12V-400W adapter based on L4984, L6699 and SRK2001

The architecture is based on a two-stage approach: the front-end PFC pre-regulator is based on a CCM (continuous conduction mode) boost PFC controller using the L4984, and the downstream LLC resonant half-bridge converter is designed around the L6699.
On the secondary side, synchronous rectification is implemented by SRK2001, which guarantees very high rectification efficiency and therefore requires a small heat sink size.
The PFC section uses a proprietary LM-FOT (Linear Modulated Constant Off-Time), which allows the control method of the boost PFC converter to operate at a fixed frequency as long as it is operated in CCM (Continuous Conduction Mode).
The LLC part uses L6699, a double-ended controller specifically designed for resonant half-bridge topology. Output voltage regulation is achieved through operating frequency modulation.
This demo board focuses on light load efficiency, maximizing the transformer magnetizing inductance through the burst mode capabilities of the PFC and LLC controllers combined with the L6699's adaptive dead time (modulated by intrinsic logic based on the half-bridge node transient time). Reducing the primary current during light load operation) is achieved.
An active high-voltage start-up circuit based on depletion-mode MOSFETs provides very fast start-up times and minimizes residual consumption during normal operation to negligible levels