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.

interface resistance
interface resistance
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 17th November 2004, 05:52 PM   #1
alphadelta is offline alphadelta  Italy
diyAudio Member
Join Date: Nov 2004
Location: Torino
Default interface resistance

HI everybody,
this is my first post to this forum.
I wish to build a class A ampli with IRPF150 mosfet (in TO-247AC case) to polarize with 2.5-3 A.
Now I am dimensioning the heatsink and I wish know thermal resistance case to sink.
IRPF150 datasheet suggests a Rcs=0.24C/W for "flat, greased surface".
What kind of grease will I buy?
Is this the best interface material to optimize heat dissipation?
When I purchased the mosfets they give me also any grey little sheet. How can I utilize them and what is their thermal resistance?
Is TO-247AC thermal resistance similar to TOP-3?

thanks for your answer and sorry my bad English!

  Reply With Quote
Old 17th November 2004, 07:18 PM   #2
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
T03p is nearly the same as TO247. The grease should be thermal, the suppliers will probably stock a variety. I've seen reference to silicon drying out but I cannot confirm.
Rcs for an insulator varies on which material you use - from 0.4 to 1 degree/watt. Some insulators are dry fit, they are more reliable, cleaner but often more resistance than mica and thermal grease. Thin Kapton is another option, 6thou has too much resistance imo. try to find 1thou.
regards Andrew T.
  Reply With Quote
Old 17th November 2004, 07:19 PM   #3
Mr Evil is offline Mr Evil  United Kingdom
diyAudio Member
Join Date: Aug 2004
Location: Behind you
Silicone thermal paste is the norm, being cheap. Better is something like Arctic Silver, which can gain an order of magnitude improvement.

The interface resistance depends a lot on how much pressure you use to clamp the devices down, and how evenly it is applied. Putting a bolt through the hole in the plastic package is the worst. Clamping them down with a flat bar across the device is much better. Doing that you can get down lower than 0.24C/W.

If you need to electrically insulate the devices from the heatsink then the thermal resistance will be somewhat higher.
  Reply With Quote
Old 18th November 2004, 12:53 AM   #4
anatech is offline anatech  Canada
diyAudio Moderator
anatech's Avatar
Join Date: Jun 2004
Location: Georgetown, On
interface resistance
Hi alphadelta,
Clamp using even pressure, but not too much pressure. Make sure the heatsink is smooth and not cupped or bowed. Screws are fine as long as you follow the mounting guidlines. Basically, snug but not real tight. A lockwasher will help here. Don't try to get close to the thermal limits of your heatsink and you will be fine. With heatsinks, too big is far better than a little small.
  Reply With Quote


interface resistanceHide 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
Interface : USB or NOT renaudagnes Digital Source 40 9th December 2009 06:13 PM
HDD to I2s interface elnec Digital Line Level 6 15th September 2008 08:43 PM
resistance impsick Solid State 7 28th May 2007 04:41 PM
interface I2S with USB mermoz Digital Source 0 21st February 2003 10:34 AM

New To Site? Need Help?

All times are GMT. The time now is 09:22 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