The LLC converter is a resonant inverter with three reactive elements where the DC input voltage is turned into a square wave by a switch network arranged as either a half- or full-bridge to feed the resonant LLC tank that effectively filters out harmonics providing a sinusoidal like voltage and current waveform. This in turn feeds a transformer that provides voltage scaling and primary-secondary isolation. The converter power flow is controlled by modulating the square wave frequency with respect to the tank circuit's resonance. In an LLC resonant converter, all semiconductor switches are soft-switching, or zero-voltage switching (ZVS), at turn-on for the primary MOSFETs and zero-current switching (ZCS) at both turn-on and turn-off for the rectifiers in the secondary; resulting in low electro-magnetic emissions levels (EMI). In addition, it can enable a high degree of integration in the magnetic parts, enabling the design of converters with higher efficiency and power density.
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