EMI Filter
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`NETWORK-1 EXHIBIT N1 -2008
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`Dell Inc. V. Network-1
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`IPR2013 -003 85
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`ISBN: 0-8211-3924-5
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`This heck is printed an acid—free paper.
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`Copyright ® 2001 by Mnrcel Dekker, Inc. All Righls Reserved.
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`2 C
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`ommon Mode and Differential
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`Mode—Definition, Cause, and
`Elimination
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`There is a wide range of opinion about the definition, cause1 and elimination of
`common mode noise and differential noise. This should cover most of these ideas.
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`2.1. COMMON AND DIFFERENTIAL MODE DEFINIHONS
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`A basic definition of common mode and differential mode is required. Differential
`mode means the normal transfer of energy down the line. In fact, this is also called
`normal mode. A voltage across the line with a current flowing in one direction in
`one wire and the opposite direction in the other wire is normal mode. In this case.
`the Subject is difi'ecnential mode noise. In other words.
`it flows just like normal
`power in the line energy.
`Common mode means a voltage impressed across both. or all. lines. This
`voltage is between all these lines and ground. If there is only one line. then the
`pulse is still between this line and ground. In this unbalanced case. differential
`mode and common mode act the same—between line and ground.
`A current flows in the same direction in all the lines and the return is
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`ground. Again, the subject is common mode noise. I have found that opinions
`vary from EM! guru to guru with little agreement. I hope this section will, at least.
`achieve some agreement among the various groups. Man}r claim that if the
`common mode noise 1roltage impressed on these lines is not exactly,r equal, then
`it is not common mode.
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`15
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`to
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`Chapter 2
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`Two signals cannot be equal on both lines because of differences between
`the lines, the different spacing between the lines and ground. different capacitance
`to ground between the lines. and so forth. Even the EM! filter input feed-through
`capacitors. MDVS. transzorbs. and the like upset the common mode according to
`some groups. Therefore, using that definition, common mode does not exist.
`But common mode does exist, so this definition must be lacking or faulty.
`To sum up, differential mode noise voltage is impressed between the lines
`whereas the common mode noise is across the lines—typically two—and ground
`(Fig. 2.1}.
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`2.2. WHAT CHEATES COMMON MODE NOISE ON THE
`LINE SIDE?
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`The simple definition of common mode noise is a pulse of voltage on both power
`lines of equal value (Fig. 2.1}. This pulse is between the power line wires and
`ground. The EMI filter should be designed to handle this energy. A lightning strike
`on the power line side will create a magnetic field that will cut the two. or more.
`power line wires. This voltage is impressed between the lines and ground.
`This strike will be several quick high-voltage pulses typically around 50 kHz.
`The spacing between the lines may be 3 or 4 feet. depending on the voltage and
`location. creating a slightly different voltage in the two power lines. This voltage
`will be added algebraically to the AC power line voltage on all the lines. All of
`this section assumes that the lines do not fuse and that transformers will take this
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`pulse without failing. if any failure occurs on the line, this reduces the high-pulse
`problem at the filter and equipment following. but the power will be down. It will
`be the difference in the two line voltages feeding the transformer that is trans-
`formed to the secondary. This difference between the lines is now transferred to
`differential mode noise. This difference voltage will be transformed [stepped
`down) to the user side. There will be extra transformer losses due to the
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`high—frequency core losses. These noise pulses are at higher frequencies, accen-
`mating core losses. The skin effect within the transformer and on the lines where
`this high-frequency pulse is being conducted adds to the pulse losses. The primary
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`I.
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`-
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`'v"1
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`.i
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`V2
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`Dlt'rerertiet Hode
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`-
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`Comm lute
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`Flo 2.1 U1. diflerential mode. and v2, common mode.
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