The EVL400W-EUPL7 demonstration board is a 12 V - 400 W converter, tailored for the typical specification of an AC/DC adapter with wide input mains range, very low power consumption at light load and good average efficiency.
The architecture is based on a two-stage approach: a front-end PFC pre-regulator based on a CCM (continuous conduction mode) boost PFC controller using the L4984, and a downstream LLC resonant half-bridge converter, designed around the L6699.
At the secondary side, synchronous rectification is implemented by means of the SRK2001 that assures a very high rectification efficiency with consequent small Heat Sink required.
The PFC section uses a proprietary LM-FOT (line-modulated fixed-off-time) that allows control methodology at fixed frequency operation for boost PFC converters as long as its operating in CCM.
The LLC section uses the L6699, a double-ended controller specific to series-resonant half-bridge topology. The output voltage regulation is obtained by modulating the operating frequency.
The main focus of this demonstration board is the light-load efficiency, achieved through the burst mode function of both PFC and LLC controllers with the self-adaptive deadtime of the L6699, modulated by the internal logic according to the half-bridge node transition times, which allows the maximization of the transformer magnetizing inductance, reducing the primary current at light load operation.
An active high voltage start-up circuitry based on a depletion MOSFET provides a very fast start-up time and minimizes the residual consumption during normal operation to a negligible level.