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AB06 LUXEON LEDs Application Brief ©2016 Lumileds Holding B.V. All rights reserved. LUXEON Illumination LEDs Circuit Design and Layout Practices to Minimize Electrical Stress Introduction LED circuits operating in the real world can be subjected to various abnormal electrical overstress situations. Among the most common are:

  • Isolation test during validation or production of the luminaire (“hi-pot test”)
  • Lightning strikes and line transients
  • Hot-swapping of LED circuits (disconnecting and reconnecting an LED circuit board to the driver while the driver remains powered up)
  • Driver failures
  • ESD (Electro-Static Discharge) Scope This paper presents background information on some of these overstress modes and discusses recommendations to minimize the potentially destructive effects of electrical overstress on LEDs.

AB06 LUXEON LEDs Application Brief 20170605 ©2017 Lumileds Holding B.V. All rights reserved. 2 Table of Contents

Electrical Overstress (EOS) can present itself to an LED array in two forms, either as excess voltage or excess current. this paper are geared towards minimizing the potential for common mode fault currents.

  1. Isolation Test Requirements

Isolation tests are required for all electrical appliances that are connected to an AC power line, including luminaires. diffusers, and a power supply. addressed are the power supply and the LED board. Figure 1. Differential mode (top) and common mode (bottom) currents.

  1. LUXEON Rebel LED Circuit Model on a Board

represent the short distance between anode/cathode and the LED’s thermal pad. Figure 4. Equivalent electrical circuit model of a LUXEON Rebel LED on a PCB. description of the typical relationship between the drive current If and the forward voltage Vf of an LED.

ensure all relevant performance and safety specifications are met for the application of interest. testing, the LED negative voltage value will depend on the choice of the circuit board material as well as the wiring patterns. will reduce the likelihood of electrical stress. cathode and thermal pad is less than a couple of volts in the simulation and discharge is not likely to happen. is recommended to ensure optimum LED reliability in the application. Figure 10. Protection capacitors during normal operation.

  1. Lightning Strikes and Line Transients

design and the protection ratings that need to be met. A safety approved MOV is recommended to simplify the safety tests. thermal pads and by electrically separating those pads.

  • Minimize the capacitance of circuit board traces to ground by eliminating all unnecessary copper surfaces on the top of a double sided FR4 board or the circuit layer of a MCPCB/IMS board. The surface area around a thermal pad does not have to be larger than 3mm outside of the LED package. Increasing the copper area does not significantly improve heat spreading, but does increase parasitic capacitances.
  • Keep board traces at least 2mm away from the board edge in an MCPCB/IMS board and at least 2mm away from any grounded surface to prevent arcing during isolation tests.
  • When using FR4 boards, try to keep the thermal pads of the LEDs electrically “floating” and separated from each other, or connect them to either anode or cathode. This will minimize the voltage difference between anode/cathode and the thermal pad, thereby minimizing the possibility of electrical discharge across the LED body.
  • Add bypass capacitors and discharge protection capacitors whenever possible.
  • Provide an MOV pack at the mains input of the luminaire to prevent transients and lightning strikes from damaging the LED array.
  • NEVER hot-swap LED boards. Always switch off the power supply or driver before disconnecting and reconnecting an LED array.
  • Use common ESD protection methods during manufacturing and installation of LED luminaires (e.g. ankle-straps, wrist-straps, conductive mats etc.).
  • Isolation tests are not required if an isolated power supply is used and the output is SELV (< 60V DC). This can be accom- plished by reducing the number of LEDs in series in a single string.

Figure 13. Protection against line transients and lightning strikes.

©2017 Lumileds Holding B.V. All rights reserved. LUXEON is a registered trademark of the Lumileds Holding B.V. in the United States and other countries. lumileds.com Neither Lumileds Holding B.V. nor its affiliates shall be liable for any kind of loss of data or any other damages, direct, indirect or consequential, resulting from the use of the provided information and data. Although Lumileds Holding B.V. and/or its affiliates have attempted to provide the most accurate information and data, the materials and services information and data are provided “as is,” and neither Lumileds Holding B.V. nor its affiliates warrants or guarantees the contents and correctness of the provided information and data. Lumileds Holding B.V. and its affiliates reserve the right to make changes without notice. You as user agree to this disclaimer and user agreement with the download or use of the provided materials, information and data. AB06 LUXEON LEDs Application Brief 20170605 About Lumileds Lumileds is the global leader in light engine technology. The company develops, manufactures and distributes groundbreaking LEDs and automotive lighting products that shatter the status quo and help customers gain and maintain a competitive edge. With a rich history of industry “firsts,” Lumileds is uniquely positioned to deliver lighting advancements well into the future by maintaining an unwavering focus on quality, innovation and reliability. To learn more about our portfolio of light engines, visit lumileds.com.