Highly Integrated Green-Mode PWM Controller # Technical Documentation: FAN6747LMY PWM Controller
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component Type : Quasi-Resonant Current Mode PWM Controller
Primary Function : High-performance offline power supply controller for switched-mode power supplies (SMPS)
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## 1. Application Scenarios (≈45% of content)
### Typical Use Cases
The FAN6747LMY is specifically engineered for offline quasi-resonant (QR) flyback converters , making it ideal for applications requiring high efficiency and low electromagnetic interference (EMI). Its primary use cases include:
* AC/DC Power Adapters and Chargers : For consumer electronics such as laptops, monitors, routers, and gaming consoles (typically in the 30W to 120W range).
* Auxiliary (Standby) Power Supplies (PSU) : In desktop computers, servers, and industrial equipment, providing the +5VSB rail.
* LED Driver Power Supplies : For commercial and industrial LED lighting systems requiring stable, efficient constant-voltage or constant-current output.
* Open-Frame Switching Power Supplies : Used in various industrial control systems, appliances, and set-top boxes.
### Industry Applications
* Consumer Electronics : The dominant application area, driven by demand for smaller, cooler, and more efficient chargers/adapters that meet global energy efficiency standards (e.g., DoE Level VI, CoC Tier 2, ENERGY STAR).
* IT & Communications : Power supplies for networking equipment (routers, switches, modems) and computing peripherals.
* Industrial Automation : Control system power modules where reliability and wide input voltage range are critical.
* Lighting : As the driver for mid-to-high-power LED luminaires and retrofit bulbs.
### Practical Advantages and Limitations
Advantages:
* High Efficiency: Quasi-resonant operation minimizes switching losses by enabling valley switching (Zero Voltage Switching - ZVS), leading to excellent efficiency across a wide load range.
* Low Standby Power: Integrated proprietary "Green Mode" function provides burst-mode operation at light loads, significantly reducing standby power consumption to well below 1W.
* Excellent EMI Performance: Valley switching reduces high-frequency harmonic content (dv/dt), simplifying EMI filter design and cost.
* Robust Protection Suite: Includes comprehensive built-in protections:
* Overload Protection (OLP)
* Over-Voltage Protection (OVP)
* Over-Temperature Protection (OTP) via external NTC
* Open-Loop Protection
* Leading-Edge Blanking (LEB) for noise immunity on current sense.
* Frequency Modulation: Jitter function spreads switching frequency spectrum, further reducing conducted EMI.
Limitations:
* Power Range Constraint: Optimized for low-to-mid power flyback topologies. For powers significantly above 150W, full-bridge or LLC resonant topologies with dedicated controllers may be more suitable.
* QR Operation Dependency: Maximum efficiency benefits require careful transformer design to ensure proper valley switching. At very light loads or high line input, the controller may exit QR mode, reducing efficiency.
* External MOSFET Required: Unlike some integrated switcher ICs, this is a controller only, requiring selection and heatsinking of an external power MOSFET.
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## 2. Design Considerations (≈35% of content)
### Common Design Pitfalls and Solutions
1. Pitfall: Transformer Design Causing Poor Valley Locking.
* Symptom: Inefficient operation, audible noise, or erratic switching.
* Solution: Accurately design the transformer's magnetizing inductance (`Lm`) and leakage inductance. Use the IC's minimum off-time (`Toff
