common mode choke help - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th March 2011, 04:26 PM   #1
diyAudio Member
 
Join Date: Dec 2007
Default common mode choke help

hi

can someone help me make an intelligent guess on how much current can this common mode choke passes?

outer diameter is: 30mm
height is: 20mm
wire diameter is: 1.5mm

i saw in ebay the one thats almost the same with this has 0.5mH 20A

i wanna use this choke for less than 5A of +-35vdc. is this good for it?

thanks in adv
erwin
Attached Images
File Type: jpg photo.JPG (377.5 KB, 220 views)
  Reply With Quote
Old 9th March 2011, 02:54 AM   #2
jfitz57 is offline jfitz57  United States
diyAudio Member
 
Join Date: Mar 2010
Location: Western Massachusetts U.S.A.
Looks like it will handle 5 amps no problem. Why do you want to use a common mode choke for DC?
  Reply With Quote
Old 9th March 2011, 03:39 AM   #3
diyAudio Member
 
Join Date: Apr 2006
Location: Minnesota
As a rough rule of thumb current density for wire in magnetic devices should not exceed 450 amps/cm^2. Using this your wire is good for 8 amps RMS.

Your core needs to be a low permeability core that will not saturate under DC current.
  Reply With Quote
Old 9th March 2011, 06:50 AM   #4
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by sawreyrw View Post
Your core needs to be a low permeability core that will not saturate under DC current.
For a CMC, this is not required. Quite the opposite in fact.

Small magnetic components having a few turns in direct contact with the ambient air can tolerate current densities in excess of 8A/mm≤, so the 20 amp rating is probably realistic.
  Reply With Quote
Old 9th March 2011, 06:58 AM   #5
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Blog Entries: 100
Send a message via MSN to abraxalito Send a message via Yahoo to abraxalito Send a message via Skype™ to abraxalito
Quote:
Originally Posted by sawreyrw View Post
Your core needs to be a low permeability core that will not saturate under DC current.
As Elvee points out, saturation isn't an issue for CMCs because they're designed to run with very low net flux. The magnetization of the two windings cancels out leaving a very low differential-mode inductance and a much higher common-mode one. Saturation only becomes an issue if the two currents become unbalanced. Low permeability cores though are very useful for filtering out higher frequencies (say above a few MHz) where the higher mu cores give up.
__________________
When you design something for other people you don't have as much motivation to make it beyond excellent - Woz
  Reply With Quote
Old 9th March 2011, 06:59 AM   #6
diyAudio Member
 
Join Date: Dec 2007
thanks guys for all the replies.

i can conclude that i can use these choke for the 5A circuit. thanks

jfitz57, i dont know to be honest. i saw few schematic using it and i would like to try it as it incur less losses in voltage. any insight? idea or suggestion? enlightenment?

erwin
  Reply With Quote
Old 9th March 2011, 10:50 AM   #7
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
You use a common-mode choke when you have a common-mode noise/interference problem. Otherwise, you are simply adding some impedance (mainly winding resistance) to your PSU output impedance. Worth doing when necessary.
  Reply With Quote
Old 13th March 2011, 08:39 PM   #8
diyAudio Member
 
Andersonix's Avatar
 
Join Date: Jan 2004
Location: Silicon Valley
Can one use this type of common mode choke in the CLC section of a linear +/- PS? They're so much cheaper and smaller than an air core inductor....

F.ex. D-K has a Triad Magnetics 2mH 7.5A CMC for under $5: 237-1230-ND
  Reply With Quote
Old 13th March 2011, 09:55 PM   #9
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Not, a common mode choke is for choking common mode noise. It needs the two currents through it to be equal and opposite. It will not act as the L in a CLC filter.
  Reply With Quote
Old 13th March 2011, 11:41 PM   #10
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Blog Entries: 100
Send a message via MSN to abraxalito Send a message via Yahoo to abraxalito Send a message via Skype™ to abraxalito
Quote:
Originally Posted by Andersonix View Post
F.ex. D-K has a Triad Magnetics 2mH 7.5A CMC for under $5: 237-1230-ND
I think what you'll find is that the 2mH is either a single coil's inductance or perhaps the common-mode inductance. It won't give you 2mH at 7.5A because as DF96 says its designed to work with the two coils in opposition. Try to use it as a normal choke (either with just one winding or with both windings in parallel) and it'll saturate long before you get anywhere near 7.5A. That explains why its so much cheaper than an air-cored choke. If you want to do CLC filtering I suggest looking for powdered iron cores - they have a useful increase in permeability over air and saturate at fairly high currents. Ferrites aren't a good choice unless the currents are fairly low.
__________________
When you design something for other people you don't have as much motivation to make it beyond excellent - Woz
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Common-mode choke discussion please stellavox Power Supplies 8 25th July 2009 12:00 AM
Common mode choke model eyalne Tubes / Valves 4 25th February 2008 10:22 AM
common mode choke question schiller Tubes / Valves 4 13th February 2008 09:34 AM
isolation transformer as common mode choke? av-trouvaille Power Supplies 3 4th July 2005 10:33 AM
Common mode filter choke... JojoD818 Solid State 11 27th November 2003 01:59 PM


New To Site? Need Help?

All times are GMT. The time now is 02:51 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2