Critical Conduction Mode PFC Controller# Technical Documentation: FAN7529 Critical Conduction Mode PFC Controller
Manufacturer : Fairchild Semiconductor (FSC)
Component Type : Critical Conduction Mode (CRM) Power Factor Correction (PFC) Controller IC
Document Version : 1.0
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## 1. Application Scenarios
The FAN7529 is a specialized integrated circuit designed to implement a high-efficiency, cost-effective Power Factor Correction (PFC) stage in AC-DC power supplies. Its operation in Boundary/Transition/Critical Conduction Mode (CRM) makes it suitable for specific power ranges and applications where component size, cost, and efficiency are balanced.
### Typical Use Cases
* Mid-Power Offline SMPS Pre-regulators : Primarily employed in switch-mode power supplies (SMPS) with output power ranging from approximately 100W to 300W . This covers a broad array of consumer and industrial electronics.
* Standalone PFC Boost Converters : It serves as the core controller for a boost converter topology, shaping the input current to follow the input voltage waveform, thereby achieving a high power factor (typically >0.95).
* Lighting Ballasts : Used in electronic ballasts for high-intensity discharge (HID) lamps and high-power LED drivers where PFC is mandated by regulations (e.g., IEC 61000-3-2).
* Adapter and Open-Frame Power Supplies : For laptop adapters, gaming console power bricks, and industrial open-frame power modules requiring compliance with energy efficiency standards (80 PLUS, ErP, etc.).
### Industry Applications
1. Consumer Electronics : Power supplies for LCD/LED TVs, audio amplifiers, gaming systems, and desktop computers.
2. Industrial Equipment : Motor drives, automation control panels, and test/measurement instrumentation requiring clean input current.
3. Telecommunications : Power shelves and rectifiers for networking equipment.
4. Lighting Industry : Drivers for commercial and industrial LED luminaires and HID lamp ballasts.
### Practical Advantages and Limitations
Advantages:
* High Power Factor & Low THD : Naturally achieves near-unity PF and low total harmonic distortion (THD) due to CRM operation without complex current sensing.
* Zero-Current Switching (ZCS) : The MOSFET turns on at zero inductor current, minimizing turn-on switching losses and reducing EMI noise generation.
* Simple & Cost-Effective Design : Requires fewer external components compared to continuous conduction mode (CCM) PFC controllers, as it does not need a dedicated current sense resistor or its associated signal conditioning circuitry. Current sensing is done via a transformer or the MOSFET's `R_DS(on)`.
* Built-in Protections : Integrates essential safeguards like Over-Voltage Protection (OVP), Under-Voltage Lockout (UVLO), and Open-Loop Protection.
Limitations:
* Limited Power Range : CRM operation leads to high peak and RMS currents in the boost inductor and MOSFET at high line voltage and high output power, making it less suitable for applications above ~300-400W.
* Variable Switching Frequency : The switching frequency varies with line voltage and load (inversely proportional to inductance). This complicates EMI filter design, as the filter must be effective across a wide frequency band.
* Higher Inductor Core Losses : The high ripple current necessitates a larger inductor with a core material capable of handling high-frequency AC flux, which can increase size and cost at higher powers.
* Audible Noise Risk : At light loads, the switching frequency can drop into the audible range (<20kHz), potentially causing inductor or capacitor whine.
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## 2. Design Considerations
Successful implementation of the FAN7529 requires careful attention to several key design aspects to ensure stability, efficiency, and reliability.
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