What are the different ways that Shimmer in AC Line connected (offline) LED drivers be reduced? What MPS solution can be used for meeting the toughest Shimmer standards for LED drivers?
The shimmer in LED drivers is due to the 120Hz ripple that is generated by the full wave rectification of the AC line. The isolation transformer couples a portion of this 120Hz to the output depending on the turns ratio of the transformer. This shimmer can be reduced by using a “double power stage” approach with the first stage as a power factor correction boost and the second stage as a Flyback or LLC converter. We have reference designs for the PFC stage using the MP44014 and for the Flyback stage using the HFC0300 with synchronous rectification using MP6908. For higher efficiency, the Half Bridge LLC topology can be used for the second stage. We have reference designs for this topology too using the HR1001C and the MP6925 for secondary synchronous rectification.