Application Note
LED Lighting Solutions
The explosion in LED lighting usage is plain to see all around us. From kitchen recessed
lighting to the latest LED backlights in LCD TV sets, the growth seems unstoppable. This isdriven partly by environmental concerns forcing consumers and businesses to re-examine
their energy expenses. Despite the current financial downturn, LED sales are still forecast togrow by an estimated 3 % in 2009.

Controlling the Current
LED drivers can be either linear or switching current supplies. Linear drivers are best suitedwhen the supply voltage is slightly greater than the load voltage. Linear drivers use resistors
to limit the current.
Switching supplies are often used for LED drivers as they are more efficient than linear
supplies, generating less heat. Generally LED applications require a shielded inductor as
they require fewer turns to achieve a specific inductance. This results in lower DC resistance.
Less DC resistance is required for low energy consumption. Current Sense resistors provide
the feedback necessary to the current regulation controller to monitor and limit the current
fed to the LED diode string.

OvertemperatureUnlike filament and plasma-based lighting (light bulbs and neon), LEDs are very sensitive toheat. The PN junction should not be allowed to reach temperatures greater than +85 ˚C toensure normal operating life times and as high reliability as possible.
Controlling the temperature of the LEDs to below +85 ˚C has proven to be critical to theirlife span. Polymer PTC thermistors limit current and react to increases in temperature bychanging from a low-resistance state to a high-resistance state. This temperature regulation
provides overtemperature protection for the LED as well as aiding in limiting current.

Surge and ESD
The mechanical housing for the placement of LED diodes can expose the LED device
package to the outside world where external ESD transients may be applied. The ESD
transients can damage the LEDs or the downstream circuitry. To help avoid damage, theuse of ESD Protection devices (meeting IEC 61000-4-2 Level 4 ESD standard requirements)
across the LEDs is required.

LED Lighting Solutions
Bourns’ Solution
The SMAJxxCA series can provide voltage signal clamping and protection against ESD, EFT andSurge transients applied within the circuitry.
The SRU1048 series offers high-current handling and low DC resistance in a compact form factor.
The CRA2512 series are current sense resistors in standard 2512 chip sizes with a high-power
density (3 W) and low TCR (75 PPM). The surface temperature of the resistor is lower than similarparts of the same size from other manufacturers, reaching typically 48 ˚C under a load of 1 W.
The PWR263S-20 series are SMD resistors in D2PAK casings with very low-inductance and highpower ratings. They can be used with linear current regulators to limit the current especially inhigh luminosity LEDs which consume a lot of current. These resistors also do not exhibit highsurface temperatures which is a requirement in many designs.
The Bourns® MF-MSMF075 Multifuse® polymer PTC provides overcurrent andovertemperature protection.

80

SRU1048-3R3Y

15 µF

CD1005-B0520

LEDDriver60

SMAJ10A

VDC in100

MF-MSMF075
SMAJ60CA

Surface Temperature (˚C)

120

15 µF

40

CRA2512-FZ-R017ELF
200.5

1.0

1.5

2.0

2.5

CRM2512-FX-R800ELF

3.0

Power (W)

Bourns® products are available throughan extensive network of manufacturer’s
representatives, agents and distributors. To obtain
technical applications assistance, a quotation, or toplace an order, contact a Bourns representative inyour area.

Specifications subject to change without notice.
Actual performance in specific customer
applications may differ due to the influence ofother variables. Customers should verify actual
device performance in their specific applications.

For more information on Surge and ESD
protection and other products from Bourns,
please visit

COPYRIGHT© 2010 • BOURNS, INC. • 04/10 • e/CPK1031“Multifuse” is a trademark of Bourns, Inc.
“Bourns” is a registered trademark of Bourns, Inc. in the U.S. and other countries.

www.bourns.com

Americas: Tel +1-951 781-5500

Fax +1-951 781-5700

Europe: Tel +41-(0)41 768 55 55

Fax +41-(0)41 768 55 10

Asia-Pacific: Tel +886-2 256 241 17

Fax +886-2 256 241 162