What is the difference between an isolated IC and a non-isolated IC?

[DJ Exprice]

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?)

[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.

[Bazukaz]

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.

[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.

[Bazukaz]

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.

[!]

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.

[Crash&Burn]

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.

[-_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 !

[mobyd]

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

[BrianDonegan]

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.