First, interturn capacitance
We know that the basic building block of capacitance is two plates, and when the appropriate voltage is applied between the plates, an electric field is generated between the plates and the charge is stored.
So, can we regard the two adjacent windings of the transformer as connecting plates? The answer is yes, this capacitance is the interturn capacitance of the windings.
Taking the primary windings of high frequency transformer as an example, when the dc bus voltage is added at both ends of the windings, the windings will distribute the voltage equally, and the voltage of each turn is Vbus/N, that is to say, the voltage difference between each turn is also Vbus/N. When the primary MOS switch is switched, this voltage difference will repeatedly charge and discharge this inter-turn capacitor, especially for high-power power supply. Since the number of primary turns is small and the voltage allocated per turn is high, this effect will be more serious. But in general, the effect of interturn capacitance can be almost ignored compared with other distributed capacitors.
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