The STMicroelectronics EVL400W-80PL demonstration board is a 12 V - 400 W converter, tailored to the typical specifications of an AC/DC adapter with wide input mains range, very low power consumption at light load and good average efficiency.

It is composed by a motherboard mounting the high voltage power devices, the primary control board mounting the IC controllers L4985A and L6699 and the secondary control board for the synchronous rectification.

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 L4985A, 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 a reduction in the size of the heatsink required.

The PFC section uses the L4985A, a peak current-mode PFC controller for boost converter with a proprietary multiplier “emulator” which, in addition to the innovative THD optimizers, guarantees very low Total Harmonic Distortion (THD) performance in all operating conditions.

The device operates in quasi-fixed frequency in all operating conditions thanks to a proprietary off-time modulator and includes the high voltage startup block with the circuitry to discharge the X-capacitors of the EMI filter.

This level of integration allows a low-component count solution for boost PFC pre-regulators.

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.