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Date: 28/09/2022

New PFC boost controllers from STMicro saves a lot of external circuitry

Maintaining power factor at 1 or closest to 1 is important in lot of inductive and capacitive loaded high-power switching power supplies or any such power systems. There is also regulations such as IEC 61000-3-2, IEC 61010-1 or IEC 62368-1, which demands use of power factor correction (PFC) system at power supply input end. The PFC boost converter provides continuous current while maintaining lowest phase difference with voltage.

There are good number of vendors supplying power factor correction boost controllers in the market, added to this list is new STMicroelectronics' L4985A/B and L4986A/B power-factor correction (PFC) boost controllers chips where they have on chip 800V startup circuitry and other features. This built-in feature saves from the use of additional circuit. It also has internal logic to discharge stored energy from the input capacitors when input AC line is switched off. This particular feature saves power what used to be dissipated by a traditional discharge resistor and also meets safety regulations such as IEC 61010-1 or IEC 62368-1.

SO-8 packaged L4985A/B and SSOP-10 packaged L4986A/B power-factor correction (PFC) boost controllers suggested for multiple applications such as desktop PCs, servers, game consoles, and televisions, industrial and medical switched-mode power supplies (SMPS), and e-scooter chargers. These devices can be used as PFC pre-regulators in equipment fulfilling the harmonic distortion requirements specified in standards such as IEC 61000-3-2 and equivalents. These are also good choice for LED lighting lumanaire systems, where they support by featuring proprietary multiplier emulator, and a exclusive circuitry to minimize total harmonic distortion (THD) in all operating conditions.

The proprietary off-time modulator supports quasi fixed-frequency operation in any load situation such burst mode, light load and zero load. 65kHz operating L4985A and L4986A and 130kHz operating L4985B and L4986B provide an external pin to initiate idle mode and save power. The L4986A/B variants also provide pins for power-good, where they produce a logic signal to help in system management when the PFC output reaches a user decided threshold.

These devices have built-in protection features to protect against overvoltage, feedback loop failures, setting errors, inductor saturation, inrush current limiting, excessive RMS current, brown-out and brown-in detection. Due to the availability of brownout protection, this device can be used in designing power supplies of medical electronic equipment fulfilling IEC 60601-1-2, where it need to maintain output regulation if line voltage goes off for up to 500ms.

ST is providing EVL400W-80PL evaluation board to evaluate these chips. L4985 and L4986 variants are in production now and are priced starting from $1.21 for orders of 1000 pieces.