Bridge with two self-osc ClassD amps? - 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 30th October 2005, 11:10 AM   #1
TroelsM is offline TroelsM  Denmark
diyAudio Member
 
TroelsM's Avatar
 
Join Date: May 2003
Location: AARHUS. DK
Default Bridge with two self-osc ClassD amps?

Hi!

I have been following the ClassD-forum for a while but I haven't seen any real info on this topic.

If you take two self-osc-amps and connect them as a bridge then there is no synchronization between the two amp's. There should be a fair chance of getting a lot of noise at the output as a result of inter-modulation.

If the two half's of the bridge is controlled from the same modulator then they would be in sync. But then there's a problem with the feedback as it is pretty complicated to take the feedback from the analog output. Taking the feedback's before the LPF would be easier, but those are out of phase. I can't figure out how this is to be fed back to the modulator?

I've tried to make a bridge that's in sync and with feedback taken before one of the LPF. This works fine but one half of the bridge is running without feedback and this should/could cause a lot of problems.

Does this make any sense? Any inputs/comments are of cause welcome.
  Reply With Quote
Old 30th October 2005, 05:39 PM   #2
diyAudio Member
 
Join Date: Dec 2002
Location: Slovenia
Hi,

here is link to the US patent application 20050068121. I think you will find some ideas in there.

Basically, bridged synchronised modules only need good coupling at the switching frequency. With UcD this can be achieved by placing capacitor across the load and also has added benefit of almost eliminating output HF ripple. For feedback before output filter look at provided link. With one modulator you only need to apply fully differential feedback.

Best regards,

Jaka Racman
  Reply With Quote
Old 30th October 2005, 09:39 PM   #3
TroelsM is offline TroelsM  Denmark
diyAudio Member
 
TroelsM's Avatar
 
Join Date: May 2003
Location: AARHUS. DK
Thanks for you reply.

I must admit that I don't get it... if I bridge two half-bridges and connect a capacitor across the load the to outputs will be in sync and I only need feedback from one of them?

Jaka: "With one modulator you only need to apply fully differential feedback." Is that a diff feedback before or after the LPF? Before the filter the signal is a fast square wave and I cant See how a diff-amp could be fast enough to process this signal.

After the filters the signal is mostly a sine wave and the a "normal" diff-amp would do the job. I get that part, but then there's the problem with the phase-shift in the filter. Please comment.

I'm trying to simulate the freq-response of the amp with a feedback path after the LPF but that's a real pain in PSpice. Wouldn't it give the same result if a take an ideal op-amp and ad a LPF instead of the Self-Osc-ClassD-amp?

Regards

TroelsM

EDIT: Forgot one thing: I can't see the pics/drawings in the patent-link.. Any ideas?
  Reply With Quote
Old 31st October 2005, 07:45 AM   #4
diyAudio Member
 
Join Date: Dec 2002
Location: Slovenia
Hi,

first how to view images .

Cap across load works only with two UcD modules each having it's own modulator. That works because their feedback is taken after the filter.

With one modulator things are no different in full bridge than in half bridge. If you take feedback before output filter you need integrator for the modulator. Just use differential integrator instead of a single sided one.

You are right about the model, but results are accurate up to the one half of the switching frequency (in clocked designs).

A little more accurate model is presented below. It takes bidirectional power flow into account, so it also models power supply pumping in half bridge.

*
* Snchronous Buck power stage operating in continious mode.
* Based on Generalized Switched Inductor Model from
* Sam Ben-Yaakov presented on APEC03.
* Translated to LTSpice.
* Includes duty cycle limiting from 1% to 99%
*
.subckt YaakovSynchronousBuck Vin+ Vin- a gnd Din
Rinductor 2 1 {Rinductor}
Lmain gnd 2 {Lmain}
RswU b Vin+ {Rsw}
BEDoff Doff gnd V=table((1-V(Don)),0.01,0.01,0.99,0.99)
BGa gnd a I=I(Lmain)
BEL 1 gnd V=(V(a,b)*V(Don)+V(a,c)*V(Doff))
BGb b gnd I=I(Lmain)*V(Don)
BGc c gnd I=I(Lmain)*V(Doff)
RDin Din gnd 1Meg
BEDon Don gnd V=table(V(Din),0.01,0.01,0.99,0.99)
RswL c Vin- {Rsw}
.param Lmain = 100uH
.param Rinductor = 100m
.param Rsw = 100m
.ends YaakovSynchronousBuck

More about the model can be seen here.


