The Nuts & Bolts of LEDs—Part V

Steve Winder -September 04, 2012

Editors’ Note: This segment is adapted from Chapter 2 of Power Supplies for LED Driving by Steve Winder.

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Part IV

Common Mistakes

The most common mistake is to use expensive high power LEDs when testing a prototype circuit. Instead, 3.6 V, 5 W Zener diodes should be used in place of each LED. Only once the circuit has been tested under all conditions should LEDs be used.


A voltage regulated LED driver is preferred when there are a number of LED modules that can be connected in parallel. Each module will have its own linear current regulator. An example would be channel lighting, as used in shop name boards.

A current regulated LED driver is preferred when it is desirable to have a number of LEDs connected in series. A series connection ensures that all the LEDs have the same current flowing through them and the light output will be approximately equal.

A switching driver with constant current output is the favored option when driving high power LEDs, for reasons of efficiency. An efficiency of 75–90% can be achieved. If a constant voltage source were used, the LEDs would also need a high current linear regulator in series, which is very inefficient and would increase heat dissipation problems.


About the Author

Steve Winder specializes in designing circuits for telecommunications applications, but has experience in a number of fields. As the current European Applications Engineer for Supertex Inc. Steve works alongside design engineers throughout Europe to design circuits using components made by Supertex, a U.S. based manufacturer of high voltage MOSFETs, CMOS integrated circuits and ASICs. Prior to joining Supertex, Steve was for many years a team leader for a group of analogue and digital design engineers at British Telecom's research and development laboratories, now known as Adastral Park, based near Ipswich, UK. Here, Steve applied his analytical skills to many technical areas but specialized in wideband analogue and digital transmission systems using copper pairs and optical fibre. In this role, Steve's strength was in radio frequency design, low-power design, low-noise design and systems engineering.


©2012 Elsevier, Inc. All rights reserved. Printed with permission from Newnes, a division of Elsevier. Copyright 2012. For more information on this title and other similar books, please visit

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