EMC Considerations in the Design of Switch Mode Power Supplies

מק"ט: #50109 | משך קורס: 16 שעות אק'

Almost every electronic product requires converting efficient conversion of some primary AC or DC power source to some DC voltages for powering its electronic circuits. Switch Mode Power Supplies are the current state of the art in high efficiency power supplies.
Conventional series-regulated linear power supplies maintain a constant voltage by varying their resistance to cope with input voltage changes or load current demand changes. The linear regulator can, therefore, tend to be very inefficient. The switch mode power supply, however, uses a high frequency switch (in practice a transistor) with varying duty cycle to maintain the output voltage. The output voltage variations caused by the switching are a source of significant electromagnetic interference (EMI) filtered out by an LC filter.
In recent years, switch mode power supplies have become particularly popular when multiple and diverse DC voltages (e.g., 5V, 3.3V, 2.5V…) are required in any single printed circuit board with maximum power conversion efficiency. Increase in switching frequency is desired for achieving goals of size, conflicting with production of harmonics and subsequently... noise, or EMI.
For the adequate control of electromagnetic interference (EMI) emanating or entering the product via their power ports, strict international commercial and military standards have been developed. These standards require the suppression of electromagnetic emissions from circuits and systems, and their increased immunity to externally induced interference. Indeed, switch mode power supplies are major sources of EMI and if EMC
is not embedded in the design, high level emissions, and increased immunity will be the result, with possible non compliance with the very stringent commercial and military standards.
Embedding EMC considerations in the design of switch mode power supplies is a cost effective approach for the control of EMI on the power port in particular and in the equipment and system level, in general.

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This two-day comprehensive course provides the trainees with the necessary tools for identification, analysis and understanding of the electromagnetic phenomena in switch mode power supplies and their associated circuits.
In addition, the Course is intended to teach the engineering know-how and analytical methods for enabling the engineer to implement EMI control measures when specifying, procuring, designing and integrating switch mode power supplies in order to achieve the necessary EMC compliance.
The course emphasizes the basic principles and practical applications, with mathematical derivations and calculations kept to the minimum necessary. In addition, case studies and practical “real life” examples are provided.
Inasmuch as the course is not intended to be a "switch mode power supply design course" it will provide deep insight into the considerations associated with the selection and design of the power supplies as applicable to EMI control.


  • Obtain a fundamental knowledge of the problem and interference sources associated with switch mode power supplies
  • Study the EMI control requirements applicable to the design of switch mode power supplies
  • Acquire the proper know-how for the design of switch mode power supplies for EMC compliance
  • Obtain a systematic approach for the proper design of switch mode power supplies while implementing EMI control measures


In addition, participants are encouraged to bring forward actual design problems and questions they have encountered, which the instructor will attempt to assist in their solution.

קהל יעד

The Course is intended for electrical and electronic engineers and technicians involved in the design and development, integration and qualification of electronic and electrical equipment embedded or supplied from switch mode power supplies.

תנאי קדם

Basic understanding of electronic components and circuits


Module 1: Introduction – Why Design for EMC?

  • Nature of an EMI problem
  • Why consider EMC in switch mode power supplies (an EMI Study)?
  • Spectral contents of signals
  • Models of interference modes
  • Common-Mode vs. Differential-Mode Signal
  • "Real World" Circuit Elements and Current Propagation Paths


Module 2: Fundamental Switch Mode Power Supply Topologies

  • Buck (or Forward) Regulator
  • Boost Regulator
  • Flyback Regulator
  • Off-Line Switch Mode Power Supply Circuits


Module 3: Noise Sources in Switch Mode Power Supplies

  • EMI Created by AC to DC Rectification
  • EMI from Switching Mode Conversion


Module 4: Commercial/Military EMI Control Requirements on Power Ports

  • Conducted and Radiated Emission Requirements
  • Immunity/Susceptibility to Conducted and Radiated EMI Requirements
  • Power Quality Requirements


Module 5: EMI Control in Switch Mode Power Supplies Components and Circuits

  • Selection of Semiconductor Switching Devices
  • Passive EMI Filters and Inductors
  • Transient Voltage Suppression Circuits
  • Shielding
  • Grounding and Isolation Considerations
  • Layout of Switch Mode Power Supply Circuits
  • Heat Sink Design


Module 6: EMI Fixes in for Power-Line EMI

  • Retrofit and Field Fixes


Module 7: Electrical Safety vs. EMI

  • EMI Filters as an Electrical Safety Concern


Module 8: Power-Supply related Case Studies


Module 9: Summary, Q&As