ST's L4985A/B and L4986A/B power factor correction (PFC) boost converters integrate an 800V start-up circuit, as well as useful STMicroelectronics-specific auxiliary functions to help simplify application design and increase design flexibility.
The high-voltage startup function built into the chip can save auxiliary circuits, support "no auxiliary circuit" design, reduce bill of materials costs, and ensure startup reliability. In an additional auxiliary circuit, the internal logic circuit can perform a safe discharge operation of the input filter X capacitors when the AC line is disconnected, solving the power loss problem of traditional discharge resistors and simplifying safety such as IEC 61010-1 or IEC 62368-1 Regulatory compliance design.
Both converters can be used as PFC preconditioners to help a variety of applications meet harmonic distortion requirements, such as IEC 61000-3-2 and equivalent standards. Target applications include power supplies for product equipment such as desktop computers, servers, game consoles, and televisions; Switch Mode Power Supplies (SMPS) for industrial and medical equipment; and electric scooter chargers. The converter also integrates a proprietary multiplier simulator and dedicated circuitry to minimize total harmonic distortion (THD) under all operating conditions, ensuring stable power quality for LED luminaire power supplies.
The new converters benefit from ST's proprietary off-time modulator, which ensures that the converter maintains quasi-fixed frequency operation at full load 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 L4985B and L4986B are 130kHz. L4986A/B products have added power good input and output pins, which can generate a logic signal to assist system management when the PFC output reaches the user-preset threshold.
The new products also have comprehensive built-in protection and monitoring functions, including overvoltage protection, feedback loop fail-safe, wrong setting protection and boost inductor saturation protection. Soft-start circuitry limits inrush current and helps maintain output voltage regulation, while brown-out/brown-in brown-out detection ensures reliable start-up of the converter under all AC line conditions and prevents excessive RMS current. Brownout protection enables medical devices to meet the requirements of IEC 60601-1-2. The IEC 60601-1-2 standard requires that the power supply must maintain a stable output voltage when the grid line voltage drops within 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 supply solution. The EVL400W-80PL board integrates the L4985 PFC controller with ST's L6699D resonant controller and SRK2001 synchronous rectifier controller, with a full load energy efficiency of 90.2% and 92.49% at 50% load.
