BOUNDARY MODE PFC CONTROL IC# Technical Documentation: FAN7527BM Power Factor Correction Controller
Manufacturer : FAI Semiconductor
Component : FAN7527BM
Type : Critical Conduction Mode (CRM) Power Factor Correction (PFC) Controller IC
Document Version : 1.0
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN7527BM is a monolithic controller IC specifically designed for building efficient, low-cost, and compact Boost-type Power Factor Correction (PFC) pre-regulators . 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 > 0.99). It operates in Critical Conduction Mode (CRM) , also known as Transition Mode (TM), where the boost inductor current returns to zero at the end of every switching cycle.
Primary Circuit Topology : It is used in a Boost Converter configuration placed between the bridge rectifier and the main DC-DC conversion stage.
* Input : Full-wave rectified AC line voltage (e.g., 85-265VAC).
* Output : Regulated high-voltage DC bus (typically 380-400VDC for universal input applications).
### 1.2 Industry Applications
This controller is a cornerstone component in modern power supplies requiring compliance with international harmonic current emission standards (e.g., IEC 61000-3-2).
* Switched-Mode Power Supplies (SMPS) :
* Desktop PC & Server Power Supplies : Used in 80 PLUS certified ATX/EPS power supplies to meet efficiency and PF requirements.
* LCD TV & Monitor Power Supplies : Essential for flat-panel displays with power ratings from 50W to 300W.
* Adapter/Charger Applications : For high-power laptop adapters, gaming consoles, and industrial battery chargers.
* Lighting :
* High-Intensity Discharge (HID) Ballasts : Improves system efficiency and mains power quality.
* High-Power LED Drivers : For commercial and industrial LED lighting fixtures.
* Industrial Equipment : Used in motor drives, welding equipment, and UPS systems to reduce input current harmonics and improve overall plant power quality.
### 1.3 Practical Advantages and Limitations
Advantages:
* High Power Factor & Low THD : Enables easy compliance with harmonic standards.
* CRM Operation : Eliminates turn-on switching losses in the boost MOSFET (Zero Current Switching - ZCS at turn-on), leading to high efficiency, especially at low line voltages.
* Simplified Design : Internal start-up timer and one-pin multi-function (ZCD, OVP, Disable) reduce external component count.
* Integrated Protections :
* Over-Voltage Protection (OVP) : Protects against open-loop or load-disconnect faults.
* Under-Voltage Lockout (UVLO) : Ensures reliable start-up and shutdown.
* Open-Loop Protection : Detects feedback network failure.
* Low Start-up Current : Minimizes power loss in the start-up circuitry.
Limitations:
* Variable Frequency Operation : In CRM, switching frequency varies inversely with input voltage and load. At high line voltage and light load, frequency can become very high, increasing switching and core losses. This necessitates careful magnetic design and can limit maximum power application (typically up to 300W).
* Higher Peak/RMS Currents : Compared to Continuous Conduction Mode (CCM) PFC, CRM has higher peak inductor current for the same output power, requiring a MOSFET with higher peak current rating and an inductor with a larger core to avoid saturation.
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