mosfet matching wide variations/swings mosfet matching wide variations/swings - diyAudio
Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

mosfet matching wide variations/swings
mosfet matching wide variations/swings
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 4th April 2015, 12:01 AM   #1
vdi_nenna is online now vdi_nenna  United States
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
mosfet matching wide variations/swings Send a message via Yahoo to vdi_nenna
Default mosfet matching wide variations/swings

Purchased 20 irfp140 and 20 irfp9140 mosfets.
Matching them has been less than fun.

Setup:

Mastech 30v 10A power supply
Large-ish blank anodized heat sink 4x6x1 inch
Sheathed alligator clip leads
Silicon iso pad.
15v, 60 ohm power resistor .13A

I thought I was getting good readings but if the dmm lead are touched or if I reach over the setup, the voltage swings but never settles to it was originally.
If i re-test, the Vgs is different.
If i touch the heat sink the voltage changes.

I don't trust the readings so I can't continue with the build. I don't remember it being this difficult.
I tried 4 meters and different meter leads.

How is matching done properly?
__________________
I build, therefore I am.

Last edited by vdi_nenna; 4th April 2015 at 12:07 AM.
  Reply With Quote
Old 4th April 2015, 12:56 AM   #2
Zen Mod is offline Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
mosfet matching wide variations/swings
pics
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 4th April 2015, 01:39 AM   #3
vdi_nenna is online now vdi_nenna  United States
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
mosfet matching wide variations/swings Send a message via Yahoo to vdi_nenna
Gate to drain
15v to drain
Ground to source pin
Attached Images
File Type: jpg IMG_20150403_213313.jpg (99.2 KB, 215 views)
__________________
I build, therefore I am.
  Reply With Quote
Old 4th April 2015, 01:49 AM   #4
flg is offline flg  United States
diyAudio Member
 
flg's Avatar
 
Join Date: Jul 2005
Location: North East
Are you using a gate stopper resister?
__________________
"It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
  Reply With Quote
Old 4th April 2015, 01:49 AM   #5
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
mosfet matching wide variations/swings
First, don't put a lot of trust in the meters which come with the regulated supplies.

Second, you may be seeing some parasitics - use a 470 to 1Kohm Gate resistor.

If this doesn't work, try an analog meter.

  Reply With Quote
Old 4th April 2015, 01:54 AM   #6
flg is offline flg  United States
diyAudio Member
 
flg's Avatar
 
Join Date: Jul 2005
Location: North East
From http://www.firstwatt.com/pdf/art_mos_test.pdf :
"P4 doesn’t matter here , as the DC is blocked by the
capacitor, but it is always nice to have a few ohms in series
with the Gate of any Mosfet to prevent high frequency
(parasitic) self-oscillation, which will alter the voltage
reading."

__________________
"It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
  Reply With Quote
Old 4th April 2015, 01:57 AM   #7
flg is offline flg  United States
diyAudio Member
 
flg's Avatar
 
Join Date: Jul 2005
Location: North East
Sorry, I'm a little slow sometimes...
__________________
"It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
  Reply With Quote
Old 4th April 2015, 02:00 AM   #8
vdi_nenna is online now vdi_nenna  United States
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
mosfet matching wide variations/swings Send a message via Yahoo to vdi_nenna
Thanks everyone.

So the output reading on the regulated supply is not to be trusted. Check.
Use a gate stopper. Check.
Will recheck tomorrow. Check.
__________________
I build, therefore I am.
  Reply With Quote
Old 4th April 2015, 12:04 PM   #9
vdi_nenna is online now vdi_nenna  United States
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
mosfet matching wide variations/swings Send a message via Yahoo to vdi_nenna
Appears to be solid now. Moving the cables doesn't move the meter.

Used 1/2w 750 ohm.

Thanks!
Attached Images
File Type: jpg IMG_20150404_080131.jpg (120.4 KB, 176 views)
__________________
I build, therefore I am.
  Reply With Quote
Old 6th April 2015, 09:32 AM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
You must keep Tj at the same value for every test/DUT, that is really difficult !
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote

Reply


mosfet matching wide variations/swingsHide 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 Matching - My new rig Zero Cool Parts 12 29th July 2013 03:59 PM
Matching Power Mosfet Forte Pass Labs 13 10th March 2013 06:28 AM
Shunt Regulator variations (Parallel voltage regulator variations) for SS Pre-Amp tiefbassuebertr Solid State 2 15th December 2012 10:09 AM
Matching MOSFET's for Aleph 2 Thago Pass Labs 4 5th June 2007 07:05 PM
Matching Mosfet's Jena Pass Labs 4 5th April 2004 06:23 AM


New To Site? Need Help?

All times are GMT. The time now is 02:57 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki