IcePower slew rate - 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 23rd April 2009, 08:57 AM   #1
diyAudio Member
 
Join Date: Aug 2008
Default IcePower slew rate

Anybody knows how good the IcePower slew rate is?
I can´t find any figures.

  Reply With Quote
Old 24th April 2009, 02:00 AM   #2
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
The concept of slew rate does not make sense for class D amplifiers, or even for modern linear audio amplifiers at all. It's mostly operational-amplifier related, where it still makes a lot of sense, particularly for non-audio applications, where waveforms can have sharp edges.

Audio people started to consider slew rates many years ago in the context of linear amplifiers that could not produce full output up to 20Khz, (or whatever upper frequency was required in each application, not only audio!). This was because some internal stage would clip before delivering enough current to charge the input capacitance of the next stage fast enough. This results in "triangulation" of the output waveform (when maximum slope is reached).

Nothing of this exists on class D, there are no linear power amplification stages and no triangulation is possible (at least not unless the designer did something really wrong, like using a too big output capacitance with a too low current limit, so unlikely).

Anyway, modern audio amplifiers, both class D and linear, can produce full output well above 20Khz, so they cannot distort the signal in the way the old "slow" ones could do, and by "slow" I mean stuff from LM741 age, 1970s, germanium, tubes with high capacitances (yes tubes!), etc.., so way way outdated!
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 24th April 2009, 10:07 AM   #3
Javin5 is offline Javin5  Switzerland
diyAudio Member
 
Join Date: Mar 2006
Location: Switzerland
Eva, I fully agree. If an amp can produce full power at 20 kHz with low distortion (and full stability at actual speaker loads), that's already in excess of anything that will ever appear in real music signals.

Reminds me a little bit on the damping factor discussion, where totally meaningless numbers are claimed by not including the voice coil resistance.

Kurt
  Reply With Quote
Old 24th April 2009, 11:37 AM   #4
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
I agree with Eva regarding 'slew-rate' in class-D amplifiers. Just consider: the output of the switching transistors (at the node before the output LP filter) is switching from rail-to-rail at a slew rate that is orders of magnitude higher than the rate-of-change of any audio output signal. This switching signal is then low-pass filtered by a passive filter that imposes a 2nd-order response, but cannot cause any slew-rate limiting in itself.

I don't know the details of the self-oscillating modulator used in IcePower amplifiers, and it is conceivable that the modulator stage (if not designed properly) could cause a slew-rate limit, but even if it did, it should be appreciably higher than any audio signal will require.
  Reply With Quote
Old 24th April 2009, 03:49 PM   #5
Gyula is offline Gyula  Hungary
diyAudio Member
 
Gyula's Avatar
 
Join Date: Feb 2004
Location: Kunszentmárton, Hungary
Send a message via Yahoo to Gyula
Quote:
a passive filter that imposes a 2nd-order response, but cannot cause any slew-rate limiting in itself
Just think about the step-responce of that filter. The time-constant of the poles' radius determines the slope.
  Reply With Quote
Old 24th April 2009, 03:56 PM   #6
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
Yes, but it's NOT slew-rate limiting! The L-C filter is a linear circuit element. S-R limiting is caused by a non-linear limiting case.
  Reply With Quote
Old 24th April 2009, 08:40 PM   #7
Pafi is offline Pafi  Hungary
diyAudio Member
 
Join Date: May 2004
Location: Budapest
In this case I agree with Gyula. I think if slew rate is limited, then it's slew-rate limiting. And slew rate is limited indeed. Limitation comes from the supply voltage, but it exist. The saturated element is PW modulator (at 0% or 100%).

In some cases the power bandwidth can be significantly lower then small-signal bandwidth (because of the efficient feedback), so I think SR is a relevant parameter in ClassD also. But it's soooo low (compared to linear amps), that nobody dares to specify it. :-)
  Reply With Quote
Old 24th April 2009, 08:49 PM   #8
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
But where is the triangulation? The output from a class D amp fed with a sinewave is always sine shaped.
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 24th April 2009, 08:56 PM   #9
Mr Evil is offline Mr Evil  United Kingdom
diyAudio Member
 
Join Date: Aug 2004
Location: Behind you
Quote:
Originally posted by Pafi
In this case I agree with Gyula. I think if slew rate is limited, then it's slew-rate limiting. And slew rate is limited indeed. Limitation comes from the supply voltage, but it exist. The saturated element is PW modulator (at 0% or 100%)...
The two are different! I've attached a sketch showing the difference. With a pulse input (top), a low-pass filter results in a curved output (middle), whereas a slew rate limit results in the edges being limited to a fixed slope (bottom).
Attached Images
File Type: png limited.png (5.5 KB, 382 views)
__________________
https://mrevil.asvachin.eu/
  Reply With Quote
Old 24th April 2009, 09:13 PM   #10
Pafi is offline Pafi  Hungary
diyAudio Member
 
Join Date: May 2004
Location: Budapest
At linear amps the SR limit not neccessarily manifested in triangular waveform neither. This is just an idealisation. In reality maximal SR doesn't have to be constant! If there is a limit, then it's done. It can be a function of load impedance, supply voltage, instanteous output voltage, previous states, etc..., but if increasing input doesn't make it faster, then it's slew rate limit. At least I call it this way. (And semiconductor companies too, because otherwise they couldn't specify some of their OPAs.)
  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
Slew rate calculations - how much do I need? peranders Solid State 232 20th November 2011 06:02 PM
slew rate adjustment... chipmonster Parts 7 25th January 2008 10:01 AM
Taming of the slew rate measurement jackinnj Solid State 4 4th February 2007 04:38 AM
Slew rate value Luke123 Chip Amps 5 7th April 2005 12:30 AM
Slew rate Aleph 5 - opinions! bbakota2000 Pass Labs 9 25th March 2004 10:29 AM


New To Site? Need Help?

All times are GMT. The time now is 01:30 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