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

Class D Switching Power Amplifiers and Power D/A conversion

Composite amplifier with Class-D
Composite amplifier with Class-D
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 15th August 2017, 03:53 AM   #11
jeff5may is offline jeff5may  United States
diyAudio Member
 
Join Date: Apr 2015
Location: kentucky USA
Send a message via Yahoo to jeff5may
Your question is flawed. If you look into class D amp design, they indeed have op-amps and other linear devices embedded in them. As with class A and AB amplifiers, crappy linear componentry is a recipe for crappy sound. As Eva has stated, there are subjective and objective elements to the answer of your question. Yes, you can do it, but how is another question. Your answer lies in your domain.
  Reply With Quote
Old 15th August 2017, 05:41 AM   #12
benb is offline benb  United States
diyAudio Member
 
Join Date: Apr 2010
Quote:
Originally Posted by b_force View Post
Composite amplifiers with Class-A or Class-(A)B are a well known technique to extensively improve the total performance of a system.

I was wondering if this could be used with a Class-D output stages as well?
What are the practical (and theoretical) limits and issues?

So in other words, using an high performance (linear) opamp with a Class-D output stage in the loop.
It may help to have an intuitive feel for how an all-linear (okay, almost-linear) composite amplifier works. I resist the claim that I have this, but I remember reading through much of the MyRef and similar threads for composite chip-amps.

Composite amps have a lot of careful compensation for the increasing phase shift with increasing frequency (this happens with each amplifier alone, and cascading two amplifiers complicates the situation). I recall the use of 1 percent components in places where 20 percent would good enough to make a stable single-amplifier circuit (well, a single-amp circuit doesn't even have those intermediate 'places', but I hope the point comes across).

The phase shift of a Class D amplifier is way beyond that of most linear amps, due to several things. There's the input sampling, which causes the output to be an inherently delayed version of the input. Then there's the output filter, often a two-pole (inductor and capacitor) circuit which adds its phase shift, and then the feedback is taken from that point. The output must be low-pass filtered for many reasons - the one pertinent here is that you can't use the raw output, a PWM'ed square wave, as feedback for a linear amplifier.

I suppose the way to do this is to plot both gain and phase shift with frequency of a Class D amp, and figure out what kind of response the other amplifier would need to have to prevent the gain/phase shift situation that would give oscillation. As I mentioned, composite amps already use high precision components to "work right" and be flat up to 20kHz. No doubt it would be that much more difficult for a Class D composite amp. Yes, you could "do it" but with the much greater accuracy needed, things such as adding shielding (thus changing the capacitance to ground) and temperature variation (causing slight component value changes) may be enough to make the circuit unstable.
  Reply With Quote
Old 16th August 2017, 04:22 AM   #13
bimbla is offline bimbla
diyAudio Member
 
Join Date: Jun 2002
Location: Where work is
Quote:
Originally Posted by doctormord View Post
I wonder if the same principle can be applied to feedback the load current instead of output voltage.
  Reply With Quote
Old 16th August 2017, 02:46 PM   #14
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
This plot shows phase shift of state-of-the-art class D modulator (post-filter feedback), a constant 6.7us delay across the audio band (equivalent to 2.3mm), frequency response deviation is +/-0.05dB, output impedance at 20khz is less than 0.005 ohms.
Attached Images
File Type: png class_D_phase_shift.png (3.5 KB, 72 views)
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 16th August 2017, 03:11 PM   #15
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
And this plot shows same modulator in action:
- Magenta trace: input voltage
- Green trace: output voltage
- Red trace: PWM
- Cyan trace: current (load: 100uH+4r load simulating a tweeter)
- Blue trace: input to comparator
- Grey trace: integrator volt
- Dotted rectangle: phase shift, indicated at bottom left.

No ornaments.
Attached Images
File Type: png class_D_phase_shift_2.png (48.8 KB, 70 views)
__________________
I use to feel like the small child in The Emperor's New Clothes tale

Last edited by Eva; 16th August 2017 at 03:14 PM.
  Reply With Quote
Old 17th August 2017, 03:42 AM   #16
jeff5may is offline jeff5may  United States
diyAudio Member
 
Join Date: Apr 2015
Location: kentucky USA
Send a message via Yahoo to jeff5may
POw! And there you have it folks. Happy birthday.
  Reply With Quote

Reply


Composite amplifier with Class-DHide 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
Modulus-86: Composite amplifier achieving <0.0004 % THD+N. tomchr Vendor's Bazaar 2405 13th September 2017 06:10 AM
composite amplifier design: advice and thoughts before I start please. mondogenerator Chip Amps 37 2nd October 2015 07:37 PM
V.2012 PRO. Composite Audio amplifier waso Solid State 22 17th February 2015 03:32 PM
Composite amplifier in class A Shaq888 Headphone Systems 0 5th May 2013 12:13 PM
The Composite / Hybrid- Linear + Switching Power Amplifier Craig405 Solid State 27 10th March 2011 01:45 PM


New To Site? Need Help?

All times are GMT. The time now is 03:31 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki