Filter capacitor use experience

Simple inductive circuits work well in low-impedance circuits, with attenuations exceeding 40 dB, but may not be effective in high-impedance circuits.

The circuit of a single capacitor works well in high impedance circuits, but it works poorly in low impedance circuits.

A multi-element filter will have a good effect, but only if it is constructed correctly, the capacitor should face high impedance and the inductor face low impedance.

Since the capacitor leads have parasitic inductance, resistance, the actual capacitor model is a capacitor, inductor (equivalent series inductance ESL), resistor (equivalent series resistance ESR) series structure, with self-resonant frequency, the capacitor should work at its self-resonant frequency Only then can it work.

It can be seen that the resonant frequency of a general capacitor is very low and cannot be applied to the high frequency and microwave frequency bands. In order to increase the resonance frequency, surface mount capacitors, three-port capacitors, and feedthrough capacitors can be used.

Installation of three-terminal capacitors:

The grounding terminal is as short as possible to reduce the lead inductance of the grounding terminal.

Through the heart capacitor:

Because the ground terminal can be in close contact with the ground, the lead inductance is smaller, so the performance is superior. Feedthrough filters based on feedthrough capacitance are widely used in RF filtering.

The core input and output terminals are connected through the upper and lower grounding plates (namely, the core through the capacitor), which is equivalent to connecting the upper and lower capacitors in parallel to form a total capacitor. Since the ground portion is 360° connected to the ground in the circuit, the grounding inductance is small.

In addition, temperature and voltage have a great influence on the capacitance value.