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Old 3rd July 2007, 06:06 AM   #1
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Default common mode choke question

Hallo everyone, does anybody knows how is a common mode (dual chamber bobbin) wound and connected?
Thanks in advance
Greetings from Greece
Konstantinos
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Old 13th July 2007, 04:31 AM   #2
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Default Common Mode Choke

A common mode choke has 2 windings on the same core. Imagine a single inductor on the AC high side with a phasing dot on the left of the coil. Now, place an exact inductor on the neutral line of the AC input with the phasing dot to the left of the coil. Now imagine these 2 coils on the same core and you have a common mode choke. One method of winding one is to "bifilar" wind two coils on a core at the same time. The "start" of the wind is the phasing dot for both coils. A better method and one that has a higher highpot voltage between the coils is to get a segmented bobbin. Wind the first coil in the left segment and the other coil in the right segment with both coils wound in the same direction. Again, the start of each wind is the phasing dot. Add the core to the coil and connect to the circuit as explained above -phasing dots to the left of each coil. Use a high perm core material and do not add any gaps and your good to go.
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Old 11th February 2008, 03:13 PM   #3
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Default Re: Common Mode Choke

Quote:
Originally posted by artnace@cox.net
A common mode choke has 2 windings on the same core. Imagine a single inductor on the AC high side with a phasing dot on the left of the coil. Now, place an exact inductor on the neutral line of the AC input with the phasing dot to the left of the coil. Now imagine these 2 coils on the same core and you have a common mode choke. One method of winding one is to "bifilar" wind two coils on a core at the same time. The "start" of the wind is the phasing dot for both coils. A better method and one that has a higher highpot voltage between the coils is to get a segmented bobbin. Wind the first coil in the left segment and the other coil in the right segment with both coils wound in the same direction. Again, the start of each wind is the phasing dot. Add the core to the coil and connect to the circuit as explained above -phasing dots to the left of each coil. Use a high perm core material and do not add any gaps and your good to go.
Hi Art (?),

If I may revive this thread: if I have a common mode chke, can I connect the two coils in series using it a a simple/single line choke? If so, does it halve the allowed current?

Jan Didden
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Old 11th February 2008, 06:41 PM   #4
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These common mode chokes normally (always) do not have any core air-gap because the two windings are used with opposing currents (cancelling flux in the core). So they have a very tiny ampere-turn rating. Trying to use them as normal single ended chokes will cause them to saturate immediately (ie, with dotted end to un-dotted end series connections). (connecting dotted to dotted ends will of of course give you no inductance, but they will be non-saturating at least!)

In other words, to sumarize, these common mode chokes are completely useless for ordinary (non-common mode) choke use.

Don
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Old 13th February 2008, 10:34 AM   #5
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Quote:
Originally posted by smoking-amp
These common mode chokes normally (always) do not have any core air-gap because the two windings are used with opposing currents (cancelling flux in the core). So they have a very tiny ampere-turn rating. Trying to use them as normal single ended chokes will cause them to saturate immediately (ie, with dotted end to un-dotted end series connections). (connecting dotted to dotted ends will of of course give you no inductance, but they will be non-saturating at least!)

In other words, to sumarize, these common mode chokes are completely useless for ordinary (non-common mode) choke use.

Don

Thank you Don, I suspected it but wasn't sure.

Best,

Jan Didden
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