Stmicro's L4985A/B and L4986A/B power factor correction (PFC) boost converters with integrated 800V start circuits and proprietary, practical auxiliary features help simplify application design and improve design flexibility.

     The built-in high voltage startup function saves auxiliary circuits, supports "no auxiliary circuit" design, reduces bill of materials cost, and ensures startup reliability. In the additional auxiliary circuit, the internal logic circuit can perform a safe discharge operation on the input filter X capacitor when the AC line is disconnected, solving the power loss problem of traditional discharge resistors and simplifying the design of safety regulations such as IEC 61010-1 or IEC 62368-1 compliance.

     Both converters can be used as PFC premodulators to help a variety of applications comply with harmonic distortion requirements, e.g., IEC 61000-3-2 and equivalent standards. Target applications include power supplies for desktop computers, servers, game consoles, televisions and other product devices; Switching power supplies (SMPS) for industrial and medical equipment; Electric scooter charger. The converter also integrates a proprietary multiplication simulator and dedicated circuits to minimize total harmonic distortion (THD) in all operating conditions, ensuring a stable power quality for LED luminaires.

     The new converter benefits from stmicroelectronics' proprietary turn-off time modulator, which ensures that the converter maintains quasi-fixed frequency operation under full load conditions and enters burst mode at light and zero loads, further simplifying the design. The switching frequency of the L4985A and L4986A is 65kHz, while the switching frequency of the L4985B and L4986B is 130kHz. L4986A/B product adds the power normal input/output pin, when the PFC output reaches the user's preset threshold, it can generate a logical signal to assist system management.

     Comprehensive protection and monitoring features are also built into the new products, including overvoltage protection, feedback loop failure protection, set error protection and boost inductance saturation protection. Soft start circuits limit inrush current and help keep output voltage stable, while brown-out/brown-in undervoltage detection ensures that the converter starts reliably in all AC line conditions and prevents excessive RMS current. brownout protection enables medical devices to meet the requirements of IEC 60601-1-2. IEC 60601-1-2 requires that the output voltage of the power supply be kept stable when the line voltage of the grid drops less than 500ms.

     Engineers can speed up the project design cycle with the EVL400W-80PL Evaluation Board, a CLEAResult 80PLUS Platinum Level certified total AC/DC power solution. EVL400W-80PL board integrates L4985 PFC controller with stmicroelectronics L6699D resonant controller and SRK2001 synchronous rectifier controller, full load energy efficiency of 90.2%, at 50% load 92.49%.