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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old Today, 10:15 PM   #29031
jneutron is offline jneutron  United States
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Join Date: Jan 2004
Location: In fear
Originally Posted by benb View Post
The proximity effect of WHAT? Something being in proximity to the coil?
No. Proximity effect causes the current within an inductor's turns to shift to one side of the wire. It is essentially the same thing as skin effect, but in a round conductor not close to anything, skinning occurs symmetrically. In a multi turn inductor, the rate of change of the magfield caused by the lots of turns will cause the current to tend to one side of the conductor. This can sometimes be seen on a frequency scan of an inductor, for example the ones in my gallery. An air coil inductor will show as flat up to some frequency, then it will start to decrease as the current starts to shift. When that happens, you can see the resistance also start to increase.

Sometimes this is called skin effect..large inductors run at high frequencies will dissipate more because less of the conductor is actually involved in the transport of current. The correct term is proximity effect, but it is used interchangeably with skin effect. No big deal..

In a gapped toroid for example, when the windings get close to the gap, they will tend to dissipate more because the field lines are seriously "bent" by the gap. Sullivan from Dartmouth College had some good writeups on that, as well as some good write-ups on skin and proximity.

I hate all these smart gadgets..I refuse to buy things that are smarter than me. I've made a list of those things... Cabbage just made the list.

Last edited by jneutron; Today at 10:18 PM.
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