STMicroelectronics EVL400W-EUPL7 Converter Demonstration Board

The PFC section uses a proprietary line-modulated fixed-off-time (LM-FOT) that allows control methodology at fixed frequency operation for boost PFC converters, as long as it's operating in CCM. The LLC section uses the L6699, a double-ended controller specific to the 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 dead time of the L6699. The L6699 is modulated by the internal logic according to the half-bridge node transition times. This 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.