AC/DC controller with integrated PFC reduces standby power in 100W PSUs

January 23, 2014 // By Graham Prophet
Rohm has designed a high-efficiency AC/DC converter that integrates PFC (Power Factor Correction) and QR (Quasi-Resonant) controllers into a single package, for 100W-class equipment such as TVs and industrial power supplies.

The BM1C001F incorporates an ON/OFF setting function and a new PFC output control method within the PFC controller. This improves efficiency during light loads and significantly reduces standby power. Power supplies using this IC achieve compliance with Energy Star 6.0. The 2-controller-in-one design reduces the number of external parts.

In equipment over 75W, which can be harmful to other devices, a PFC controller is required, which may have a negative effect on efficiency. Power supply adapters are being adopted in 100W-class equipment such as large LCD TVs. However, conventional solutions combine an AC/DC converter with built-in QR controller with a separate PFC circuit, which can present problems regarding board space and power supply size.

Rohm has integrated a function that allows for flexible ON/OFF setting of the PFC controller. This improves conversion efficiency during light loads while reducing standby power consumption. In addition, a new proprietary PFC output control method is included in the PFC controller for boost converter operation, significantly increasing efficiency - particularly in 100 VAC systems. For example, integrating this IC in a 100W class power supply will result in 89% efficiency at 100 VAC and 89.5% efficiency at 230 VAC, exceeding the latest Energy Star standard (6.0) stipulating at least 88% efficiency. Layout optimisation makes it possible to integrate the PFC and QR controllers in a single package, reducing parts count by 20% compared with conventional solutions.

The design monitors the load power on the secondary side and switches the PFC controller ON/OFF, including in the load region where PFC is not required (below 75W), improving power supply conversion efficiency. Although the input AC voltage will vary depending on country/region, conventional PFC ICs provide a constant output voltage, possibly resulting in higher switching loss.

In response, Rohm developed a PFC control method that delivers an output voltage optimised to the input AC voltage. This can improve conversion efficiency in 100W-class power supplies by 1-2% compared to