FTM Board Club
12V - 400W SMPS for Adapter, Desktop and AIO using L4984D, L6699 and SRK2000A

The EVAL400W-ADP/ATX evaluation board is a 400 W, wide input mains range, power factor corrected solution for high power adapters and ATX power supplies with very low power consumption at no/light-load operation without a dedicated standby supply.

The application architecture is based on two stages: a front-end PFC pre-regulator based on a CCM (continuous conduction mode) boost PFC controller, using the L4984D, and a downstream LLC resonant half bridge converter, designed around the L6699 device, providing a 12 V regulated output voltage, dedicated to supply the ATX or similar applications requiring to meet the most stringent efficiency and standby regulations.

The main focus of this evaluation board is the light-load efficiency, achieved through the burst mode function of both PFC and LLC controllers and the self-adaptive deadtime of the L6699 device, 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 startup circuitry based on a depletion MOSFET provides a very fast startup time and minimizes the residual consumption during normal operation to a negligible level.

The very high efficiency during normal load operation and the very small heatsink used at the secondary side is obtained by using synchronous rectification, based on the SRK2000A device.

  • Universal input mains voltage range: from 90 Vac to 264 Vac - frequency from 45 to 65 Hz
  • Output voltage: 12 V 2% at 33 A continuous operation
  • Overall efficiency at full load: above 87% according to ENERGY STAR 6.1 for computers and compliant with 80PLUS Gold Level
  • Average efficiency: > 89%, according to European CoC ver. 5 Tier 2 for external power supplies
  • No load mains consumption: < 0.15 W at 230 Vac, according to European CoC ver. 5 Tier 2 for external power supplies
  • Light-load efficiency: European CoC ver. 5 Tier 2 requirements for external power supplies and EuP lot 6 Tier 2 for office equipment (Pin < 500 mW for Pout = 250 mW at 115 Vac and 230 Vac)
  • Mains harmonics: meets EN61000-3-2 Class-D and JEITA-MITI Class-D
  • EMI: according to EN55022 Class-B
  • Safety: meets EN60950 standards
  • RoHS compliant