This article introduces the design of a half-bridge LLC resonant converter using FSFR-Series Fairchild Power Switch (FPS™). Resonant switching techniques are used to reduce switching losses and enable high-frequency operation, leading to a significant reduction in noise.
This document is an application note (AN-4151) from Fairchild Semiconductor Corporation that details the design of a half-bridge LLC resonant converter. It focuses on the FSFR-Series Fairchild Power Switch (FPS) as the primary switching component.
The text explains the operating principles of the LLC resonant converter, including the fundamental approximation, the role of the magnetizing inductance, and the rectifier network. It discusses the advantages of the topology, such as zero voltage switching (ZVS) and reduced switching losses at high frequencies. The document also covers the derivation of the voltage gain and equivalent load resistance.
It can regulate the output voltage over wide line and load variations with only a relatively small variation in switching frequency.
The current flowing through the anti-parallel diode ensures that the voltage across the MOSFET is zero when it turns on.
The peak gain frequency moves toward the series resonant frequency (f_s), and the maximum achievable peak gain drops.