BOUNDARY MODE PFC CONTROL IC# Technical Documentation: FAN7527BN Power Factor Correction (PFC) Controller
Manufacturer : FAIRCHILD SEMICONDUCTOR (FAIR)
Component Type : Critical Conduction Mode (CRM) Power Factor Correction (PFC) Controller IC
Document Revision : 1.0
---
## 1. Application Scenarios
The FAN7527BN is a specialized integrated circuit designed to implement a high-efficiency, low-cost Power Factor Correction (PFC) stage in AC-DC power supplies. Its primary function 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 (PF). This is crucial for compliance with international regulations like IEC 61000-3-2.
### Typical Use Cases
* Standalone PFC Pre-regulators : The IC is the core controller for a boost converter topology placed between the bridge rectifier and the main DC-DC converter stage. It generates a regulated, high-voltage DC bus (typically 380-400V) from a universal AC input (85V to 265V).
* Switched-Mode Power Supplies (SMPS) : It is ubiquitously integrated into the front-end of medium-to-high power AC-DC adapters, desktop PC power supplies, server PSUs, and telecom rectifiers where input power exceeds 75W.
* LED Driver Systems : Used in high-power, high-performance LED lighting drivers to ensure efficient power usage and meet harmonic current limits.
* Industrial Power Systems : Employed in motor drives, welding equipment, and other industrial systems requiring clean input current and stable high-voltage DC rails.
### Industry Applications
1. Information Technology Equipment (ITE) : Power supplies for servers, workstations, and networking gear.
2. Consumer Electronics : Gaming consoles, large audio/video receivers, and high-wattage external power adapters.
3. Industrial Automation : Control panels, PLC power modules, and test/measurement equipment.
4. Lighting : Commercial and industrial LED luminaires and drivers.
### Practical Advantages and Limitations
Advantages:
* Critical Conduction Mode (CRM) Operation : Also known as Transition Mode (TM). This ensures the boost inductor current returns to zero every switching cycle (Zero Current Switching - ZCS at turn-on), minimizing turn-on losses in the MOSFET and reducing reverse recovery stress on the boost diode. This leads to higher efficiency, especially at low line voltages.
* Inherently High Power Factor : The control methodology naturally forces the average inductor current to follow the rectified input voltage waveform.
* Minimal External Components : The integrated multiplier, error amplifier, and zero-current detector simplify the external circuit, reducing board space and BOM cost.
* Internal Start-up Timer : Reduces power consumption during start-up and provides protection.
* Low Total Harmonic Distortion (THD) : Typically enables designs to achieve THD <10% and PF >0.95 over a wide load range.
Limitations:
* Variable Frequency Operation : In CRM, the switching frequency varies with input voltage and load (highest at low line, full load). This complicates EMI filter design, as the filter must be effective across a wide frequency range.
* Peak Current Stress : The peak inductor and MOSFET current is approximately twice the average input current. This requires components rated for higher peak currents compared to Continuous Conduction Mode (CCM) PFC controllers.
* Power Range Limitation : CRM operation becomes less practical above approximately 300W due to increasing peak currents and frequency range. For higher powers, CCM controllers (e.g., FAN7529) are more suitable.
* Output Voltage Ripple : The discontinuous input current results in higher 100
