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.
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.
Crash&Burn said:
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.
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.
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.
BrianDonegan said:
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.
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 !
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
M
DJ Exprice said:Could I attach both of my non-insulated chips to the case of my amp (its metal). There is no other connection besides the ground touching the case.
No, you wouldn't want to do it, because V- is tied to the non-isulated chip tab and it is negative, relative to ground. In other words you'd be shorting out half your power supply.
! said:
You mean ground can't touch ground?
Im confused 
The V- is ground, so i don't understand. My transformer will be insulated in it's case inside of the amp that will be screwed to the amp's metal case - no metal connection. The LM3886s will have each other's V- anyway. Do I need to connect the transformer to the amp's metal case via it's ground wire? Can I connect all of those? I will be using a 24v 6.3 amps transformer, just to clarify things.DJ Exprice said:
You mean ground can't touch ground?
No, supposing your supply is 24-0-24. The first 24 is V+, 0 is Gnd and 2nd 24 is V-.
V- is not ground in a dual supply. In this case it is 24 volts negative (lower than) the ground.
So you are going to use a single supply instead of dual, since you only mention "24V 6.3A"? It would be helpful if you post clear and complete schematics of exactly what you want to do, a mistake in this can easily damage something.
Sure (above) thats for my older one. My newer idea for an LM3886 amp is TF with connection to the case (I need to get thermal grease for this one though I figured out that V- is NOT ground and feel like a complete nincompoop for not realizing that earlier. I also know that 0v on the transformer should NOT touch AC Primary ground. I also got some wrong-size q-pads but can still attach thermal grease (when I get some) to part of the chip and most of the pad and probably still get some good transfer of heat . Thanks guys!
I figured out that V- is NOT ground and feel like a complete nincompoop for not realizing that earlier. I also know that 0v on the transformer should NOT touch AC Primary ground. I also got some wrong-size q-pads but can still attach thermal grease (when I get some) to part of the chip and most of the pad and probably still get some good transfer of heat . Thanks guys!- Status
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