AIR-Core Vs Ferrite-Core Inductor in Class-D amplifiers - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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
Thread Tools Search this Thread
Old 22nd January 2004, 05:39 PM   #11
ukram is offline ukram  Finland
diyAudio Member
Join Date: Jun 2003
Location: Espoo, Finland
I'm planning to take feedback after output filter, and the topology will be self-oscillating (+ maybe some periods of doing nothing in case of small signal, this can be changed in the programmable logic chip). Still that leaves the question open about how much does the speaker and speaker cable capacitance affect self-oscillation? I read somewhere that cable capacitance can be around 1 nF or less. Assuming i use 100 uH and 100 nF in LC filter, it would seem that cable is not a problem, adding only 1nF to the C, but i'm not sure about speakers.
  Reply With Quote
Old 23rd January 2004, 02:08 AM   #12
subwo1 is offline subwo1  United States
diyAudio Member
subwo1's Avatar
Join Date: Jan 2002
Location: North American Continent
I can see usefulness in making the choke .1mH and the capacitor .1uF. The resulting resonant frequency may blend in fairly well in a self-oscillating amp.
  Reply With Quote
Old 23rd January 2004, 09:36 AM   #13
Rhesus is offline Rhesus  Norway
diyAudio Member
Join Date: Feb 2002
Location: Vestfold
There are HUGE emc-problems associated with air core inductors in power switching. So much so that there is no point in trying, if the amplifier has to comply with IEC standards or anything similar.

DIYers can choose to ignore it.

Gapped cores also have some of these properties. To minimize stray magnetic fields in these cores, keep the gap inside the coil, like if you use a double E-core, only gap the center leg.

There are many advantages to using cores, and there are good materials out there to. If you are going for a toroid design, then MPP cores should be high on the list. These are expensive though. The cool-mu cores are a less expensive, and an ok alternative.

Gapped 3F3 or 3C90 ferrite cores are good if you use E-I og E-E combinations.
  Reply With Quote
Old 23rd January 2004, 10:14 AM   #14
diyAudio Member
Join Date: May 2002
Location: Switzerland
There are HUGE emc-problems associated with air core inductors in power switching. So much so that there is no point in trying, if the amplifier has to comply with IEC standards or anything similar.
Since it has been done it must be feasible, althoug not easily I have to admit.
Since we are DIYers and don't want to sell our stuff we don't care that much about complying with any standards.
As long as we don't disturb our neighbour's TV's and hearing-aids etc and we don't take any planes down with our equipment, it is O.K for us. We don't have any chances to test for compliance anyway.

Gapping only the center leg can be quite a task. For us DIYers it is much easier making the gap by inserting some insulating material. The EMC problems we had with a class-d amplifier were definitely not caused by the air gap.

Before I try to get some toroid made out of near unobtainium I get a standard RM, EFT or whatever core and gap it by myself.


  Reply With Quote


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
Copper coil inductor vs. round core inductor tomchaoda Pass Labs 7 21st September 2011 05:42 AM
inductor/choke/air core/ferrite core. . . same thing? poolorpond Pass Labs 24 29th March 2008 11:55 PM
air core inductor vs. iron core inductor WBS Planars & Exotics 5 8th May 2007 12:02 AM
broken ferrite core for smps sss Car Audio 4 13th April 2004 02:30 AM
Ferrite Core Inductors for Crossovers r_s_dhar Multi-Way 25 29th June 2002 06:32 PM

New To Site? Need Help?

All times are GMT. The time now is 12:38 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2