PFC/PWM controller implements dual-switch flyback power-supply topology with higher efficiency, lower parts count

In the quest for ever-greater power-supply efficiency, especially spanning light load to fully load, along with increasingly required power factor correction (PFC), designers have developed a wide array of topologies which address every source of loss and seek to minimize them.

The latest entry is the Fairchild Semiconductor FAN6920MR, a critical-mode PFC and quasi-resonant current-mode PWM controller targeting all-in-one (AOI) supplies, AC/DC notebook adapters, switching-mode power supplies (SMPS), LED LCD TV backlighting, and even LED area-illumination. A typical application circuit is shown in the figure:

Key features include:

• Integrated PFC and Flyback Controller
• Critical Mode PFC Controller
• Zero-Current Detection for PFC Stage
• Quasi-Resonant Operation for PWM Stage
• Internal Minimum tOFF 5μs for QR PWM Stage
• Internal 10ms Soft-Start for PWM
• Brownout Protection
• High /Low Line Over-Power Compensation
• Auto-Recovery Over-Current Protection
• Auto-Recovery Open-Loop Protection
• Externally Triggering Auto-Recovery Protection (RT Pin)
• Adjustable Auto-Recovery Over-Temperature Protection (RT Pin)
• VDD Pin and Output Voltage OVP (Auto-Recovery)
• Internal Over-Temperature Shutdown (140°C)

Among its other attributes, the dual-switch flyback controller recycles leakage current from the transformer and derating the MOSFET. It uses extended valley detection to detect up to the 9^th or 12^th valley voltage, thus reducing the switching losses at light load. Power consumption is under 0.3 W.

In a 19V/90W reference design measuring 65 x 90 mm, efficiency was between 89 and 91% for both 115 Vac and 230 Vac line inputs, with no-load consumption of about 0.195 W.

Price, packaging, and availability: The FAM6920MR is available now, and is housed in a 16-lead small outline package (SOP); it is priced at $0.82 (1000 pieces).

For more information: contact Fairchild Semiconductor Corp, or click here.