High frequency transformer principle - design principle

In the design of high-frequency transformers, current transformer, 220v to 380v transformer, the leakage inductance and distributed capacitance of the transformer must be minimized, because the high-frequency transformer in the switching power supply transmits a high-frequency pulse square wave signal. During transmission transients, leakage inductance and distributed capacitance can cause inrush currents and voltage spikes, as well as top oscillations, resulting in increased losses. Usually the leakage inductance of the transformer is controlled to 1%~3% of the primary inductance.                     
The leakage inductance of the primary coil ---- the leakage inductance of the transformer is caused by the magnetic flux between the primary coil and the secondary coil, between layers, and between turns and turns.

The capacitance formed between the distributed capacitance ---- the electronical transformer winding turn, between the upper and lower layers of the same winding, between different windings, and between the winding and the shielding layer is called distributed capacitance.

The primary winding ---- the primary winding should be placed in the innermost layer, so that the length of each turn of the transformer primary winding can be shortened, so that the entire winding is the least wire, which effectively reduces the distributed capacitance of the primary winding itself.

Secondary winding---- After the primary winding is wound, it is necessary to add (3~5) layers of insulation pad and then wind the secondary winding. This reduces the capacitance of the distributed capacitance between the primary winding and the secondary winding, and also increases the dielectric strength between the primary and secondary windings, which meets the requirements of insulation withstand voltage.

Bias winding---- Whether the bias winding is wound between the primary and secondary, or wound in the outermost layer, is related to whether the switching power supply is adjusted according to the secondary voltage or the primary voltage.