Italian French semiconductor high integration PFC boost converter, solving the design challenge of startup circuit

    The built-in high-voltage startup function of the chip can save the auxiliary circuit, support the design of "no auxiliary circuit", reduce the bill of materials cost, and ensure the startup reliability. In the additional auxiliary circuit, the internal logic circuit can safely discharge the input filter X capacitor when the AC line is disconnected, solve the power loss problem of the traditional discharge resistor, and simplify the compliance design of safety regulations such as IEC 61010-1 or IEC 62368-1.

    These two converters can be used as PFC pre regulators to help various applications meet harmonic distortion requirements, such as IEC 61000-3-2 and equivalent standards. Target applications include power supply of desktop computers, servers, game consoles, televisions and other product equipment; Switching mode power supply (SMPS) for industrial and medical equipment; Electric scooter charger. The converter also integrates proprietary multiplication simulator and special circuit, which can minimize total harmonic distortion (THD) under all working conditions, and ensure stable power quality of LED lamp power supply.

    The new converter benefits from the special turn off time modulator of STC, which ensures that the converter operates at a quasi fixed frequency under full load conditions, and enters burst mode under light load and zero load, thus further simplifying the design. The switching frequency of L4985A and L4986A is 65kHz, while L4985B and L4986B are 130kHz. The L4986A/B product has added normal input and output pins for power supply. When the PF output reaches the user preset threshold, a logic signal can be generated to assist system management.

    In order to achieve energy-saving design, according to the latest European ecological design directive, all products have an external standby pin to start the low power idle mode.

    The new product also has built-in comprehensive protection and monitoring functions, including overvoltage protection, feedback loop failure protection, setting error protection and boost inductor saturation protection. The soft start circuit can limit the inrush current and help maintain the stability of the output voltage, while the brown out/down in undervoltage detection can ensure that the converter can start reliably under all AC line conditions and prevent the RMS current from being too large. The brownout protection function enables medical devices to meet the requirements of IEC 60601-1-2. When the power grid line voltage drops within 500ms, IEC 60601-1-2 standard requires that the power supply must keep the output voltage stable.

    Engineers can use the EVL400W-80PL evaluation board to accelerate the project design cycle, which is a way to obtain CLEANResult ® 80PLUS Platinum Level certified AC/DC power supply overall solution. The EVL400W-80PL board integrates the L4985 PFC controller with the L6699D resonant controller and SRK2001 synchronous rectifier controller of Italy France Semiconductor. The full load energy efficiency is 90.2%, reaching 92.49% at 50% load.

    All L4985 and L4986 products have been put into mass production. L4985A/B is encapsulated by SO-8; L4986A/B added power supply normal pin, which is packaged with SSOP-10.