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 April 2011, 10:15 AM   #1
diyAudio Member
 
Join Date: Jun 2008
Location: India
Default Wide bandwidth class AB with 10mA quiescent?

Hi friends,

I would like to build a class AB with a 10mA quiescent current from +/-100V supply, and 100mA output current into 1k load? Will a moderate gm HEXFET like irf610 /9610 (1A / V) do or should I select a low gm lateral MOSFET pair? I need good slewrate and bandwidth of 1 MHz. I can take distortion upto about 2-3% at full power.

Please suggest few devices that may be suitable. Thanks in advance.
  Reply With Quote
Old 27th April 2011, 10:23 AM   #2
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
IRF610 and IRF9610 is probably the way to go.
Idle will be 1 Watt on each device.

Will you use Class AB with global negative feedback?
__________________
lineup
  Reply With Quote
Old 27th April 2011, 10:52 AM   #3
diyAudio Member
 
Join Date: Jun 2008
Location: India
Yes feedback is from point of load. MOSFET stage within loop.

But would I get the high bandwidth of 1 or 2 MHz, closed loop with gain of 50?

I think IRF610/9610 because although the gfs of these devices is near 1A/V, its lesser when Vgs near Vth (3-4V).
Am I right?

Aiming at 10mA, would I fall short of 3V (threshold) at the gates? This is my actual doubt.

Last edited by newvirus2008; 27th April 2011 at 11:05 AM.
  Reply With Quote
Old 27th April 2011, 01:49 PM   #4
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
200 Vp-p at 1 MHz is a difficult slew rate. IMO, most of the usual audio circuits you see won't do it. Combine that with 100 mA and layout without oscillation becomes difficult. Getting the devices to shut off quickly enough will be difficult. Global feedback may be difficult because of phase shift. I'd start by looking at old and new oscilloscope drive circuits and see if those can be adapted to what you want. If less than full power is needed at the high end, it will be an easier task.
__________________
May the root sum of the squares of the Forces be with you.
  Reply With Quote
Old 27th April 2011, 01:59 PM   #5
diyAudio Member
 
Join Date: Jun 2008
Location: India
Thank you, sir. But can there be cross conduction (and hence heat) at high frequencies because of this turning off problem?
I always thought of these HEXFETs (610/9610) as light devices capable of good slewrate.

Last edited by newvirus2008; 27th April 2011 at 02:21 PM.
  Reply With Quote
Old 27th April 2011, 05:04 PM   #6
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Quote:
Originally Posted by newvirus2008 View Post
Yes feedback is from point of load. MOSFET stage within loop.

But would I get the high bandwidth of 1 or 2 MHz, closed loop with gain of 50?

I think IRF610/9610 because although the gfs of these devices is near 1A/V, its lesser when Vgs near Vth (3-4V).
Am I right?

Aiming at 10mA, would I fall short of 3V (threshold) at the gates? This is my actual doubt.
I have spiced a variant that can put out 200Vp-p with low distortion.
But only tested with 1 kHz, so far.
The load is 1kOhm.
So, it is +/-100 mA out.

It was not easy. My third attempt however was successful.
In a real circuit, as has been said, you must have perfect PCB.
To avoid parasitic capacitance and such.
We are talking here RF, radio frequencies.

Anyway, the upper bandwidth of my amplifier in SPICE
is more than 10 MHz
at a gain of x100.
It is current feedback using IRF610/9610 both for VAS and for OUTPUT.
Idle bias is 10mA.

Supply is +/-110 Volt.
So, one slight problem is that IRF610/9610 are specified 200 Vds
There are HEXFET that takes more, I know.

I post it here.
Maybe it can give you some ideas.
Attached Images
File Type: png highvoltamp_1a.png (20.4 KB, 478 views)
__________________
lineup
  Reply With Quote
Old 27th April 2011, 05:32 PM   #7
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
look at output Cds - at 1 MHz, 100 V you'll be puting ~ 50-100 mA into the Mosfet device output C alone

possibly some of the VAS/predriver bjt would be better
even if you parallel 2x 2SC3503/1381 you will be way ahead of Mosfets - but SOA would need to be watched - more info about the application, signal, load would help

Last edited by jcx; 27th April 2011 at 05:35 PM.
  Reply With Quote
Old 27th April 2011, 05:51 PM   #8
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Yes, a BJT output is a strong option.
What common devices with more than 200 VCE have we?
Maybe MJE15030/31 would be an option here?
__________________
lineup
  Reply With Quote
Old 27th April 2011, 05:58 PM   #9
effebi is offline effebi  Italy
diyAudio Member
 
effebi's Avatar
 
Join Date: Nov 2010
Location: Milan
MJE15034/35
  Reply With Quote
Old 28th April 2011, 02:23 AM   #10
diyAudio Member
 
Join Date: Jun 2008
Location: India
Quote:
Originally Posted by jcx View Post
look at output Cds - at 1 MHz, 100 V you'll be puting ~ 50-100 mA into the Mosfet device output C alone
But isnt Rds is small enough...?

Last edited by newvirus2008; 28th April 2011 at 02:34 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
FS: Lundahl LL1660S/10ma LL1635/10ma dshortt9 Swap Meet 5 22nd November 2009 01:52 AM
Recomendation Please-100W Wide-Bandwidth Amp LinuksGuru Class D 4 1st November 2009 02:22 PM
Recommendation Please-100W Wide-Bandwidth Amp LinuksGuru Solid State 0 30th October 2009 09:34 PM
Quiescent Current Control in Class AB..? xitronics Solid State 27 25th September 2007 01:37 PM
Leach wide bandwidth preamp. beppe61 Solid State 21 22nd February 2005 03:46 PM


New To Site? Need Help?

All times are GMT. The time now is 01:06 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