High-Voltage Startup, Quasi-Resonant Operation # Technical Documentation: FAN6300SY High-Voltage Quasi-Resonant Current-Mode PWM Controller
Manufacturer : FAIRCHILD (ON Semiconductor)
Component Type : Integrated Circuit (IC)
Primary Function : High-voltage startup, quasi-resonant, current-mode PWM controller for offline power supplies.
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## 1. Application Scenarios
### Typical Use Cases
The FAN6300SY is specifically engineered for offline switch-mode power supplies (SMPS) requiring high efficiency and low standby power. Its core architecture makes it ideal for implementing quasi-resonant (QR) flyback converters .
* Primary Application : AC/DC Power Adapters and Chargers . It is extensively used in adapters for laptops, monitors, printers, and consumer electronics (e.g., game consoles, set-top boxes). Its ability to reduce switching losses at high line voltages makes it perfect for universal input (90-264VAC) designs.
* Secondary Application : Auxiliary/Standby Power Supplies . Within larger systems like servers, telecom equipment, or industrial controls, the FAN6300SY can power the always-on control logic due to its low startup and operating current.
* Tertiary Application : LED Driver Power Stages . Its precise current-mode control and frequency modulation capabilities are beneficial for constant-current output stages in mid-to-high-power LED lighting drivers.
### Industry Applications
* Consumer Electronics : The dominant market, driven by demand for efficient, compact, and cool-running external power supplies (EPS) meeting global energy standards (e.g., DoE Level VI, EU CoC Tier 2).
* Computing & Peripherals : Power supplies for desktop PCs (standby rail), monitors, and external storage devices.
* Industrial Electronics : Provides reliable, isolated power for control boards, sensors, and communication modules in harsh environments, leveraging its robust high-voltage integration.
* Lighting : Employed in the AC/DC front-end of commercial and industrial LED luminaires.
### Practical Advantages and Limitations
Advantages:
* High Efficiency : Quasi-resonant operation (valley switching) minimizes switching losses, especially at high input voltage and light load, enabling compliance with stringent efficiency regulations.
* Low Standby Power : Integrated high-voltage startup circuit and burst-mode operation reduce no-load power consumption to well below 100mW in typical designs.
* Simplified Design : Integrates a 700V avalanche-rugged startup FET and critical protection features (Overload Protection - OLP, Over-Voltage Protection - OVP, Over-Temperature Protection - OTP), reducing external component count.
* Enhanced Reliability : Built-in frequency jittering reduces EMI filter size and cost. Current-mode control provides inherent cycle-by-cycle current limiting and simplified feedback loop compensation.
* Wide Operating Range : Optimized for universal mains input.
Limitations:
* Topology Constraint : Primarily optimized for flyback converters . It is not suitable for forward, half-bridge, or LLC resonant topologies without significant external circuitry.
* Power Range : Best suited for low-to-medium power applications (typically up to 150W). For higher powers, other topologies (e.g., active clamp flyback, LLC) controlled by different ICs may offer better efficiency.
* Frequency Variation : The switching frequency varies with load and input voltage (quasi-resonant operation). This can complicate EMI filter design compared to fixed-frequency controllers, though jittering helps.
* Minimum Load : Burst-mode operation at very light loads can cause audible noise if the transformer or output capacitors are not properly selected.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Transformer Audible Noise in Bur
