capacitors - RFI suppression
capacitors - RFI suppression
(OP)
Could anyone help me to understand how the capacitors aid in the RFI suppression?
reference of notes, technical papers or websites would be very helpful.
Thanks in advance.
bernie
reference of notes, technical papers or websites would be very helpful.
Thanks in advance.
bernie





RE: capacitors - RFI suppression
So they are helpful in some instances in diverting unwanted high frequency components of a signal or power output to ground within a device to prevent this high frequency component from being radiated as RFI once it leaves the enclosure or circuit board. Sizing and physical placement are crucial to their effectiveness in this application.
RE: capacitors - RFI suppression
General rules of thumb for “RFI” capacitors are:
1. Place the device as close as possible to the point of interest.
2. Provide a impedance for the capacitor to work against (ie resistance/inductance)
3. Lower capacitance ESR (Effective Series Resistance) is usually good from a filtering standpoint but can cause problems in some applications like with switching power supplies.
4. Pay attention to voltage ratings and dielectric characteristics at various voltages
That is all I can think of at the moment. Henry Ott has a good book that explains this material.
http://www.hottconsultants.com/
Most capacitor manufactures also have application notes also.
Regards,
RP.
RE: capacitors - RFI suppression
The aim of a capacitor in RFI suppression is to control the resonant frequency of various circuit elements. In some cases like relay contacts this is to prevent high dV/dt from developing causing sparks that generate interference as well as damage the contacts. In other cases like a power line filter, a series of L-C elements with carefully selected characteristics create a filter that offers a low imeadance to the power line frequency but a high impedance to other frequencies.
A very good book on this topic is "Noise Reduction Techniques in Electronic Systems" by Henry W Ott.