Single Synchronous Buck PWM Controller# Technical Documentation: FAN6520AM Power Factor Correction (PFC) Controller
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component Type : Critical Conduction Mode (CrM) Power Factor Correction (PFC) Controller IC
Document Revision : 1.0
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## 1. Application Scenarios
The FAN6520AM is a specialized integrated circuit designed to implement high-efficiency, low-component-count Power Factor Correction (PFC) stages 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 > 0.99 typical) and minimizing harmonic current distortion to comply with international standards such as IEC 61000-3-2.
### Typical Use Cases
* Front-End PFC Pre-regulators : The most common application is as the control core for a boost converter topology positioned between the AC line rectifier and the main DC-DC conversion stage (e.g., a resonant LLC converter or a forward converter).
* Standalone PFC Modules : Used in modular power systems where PFC is a distinct, separable function.
* Critical Conduction Mode Operation : The IC operates the boost inductor in boundary conduction mode (transition between continuous and discontinuous modes). This ensures the boost diode turns off at zero current, eliminating reverse recovery losses, which is ideal for medium-power applications (typically 100W to 300W) .
### Industry Applications
1. Switched-Mode Power Supplies (SMPS) :
* Desktop PC & Server Power Supplies : A mandatory component in Silver, Gold, and Platinum-rated PSUs (80 PLUS certification) to meet efficiency and PF requirements.
* Industrial Power Systems : For machinery, motor drives, and automation equipment requiring clean input power and compliance with utility regulations.
* Telecom & Networking Equipment : Routers, switches, and base station power systems.
2. Consumer Electronics :
* Flat-Panel TV & Monitor Power Adapters : Especially in models over 32 inches where regulatory compliance and efficiency become critical.
* Gaming Consoles & High-End Audio/Video Equipment .
3. Lighting :
* High-Intensity Discharge (HID) Lamp Ballasts .
* High-Power LED Driver Power Supplies .
### Practical Advantages and Limitations
Advantages:
* High Efficiency : CrM operation minimizes switching losses and eliminates diode reverse recovery losses.
* Simplified Design : Internal start-up timer, one-pin error amplifier, and integrated functions reduce external component count.
* Inherent Overvoltage Protection (OVP) : Robust protection against open-loop conditions.
* Low Total Harmonic Distortion (THD) : Excellent input current waveform shaping.
* Disable Function : Allows for system power management and low standby power modes.
Limitations:
* Power Range Constraint : CrM operation becomes less optimal at very high power levels (>500W) due to increasing peak currents and EMI challenges; Continuous Conduction Mode (CCM) controllers are preferred there.
* Variable Frequency Operation : Switching frequency varies with line voltage and load, complicating EMI filter design compared to fixed-frequency controllers.
* Audible Noise Risk : At light loads, the switching frequency can drop into the audible range (<20kHz), potentially causing inductor/transformer noise.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Inductor Saturation .
* Cause : Using an undersized or poorly specified boost inductor. In CrM, peak inductor current is high.
* Solution :
