Quietly efficient power, STMicroelectronics L4985E targets leaner PFC designs

Reviewed: ad hoc news Accessory & Components desk. Edited and checked on 2026-06-18, 00:21. Details in the imprint.

With the STMicroelectronics L4985E on the board, a switching power supply suddenly feels more composed - less wasted heat, quieter coils, and a touch more headroom when the line voltage misbehaves. This tiny controller sits at the front end and quietly tidies up the power.

What the L4985E actually does

The L4985E is a transition-mode power-factor-correction controller, designed for front-end AC-DC stages up to roughly 600 W. It shapes the input current to follow the mains voltage, which improves power factor and reduces ugly harmonics on the grid.

Transition mode means the controller drives the boost MOSFET so that each switching cycle starts when the inductor current falls to zero. That keeps switching losses in check, and it allows comparatively simple magnetics and lower-cost MOSFETs for a given efficiency target.

Efficiency, heat and audible comfort

STMicroelectronics emphasizes low standby consumption and optimized dynamic response, so supplies can meet modern efficiency regulations without exotic parts. The chip integrates protection features, start-up circuitry and gate driving, trimming external component count.

In a PC or gaming console power supply, that translates into a cooler-running PFC stage at typical loads, and less stressful thermal peaks when the user launches a heavy 3D game or a rendering job. The more stable current waveform also tends to keep coil whine and mechanical buzz down.

Design freedom for engineers

The device supports input voltages from 90 to 264 VAC and is suited for both single-voltage and universal-input supplies. Designers can reuse the same controller across regions, which simplifies global SKUs and replacement inventories.

ST pitches the L4985E for cost-sensitive applications such as low-cost PCs, TVs and industrial supplies where every cent in the bill of materials counts, but compliance with standards like IEC 61000-3-2 is non-negotiable. That mix makes it attractive for high-volume OEM designs.

How it compares in practice

Compared with older fixed-frequency PFC controllers, a well-tuned transition-mode design often reaches similar or better efficiency with fewer parts and simpler magnetics. The trade-off is variable switching frequency, which needs careful EMI filter work to pass conducted emissions tests.

For engineers coming from classic UC385x-style chips, ST's documentation and reference designs help bridge that gap. Layout guidelines around the current-sense path and gate-drive loop are especially important to achieve the promised low noise and efficiency benefits.

Where you will meet it

End users will rarely see the L4985E named on a box. Instead it hides on the primary side of desktop PSUs, LCD TVs, LED lighting drivers and compact industrial power bricks, giving them slightly better efficiency labels and a cooler touch under load.

For European consumers, that can be the difference between an 80 Plus Bronze and Gold badge on a mid-range PSU. For industrial users, it may mean cabinets that run a few degrees cooler and need less forced airflow, which directly impacts fan noise and dust build-up.

Company context and the stock

With controllers like the L4985E, STMicroelectronics N.V. underlines its role as a broad-line supplier, spanning everything from microcontrollers and MEMS sensors to discrete power devices and analog front ends. These building blocks quietly power PCs, cars and factory lines alike.

Shares of STMicroelectronics N.V. (ISIN NL0000226223) trade on Euronext Paris and Borsa Italiana; the company is also listed on the New York Stock Exchange under the ticker STM.

This article was AI-assisted and editorially reviewed. Product information without guarantee; prices and availability may change at short notice. No investment advice, no buy or sell recommendation. Stock-market transactions involve risks up to total loss.