Schaffner FAQ


Frequently Asked Questions

Q) What do the part numbers mean?

(A) In general the part numbers can be explained as follows:

(Q) How do I determine what the input/output terminations are (termination type)?

(A) All standard input/output terminations can be found on each individual part number datasheet.

(Q) Are low leakage versions available?


(A) For medical applications, there is a requirement to keep leakage current (current flowing to earth) to an absolute minimum. This is mostly achieved by either removing the Y capacitors (connected between phase and earth), but this can lead to a lower performance at higher frequencies (MHz range). Schaffner defines medical grade filters as the B-version.

Capacitors of very small values (pF) can be utilized to gain a better performance while minimizing leakage current. Schaffner defines the low leakage grade filters as the A-version.

(Q) What's the difference between common mode & differential mode noise?


(A) Common mode (or Asymmetrical Mode) is any noise that travels between the earth and phases. Differential Mode (or Symmetrical Mode) is noise that propagates between phases.

(Q) What does insertion loss mean?

(A) The insertion loss is a statement of the filters attenuation characteristics, expressing in decibles (dB) the ratio of noise that would get through without the filter, to that which gets through with the filter installed. Insertion loss varies widely with frequency and with source and load impedances. It is usually presented in the form of a graph or table across the frequency range of interest, using standardized source and load impedances.

(Q) Why are there 4 curves on our insertion loss plots?

(A) On Schaffner insertion loss plots we show the insertion loss to signals based on a 50/50 system and a 0.1/100, 100/0.1 system.

What this means is we show the performance of the filter in an ideal world (50/50) and the insertion loss in a worst-case scenario (0.1/100, 100/0.1). The actual performance of the filter is very dependant upon the impedance of the noise source, but it usually falls somewhere between the worst case and ideal case.

For more information regarding insertion loss plots, please refer to Application Note: CISPR 17 Measurements

(Q) Do Schaffner EMI filters contain the CE mark?


(A) All Schaffner filters are CE marked.

(Q) Who do I contact if I want to purchase Schaffner EMI filters?

(A) Schaffner USA offers national and regional authorized distributors. A list of authorized Schaffner distributors can be found here: Authorized Distributors

For additional sales inquiries and technical support, please contact the Schaffner USA office direct at 732-225-9533.

Schaffner USA also offers a distributor stock check located here: Distributor inventory search

(Q) How do I select the correct filter for my application?

(A) Unfortunately there is no simple way to recommend a filter for an application. A starting point is to determine what the dominant noise sources are within a system and try to select a filter that is suitable. When a filter has been chosen it is essential to test the unit to see how it performs.

Please refer to the components short form catalog and our product range overview poster for an overview of all Schaffner products here: Components Short Form Catalog / Product Range Overview Poster

For additional technical support, please contact the Schaffner USA office direct at 732-225-9533.

Other helpful terms when selecting a filter

A signal (or noise) is made to decrease in intensity (power). An EMI filter attenuates noise, in that the noise coming out is less than the noise going in.

Impedance: The opposition to flow or current put up by a circuit across which voltage has been applied. Impedance varies with frequency and is best considered in relative terms. A filter works best when it impedance in the EMI filter frequency range on the line and load sides is greatly different from the impedance of the line and load circuits to which it is connected (impedance mismatch).

Line Side: The end of the filter to which the power line is connected.

Load Side:
The end of the filter to which the equipment is connected.

Rated Current: The maximum current (rms or DC) that can be continuously passed through the filter without violating safety agency approvals. It is determined by temperature rise limitations. Although this rating is independant of voltage, the differing temperature requirements of several safety agencies may cause a filter to have different current ratings at 115VAC and 250VAC. Operation at less that rated current does not compromise the filters effectiveness.

Rated Voltage: The nominal rms voltage into which the filter is designed to operate, typically 115VAC and 250VAC. Schaffner filters are designed to operate with this voltage continuously applied throughout their lifetimes. However, operation at less than this voltage does not compromise the filters effectiveness.