Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

LL1540 tolerate DC (no current)???
LL1540 tolerate DC (no current)???
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 12th May 2014, 12:21 PM   #1
DIYspaceW is offline DIYspaceW  Slovenia
diyAudio Member
Join Date: May 2009
Location: Slovenia
Default Lundahl LL1540 tolerate DC (no current)???

I want to use fixed bias for an output stage, so I dont know if the secondary can tolerate DC voltage bias?

I assume it can, cos there will be no current just voltage,
what you say?

Last edited by DIYspaceW; 12th May 2014 at 01:48 PM.
  Reply With Quote
Old 14th May 2014, 09:19 PM   #2
John Luckins is offline John Luckins  Europe
diyAudio Member
Join Date: Jul 2009
Location: Northants UK
That will depend upon the extent of the bias voltage. Each secondary of the LL1540 has 800 ohms static resistance and any DC across that will deliver a direct current through it that will, if great enough, saturate its core. Even low values will reduce the transformers AC linearity and headroom. The maximum AC headroom spec will give an indication of how much combined DC and peak AC voltage the secondary can tolerate before saturation, i.e. the peak of the B-H curve, but the distortion will increase as the voltage approaches this. Using an equal but opposite DC bias on the other secondary winding will prevent this and is what is done in push pull circuit inputs. In fact some quite good examples of this come up when you look at the google images for LL1540.

  Reply With Quote
Old 15th May 2014, 07:27 AM   #3
DIYspaceW is offline DIYspaceW  Slovenia
diyAudio Member
Join Date: May 2009
Location: Slovenia
Thank you John,
you proprably right!
  Reply With Quote
Old 20th May 2014, 08:50 AM   #4
lcsaszar is offline lcsaszar  Hungary
diyAudio Member
Join Date: Mar 2004
Location: Budapest, Hungary
I can't imagine a DC voltage without current on a transformer
  Reply With Quote
Old 20th May 2014, 06:45 PM   #5
Monte McGuire is offline Monte McGuire
diyAudio Member
Join Date: Jul 2013
LL1540 tolerate DC (no current)???
oshifis and the original poster: By 'DC voltage' this could be a DC voltage, relative to ground, that is common to both ends of a winding. In other words, the winding is floating at some voltage other than 0V, but there is no net DC across the coil, so there is no DC current through the coil. If that's the case, it's OK - all transformers are meant to have common mode isolation at DC.

If there is any DC potential _across_ a winding, then there will be DC current through the winding, and that's generally not good, unless the transformer is specifically designed for it (such as the gapped transformer used in the single ended Neve output stage) or if it is cancelled by an opposing flux induced into the core by another winding (as John Luckins described).
  Reply With Quote


LL1540 tolerate DC (no current)???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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
DC-DC variable voltage and current lab power supply bengaltiger Power Supplies 13 1st August 2012 08:50 PM
Efficient current limiting for a dc/dc SMPS? audiodane Power Supplies 10 29th May 2009 01:58 PM
12V DC/DC for amplifier. Current limiting? Pierre Power Supplies 22 1st May 2007 11:46 AM
Giant Heatsink - How large an Aleph X will it tolerate? batee Pass Labs 23 31st March 2004 06:36 AM

New To Site? Need Help?

All times are GMT. The time now is 06:22 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio