen - Rental and Stage LED billboard

Special design,flexible use,light weight,super slim,transparent,SMD technology,easy to install.Can realize any curved and creative installation horizontally and vertically.IP65 protection...

LED flexible strip and aluminum LED bar

Full range of LED strip and bar including the unique high lumen strip. Protection degree up to IP68.Epistar 3528/5050 SMD LED.Compliant with CE & RoHS.2-year warranty.3528: 60LED/m,120LED...

P3 Indoor Full Color LED Display Video screen

High-density pixel pitch,high resolution,high refresh rate,magnificent and high-definition image and video effect.P3,P5,P6,P7.62 to P10 available.Epistar SMD LED,wide viewing angle.High r...

LED Panel Light

Designed to replace T8 fluorescent tube or Phillip Grille light.Epistar 3528/3014 SMD LED.Aluminum alloy body.Even and Soft light beam.Various mounting means.50,000 hours lifetime.Environ...

Rotatable LED Down Light, beam angle adjustable 10-60°

Beam angle adjustable 10-60 degree.Shell can rotate 360°,vertical 0-40°.High power CREE LED,even and uniform light output,Die casting aluminum alloy housing,good heat sinking.Widely used ...

Solar LED Paver Light

100% solor powered.No wires, no electricians.Super capacitors instead of battery,maintenance-free.Absorb sunlight in daytime and illuminate 8-12 hours during night. Epistar LED.Activation...

T8 LED tube light

Epistar Super bright 3528/2835 SMD LED.Aluminum alloy body with plastic cover.Consist with traditional fluorescent tubes.Easy mounting.PF>0.90,CRI>72,Over 60% energy-saving,Low degradatio...

LED light Bulb – LED spotlight

The AR111,GU10,MR16,PAR30,PAR38 LED bulbs are ideal replacement of 10-75W halogen or CFL bulbs.Cree/Everlight LEDs.PMMA lens.Aluminum housing.Good heat dissipation.Surface temperature les...

360 degree 10W led bulb

360 degree 10W led bulb has high efficiency, high power factor,environmental friendly, unique heat-dissipating design and perfect thermal management.

iVAR COB LED Downlight

iVAR COB LED Downlight use die-casting magnesium alloy to make the main body,has Excellent heat dissipation performance,and Unique and delicate looking design.

LIMS - Liquid Injection Molding System

Silicone LIMS can be used to injection mold silicone components such as lenses or gaskets in an automated process. The two-component, thermoset material ranges in Shore A hardness from 5-80.







Have a press release or other announcement you'd like to share?

Submit Announcement

Miss a webcast? Watch it in the archives


LEDs Magazine Newsletter

Our weekly flagship news source

Product Focus

Monthly newsletter

Illumination in Focus

Bi-monthly newsletter

Copyright © 2007-2014. PennWell Corporation, Tulsa, OK. All Rights Reserved.