SystemD_2kW, any interest for an open design? - Page 31 - 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 26th February 2013, 08:17 PM   #301
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Hi Dimitri,
good question.
In plain theory: No.
In dirty reality: IMHO less likely than my theory with the magnetic fields. But I have no evidence. It is a guess.
Measured output impedance does not fully correlate with the loop gain in the way we would expect from simple theory. This also is pushing me to the view that the reason must be a mechanism which is not modeled in the sim.
And while doing the measurements I noticed a very obvious and strong mechanism, which is not modeled in the sim: The magnetic fields of the load wires.

Attached the theoretic loop gain with 2R load.
The low inductive resistor during my measurements of the output impedance was 2R.
Attached Images
File Type: jpeg LoopGain_V1dot2.jpeg (123.3 KB, 499 views)
  Reply With Quote
Old 27th February 2013, 03:38 AM   #302
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Choco,

Why i am not seeing a rail to rail film cap like 0.1uF close to switchers.......??

I think you must try it and see the results.....

Kanwar
  Reply With Quote
Old 27th February 2013, 07:44 AM   #303
TroelsM is offline TroelsM  Denmark
diyAudio Member
 
TroelsM's Avatar
 
Join Date: May 2003
Location: AARHUS. DK
Hi Choco

Extremely impressive results for a first-run PCB!

Could you possibly elaborate a bit on how you've done the open/closed loop-gain simulations on the amp?

I'm a bit puzzled by this. - especially when there is more than one feedback-path involved.

Anything you would have changed on the layout so far?

Kind Regards TroelsM
__________________
Need more time...
  Reply With Quote
Old 27th February 2013, 12:19 PM   #304
Cresnet is offline Cresnet  Germany
diyAudio Member
 
Join Date: Nov 2012
Shutting down at 40A? Hypex SMPS delivers 40A?
  Reply With Quote
Old 27th February 2013, 06:28 PM   #305
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Quote:
Originally Posted by Workhorse View Post
Choco,

Why i am not seeing a rail to rail film cap like 0.1uF close to switchers.......??

I think you must try it and see the results.....

Kanwar
Have a closer look to posting#251.
I learned that X7R works better than film, because the losses of X7R bring a pleasant damping by nature. Also they have less inductance than the giant film caps.
Placing multiple X7R SMD right at the rail connections of the switchers, was the first evolution coming from the films. Next evolution was to make this cap(s) center tapped with the GND plane, which ensures that not just rail vs rail becomes calm, but also rails vs. GND
You may also refer to earlier posted simulations, which showed the switching stage including PCB parasitics and rail caps with their equivalent RLC circuit.

And that's what you see in posting #251:
A battery of paralleled X7R caps between the switchers with center tapping to GND.
Weak point is the current capability of the X7R, so the parallel construction is not just helpful for low inductance, but also needed for load sharing.
IMHO even with the two times five parallel caps they are stressed to their limits when hottrodding the amp.
  Reply With Quote
Old 27th February 2013, 07:07 PM   #306
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
@Cresnet:
No, the hypex supply does not deliver 40A, but please be aware that in switch mode converters the supply currents do not equal the output currents.
It is more that the power consumption from the supply equals the output power divided by the efficiency.
For the over current check I put a load which consists of 1uH+47mOhms series connection to the output. Means a load which is close to short circuit.


@Troels
Simply break the loop at the output, where all the feedback paths start.
Insert a voltage source for signal injection.
Analyse the ratio of voltages at both ends of the injection voltage source.

http://www.google.de/url?sa=t&rct=j&...42965579,d.bGE

www.ti.com/lit/an/snva364/snva364.pdf

Ridley Engineering | - AP300 Measurement Techniques

You will find much more literature by searching for: 'loop gain measurement'
  Reply With Quote
Old 27th February 2013, 07:35 PM   #307
TroelsM is offline TroelsM  Denmark
diyAudio Member
 
TroelsM's Avatar
 
Join Date: May 2003
Location: AARHUS. DK
Hi

Yes I got as far as breaking the loop and taking the ratio of input and output, but got a bit confused shortly after that

If I have a amp with post- and pre-filter-feedback then I need to break the loop after the two are joined right? - that would be at the comperator-input for a lot of designs.

It might be very rudimentary , but especially for switching circuits I find it hard to fully grasp. For a selvf-osc D-amp, we have a delay(phase) that is dependent on the output volume (because freq drops as volume goes up) This level-dependent phase confuses me even more as a "small-signal-sim-model" would not be correct.

- Am I misunderstanding things? (please say yes, because I would really like to be able to use a small-signal model)

I'm derailing your thread. Sorry about that. Will go back to my own or start a new.

