Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 18th February 2009, 02:35 PM   #1
Dxvideo is offline Dxvideo  Turkey
diyAudio Member
 
Dxvideo's Avatar
 
Join Date: Nov 2003
Location: Turkey
Send a message via Yahoo to Dxvideo
Lightbulb Class A with LME49811...

Hi all,
Do you think is it possible to design a really good 20-25W Class A amplifier with LME49810?
Why I am asking that? Because this opamp has really good THD figure and I guess it has a class A biased driver stage (consider that it has just 9mA output capability while 49810 and 49830 has ~50mA).
So with gate drivers (AN1645 pg:14) two pairs of HEXFETs like IRFP240/9240 can handle 20W or more class A output with 2.5-3A bias..
It would be an easy and good Class A amplifier...
What do you say?
__________________
Best regards,
Ozgur
  Reply With Quote
Old 18th February 2009, 11:34 PM   #2
diyAudio Member
 
Join Date: Nov 2004
Location: Florida
Sounds like a plan.

Are you planning a CCS or Push-Pull Class A output stage?

I'm pretty sure the chip will run on the lower voltage rails, most chips do.

Keep us posted.

Eworkshop1708
__________________
You can call me Mad Professor, building crazy experiments in my Electronics Workshop
  Reply With Quote
Old 19th February 2009, 05:49 AM   #3
Dxvideo is offline Dxvideo  Turkey
diyAudio Member
 
Dxvideo's Avatar
 
Join Date: Nov 2003
Location: Turkey
Send a message via Yahoo to Dxvideo
Yes.. A plan for now!
I will use P-P output stage.. And will feed the LME with higher voltage than the outputs.
Will keep you informed.
__________________
Best regards,
Ozgur
  Reply With Quote
Old 19th February 2009, 08:28 AM   #4
Dxvideo is offline Dxvideo  Turkey
diyAudio Member
 
Dxvideo's Avatar
 
Join Date: Nov 2003
Location: Turkey
Send a message via Yahoo to Dxvideo
What about this one;
Click the image to open in full size.
__________________
Best regards,
Ozgur
  Reply With Quote
Old 19th February 2009, 02:35 PM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
what is the Vgs of your output FETs when they pass your intended bias current?

Now apply that Vgs across the 100r emitter resistors of the driver pair.
What current are you passing through the drivers?
__________________
regards Andrew T.
  Reply With Quote
Old 19th February 2009, 03:03 PM   #6
Dxvideo is offline Dxvideo  Turkey
diyAudio Member
 
Dxvideo's Avatar
 
Join Date: Nov 2003
Location: Turkey
Send a message via Yahoo to Dxvideo
In fact I expect to adjust the Vgs (and of course the bias current) via the trimpot..
This output design is from National AN1645 pg:14.. I did not make a simulation yet. But with this way I expect to have 2.5A at least... What do you think?
__________________
Best regards,
Ozgur
  Reply With Quote
Old 19th February 2009, 04:26 PM   #7
diyAudio Member
 
bobodioulasso's Avatar
 
Join Date: May 2008
one pair of mosfets at 1.3A bias would do the job? Look at Mr Pass F5.
  Reply With Quote
Old 19th February 2009, 05:33 PM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by Dxvideo
In fact I expect to adjust the Vgs (and of course the bias current) via the trimpot..
This output design is from National AN1645 pg:14.. I did not make a simulation yet. But with this way I expect to have 2.5A at least... What do you think?
you have not thought yet.
What is the Vgs of your output FETs when they pass the intended bias current.
Go and measure them, then do the rest.
__________________
regards Andrew T.
  Reply With Quote
Old 20th February 2009, 06:09 AM   #9
Dxvideo is offline Dxvideo  Turkey
diyAudio Member
 
Dxvideo's Avatar
 
Join Date: Nov 2003
Location: Turkey
Send a message via Yahoo to Dxvideo
Quote:
Originally posted by bobodioulasso
one pair of mosfets at 1.3A bias would do the job? Look at Mr Pass F5.
But my amplifier will give 25W RMS into 8R.. So;
25/8 = 3,125, SQRT(3,125) = 1,767 A RMS into load
That makes 1,767 * SQRT(2) = 2,489 A peak into load
And if you take 20% more for bias that makes ~3A...
Do you still think that 1,3A will enough?

Quote:
Originally posted by AndrewT
you have not thought yet.
What is the Vgs of your output FETs when they pass the intended bias current.
Go and measure them, then do the rest.
Ohh.. Sorry for the misunderstanding..
As I read from the datasheet of IRFP240 then the Vgs for 3A is just ~5v @ >10v Vds...
Ok I'll make the circuit, but I'd like to make a simulation first.. And have no model for LME49811 !! Do you know any solution for this?
Thanks..
__________________
Best regards,
Ozgur
  Reply With Quote
Old 20th February 2009, 08:46 AM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by Dxvideo


But my amplifier will give 25W RMS into 8R.. So;
25/8 = 3,125, SQRT(3,125) = 1,767 A RMS into load
That makes 1,767 * SQRT(2) = 2,489 A peak into load
And if you take 20% more for bias that makes ~3A...
Do you still think that 1,3A will enough?



Ohh.. Sorry for the misunderstanding..
As I read from the datasheet of IRFP240 then the Vgs for 3A is just ~5v @ >10v Vds...
Ok I'll make the circuit, but I'd like to make a simulation first.. And have no model for LME49811 !! Do you know any solution for this?
Thanks..
do the calculation in your head, or if you must use a calculator/slide rule or whatever.


A single ended amplifier current limits at the bias current level.
A push pull amplifier reaches the ClassA limit at twice the bias current. Most will then go further operating in ClassAB. Read the F5 to see how it's done.
__________________
regards Andrew T.
  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
Class D Vs Class I (Balanced Current Amplifier) rmsaudio Class D 29 26th January 2014 10:25 PM
LME49811 + Sanken STD03N/P jackinnj Chip Amps 33 8th November 2011 03:08 PM
LME49811 front-end for Gilmore amp? Artie Solid State 7 29th April 2009 08:36 PM
How about a round-up of Class A kit power amps, or collectable vintage class A? Brisso57 Solid State 4 14th February 2007 10:30 AM


New To Site? Need Help?

All times are GMT. The time now is 06:27 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