Why Do Safety-Certified High-Frequency Transformers Use Flying Leads?

In high-frequency switch-mode power supplies (SMPS), engineers often face a critical design decision: standard pin connections or flying leads? While direct PCB pin soldering seems convenient for automated assembly, high-power and safety-certified applications frequently demand external lead wires (flying leads).

Here is why lead wire design is essential for performance, reliability, and safety compliance.

International safety standards (such as IEC/UL 62368) mandate strict creepage and clearance distances between primary and secondary circuits to prevent high-voltage arcing.

• The Pin Limitation: Standard skeleton bobbins often lack the physical space to maintain required insulation distances when secondary wires wrap directly around base pins.

• The Flying Lead Solution: Extending the secondary winding via insulated flying leads bypasses the base pin array completely, instantly creating a robust physical gap to pass high-voltage isolation tests easily.

High-frequency transformers operating at elevated currents require thick secondary copper wire or triple-insulated multi-strand Litz wire.

• Pin Distortion & Short Circuits: Wrapping heavy-gauge wire around delicate bobbin pins can easily bend or tilt the pins (PIN distortion).

• Soldering Defects: Thick wire termination creates large solder bumps that exceed the bobbin base height, leading to uneven PCB mounting or accidental solder bridges/shorts.

• Reliability: Direct flying leads eliminate stress on tiny terminal pins, providing a direct, reliable connection to the main board.

Modern power electronics prioritize ultra-compact, low-profile form factors.

• Space Efficiency: When internal board space prohibits using a larger, safety-extended bobbin, flying leads allow engineers to use a compact transformer body while fully satisfying safety distance regulations.

• Flexible Routing: Flying leads give PCB designers freedom to place output connection points strategically without being locked into a rigid transformer pinout footprint.

Need high-performance magnetic components tailored to your exact creepage and power requirements?

Dongguan CHIPSEN Electronic Technology Co., Ltd. specializes in R&D and manufacturing of internationally certified magnetic components, including:

• High-Frequency & Wide-Body Safety Transformers

• SMD Power Inductors & Common Mode Chokes

• Toroidal Coils & Color Ring Inductors

• Wireless Charging Coils & EMI Filters

Contact our engineering team today to optimize your custom transformer design!