BPSemi (晶丰明源) AC/DC Power Management

AC/DC converter topology selection depends on power level, efficiency requirements, and cost constraints. For low-power applications (5-20W), simple flyback converters offer cost-effective solutions. For medium power (20-60W), quasi-resonant (QR) flyback provides better efficiency with valley switching. For high power (>60W), active clamp flyback or LLC resonant converters offer the best efficiency. BPSemi provides controllers for all these topologies. Consider input voltage range, output power, efficiency targets, and EMI requirements when selecting topology.

Contact LiTong FAEs for topology selection guidance based on your specific power requirements.

Quasi-resonant operation switches the MOSFET at the minimum voltage point (valley) of the drain voltage ringing, reducing switching losses and EMI. Benefits include: 1) Lower switching losses improving efficiency, especially at light loads, 2) Reduced EMI due to softer switching transitions, 3) Lower voltage stress on MOSFET, 4) Better light-load efficiency. BPSemi QR controllers automatically detect the valley point and adjust switching timing for optimal performance across load conditions.

Use QR controllers for applications requiring high efficiency across wide load ranges. Contact LiTong for QR design support.

Achieving low standby power (<75mW or <30mW for modern standards) requires: 1) Using controllers with burst mode operation at light loads, 2) Minimizing startup resistor current, 3) Using synchronous rectification instead of diode rectification, 4) Optimizing transformer design for low core losses, 5) Implementing X-capacitor discharge circuits. BPSemi controllers feature advanced burst mode operation and low quiescent current to help achieve stringent standby power requirements.

Select BPSemi controllers with burst mode for standby power requirements. Contact LiTong for standby power optimization.

EMI design considerations for AC/DC converters: 1) Input filtering - use common mode chokes and X/Y capacitors, 2) Snubber circuits - suppress voltage spikes on MOSFET drain, 3) Shielding - use shielded transformers for high-power designs, 4) PCB layout - minimize switching loop areas, 5) Spread spectrum - some controllers offer frequency dithering. BPSemi controllers feature frequency jitter and soft switching to reduce EMI. Plan for EMI testing early in the design process.

Follow BPSemi reference designs for EMI-optimized layouts. Contact LiTong for EMI troubleshooting support.

Flyback transformer design involves: 1) Selecting core size based on power level and frequency, 2) Calculating turns ratio based on input/output voltages and MOSFET rating, 3) Determining inductance for desired operating mode (CCM or DCM), 4) Designing winding configuration for low leakage inductance, 5) Selecting wire gauge for current handling and skin effect. BPSemi provides transformer design calculators and reference designs. Work with qualified magnetic component suppliers for custom transformers.

Use BPSemi transformer design tools or contact LiTong for transformer design support and supplier recommendations.