How to calculate Switch Mode Power Supply Design AC losses

Power loss in a Switched Mode Power Supply (SMPS) primarily comes from switching losses and magnetic losses.Magnetic losses occur in the windings and core of the inductive component used in the design.Complex equations and core characteristic data can be used to estimate core losses when selecting inductors for a SMPS design. Additional calculations may also be needed to estimate losses caused by skin effect and proximity.
Wurth has taken a different approach and developed a model to estimate power inductor loss as a DC component and AC component. Power dissipation due to DC current in the inductor windings is listed as DC loss. Power loss due to AC flux swing in the coil and the core is termed as AC loss.

Advantage of the Wurth model is that it is based on real data from actual components.

  • The empirical data is based on real time parameters with accurate estimation of losses for any given Duty Cycle being achieved.
  • The model is also accurate over wide range of frequency (10 kHz to 10 MHz) as the constants of the power equation are derived over a wide range with respect to the flux swing.
  • Considers even small change in core material and winding structure.
  • Valid for the components, which have more than one material.
  • Accurately estimates losses of Iron powder and Metal alloy materials.
  • Valid for any core shape and winding structure.
  • Includes AC winding losses.

This model has been implemented in Wurth’s online REDEXPERT design tool to select appropriate inductors and estimate AC and DC loss for each selected part and the specified SMPS design parameters (input/output voltage, frequency, current, topology) .

Detailed discussion and examples for using REDEXPERT to estimate AC losses are available in the archived REDEXPERT - World’s Most Accurate AC Loss Module Webinar with speaker John Sudol of Wurth.