SLYT800B december   2020  – december 2020 LM25180 , LM25183 , LM25184 , LM5180 , LM5181


  1. 1Introduction
  2. 2A PSR Flyback DC/DC Converter with Multimode Control
  3. 3Output Capacitor Sizing for Voltage Ripple
  4. 4Small-signal Stability Review
  5. 5Output Capacitor Sizing for Small-signal Stability
  6. 6Conclusion
  7. 7References
  8. 8Related Web Sites


Primary-side regulation (PSR) is an observer-based approach to estimate the output voltage of a flyback converter using the reflected voltage on a primary-referenced winding. Previous Analog Design Journal articles[1, 2] have described the operation and switching behavior of an auxless PSR flyback DC/DC converter for automotive and industrial applications, where appropriately timed sensing of the primary switch voltage at its resonant knee position provides a suitable proxy for the output voltage. This magnetically-sensed regulation technique supports a sub-1% output-voltage accuracy across load, line and temperature ranges.[1] Moreover, it avoids the secondary-side optocoupler and error amplifier normally used for isolated feedback, thereby eliminating a component crossing the isolation barrier and enabling a cost-effective, high-reliability design with low component count.

Within this context, this article reviews the modes of operation and salient characteristics of a PSR flyback DC/DC converter and specifically examines output capacitor selection to meet system specifications for output voltage ripple and small-signal stability.