LM3886TF Heat Sink Insulation

davidhugo · 11th June 2009, 01:41 PM

Hi

I am about to start a chip amp project using a pair of LM3886TF chips
Am I correct in thinking that LM3886 chips ending in TF have a plastic coating and do not need to be electrically insulated from the heat sink?
Also is it worth using heat conduction paste? And finally should the bolt be Metal on Nylon.

Any help would be greatly appreciated.

Thanks

dh

Juergen Knoop · 11th June 2009, 01:58 PM

all yes, and don't use nylon screws!
It is not possible to put sufficient torque on them.
regards

Ted205 · 11th June 2009, 03:59 PM

Redshift187 · 11th June 2009, 05:29 PM

Ted, I'm unsure as to the relevance of your pictures to this thread. The OP asked about LM3886TF, your pictures show LM3886T.

Atilla · 11th June 2009, 06:20 PM

I'm guessing he's showing the better way of mounting those on the heatsinks.

Ted205 · 12th June 2009, 09:08 AM

i know a great leap in imagination is needed

but yes i was trying to illustrate mounting the lm3886 using a bar

Redshift187 · 12th June 2009, 02:12 PM

Really nice amps Ted. I used a bar just like the second picture for a pair of LM4780s I built. Unfortunately, I didn't put a bolt between them, and the bar flexed and the chips weren't flat on the heatsink. Once I added another bolt in between it was fine. I prefer the bar for non-isolated, especially the larger LM4780 since they have 2 mounting holes. For an isolated LM3886, I think a single bolt in the mounting hole would be easier.

Ted205 · 12th June 2009, 03:22 PM

the pics where borrowed from - http://www.shine7.com/audio/jeff.htm

AndrewT · 12th June 2009, 03:43 PM

The TF does not need any additional electrical isolation.

If clamped direct to the heatsink then one MUST use a thermal compound to ensure there is no air in the thermal interface.

You can use one of the conformable isolators but all of these increase the thermal resistance and the TF is already partially crippled by the thermal resistance of the plastic encapsulation.

jackinnj · 12th June 2009, 03:49 PM

I use these on the chipamps -- easy to make with a round file -- easier still if you have a mill:

11th June 2009, 01:41 PM	#1
davidhugo diyAudio Member Join Date: Mar 2009	LM3886TF Heat Sink Insulation Hi I am about to start a chip amp project using a pair of LM3886TF chips Am I correct in thinking that LM3886 chips ending in TF have a plastic coating and do not need to be electrically insulated from the heat sink? Also is it worth using heat conduction paste? And finally should the bolt be Metal on Nylon. Any help would be greatly appreciated. Thanks dh __________________ Power corrupts but powerlessness destroys you absolutely.

12th June 2009, 03:43 PM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	The TF does not need any additional electrical isolation. If clamped direct to the heatsink then one MUST use a thermal compound to ensure there is no air in the thermal interface. You can use one of the conformable isolators but all of these increase the thermal resistance and the TF is already partially crippled by the thermal resistance of the plastic encapsulation. __________________ regards Andrew T.

12th June 2009, 03:49 PM	#10
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	I use these on the chipamps -- easy to make with a round file -- easier still if you have a mill: __________________ TinTin -- banned in Brooklyn

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11th June 2009, 01:58 PM	#2
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	all yes, and don't use nylon screws! It is not possible to put sufficient torque on them. regards

11th June 2009, 03:59 PM	#3
Ted205 diyAudio Member Join Date: Jun 2008

11th June 2009, 05:29 PM	#4
Redshift187 diyAudio Member Join Date: Aug 2008	Ted, I'm unsure as to the relevance of your pictures to this thread. The OP asked about LM3886TF, your pictures show LM3886T.

11th June 2009, 06:20 PM	#5
Atilla diyAudio Member Join Date: Jul 2008	I'm guessing he's showing the better way of mounting those on the heatsinks.

12th June 2009, 09:08 AM	#6
Ted205 diyAudio Member Join Date: Jun 2008	i know a great leap in imagination is needed but yes i was trying to illustrate mounting the lm3886 using a bar

12th June 2009, 02:12 PM	#7
Redshift187 diyAudio Member Join Date: Aug 2008	Really nice amps Ted. I used a bar just like the second picture for a pair of LM4780s I built. Unfortunately, I didn't put a bolt between them, and the bar flexed and the chips weren't flat on the heatsink. Once I added another bolt in between it was fine. I prefer the bar for non-isolated, especially the larger LM4780 since they have 2 mounting holes. For an isolated LM3886, I think a single bolt in the mounting hole would be easier.

12th June 2009, 03:22 PM	#8
Ted205 diyAudio Member Join Date: Jun 2008	the pics where borrowed from - http://www.shine7.com/audio/jeff.htm

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