EDNE June 2012 - (Page 52)

TEAR DOWN MA Rg E Ry C O N N E R • S E N iO R T E C h N iCA l E D iTO R + + pry further Go to www.edn.com/120315pry for the references this articles lists. Go to www.edn.com/pryingeyes for more Teardowns. I What’s inside the Samsung 40W-replacement-LED light? n February 2010, EDN tore down its first LED bulb (Reference 1). For $20, you got a nondimmable bulb that produced 500 lumens at a cool white (5000K) and consumed 7W. The warm-white version of the light produced only 450 lumens. Two years later, you can buy this fully dimmable Samsung bulb for $19.95 (list price) that puts out 550 lumens of a nice warm white (3000K), consumes 10W, and boasts a five-year warranty. As you’d expect with a snow-cone-type bulb, the light pattern does not extend as far down as the light extension of an incandescent bulb (Reference 2). It’s usually difficult to find out what power-management IC an LED bulb uses, and this one was no exception. By process of elimination, it seemed likely that the IC must be beneath the white blob of goo. The light uses only one LED component to produce its 550 lumens. Lights that are not incandescent face a challenge when you try to control them with an old-fashioned TRIACbased dimmer switch. The graph below shows the dimming characteristics of LED, compact-fluorescent, and incandescent bulbs, showing their dimming performance as a percentage of their highest light output, rather than an absolute measure—say, in lux. The incandescent bulb (yellow line) does not dim linearly with power. It does dim down to zero, however. A CFL (orange line) does a better job of dimming with power, and the Samsung LED light (green line) dims linearly with power. However, it drops out at slightly less than 20% of its maximum output light. I used a Taos light sensor from Adafruit, controlled by an Arduino development system, to take these measurements (Reference 3). PERCENTAGE OF MAXIMUM LUMEN OUTPUT 120 100 80 60 40 20 0 0 20 40 60 80 100 PERCENTAGE OF MAXIMUM INPUT POWER 120 Sure enough, the vertically mounted IC shows a Power Integrations logo and a LinkSwitch part number: LNK403EG (Reference 4). All of the electrolytic capacitors used are 125°C and most likely are properly derated, contributing to the manufacturer’s fiveyear warranty. The bulb’s packaging lists a design life of 40,000 hours. 52 EDN EUROPE | JUNE 2012 www.edn-europe.com http://www.edn.com/120315pry http://www.edn.com/pryingeyes http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE June 2012

Agilent Technologies
International Rectifier
RS Components
International Rectifier
Analog Devices
Test & Measurement
Silicon Labs
Test-driven development for embedded C: why debug?
Baker’s best
Cover story
Rohde & Schwarz
Rohde & Schwarz
Rohde & Schwarz
Rohde & Schwarz
Rohde & Schwarz
Pico-projector design uses color LEDs
Digital isolation in smart energy metering applications
Mechatronics in design
Design Idea
Product Roundup
Tales from the cube

EDNE June 2012