[SI-LIST] : Is a magnetic field influenced by trace width?

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From: Patrick Lawler (plawler@west.net)
Date: Thu May 03 2001 - 14:53:18 PDT


I have a question concerning the magnetic field generated by
switching currents in a pair of PWB traces.

The situation arises when our PWB designers make traces in our
switch-mode power supply extra wide. I'm concerned that the extra
trace area is generating a larger magnetic field, helping to
couple pulse currents into other parts of the circuit, causing
EMI problems.

Given conditions:
1) A trace pair is on one layer of a PWB.
2) A trace pair carries both outgoing and return currents.
3) The traces carry only DC voltage - there are no switching
voltages.
4) The currents are typical of switch-mode power supplies: a
100kHz fundamental of 0-6Apk, with rise & fall times of 100ns.
5) The air gap between the two traces in each configuration is
the same - only the trace width is different.

Will Configuration 1 generate a larger magnetic field than
Configuration 2?

Configuration 1:
----------------------------
copper copper copper copper
copper copper copper copper
copper copper copper copper
----------------------------
          gap
----------------------------
copper copper copper copper
copper copper copper copper
copper copper copper copper
----------------------------

Configuration 2:
----------------------------
copper copper copper copper
----------------------------
          gap
----------------------------
copper copper copper copper
----------------------------

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