Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Drift of MOSFET source voltage
Drift of MOSFET source voltage
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
Thread Tools Search this Thread
Old 5th February 2001, 07:06 AM   #1
namui is offline namui
diyAudio Member
Join Date: Nov 2000
Hi folks,
Let a simple amp be constructed this way :
1) Two single-ended class A MOSFET amps driven by a set of balanced input
and driving the load across the source pins of the two MOSFETs
2) Each amp is biased by an active current source connected between the
MOSFET's source pins and the negative supply voltage and the drain pins
are connected directly to the positive supply voltage.
So it's two followers driving the load in balanced fashion.
The potential problem is the drift in the source pin voltages of the two amps
which will appear across the load as drifting offset, caused by the temperature
increase. Unless the two MOSFETs are exactly the same, the Vgs variation will
be slightly different.
Is there any way besides capacitive coupling to the load or bias servo circuit
to keep the offset voltage practically low and constant (says within +/- 50mV) ?
Would source resistors help ?


[Edited by namui on 02-05-2001 at 02:12 AM]
  Reply With Quote
Old 5th February 2001, 12:00 PM   #2
djk is offline djk
djk's Avatar
Join Date: Feb 2001
Location: USA
If the amp is to be a no global feedback design a servo or coupling cap will be required.To eliminate the active current source see this patent. http://www.delphion.com/cgi-bin/view...d/US04229706__ This will cut power disipation in half.A FET follower may replace the BJT follower.If a discrete op-amp is used only one is required.This amp may be constructed with a single 5687 or 6H30Pi dual triode tube connected as a differential pair driving a pair of Magnetec BUZ900D.Bias and DC balance to be set up like a PP tube amp.If the pair of Magnetec outputs are on a common heatsink the Vgs is stable enough that the DC off-set will not drift.One pair of the Magnetec will deliver 100 watts in class A with this design or 200 watts in class AB.The amp described in the patent was the Sumo Model 9.
  Reply With Quote


Drift of MOSFET source voltageHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
MOSFET current source as triode load Craig405 Tubes / Valves 46 14th April 2010 12:06 PM
Do I have to match voltage Gate-Source of mosfet in SMPS? Charoenchai Car Audio 5 17th November 2006 09:28 PM
temp drift in MOSFET Vgs SemperFi Solid State 6 29th June 2006 04:50 PM
load on source follower choke or mosfet? AudioGeek Solid State 57 2nd September 2004 02:42 AM
simple MOSFET source folower suggest me please aiwonsi Solid State 22 26th July 2003 04:56 AM

New To Site? Need Help?

All times are GMT. The time now is 11:37 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio