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common mode choke question

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#2
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.
 
#3
Re: Common Mode Choke

[email]artnace@cox.net[/email] said:
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.
Click to expand...

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
 
#4
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
 
#5
smoking-amp said:
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
Click to expand...


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

Best,

Jan Didden
 
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