Due to the large number of winding layers, the transformer will produce distributed capacitance. When operating at high frequency, these distributed capacitances will have a great impact on the working state of the transformer, such as EMC deterioration, transformer heating, etc. So it's important to understand these distributed capacitances.

1. Winding inter-turn capacitance

The capacitance generated between two adjacent windings of the transformer is the winding inter-turn capacitance. The inter-turn capacitance may change the insulation strength between windings during high-voltage output. Especially in single-slot bobbins, it may cause inter-turn breakdown and short circuit in severe cases.

In order to reduce the inter-turn capacitance, you can choose enameled wire with a lower dielectric constant, you can also increase the distance between the winding turns, or you can use a multi-slot skeleton for segmented winding. Overall, the influence of inter-turn capacitance is almost negligible compared to other distributed capacitances.

2. Interlayer capacitance of winding

< p>Interlayer capacitance refers to the capacitance between the layers of each individual winding of the transformer. A transformer with more than 2 winding layers is required. The interlayer capacitance accounts for a large proportion of the total distributed capacitance of the transformer, which will increase the voltage stress on the MOSFET and secondary Diode and worsen the EMC.

There are many ways to reduce interlayer capacitance. You can increase the distance between winding layers, such as using triple insulated wires; you can also choose a bobbin with a wider winding area; you can also use the cross-stack winding method. Reduce interlayer capacitance. Each method has its advantages and disadvantages.

3. Winding capacitance

Winding Capacitance refers to the capacitance generated between windings, such as the capacitance between the primary winding Np and the secondary winding Ns.

The inter-winding capacitance is an important path for common-mode signal coupling, so it is very detrimental to EMI; the general method to reduce the inter-winding capacitance is to increase the insulation thickness, add a Faraday shielding layer, etc.