Principles of High-Frequency Transformer Design

　　When designing high-frequency transformers, it's essential to minimize both leakage inductance and distributed capacitance, as high-frequency transformers in switch-mode power supplies transmit high-frequency pulse square-wave signals. During these transient transmission processes, leakage inductance and distributed capacitance can lead to surge currents, voltage spikes, and even top-end oscillations, resulting in increased losses. Typically, the transformer's leakage inductance is kept within 1% to 3% of the primary inductance.

　　The leakage inductance of the primary coil—transformer leakage inductance arises because the magnetic flux between the primary and secondary coils, as well as within each layer and between individual turns, is not fully coupled.

　　Distribution capacitance refers to the capacitance formed between turns of a transformer winding, between the upper and lower layers of the same winding, between different windings, and between the windings and the shielding layer.

　　The primary winding—this should be placed on the innermost layer, ensuring that each turn of the transformer's primary winding uses the shortest possible wire length. This minimizes the total amount of wire used in the entire winding, effectively reducing the primary winding's inherent distributed capacitance.

　　Secondary Winding—After completing the primary winding, add 3 to 5 layers of insulating padding before starting the secondary winding. This approach helps reduce the capacitance between the primary and secondary windings, while also enhancing the insulation strength between them, ensuring compliance with the required dielectric withstand voltage specifications.

　　Bias winding—whether wound between the primary and secondary coils or placed on the outermost layer—is crucial, as the regulation of a switching power supply depends on whether it adjusts based on the secondary voltage or the primary voltage.