As a core component of power electronic equipment, the distributed capacitance of high-frequency transformers significantly impacts signal transmission quality, affecting signal integrity, electromagnetic compatibility (EMC), and equipment stability. This parasitic capacitance, naturally formed by the insulation structure between conductors, though small in capacitance, can significantly interfere with signal transmission at high frequencies by altering circuit parameters.
Regarding signal integrity, distributed capacitance and line inductance form an LC resonant circuit, directly leading to amplitude attenuation and phase distortion of high-frequency signals. When the signal frequency exceeds 1MHz, the charging and discharging process of the distributed capacitance produces a noticeable phase delay, extending the rise time of square wave signals by 30%-50%. This nonlinear distortion is particularly pronounced in audio signal transmission; the interlayer distributed capacitance of the output high-frequency transformer selectively attenuates high-frequency components, causing uneven transmission of the audio signal across the entire frequency band, ultimately resulting in muffled sound and loss of detail. Experimental data shows that when the interlayer capacitance exceeds 50pF, the resonant peak voltage can reach 3-5 times the normal value, severely damaging signal waveform integrity.
In terms of EMC, the distributed capacitance between the primary and secondary windings constitutes a common-mode interference path, providing a pathway for high-frequency noise to enter the power grid. In medical power supply design, the leakage current exceeding limits caused by such capacitors is particularly critical and must be strictly controlled within 5pF to meet safety standards. Industrial frequency converter cases show that for every 1pF increase in secondary winding distributed capacitance, radiated noise in the 30MHz band increases by 2-3dB, forming a significant source of radiated interference. This interference not only affects the stability of the equipment itself but may also cause coupling interference to surrounding precision instruments, leading to system malfunctions.
Regarding energy transmission efficiency, the periodic charging and discharging process of distributed capacitance generates additional heat loss. In a 5kW switching power supply, losses caused by winding distributed capacitance may account for 5%-8% of the total losses, leading to a temperature rise of over 10°C in the high-frequency transformer. This thermal effect accelerates the aging of insulation materials, creating a vicious cycle and ultimately reducing equipment reliability and lifespan. Especially in high-frequency, high-power applications, the energy loss from distributed capacitance has become a key factor restricting system efficiency improvements.
From the perspective of circuit parameter characteristics, distributed capacitance alters the impedance matching state of the signal transmission link. In high-speed digital signal transmission such as SPI, impedance mismatch caused by distributed capacitance can trigger signal reflection, reducing eye diagram opening and increasing jitter. This effect is particularly pronounced in long-distance transmission or high-speed interfaces, potentially leading to a significant increase in data transmission error rates. For analog signals, the low-pass filtering characteristics formed by distributed capacitance and resistance limit signal bandwidth, causing excessive attenuation of high-frequency components.
From a process design perspective, the presence of distributed capacitance places stringent requirements on the winding process of high-frequency transformers. Traditional lap winding methods, due to large inter-layer voltage differences, easily form large distributed capacitance. However, using Z-shaped winding, by alternately changing the winding direction, can reduce the voltage difference between adjacent layers by 40%-60%; segmented winding technology, by dividing a single winding into multiple parallel segments, effectively reduces the inter-line voltage difference; inserting a Faraday shield between the primary and secondary windings can, in practice, reduce the common-mode capacitance to below 1pF. The essence of these process improvements is to suppress the formation of distributed capacitance by controlling the electric field distribution between conductors.
In terms of material selection, insulating materials with low dielectric constants (ε<3) become a key solution. Novel materials such as modified polyimide films can reduce capacitance by 30%-50%, and boron nitride (ε=4) has begun to be used as a filling medium in the aerospace field. The choice of core material is equally important. While high μ-value cores can broaden the operating bandwidth, core losses increase sharply beyond the optimal frequency range, exacerbating high-frequency performance degradation. Therefore, modern high-frequency transformer design requires a dynamic balance between core losses and distributed capacitance.
