Filters on Idle Outputs - 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 10th September 2008, 01:27 AM   #1
diyAudio Member
 
Join Date: Feb 2006
Location: Willy, VIC
Default Filters on Idle Outputs

I can't see that I need a filter on an output which is permanently idle.

By my understanding, the output devices are switching at 50% duty cycle (see illustration in www.national.com/an/AN/AN-1497.pdf) so there is no net current.

I am using a four channel amp (TAA4100A) in a three channel configuration (three phase motor drive). The fourth channel will be permanently mute and I'd like to be able to leave out the extra filter components.
  Reply With Quote
Old 15th September 2008, 03:48 PM   #2
diyAudio Member
 
Join Date: Feb 2006
Location: Willy, VIC
I guess the question I'm asking is "Can anyone see a good reason to include the filter components on the unused channels output?"
  Reply With Quote
Old 15th September 2008, 04:25 PM   #3
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: Milliways
Blog Entries: 4
it's a very good question. I don't have a good answer, but maybe someone here will.

FWIW, with the Tripath chips most of the "harm" done to the output transistors comes from boounce and overshoot in the filter. Thus the protection diodes. Maybe no worries without?
__________________
Take the Speaker Voltage Test!
  Reply With Quote
Old 15th September 2008, 07:00 PM   #4
Pafi is offline Pafi  Hungary
diyAudio Member
 
Join Date: May 2004
Location: Budapest
Quote:
"Can anyone see a good reason to include the filter components on the unused channels output?"
Maybe. The inductive load current can help decreasing switching losses (and radiated noise). But I don't know if it's significant in this particular case.
  Reply With Quote
Old 15th September 2008, 09:10 PM   #5
diyAudio Member
 
theAnonymous1's Avatar
 
Join Date: Feb 2004
Location: Anonymityville
Looking at the sad dead carcus of a Motorola DCP501 board, the TA3020 used for the fifth channel only has the source to drain diodes connected on the unused channel.

The TAA4100 is different than the TA3020 with the MOSFETs being internal, so I don't know how that effects things. Maybe all you need to do is remove the output inductors.

Here are pics of the bottom of the TA3020 single channel and two channel.....

Single channel
Two channel
  Reply With Quote
Old 21st September 2008, 09:44 AM   #6
diyAudio Member
 
Join Date: Feb 2006
Location: Willy, VIC
OK

After some experimenting I can state that the answer is no.

In the absence of the LC filter the TAA4100 goes in to rail to rail oscillation at about 50 kHz (presumably the switching frequency).

I'm prototyping with a board with limited ability to add different parts (the AMP9 from 41 Hz) so the easiest solution is to re-instate the existing filters but I shall do some further experiments with a new board I'm laying out myself.
  Reply With Quote
Old 21st September 2008, 04:38 PM   #7
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: Milliways
Blog Entries: 4
It should certainly be in rail to rail square wave oscillation, - that is how it works - but not a 50KHz. More like 500~700Khz

Was that just a typo?
__________________
Take the Speaker Voltage Test!
  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
Amp for IB with low idle consume wingman Class D 5 23rd July 2009 12:53 PM
P3- P3A idle/ temperature question east electronics Solid State 7 5th January 2009 09:28 PM
Balanced outputs used as inverting & Non-inverting preamplier outputs gni Solid State 4 19th September 2008 03:25 AM
nad 3020b idle current reddish75 Solid State 4 4th July 2008 02:46 PM
JL AUDIO 250/1 idle current Pioneer621 Car Audio 2 24th April 2008 10:31 PM


New To Site? Need Help?

All times are GMT. The time now is 01:42 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