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 20th May 2006, 03:10 PM   #1
diyAudio Member
 
DJ Exprice's Avatar
 
Join Date: Mar 2006
Location: San Francisco, California
Send a message via AIM to DJ Exprice Send a message via MSN to DJ Exprice
Default What is the difference between an isolated IC and a non-isolated IC?

I'm thinking of making another LM3886 amp but I need to know what's better - the isolated integrated circuit, or the non-isolated integrated circuit?

(PS: what does it mean when they say "isolated" anyway?)
  Reply With Quote
Old 20th May 2006, 03:32 PM   #2
diyAudio Member
 
Join Date: Dec 2004
Location: Not quite the middle
The isolated refers to the rear "tab" of the chip, the non-isolated has the metal tab showing and at V+. So to attach it to the heatsink it must have a isolating heat-transfer pad (sil-pad) or mica etc. Otherwise you'll get a short to ground/chassis.

The isolated doesn't suffer this but it's heat transfer characteristics aren't quite as good, the metal tab is covered the plastic the rest of the chip is encapsulated in. So no sil-pads required just grease.

Most here prefer the non-isolated for the better heat transfer, I myself built my first GC with the isolated version for simplicities sake (less to screw up).
If you have the choice the non-insulated would be slightly better with a high quality sil-pad.
  Reply With Quote
Old 20th May 2006, 03:43 PM   #3
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
Quote:
Originally posted by Crash&Burn
The isolated refers to the rear "tab" of the chip, the non-isolated has the metal tab showing and at V+. So to attach it to the heatsink it must have a isolating heat-transfer pad (sil-pad) or mica etc. Otherwise you'll get a short to ground/chassis.

The isolated doesn't suffer this but it's heat transfer characteristics aren't quite as good, the metal tab is covered the plastic the rest of the chip is encapsulated in. So no sil-pads required just grease.

Most here prefer the non-isolated for the better heat transfer, I myself built my first GC with the isolated version for simplicities sake (less to screw up).
If you have the choice the non-insulated would be slightly better with a high quality sil-pad.
Hi,
The non-isolated version has V- connected to rear tab , not V+.
When choosing insulator , it is important to select one with the lowest thermal resistance possible.For this reason it is useful to split mica insulators through thickness wia sharp knife - they usually come quite thick in stores.
  Reply With Quote
Old 20th May 2006, 05:53 PM   #4
diyAudio Member
 
BrianDonegan's Avatar
 
Join Date: Dec 2004
Location: Rock Ridge
I've built about 25 3886 amps of various designs for different people. I started using the insulated version a while back, as it is a lot easier. I was initially concerned about thermal transfer after reading the datasheet, but in real world conditions, including some very loud listeners, I have never had a problem with heat.

The thermal transfer of the non-insulated version is definitely better, but only if you spent a lot of time on your insulator. Easy to make it worse. I find, though, that hey just don't get that hot unless you are driving very low impedence loads or using very high voltage rails (over 37V), or both.

Anyway, just my 2 cents.
__________________
Twisted Pear Audio
  Reply With Quote
Old 20th May 2006, 07:29 PM   #5
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
Quote:
Originally posted by BrianDonegan
I've built about 25 3886 amps of various designs for different people. I started using the insulated version a while back, as it is a lot easier. I was initially concerned about thermal transfer after reading the datasheet, but in real world conditions, including some very loud listeners, I have never had a problem with heat.

The thermal transfer of the non-insulated version is definitely better, but only if you spent a lot of time on your insulator. Easy to make it worse. I find, though, that hey just don't get that hot unless you are driving very low impedence loads or using very high voltage rails (over 37V), or both.

Anyway, just my 2 cents.
Hi,
You don't need such a high voltages to activate spike protection.
For example , i have a clone with +-32V rails , and drive 4 ohms speakers. Spike protection still activates when listening at full volume levels for a longer period of time.It is non-insulated package.
The difference between "T"(non-insulated) and "TF"(insulated) package thermal resistance(case-to-sink) can be something around 0,5C/W or more. This means higher case temperature , than for "T" package.


Regards,

Lukas.
  Reply With Quote
Old 20th May 2006, 11:01 PM   #6
! is offline !  United States
diyAudio Member
 
Join Date: Jun 2005
Location: Midwest
Isolation can be relative, if you want to get best heat transfer you might consider isolating the heatsink from the chassis instead of the chip from the 'sink... just make SURE it's secure and if you did that it might be wise to fuse the PSU rails.
  Reply With Quote
Old 21st May 2006, 02:01 PM   #7
diyAudio Member
 
Join Date: Dec 2004
Location: Not quite the middle
Quote:
The non-isolated version has V- connected to rear tab , not V+.
Thanks, I originally had written "and at V+ (I think)" and decided my memory was ok so the (I think) came out... either way the end result is the same.
  Reply With Quote
Old 21st May 2006, 06:24 PM   #8
diyAudio Member
 
Join Date: Dec 2005
Location: Sao Paulo
Send a message via MSN to -_nando-_ Send a message via Skype™ to -_nando-_
The Isolated is more easy to implement, because it already have the insulation ! But, as the insulation is heat isolant too, they aren't good as the non isolated for heat dissipation. So, for high power designs, go with the non isolated, and a good quality insulation. But, if you want to do anything like "PC Speakers", heheheh, go with the isolated ! Anyway, I do prefer non isolated because isn't any dificult to isolate them, and you don't have to isolate them necessarily! If your heatsink isn't touching anything is ok! Remember that the back of the LM is connected do -V of the supply !



  Reply With Quote
Old 22nd May 2006, 08:41 PM   #9
mobyd is offline mobyd  New Zealand
diyAudio Member
 
mobyd's Avatar
 
Join Date: Sep 2004
Location: Auckland
For LM3886s I prefer the non insulated version and use an orbital sander with the finest grit paper to ensure that the heatsink is dead smooth, then anodise the heatsink black, and use no mica or silpad. The anodised surface is a great insulator !. A smear of white goop finishes the job. I prefer not to use the mounting hole on the chip, instead using a bar across the back of the chip(s) and screws on both sides.
M
  Reply With Quote
Old 22nd May 2006, 08:59 PM   #10
diyAudio Member
 
BrianDonegan's Avatar
 
Join Date: Dec 2004
Location: Rock Ridge
It does. Best to get hard anodizing, or else be very gentle, as it is easy to scratch through with the corner of the metal tab. I think Nelson Pass does this on some of his amps.
__________________
Twisted Pear Audio
  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
12 vdc to 18 vdc isolated P-P jamesrnz Power Supplies 89 4th February 2009 03:36 PM
isolated or non-isolated psu for UcD in a car? zilog Class D 1 2nd February 2009 02:56 AM


New To Site? Need Help?

All times are GMT. The time now is 07:30 AM.


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