Designing a High-Performance PFC Stage with the onsemi NCP1605DR2G

In the quest for greater energy efficiency and regulatory compliance in modern power supplies, the Power Factor Correction (PFC) stage has become a critical front-end component. Its primary role is to shape the input current to be sinusoidal and in phase with the input voltage, thereby achieving a near-unity power factor. This not only reduces harmonic distortion injected back into the AC mains but also maximizes the real power available from the utility. Designing a high-performance, reliable PFC circuit requires a sophisticated controller, and the onsemi NCP1605DR2G stands out as a premier choice for this demanding task.

The NCP1605DR2G is a versatile, critical conduction mode (CrM) PFC controller that offers a compelling blend of performance, integration, and protection features. Its operation in boundary conduction mode ensures that the boost inductor’s switching cycle begins exactly as its current reaches zero. This Zero-Current Switching (ZCS) at turn-on minimizes switching losses, leading to higher overall efficiency, especially at low line voltages and light loads. This makes the controller exceptionally well-suited for applications ranging from 100 W to over 300 W.

A key to its high-performance capability is its innovative frequency clamping and foldback mechanism. As output load decreases, the switching frequency in a standard CrM controller would rise indefinitely, leading to increased core losses and potential EMI issues. The NCP1605DR2G intelligently clamps the maximum switching frequency to a programmable level. Under very light load conditions, it transitions into a frequency foldback mode, further reducing the frequency to maintain stable operation and excellent light-load efficiency.

The design process begins with the careful selection of external components, guided by the controller’s features. The boost inductor value is calculated to ensure CrM operation across the intended load and line range. The integrated active filter for the AC sense input simplifies the design by eliminating the need for an external low-pass filter network, reducing component count and board space. The controller also provides a programmable over-voltage protection (OVP) and an open-loop detection feature, enhancing system robustness.

Furthermore, the device incorporates a brown-out detection circuit and an internal startup timer, ensuring safe and reliable operation under fault conditions. Its ability to operate over a wide input voltage range (typically up to 275 VAC) makes it ideal for universal input applications. By leveraging the controller’s comprehensive feature set, designers can create a PFC stage that not only meets stringent regulatory standards like IEC 61000-3-2 but also delivers superior efficiency across a wide load range.

ICGOODFIND: The onsemi NCP1605DR2G CrM PFC controller is an integrated and intelligent solution that empowers designers to build highly efficient, compact, and robust front-end PFC stages. Its advanced frequency management, integrated protections, and simplified design approach make it an outstanding choice for modern switch-mode power supplies.

Keywords: Power Factor Correction (PFC), Critical Conduction Mode (CrM), NCP1605DR2G, Zero-Current Switching (ZCS), Frequency Clamping