Measurement of the interference voltage on DC/DC switching regulators


Developers of switched-mode power supplies face the challenge of developing their circuit to be EMC-compliant. Conducted interference particularly occurs in the input circuit whereby other electrical equipment can be disrupted. Therefore the conducted interferences are first checked at the beginning of an EMC test of power supplies. The developer can already perform measurements accompanying the development during the development phase to obtain an impression of possible interference. This Application Note describes the procedure for examining differential mode interference in the input circuit of DC/DC switching regulators.


This Application Note illustrates the necessity of accompanying EMC measurements on switched-mode power supplies during development. An oscilloscope can already make an important statement in advance about EMC interference at the input of the switching regulator. However, measurement of the interference voltage with a spectrum analyser and an LISN are still decisive. If an input filter is already taken into account during the development phase of switching regulators, the filter effect can be checked in the development laboratory using a simple spectrum analyser. Using this method, the developer can determine unwanted interference levels at the switching regulator. With the selective use of filter elements, the developer can ensure that his application passes the final EMC test.