Best regards,

Jaka Racman
  Reply With Quote
Old 31st October 2005, 11:40 AM   #5
diyAudio Member
 
darkfenriz's Avatar
 
Join Date: Jun 2004
Location: Warsaw
Default Re: Bridge with two self-osc ClassD amps?

Quote:
Originally posted by TroelsM

If the two half's of the bridge is controlled from the same modulator then they would be in sync. But then there's a problem with the feedback as it is pretty complicated to take the feedback from the analog output.
Wait till Nelson invents self-oscilating class D super symetry.

  Reply With Quote
Old 31st October 2005, 11:33 PM   #6
TroelsM is offline TroelsM  Denmark
diyAudio Member
 
TroelsM's Avatar
 
Join Date: May 2003
Location: AARHUS. DK
Default ehh..?

I'm sorry but I don't get it. Please see the attached picture.
Circuit 1 is a standard diff. int. but it cannot be used here without some modification. Curcuit 2 is my first idea, but I cant figure out if this is the right way to go?

The "OutputA" and "OutputB" are the feedback's from each side of the bridge before the LPF's.

If anyone could recommend literature about this topic I would be glad.

Regards

TroelsM

EDIT: I can't see the pic.. only a red cross? Can you see it?
  Reply With Quote
Old 1st November 2005, 06:43 AM   #7
diyAudio Member
 
Join Date: Dec 2002
Location: Slovenia
Sorry, pic is missing.

Best regards,

Jaka Racman

edit: another patent that can make things clearer :
6707337
  Reply With Quote
Old 1st November 2005, 08:35 AM   #8
TroelsM is offline TroelsM  Denmark
diyAudio Member
 
TroelsM's Avatar
 
Join Date: May 2003
Location: AARHUS. DK
Circuit 1 and 2

Regards

Troels

EDIT: The problem was a cookie I had blocked in IE. Which is it?
Attached Images
File Type: jpg diffint_2.jpg (20.8 KB, 918 views)
  Reply With Quote
Old 4th November 2005, 10:32 AM   #9
Kenshin is offline Kenshin  China
diyAudio Member
 
Kenshin's Avatar
 
Join Date: Jan 2005
Location: China
Default Re: Re: Bridge with two self-osc ClassD amps?

Just Hypex's full bridge ucd idea in technical information on their site?

differential in / differential out power comparator + differential NFB
Quote:
Originally posted by darkfenriz


Wait till Nelson invents self-oscilating class D super symetry.

__________________
Ideal OP doesn't make perfact linars but make perfact switchers.
  Reply With Quote
Old 4th November 2005, 01:31 PM   #10
Account Disabled
 
Join Date: Feb 2004
Send a message via AIM to classd4sure Send a message via MSN to classd4sure
Default Re: Re: Re: Bridge with two self-osc ClassD amps?

Quote:
Originally posted by Kenshin
Just Hypex's full bridge ucd idea in technical information on their site?

differential in / differential out power comparator + differential NFB

Exactly. They don't sell such a beast though, but there's enough info on here that you can possible make your own. I made a few sims to that effect. However the half bridge is just as good.

If you wait for others to do for you you'll be waiting a long time, and honestly I don't find IcePower all that impressive, could we for instance expect super symetrical smoking zobel's? Nah thank you.

KM has done excellent work as a scholar, his papers are excellent, but I think IcePower could well be refined, and there hasnt' been anything new from him in awhile, so don't hold your breath.

I think it far more productive to give someone who's interested a little push and a tip here and there, they're likely to produce something long before some commercial fat cat, and even be willing to share with those who've helped them get there, whereas with the commercial fat cat's we're lucky if we can even steal it off a shelf.
  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
The difference of Push-pull,Half-bridge,Full-bridge digi01 Chip Amps 0 8th September 2006 02:10 AM
LED meter bridge for power Amps swagboy Solid State 2 17th June 2005 05:40 PM
Help needed - H-bridge, ClassD output stage IC for digital amplifier gretzteam Digital Source 12 19th January 2003 06:08 PM
Help needed - H-bridge, ClassD output stage IC for digital amplifier gretzteam Solid State 0 16th January 2003 12:32 AM


New To Site? Need Help?

All times are GMT. The time now is 07:19 AM.


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