Abstract-Conducted EMC noise qualification tests are normally carried out after a prototype has been designed, built and tested and the process is repeated in the event of non-compliance. The ability to determine compliance with EMI standards at the design stage is therefore desirable. This paper will present conducted EMC noise modelling and measurement techniques, yielding simulated and measurement noise results accurate enough to serve as a prequalification test at the design and prototyping stages respectively.Accurate models of the power feed-line connecting the LISN to the DUT (converter), including the load are developed. Predictive conducted EMC modelling is accomplished using detailed active level 3 SPICE-based models, creating a real-time circuit model consisting of a complete converter in its operational state, without the need to separate into equivalent models. Effects of the power feed-line length on EMI noise measurements are investigated as currently available literature has not dealt adequately with this issue. To detect possible radiating frequencies that might emerge with the conducted noise and are detectable in the conducted emission test, results have to be accurate not just in the prescribed frequency band, but all the way up to 100 MHz. The modelling and measurements are performed using software and instruments available in a development laboratory.
Abstract-Effects of polymer heatsink materials on EMI noise in converters have not been adequately investigated. Heatsinks provide a path to ground for the common-mode noise. Selecting an appropriate heatsink material can therefore help reduce common-mode noise by increasing noise path impedance.Effects of heatsinks on EMI noise over the conducted frequency band will be investigated. The critical parameter is the heatsink-to-device capacitance and accurate models of the heatsink impedance need to be developed. This is necessary for results that are accurate enough to allow prequalification of a converter as would happen in an accredited environment. However, simplified common-mode and differential-mode models of the step-down DC-DC converter circuit are adequate to predict the effects of the heatsink on the conducted noise. This paper will demonstrate that compared to a solid aluminium material, using polymer material incorporating conductive fillers in low power converters can greatly lower the device-to-heatsink capacitance, and still be adequate for heat dissipation in lower powered converters. This in turn reduces common-mode noise in the frequency band below 30 MHz. The measurement test setup is configured according to the MIL-STD-461F accredited test environment. It consists of a wideband two-port LISN, a properly grounded copper sheet as required by the standard, a suspended feed-line from the LISN to the DUT and an oscilloscope recording the data.
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