Incorrect fetdriving? - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 5th March 2012, 11:06 AM   #1
diyAudio Member
 
Join Date: Mar 2012
Location: Arnhem
Default Incorrect fetdriving?

Hi folks,

I'm busy trying to understand fetdriving.
I tried something in Multisim v10.0

Click the image to open in full size.

This seems to work a bit, but the highside does have a lower amplitude as the lowside.
Any suggestions how to improve this schedule, or which schedule to use otherwise?

My class D is single supplied with 120Vdc.
I have to get 1500W in a 4ohm load.

I'm not a very experienced user of class D equipment, so please try to explain things simple.
  Reply With Quote
Old 5th March 2012, 11:32 AM   #2
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Firs of all: the supply for the high side FET should be floating!
The level shift also bad, see some application notes first.
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 5th March 2012, 12:16 PM   #3
diyAudio Member
 
Join Date: Mar 2012
Location: Arnhem
Quote:
Originally Posted by lorylaci View Post
Firs of all: the supply for the high side FET should be floating!
The level shift also bad, see some application notes first.
Where should the - of the floating supply connected?
And where do I find decent application notes?
I found some application notes, but they're not to helpfull
  Reply With Quote
Old 5th March 2012, 12:16 PM   #4
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
The upper transistor, operating as common base is bad biased. And the diode at the collector of the driver is unnecessary.

Why not to try IR2110?
__________________
LW1DSE

Last edited by Osvaldo de Banfield; 5th March 2012 at 12:18 PM.
  Reply With Quote
Old 5th March 2012, 12:26 PM   #5
diyAudio Member
 
Join Date: Mar 2012
Location: Arnhem
If I understood you guys right, this should be an improvement,
Though I can't find anything about the 'bad-biasing' you spoke about.
I found some application notes, which are poorly explained and because of that not to helpfull.

The only thing I got from those apllication notes, is seeing that they use 2 FETs instead of BJTs.

Click the image to open in full size.

The schedule with some adjustments.
  Reply With Quote
Old 5th March 2012, 01:05 PM   #6
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by Blackdrake View Post
Where should the - of the floating supply connected?
And where do I find decent application notes?
I found some application notes, but they're not to helpfull
Read this:
http://www.ti.com/lit/ml/slup169/slup169.pdf
From page 22 starts the bootstrap drive.
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 5th March 2012, 01:54 PM   #7
diyAudio Member
 
Join Date: Mar 2012
Location: Arnhem
Thank you for that link, there is quite some usefull information in it, though I have no clue how to implement it into my schedule.
I also checked the IR2011, which seems easier to get working in a practical situation.

I'll be busy for a bit with the new information for a while, if I encounter more problems I will post them right away.

Class D is still witchcraft to me afterall.
  Reply With Quote
Old 5th March 2012, 02:14 PM   #8
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
Quote:
Originally Posted by Blackdrake View Post
Though I can't find anything about the 'bad-biasing' you spoke about.
In the first circuit, base is more positive than collector, so it has no room to amplify, then upper MOS is not well drive.
__________________
LW1DSE
  Reply With Quote
Old 5th March 2012, 02:16 PM   #9
diyAudio Member
 
lorylaci's Avatar
 
Join Date: Aug 2008
Location: Dabas, Hungary
Send a message via MSN to lorylaci
Quote:
Originally Posted by Blackdrake View Post
Thank you for that link, there is quite some usefull information in it, though I have no clue how to implement it into my schedule.
I also checked the IR2011, which seems easier to get working in a practical situation.

I'll be busy for a bit with the new information for a while, if I encounter more problems I will post them right away.

Class D is still witchcraft to me afterall.
Read, Read and Read more... until it's is aint witchcraft.
__________________
Olyan nem volt még, hogy ne lett volna valahogy
  Reply With Quote
Old 5th March 2012, 02:25 PM   #10
diyAudio Member
 
Join Date: Mar 2012
Location: Arnhem
Quote:
Originally Posted by lorylaci View Post
Read, Read and Read more... until it's is aint witchcraft.
I will for sure, I think the first knowledge is starting to come:

Click the image to open in full size.

Click the image to open in full size.
Simulation of Loadvoltage and Loadcurrent
  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
Micromega Stage 2 modification - and incorrect info... jono799 Digital Line Level 59 13th June 2011 06:27 AM
post time is incorrect geraldfryjr Forum Problems 4 8th April 2011 03:04 PM
Incorrect Link on Transcendent Sound LuckyLyndy Everything Else 1 18th August 2002 10:02 PM


New To Site? Need Help?

All times are GMT. The time now is 09:30 PM.


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