Power Factor Correction Controller# Technical Documentation: FAN7527 Critical Conduction Mode PFC Controller
## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN7527 is a dedicated Power Factor Correction (PFC) controller designed for offline switch-mode power supplies operating in critical conduction mode (CRM) . Its primary function is to shape the input current waveform to match the input voltage waveform, thereby achieving near-unity power factor and reducing harmonic distortion.
Primary Applications Include:
- AC-DC Power Supplies : Used in front-end PFC stages for power supplies ranging from 100W to 300W, particularly where cost-effective, compact solutions are required.
- LED Drivers : Provides stable DC bus voltage for high-power LED lighting systems while meeting power quality standards like EN61000-3-2.
- Adapter/Charger Systems : Implements PFC in laptop adapters, server power supplies, and industrial battery chargers where efficiency and regulatory compliance are critical.
- Consumer Electronics : Integrated into televisions, audio amplifiers, and gaming consoles to improve overall system efficiency and reduce input current harmonics.
### 1.2 Industry Applications
- IT Equipment : Server power supplies, UPS systems, and telecom rectifiers requiring high power factor (>0.9) and reduced input current THD (<10%).
- Industrial Systems : Motor drives, welding equipment, and automation controllers where stable DC bus voltage is essential for downstream converters.
- Renewable Energy : Grid-tied inverters and energy storage systems that must maintain high power quality when drawing from the AC mains.
- Medical Devices : Power supplies for diagnostic and therapeutic equipment requiring reliable, high-efficiency operation with minimal electromagnetic interference.
### 1.3 Practical Advantages and Limitations
Advantages:
- High Power Factor : Typically achieves PF >0.99 at full load with proper design.
- Zero-Current Switching (ZCS) : CRM operation minimizes switching losses in the MOSFET, improving efficiency (typically 92-95%).
- Built-in Protections : Includes over-voltage protection (OVP), open-loop protection, and under-voltage lockout (UVLO).
- Low Component Count : Requires fewer external components compared to continuous conduction mode (CCM) PFC controllers, reducing BOM cost and board space.
- Line Surge Protection : Internal multiplier design provides inherent protection against AC line surges.
Limitations:
- Power Range Constraint : Best suited for low to medium power applications (<300W) due to CRM operation; higher powers may require CCM controllers.
- Variable Frequency Operation : Switching frequency varies with line voltage and load, complicating EMI filter design.
- Higher Peak Currents : CRM results in higher peak inductor currents compared to CCM, potentially requiring larger magnetic components.
- Audible Noise Risk : At light loads, switching frequency may enter audible range, necessitating frequency clamping or burst mode implementation.
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
Pitfall 1: Incorrect Current Sensing
- Problem : Using inappropriate current sense resistor value or poor layout causing noise injection.
- Solution : Select sense resistor for 1V peak at maximum input current. Place resistor close to controller with Kelvin connection. Use 100pF-220pF RC filter on ISENSE pin.
Pitfall 2: Unstable Output Voltage
- Problem : Oscillations in output voltage due to improper compensation network.
- Solution : Implement Type II compensation with careful pole-zero placement. Typical values: Rcomp=10kΩ, Ccomp1=10nF, Ccomp2=470pF. Ensure compensation network is placed adjacent to COMP pin.
Pitfall 3: Excessive EMI
- Problem : Variable frequency operation generates broadband EMI.
- Solution : Implement frequency
