Highly Integrated Green- Mode PWM Controller # Technical Documentation: FAN6754MRMY PWM Controller
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component : FAN6754MRMY
Description : Highly Integrated, Low-Power, Current-Mode PWM Controller for Quasi-Resonant Flyback Converters
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## 1. Application Scenarios
### Typical Use Cases
The FAN6754MRMY is specifically engineered for offline switch-mode power supplies (SMPS) requiring high efficiency and low standby power. Its primary function is to serve as the control core in quasi-resonant (QR) flyback converter topologies. Key use cases include:
* AC/DC Adapters and Chargers : For consumer electronics such as laptops, monitors, routers, and small appliances. The controller's ability to operate in a variable-frequency, valley-switching mode minimizes switching losses, making it ideal for adapters with wide input voltage ranges (e.g., 90-264VAC).
* Auxiliary/Standby Power Supplies : In larger systems like TVs, servers, or industrial equipment, where a highly efficient, low-power (<30W) rail is needed for standby or control circuitry. Its proprietary "Green Mode" function dramatically reduces switching frequency under light-load conditions, achieving excellent standby power performance, often below 100mW.
* LED Driver Power Supplies : For low-to-medium power LED lighting applications where constant voltage or constant current output with high power factor (when combined with external circuitry) and good efficiency is required.
### Industry Applications
* Consumer Electronics : Power supplies for TVs, set-top boxes, audio equipment, and gaming consoles.
* IT & Communication : Adapters for networking equipment (routers, modems), desktop PC standby power, and peripheral devices.
* Industrial Controls : Low-power rails for sensors, relays, and microcontroller boards within larger systems.
* Lighting : Drivers for residential and commercial LED lighting fixtures.
### Practical Advantages and Limitations
Advantages:
* High Efficiency Across Loads : QR operation reduces turn-on switching losses by switching at the valley of the drain voltage. The proprietary Burst Mode operation at very light loads minimizes switching and gate drive losses.
* Low Standby Power : Integrated functions like start-up current source, frequency reduction, and burst mode enable designs to meet stringent international energy efficiency standards (e.g., ENERGY STAR, CoC, DoE Level VI).
* Robust Protection Suite : Integrates multiple protections including Overload Protection (OLP), Over-Voltage Protection (OVP) with latch or auto-restart, and Over-Temperature Protection (OTP) via an external NTC. This enhances system reliability.
* Minimal External Components : Internal high-voltage start-up circuit eliminates the need for an external start-up resistor, saving board space and reducing power loss.
* Improved EMI Performance : Valley switching and frequency jittering help spread EMI spectrum, simplifying filter design.
Limitations:
* Power Range Constraint : Optimized for low-to-medium power applications (typically up to 30-40W). For higher power flyback designs, other controllers or topologies may be more suitable.
* QR Mode Limitation : At very high input voltage or very light load, the switching period may become shorter than the controller's minimum off-time, forcing operation in a fixed-frequency mode, which can slightly reduce efficiency under those specific conditions.
* Design Complexity for Peak Performance : Optimizing the feedback loop, transformer design (especially leakage inductance), and valley-lockout timing requires careful consideration to fully exploit QR benefits.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Poor Efficiency at Light Load :
* Pitfall : Not properly tuning the `FB
