Hi,
While I was cleaning my room I found this coil looking thing and so I surf the net and found out it was called a common mode choke. I have a bunch of this lying around, what are they for? Can I use them for filtering my supply rails? Are they for AC or DC? What should I do with them?
JojoD
While I was cleaning my room I found this coil looking thing and so I surf the net and found out it was called a common mode choke. I have a bunch of this lying around, what are they for? Can I use them for filtering my supply rails? Are they for AC or DC? What should I do with them?
JojoD
JoJoD,
those are very good for blocking common noise (i.e. noise which is present on both wires).
You can use them in your mains AC line input, or if they are beefy enough at the secondary of your transformer before the rectifier.
Make shure the coil doesn't get saturated by to much current going through, as it won't work anymore. Because of this it is not recommanded to use it with DC current.
Dick.
those are very good for blocking common noise (i.e. noise which is present on both wires).
You can use them in your mains AC line input, or if they are beefy enough at the secondary of your transformer before the rectifier.
Make shure the coil doesn't get saturated by to much current going through, as it won't work anymore. Because of this it is not recommanded to use it with DC current.
Dick.
JoJod,
no don't rewind these chokes but use them in your AC line filter as well !
For instance, put then in series with each half of the commonmode choke or after your rectifier diodes for noise surpressing.
As you may understand these chokes work only with high frequencies usually those out of the audio bandwith.
Dick.
no don't rewind these chokes but use them in your AC line filter as well !
For instance, put then in series with each half of the commonmode choke or after your rectifier diodes for noise surpressing.
As you may understand these chokes work only with high frequencies usually those out of the audio bandwith.
Dick.
carefull!
JojoD,
you must ensure that those chokes are really meant for common mode filtering
Check the winding directions on both coils on that torroid. If they are not wound for common mode use, then the flux in the ferrite core would cause huge currents to flow in the core, heating it up and cracking it. The heat could burn the insulation off the windings as well, and cause a mains short. I know because this is exactly what happened to me! I wound the coils for a common mode choke the wrong way and had some nice fireworks
As I understand it, a common mode choke must have negligible flux in the core during normal operation (i.e. the fluxes from the two windings must cancel each other). Only in the presence of common mode noise is some net flux generated in the core. What this means essentially is that the choke acts as a short for differential mode AC, and a high inductance for common mode AC line noise, thus allowing it to pass the normal (diff-mode) AC and block the common mode noise.
- Ashwin
JojoD818 said:
JojoD,
you must ensure that those chokes are really meant for common mode filtering
Check the winding directions on both coils on that torroid. If they are not wound for common mode use, then the flux in the ferrite core would cause huge currents to flow in the core, heating it up and cracking it. The heat could burn the insulation off the windings as well, and cause a mains short. I know because this is exactly what happened to me! I wound the coils for a common mode choke the wrong way and had some nice fireworks As I understand it, a common mode choke must have negligible flux in the core during normal operation (i.e. the fluxes from the two windings must cancel each other). Only in the presence of common mode noise is some net flux generated in the core. What this means essentially is that the choke acts as a short for differential mode AC, and a high inductance for common mode AC line noise, thus allowing it to pass the normal (diff-mode) AC and block the common mode noise.
- Ashwin
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