Medical Power Supplies and Electromagnetic Interference

One of the challenges of using commercial power supplies in medical instruments is electromagnetic interference (EMI). Commercial power supplies often list “meets Class B” for EMI, but this is often with conditions that are completely unrealistic or impossible for a medical system designer to meet. If designers assume electromagnetic compliance (EMC) in the power supply, they may find themselves chasing EMI problems and making last-minute system design changes, such as adding filtered power entry modules, shielding, and other compensation, before they can launch the product. This article discusses critical details to look for in commercial medical power supplies with respect to EMI. It also explores why it can be advantageous to consider a custom design to meet EMC as well as cost, performance, and lead time requirements.