Kind Regards TroelsM
__________________
Need more time...
  Reply With Quote
Old 28th February 2013, 04:10 AM   #308
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Quote:
Originally Posted by ChocoHolic View Post
Have a closer look to posting#251.
I learned that X7R works better than film, because the losses of X7R bring a pleasant damping by nature. Also they have less inductance than the giant film caps.
Placing multiple X7R SMD right at the rail connections of the switchers, was the first evolution coming from the films. Next evolution was to make this cap(s) center tapped with the GND plane, which ensures that not just rail vs rail becomes calm, but also rails vs. GND
You may also refer to earlier posted simulations, which showed the switching stage including PCB parasitics and rail caps with their equivalent RLC circuit.

And that's what you see in posting #251:
A battery of paralleled X7R caps between the switchers with center tapping to GND.
Weak point is the current capability of the X7R, so the parallel construction is not just helpful for low inductance, but also needed for load sharing.
IMHO even with the two times five parallel caps they are stressed to their limits when hottrodding the amp.
Choco,

In my experience SMD X7R are very poor when it comes to current handling capability, you have to parallel them almost 30X in order to ensure trouble free operation when pumping multikilowatt into 2 ohms load.You haven't seen them blasting and evaporating in the air.

I use 10X 0.1uF film capacitors in order to ensure high current capacity. In my setup i use caps from Rail to Rail and Rail to GND both ways, it helps in taming differential as well as common mode ripple currents as well.


Kanwar
  Reply With Quote
Old 1st March 2013, 08:19 AM   #309
Cresnet is offline Cresnet  Germany
diyAudio Member
 
Join Date: Nov 2012
@ ChocoHolic

Then I think that you get around 620W @ 8R Load?

if I understand you properly, its much harder to make a stable D amplifier @ 8R load?
  Reply With Quote
Old 1st March 2013, 10:55 AM   #310
diyAudio Member
 
Reactance's Avatar
 
Join Date: Jun 2005
Location: Cape Town
Quote:
Originally Posted by Cresnet View Post
@ ChocoHolic

Then I think that you get around 620W @ 8R Load?

if I understand you properly, its much harder to make a stable D amplifier @ 8R load?
Quote:
Originally Posted by Eva
Here are some hints left in 2010 by eva regarding self oscillating amplifiers

Self oscillating loops have several interesting properties. For example, open loop gain is automatically compensated against changes in supply voltage, while in clocked modulators it's a direct function of supply voltage. This makes self-oscillating amplifier performance quite independent of supply rail voltage and sagging and improves PSRR dramatically.

Another advantage of self oscillating loops is that switching frequency is automatically reduced as the output approaches the rails, while keeping constant carrier residual amplitude at the output. This results in the minimum amount of switching events for a given carrier residual amplitude. In other words, switching losses are always as low as possible in self oscillating amplifiers. Switching frequency usually drops 2:1 or more before clipping.

Clocked modulators force the output stage to switch always at the same frequency, resulting in many switching events that are not really required, as the output gets closer to the rails and carrier residual amplitude becomes smaller and smaller.

Additionally, post-filter self-oscillating recycles the extra gain due to filter resonance as open loop gain, thus reducing output impedance (and THD too). In other words, the filter can resonate close to 20khz or even at a lower frequency without compromising frequency response.

Once you have put together a prototype which takes advantage of all this (and more), you don't feel like going back to clocked modulators.

Quote:
Originally Posted by Eva
Your main misconception about PWM amplification is assuming that a non-constant switching frequency results in non linearity.

The absolute minimum switching frequency is 2 times the maximum frequency you want to amplify, 44Khz for 22Khz audio.

The main reason for using 10 times higher frequencies (400Khz) is being able to deal with carrier residual with a 12db/oct output filter.

In clocked modulators carrier residual amplitude is maximum near 0V output and drops to 0 when the output approaches the rails (ugly looking waveform btw). Carrier residual amplitude is modulated by audio signal.

In self-oscillating modulators carrier residual amplitude is almost constant and frequency is smoothly reduced to keep it constant. There is no penalty, it just takes advantage of a "feature" of the output filter that you can't use with a fixed clock.

This reduction in switching frequency does not involve any reduction in the amount of negative feedback, so linearity is unchanged.

Another advantage of variable switching frequency is spread spectrum EMI. Variable switching frequency is now being used in many SMPS control ICs. I nearly always use it in clocked modulators too, for example in PFC.
__________________
There’s nothing worse than the smell of burned output transistors!!

Last edited by Reactance; 1st March 2013 at 11:00 AM.
  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
O2 Front Panel INTEREST POLL your own design Llama16 Group Buys 1 12th September 2012 05:23 PM
Probing interest in My inrush limiting design nattawa Power Supplies 2 19th November 2011 01:08 PM
Custom open baffle 12" woofer - any interest? SimontY Group Buys 2 4th March 2009 01:53 PM
Open baffle design lawbadman Multi-Way 1 17th January 2008 12:15 AM
Open call for suggestions on Open Source DIY Audio Design gfergy Everything Else 1 15th April 2007 07:33 AM


New To Site? Need Help?

All times are GMT. The time now is 11:15 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