046-047-048_EETE-VF-NEW

EETE NOVEMBER 2012

DESIGN & PRODUCTS POWER ELECTRONICS Powering LED luminaires: is EMC mitigation or prevention the best option? By Arnoldas Bagdonas compromises And work-Arounds undertaken in an effort higher-frequency emissions radiated by the mains cable persist, to meet the requirements of electro-magnetic compatibility (emc) and must be blocked by a more expensive filter with higher at- have had the potential in the past to markedly impair the reliabil- tenuation. The root cause of the problem in Led luminaires is the ity and efficiency, and increase the total production cost, of the power supply’s high-speed switching circuits, which create wide- power circuit in an Led luminaire. spectrum current and/or voltage ripples. Shielding and filtering A typical example of a power circuit for an Led luminaire using might mitigate the emission problem, but do not eradicate it. A conventional power components is shown in figure 1. Excessive better solution would be to avoid generating high emissions at radiated emissions will normally lead the design team to shield particular frequencies in the first place – and this is now possible the entire housing. In practice, however, this increases the para- through the use of new power components that use soft switch- sitic capacity between the (now larger) conductive area – that is, ing to minimise ripple currents, or to spread the noise energy over the chassis plus its shield – and the reference ground of any emc a wide frequency band. measurement equipment. Figure 2 shows that there are broadly five architectures used common-mode conducted interference then becomes a large today, each suited to different power outputs. Each of these LED enough phenomenon to require attention. while a low-cost emi driver topologies enables the designer to comply with the strict filter will eliminate this problem, this author has seen designs requirements of today’s EMC regulations. While figure 2 indicates in which even these counter-measures are not sufficient, since the power range in which each topology is most commonly used, it should be noted that each can be adapted for use in a higher or Arnoldas Bagdonas is Field Application engineer at Future lower power output range. electronics (Lithuania) - www.futureelectronics.com Your Vision Visit us at Electronica 2012 Hall A2, Booth #163 Hall A4, Booths W15/W16 - EMI Solutions - Antennas & Reception - Thermal Management - Embedded Wireless - Signal Integrity Products Click to fi nd your solutions at www.lairdtech.com 46 Electronic Engineering Times Europe November 2012 www.electronics-eetimes.com


EETE NOVEMBER 2012
To see the actual publication please follow the link above