Power Factor Correction (PFC) Preregulator# Technical Documentation: FAN4810N Power Factor Correction (PFC) Controller
Manufacturer : FAI
Component Type : Average Current Mode PFC Controller IC
Primary Function : Provides active power factor correction for AC-DC power supplies, enabling compliance with international harmonic current standards (e.g., IEC 61000-3-2).
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## 1. Application Scenarios
### Typical Use Cases
The FAN4810N is specifically designed for boost-type pre-converter stages in off-line switch-mode power supplies (SMPS). Its primary use case is to shape the input current drawn from the AC mains to be sinusoidal and in phase with the input voltage, thereby achieving a near-unity power factor (typically >0.99). It is commonly deployed in a continuous conduction mode (CCM) boost converter topology positioned between the input bridge rectifier and the main DC-DC converter stage.
### Industry Applications
* Computer Power Supplies: Server, desktop (PSU), and workstation power supplies where meeting mandatory PFC requirements is essential.
* Industrial Equipment: Motor drives, automation controllers, and large-scale instrumentation requiring efficient and compliant AC line utilization.
* Telecommunications Infrastructure: Rectifiers and power shelves for telecom systems demanding high reliability and power quality.
* Consumer Electronics: High-power (>75W) adapters for appliances like gaming consoles, large monitors, and audio amplifiers.
* Lighting: High-intensity discharge (HID) ballasts and high-power LED drivers.
### Practical Advantages and Limitations
Advantages:
* High Power Factor: Enables designs to easily exceed regulatory requirements (IEC 61000-3-2, ENERGY STAR®).
* Average Current Mode Control: Provides inherently stable operation, low distortion input current, and reduced noise sensitivity compared to peak current mode control.
* Integrated Features: Includes critical protection functions (overvoltage, undervoltage lockout) and a precision multiplier/divider, reducing external component count.
* Wide Operating Range: Suitable for universal input voltage (85VAC to 265VAC) applications.
* Improved Efficiency: Reduces RMS input current, lowering conduction losses in upstream components and distribution wiring.
Limitations:
* Added Complexity: Introduces an additional power stage (boost inductor, MOSFET, diode) to the overall power supply design.
* Cost Impact: Increases Bill of Materials (BOM) cost and requires more board space.
* Thermal Management: The PFC boost MOSFET and diode handle high currents and require careful thermal design.
* Start-up Inrush: Requires an additional inrush current limiting circuit (e.g., thermistor or relay) to protect the bulk capacitor and bridge rectifier during power-up.
* Minimum Power Threshold: CCM operation is most effective above ~100W; for very low-power applications, it may be less efficient than passive or critical conduction mode solutions.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Poor Current Sensing Accuracy.
* Cause: Incorrect placement or sizing of the current sense resistor (`R_sense`), leading to signal noise or excessive power loss.
* Solution: Use a low-inductance, surface-mount current sense resistor with adequate power rating. Place it directly between the source of the PFC MOSFET and ground. Kelvin connect the sense lines directly to the IC's `ISENSE-` and `ISENSE+` pins.
2. Pitfall: Excessive Output Voltage Ripple or Instability.
* Cause: Improper compensation network design for the voltage error amplifier (pins `VAOUT` and `VFB`).
* Solution: Follow the manufacturer's datasheet guidelines
