Designing a High-Performance PFC Stage with the onsemi NCP1605BDR2G CRCM PFC Controller
Modern switch-mode power supplies (SMPS) must comply with stringent international regulations regarding harmonic current emissions. The Power Factor Correction (PFC) stage is, therefore, a critical front-end circuit designed to draw a sinusoidal current in phase with the AC line voltage, maximizing real power delivery and minimizing reactive power. Among the various topologies, Critical Conduction Mode (CrM or CRM) offers an excellent balance of simplicity, cost-effectiveness, and performance. The onsemi NCP1605BDR2G is a highly integrated controller engineered specifically to implement a high-performance CrM PFC boost converter.
The NCP1605BDR2G operates in Critical Conduction Mode, also known as Transition Mode (TM). This mode ensures that the boost power MOSFET is switched on exactly when the inductor current reaches zero (Zero Current Detection - ZCD), minimizing switching losses and reducing electromagnetic interference (EMI). This makes it exceptionally efficient for mid-power applications. The controller features a proprietary Time-Based Management (TBM) approach for output voltage regulation. Unlike traditional frequency-varying CrM controllers, the TBM technique provides superior audio-noise immunity and more stable operation across a wide range of load and line conditions.
A typical application circuit built around the NCP1605BDR2G includes a boost inductor, power MOSFET, boost diode, and a set of feedback components. Key to its performance is the internal startup timer that prevents bus voltage overshoot during initial startup and ensures smooth operation. The controller also incorporates comprehensive protection features, including VCC under-voltage lockout (UVLO), open-loop detection, and over-voltage protection (OVP), safeguarding the converter and downstream circuitry from fault conditions.
Designing with this IC involves careful selection of external components. The boost inductor value is calculated based on the desired power level, switching frequency range, and the CrM operating principle. The feedback network, consisting of resistors dividing the output bus voltage (typically 390V-400V), is critical for setting the regulation point. The current sense resistor must be chosen to ensure the peak inductor current remains within safe limits, triggering the controller's internal comparator for cycle-by-cycle current limiting.
The resulting PFC stage achieves a near-unity power factor (PF > 0.99) and extremely low total harmonic distortion (THD < 5%), easily exceeding standards like EN61000-3-2. Its high efficiency across the load range contributes to lower energy consumption and reduced thermal management requirements.
The onsemi NCP1605BDR2G CRCM PFC controller is an optimal solution for designing efficient, compact, and compliant front-end PFC stages. Its innovative Time-Based Management ensures robust performance, while its high level of integration simplifies design and reduces time-to-market for power supplies ranging from 100W to 300W.
Keywords: Power Factor Correction (PFC), Critical Conduction Mode (CrM), NCP1605BDR2G, Total Harmonic Distortion (THD), Boost Converter
