A filter is a circuit designed to selectively separate or eliminate a frequency or range of frequencies that is desired for the proper operation of a device or system.
Filters can be subjected to all sorts of Impulses and Surges. Filters are used to remove the undesirable frequency components for the suitable operation of some systems.
Many times it is necessary to provide protection when using a filter. The filter will usually provide the frequency control required but due to transients and the pulse response of the filter it may be necessary limit the input and to control the output when the filter is connected to a sensitive load,
The same logic can be applied to High Pass and Band Pass filters, an example follows:
In addition if the performance is not as desired and the let-thru voltage is too high, it may be prudent to add a second TVS in parallel at the location needed.
These TVS as applied to filters can also be applicable to any other type of protection that is required.