Feedthrough filter, sometimes also known as RF filter. In order to meet the requirements of different occasions, this kind of filter generally has five forms: C-type filter, LC type filter, π type filter, T-type filter and double-t-type filter.
1. C-type filter
C-type filter is composed of three terminal capacitors or through core capacitors, which is suitable for suppressing high-frequency signals. It is a low self induction device to avoid high frequency noise interference to the ground. It is low cost and suitable for high impedance source and high load.
2. LC filter
LC filter is a kind of feed through filter with inductance and capacitance. This kind of filter is typically used in the circuit with low impedance source and high impedance load, and vice versa. Note: the inductor should face the low impedance source
3. π – type filter
π – type filter is composed of two capacitor elements and an inductance element between the two capacitor elements, which shows low impedance to both impedance source and load. π – type filter provides better high frequency filtering performance than C – type and LC – type structure
T-type filter consists of two inductors and one capacitor. The circuit structure shows that the input from any end is high impedance. It is similar to π – type filter in structure, but not widely used in switching field
5. Double T filter
The double-T filter is composed of two T-shaped filters, which is a high-performance filter with strict circuit requirements
It should be noted that the simple through core structure consists of one (C type) or two capacitors (π type) composed of inner and outer electrodes and ceramics. The capacity of the capacitor can be from 10PF and the working voltage can reach 2000vdc. As shown in the figure below is the C-type feedthrough filter, which is plug-in. However, for electronic products with narrow installation space, the use of welding type feedthrough filter is particularly important.