Led Design Guide Page 24 LED Design Guide

LED Lighting Design Guide 2015 Littelfuse LED Lighting Design Guide www.littelfuse.com Application testing is strongly recommended in order to establish whether or not the selected fuse can withstand the energy under a relevant waveform. If your lab does not have this type of test capabilities, contact Littelfuse about its Testing Services. Design Considerations for TVS Diodes In order to adequately protect sensitive circuits and components in LED drivers, transient voltage suppression must be part of the initial design process - not merely an afterthought. To ensure effective transient suppression, the device chosen must dissipate the impulse energy of the transient at a sufficiently low voltage so that driver circuit capabilities are not affected. The most successful type of suppression device used is the avalanche or transient voltage suppression (TVS) diode. Some transients may be created in the circuit due to intentional inductive load switching, commutation voltage spikes, or relay operation, etc. These transients are easy to suppress since their energy content is known or can be readily calculated. It is the transients generated external to the circuit and coupled into it that require specific analysis. These can be caused by the discharge of electromagnetic energy, lightning, adjacent inductive loads, or electrostatic discharge. These transients can be more difficult to identify, measure and suppress. Regardless of their source, transients have one thing in common; all of them can be destructive. The destruction potential of transients is defined by their peak voltage, the follow-on current, and the time duration of the current flow. The time required for a transient suppressor to begin functioning is extremely important when it is used to protect sensitive components like driver ICs and LEDs. If the suppressor is slow acting and a fast-rise transient spike appears on the system, the voltage across the protected load can rise to damaging levels before suppression begins. A TVS diode is specifically designed to protect electronic circuits against transient over voltage events. Being a silicon avalanche device, it is available in both uni-directional and bi-directional configurations. In the uni-directional version, the specified clamping characteristic is only apparent in one direction, with the other direction exhibiting a forward voltage, V F , characteristic similar to a conventional rectifier diode. (All electrical characteristics are specified at 25C.) LED lighting power supplies (drivers) typically need TVS diodes at one or more locations in their circuits. When selecting a TVS diode the important parameters to be considered are: Reverse Standoff Voltage (V R ) Peak Pulse Current (I PP ) Maximum Clamping Voltage (V C ) Design Considerations for TVS Diodes 24

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