Reducing the Complexity of Meeting EMI Standards

Most electronic systems, especially those powered from the AC line, are required to meet stringent standards with regards levels of EMI conducted on input power cables or radiated by the system itself.  For many design engineers minimizing EMI is a black art, which is time consuming, costly and can take up precious system space.

Compliance should be met under all combinations of input voltage or load.  Because of the complexity involved, statutory EMI tests are usually performed by certified test labs that have all the equipment suitably calibrated.  Certification can be a costly process when multiple retesting is required.

EMI filtering adds to the size and cost of the power supply.  Reducing the number of stages of filtering, or the size of each of the filter components, can, therefore, yield a competitive advantage.

How Vicor products simplify the process, reducing cost and size

Vicor products utilize inherently low noise, low EMI, soft switching topologies like Zero Current Switching (ZCS) and Sine Amplitude Conversion (SAC).  These eliminate the high current switching transients associated with hard-switching topologies like Pulse Width Modulation used in many traditional switching power supplies. Soft switching minimizes energy losses over the switching cycle and allows higher switching frequencies to be used – typically over 1 MHz – while retaining high efficiency.  This higher frequency operation allows the use of smaller passive components and, for a given filter design, reducing system size.

Designing filters can be a difficult process so Vicor offers many standard filter solutions that, when used together with the appropriate switching power components, meet common EMI standards, speeding time to market and saving development cost.  For lower voltage (48Vdc) systems, Vicor also provides active filter solutions that can replace a single stage common-mode input filter.  With solutions typically just 3mm high, these provide significant space savings.

A real-life example

Distributed antenna power system

Distributed Antenna Whiteboard (click to enlarge)

Reducing system size was a major focus for a manufacturer of distributed antenna systems for use in large public spaces and buildings.  Reduced size made the antenna less visible and simplified installation.  Each antenna took its 48V power from the Ethernet cable (PoE) and the RF stage required 9.6V for operation.

The power supply design was based on Vicor’s PI31xx Isolated DC-DC Converter Modules, which provided up to 50W of power.  A standard off-the-shelf QuietPower EMI Input Filter Module provided the necessary EMI suppression at the input.  The system was quickly prototyped and tested and the complete solution required a footprint of just 6.7 cm2.

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