Class-A-Burn: an amp with capacitive feedback divider around MOSFET - Page 4 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 27th August 2009, 06:58 PM   #31
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by Bigun View Post
Still learning....


The latest schematic shows no d.c. path to the gate of the lower MOSFET. Yet it has to be biassed. Is it self-biassing ?
R4

R3 and R5 provide negative feedback by DC current stabilizing working point on the level defined by voltage divider of regulated bials voltage.
  Reply With Quote
Old 27th August 2009, 08:05 PM   #32
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
OK I see it, the output from the Opamp provides the dc biass for the gate of the MOSFET. So you have global resistive feedback and the MOSFET has local capacitive feedback.

So in terms of overall compensation, does C1 or C4 represent Cdom or "how does the compensation work" ?
  Reply With Quote
Old 27th August 2009, 10:17 PM   #33
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Does it matter that feedback caps aren't non-linear in the quite same way
as the gate? Is gate lead or feedback path inductance of any significance?
  Reply With Quote
Old 27th August 2009, 10:53 PM   #34
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by Bigun View Post
OK I see it, the output from the Opamp provides the dc biass for the gate of the MOSFET. So you have global resistive feedback and the MOSFET has local capacitive feedback.
Capacitive feedbacks by voltage in each stage on AC, and DC servo by quiescent current.

Quote:
So in terms of overall compensation, does C1 or C4 represent Cdom or "how does the compensation work" ?
No, for compensation resistors in series with feedback cap only for MOSFET ("gate stopper"), the OpAmp is already unity gain stable, inside.

Quote:
Originally Posted by kenpeter View Post
Does it matter that feedback caps aren't non-linear in the quite same way
as the gate? Is gate lead or feedback path inductance of any significance?
In the quite same way?

Are you kidding, Peter?

Last edited by Wavebourn; 27th August 2009 at 11:03 PM. Reason: mistake corrected
  Reply With Quote
Old 27th August 2009, 11:40 PM   #35
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Let me guess Peter: are you thinking currently of the way to create an Anti-Varactor?
  Reply With Quote
Old 30th August 2009, 07:41 AM   #36
Banned
 
Join Date: Apr 2005
Location: Stockholm
Wavebourn,
Quote:
The world is not perfect!
Certainly not, and you are making it even less perfect.
Now I`m only paying attention to the reverse transfer capacitance, which is a substantial cause of amplifying device nonlinearity. Suffering from voltage amplification, its value can easily change by a factor of 100. While introducing feedback, the signal voltages are effectively shorted out, restricting the bandwidth.
Crss for IRFP054 is 300pF specified @ Vds 25 and 1MHz, now expanded with 10000pF (for comparable laterals 8-10pF @10Vds, 1MHz). This is not the way to achieve linearity, regardless what you get in simulation. Manufacturers and designers desperately try to keep the parasitic capacitances small, as they severely degrade the performance in every application.
  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
SE J/MOSFET Class A Amp, no Feedback widowmaker Solid State 5 11th July 2013 06:38 PM
Resistor values in feedback loop/voltage divider??? vynuhl.addict Solid State 29 13th February 2007 02:05 PM
Capacitive feedback, anyone tried this? scott wurcer Solid State 22 2nd February 2007 11:57 PM
New capacitive motional feedback method Nuutti Multi-Way 31 14th March 2006 02:04 AM
Mosfet class A p/p amp... is feedback required? nobody special Solid State 13 11th September 2004 06:30 PM


New To Site? Need Help?

All times are GMT. The time now is 08:02 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