SystemD_2kW, any interest for an open design? - Page 21 - 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 3rd January 2013, 11:31 AM   #201
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
....vertical through hole SMD cercaps..

4 Layers:
Well, 4 layers would definitely be more fortunate and allow lowest parasitic inductances, but with two layers you can already achieve good results and realize a mostly continuous ground plane design.
And there is a nice advantages of the 2 layer design (beside cost):
You can easily debug every trace. In a 4 layer PCB all inner layers except full planes are unpleasant.
  Reply With Quote
Old 3rd January 2013, 11:40 AM   #202
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
"Mostly continuous" is the issue. Even a small split in the ground plane can increase noise levels by very large amounts unless you are VERY careful with component positioning.
I guess I'm too used to the fact that nearly everything I design for my employer uses 4-layer boards, that apart from the connectors are 95% SMD. It's the easy (but expensive) option of course.
  Reply With Quote
Old 3rd January 2013, 12:54 PM   #203
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Quote:
Originally Posted by Ouroboros View Post
"Mostly continuous" is the issue. Even a small split in the ground plane can increase noise levels by very large amounts unless you are VERY careful with component positioning.
..terrible truth in your words..
It will consume some more time to settle the right trade off for my cup of tea with just two layers. No pain, no gain.
  Reply With Quote
Old 3rd January 2013, 02:16 PM   #204
dimitri is offline dimitri  United States
diyAudio Member
 
dimitri's Avatar
 
Join Date: Oct 2002
Location: retired
Send a message via ICQ to dimitri
I would like to mention that the post-filter NFB topology response can be severely impaired when the opamps with finite GBP are taken into account. Here are open loop signals on the outputs of opamps (post #122).
1)VCVS, gain 1000
2)OPA134
3)TL082
Attached Images
File Type: gif openloop-vcvs.gif (12.5 KB, 548 views)
File Type: gif openloop-opa134.gif (13.1 KB, 543 views)
File Type: gif openloop-tl082.gif (12.1 KB, 539 views)
  Reply With Quote
Old 3rd January 2013, 04:08 PM   #205
dimitri is offline dimitri  United States
diyAudio Member
 
dimitri's Avatar
 
Join Date: Oct 2002
Location: retired
Send a message via ICQ to dimitri
Previous plots were calculated for R104=47k. Attached are simulations for correct value R104=4.7k
1)VCVS, gain 1000
2)OPA134
3)TL082

Charles, what was your target for phase margin?
Attached Images
File Type: gif openloop-vcvs-4.7k.gif (11.6 KB, 515 views)
File Type: gif openloop-opa134-4.7k.gif (12.4 KB, 509 views)
File Type: gif openloop-tl082-4.7k.gif (12.3 KB, 15 views)
  Reply With Quote
Old 3rd January 2013, 04:11 PM   #206
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Hi Dimitri !
Absolutely right. Charles is implementing the D portion in the forward path with OPamps, in order to avoid the caps in the feedback. He does not like feedback caps, because in many designs their values turn very small and it is hard to get types which are welcome in the audio path.

Some insights of my design:
I am not afraid of the caps in the feedback, because I found simple ways to keep the values large enough which allows to get preferable cap types easily.
But I am generally afraid of running the D-portion through the OP amps.
This concern is independent from an implementation with feedback caps or in the forward path.
In case your OP amp is to slow, the oscillation frequency will drop remarkably below the theoretic value . The triangular shape of the carrier will be impacted and consequently distortion will go up.
Furtheron it can be expected that large HF sloping would activate multiple additional distortion mechanisms inside the slow OP amp itself.
For all these reasons I am running the D-portion through the common base arrangement of the BJTs only (post#151).
And already in my configuration a TL082 would be much to slow and an OPA2134 still slightly to slow. The NE5532 is really the limit of acceptable speed. Real measurements with NE5532 showed that in terms of HF accuracy high voltage levels are more critical rather than high output currents.
Consequently I designed the loop on purpose with small HF voltage at the OP amp, but make use of the driving capability to keep the gain behind the OPamp reasonably high. Last but not least I have to drive the NE5532 with low impedances, otherwise its low differential input impedance would divide down the signal and the results would deviate from what the GBW graph in the data sheet makes us think.
Also the shaping network (R220, C209) is a questionable attempt, when using the NE5532. This network is more intended for upgraded builds with LM4562, or LT1364, or any fast OP amp of the DIYers choice.

In most cases of class D amps running the D-portion through the OP amp would demand to use types like LT1364 or AD2652 in order to avoid increased distortion (clocked & self osc.) and frequency drop (self osc.). Even then I am not convinced that it is a fortunate configuration. High gain for high frequencies through a long chain, might be more critical from perspective of disturbances, I guess.

Last edited by ChocoHolic; 3rd January 2013 at 04:14 PM. Reason: ...to many typos...
  Reply With Quote
Old 3rd January 2013, 04:53 PM   #207
diyAudio Member
 
dudaindc's Avatar
 
Join Date: Sep 2005
Location: Metro Washington DC
Quote:
Originally Posted by Workhorse View Post
Well i prefer 2.4mm thick PCBs which allow me to directly solder SMD 805 chip ceramics vertically from TOP to Bottom layer thru holes[NPTH] in key places and works like a magic.
Wow... I never thought about doing that...

Thanks for sharing Workhorse!
__________________
Rubycon || Nichicon
  Reply With Quote
Old 10th January 2013, 03:51 PM   #208
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
The updated schematic now contains tons of provisions for different comparators including LM361.
Supplies upgraded.
Multiple minor adjustments in interaction with ongoing layout.
(Snubbers, CuBars,...)
Attached Files
File Type: pdf SystemD_2kW_Supply_V0dot2.pdf (72.7 KB, 148 views)
File Type: pdf SystemD_2kW_Modulator_V0dot2.pdf (116.6 KB, 151 views)
File Type: pdf SystemD_2kW_Power_V0dot2.pdf (149.6 KB, 173 views)
  Reply With Quote
Old 10th January 2013, 04:02 PM   #209
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Some screen shoots from my ongoing layout activities...

- Back2Back placement of MosFet and series diode ==> short wide CuBar between drain and cathode.
- SMD rail caps between power devices ==> critical loops minimized with front/back position of tracks with high di/dt and return path.
- Freewheeling diodes on the back side ==> no additional track inductances.
-OCP sensing nodes separately snubbered directly at the IRS20957S.
Attached Images
File Type: jpeg Overview.jpeg (264.5 KB, 174 views)
File Type: jpeg Zoom_all_layers.jpeg (297.5 KB, 202 views)
File Type: jpeg Zoom_front_layer.jpeg (278.1 KB, 156 views)
File Type: jpeg Zoom_back_layer.jpeg (272.2 KB, 171 views)
  Reply With Quote
Old 11th January 2013, 04:44 PM   #210
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Hi Kanwar,
...your request to add the LM361 is leading to a third comparator outline.
Altogether this is breaking up my GND plane below the comparator.
Nevertheless, I would not expect immediate noise catastrophies - still reasonable GND paths close to the signal available. So I am intending to go for it.
Attached Images
File Type: jpeg triplecomp.jpeg (839.0 KB, 145 views)
  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 10:35 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