Interleaved Dual BCM PFC Controller# Technical Documentation: FAN9611 Interleaved Boundary Conduction Mode (BCM) PFC Controller
Manufacturer : FAI (Fairchild Semiconductor)
Component : FAN9611
Description : Dual-Phase, Interleaved, Boundary Conduction Mode (BCM) Power Factor Correction (PFC) Controller IC.
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## 1. Application Scenarios
The FAN9611 is a specialized controller designed for high-performance, efficient AC-DC power conversion where power factor correction is mandated or highly beneficial. Its architecture is optimized for medium to high-power offline power supplies.
### Typical Use Cases
* Server & Telecom Power Supplies : Provides high-efficiency, high-power PFC front ends (typically 500W to 3kW+) for blade servers, routers, and base station power systems. Interleaving reduces input current ripple, easing EMI filter design.
* Industrial Power Systems : Used in welding equipment, large-scale industrial automation controllers, and test/measurement instrumentation where robust, high-power AC input stages are required.
* High-End Computing & Gaming PSUs : Enables compact, high-efficiency (>80 Plus Platinum/Titanium) power supplies for workstations and gaming PCs by improving power factor and reducing conduction losses.
* LED Driver Arrays : For high-power commercial and industrial LED lighting systems (e.g., stadium lights, street lights) requiring PFC to meet regulatory standards like IEC 61000-3-2.
* Uninterruptible Power Supplies (UPS) : Improves the utility power draw quality and efficiency of the online double-conversion stage in medium to large UPS units.
### Industry Applications
* Information Technology (IT) : Data center power infrastructure.
* Telecommunications : Network equipment power shelves.
* Industrial Automation : Motor drives and control cabinet power modules.
* Consumer Electronics : Premium high-wattage external power adapters.
* Renewable Energy : Grid-tied inverter front-end stages.
### Practical Advantages and Limitations
Advantages:
* High Efficiency : Interleaved BCM (Critical Conduction Mode) operation minimizes switching losses, especially at high line voltages, and reduces MOSFET turn-on losses (near-zero voltage switching).
* Reduced Component Stress : Current is shared between two phases, lowering RMS current through each inductor, MOSFET, and diode, which improves thermal performance and can allow for smaller, lower-cost components.
* Lower Input Current Ripple : The interleaving technique significantly cancels high-frequency ripple current at the input, leading to a smaller, less expensive input EMI filter and reduced conducted EMI.
* Scalable Power : The dual-phase design inherently supports higher power levels than single-phase controllers.
* Integrated Features : Includes critical protection features (over-voltage, open-loop, brown-out) and synchronization capability for multi-controller operation.
Limitations:
* Design Complexity : Requires two independent power stages (inductors, MOSFETs, diodes, sense resistors), increasing component count and PCB real estate compared to single-phase solutions. Control loop stability for two interleaved phases is more complex.
* Cost vs. Benefit Trade-off : For lower power applications (<300W), the added cost and complexity of a dual-phase interleaved design may not be justified versus a single-phase Continuous Conduction Mode (CCM) or Transition Mode (TM) PFC.
* Control Algorithm Dependency : Optimal performance relies on precise current sensing and the internal interleaving logic. PCB layout and component tolerances are more critical.
* Audible Noise Potential : BCM operation has a variable switching frequency that can enter the audible range at light loads, which may require frequency clamping.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Unbalanced Phase Current
