I've seen a lot of talk about external heat sinks but not how to actually mount them. Can I mount my amplifier IC's onto my case inside, and heatsink at the same place outside and use the case for heat transfer? Or should I cut out the case so the IC mounts directly to the heat sink (with isolating material + continuity test)? I have heat sinks at home that are flat on one side and have fins on the other.
Devices should mount directly on the sink, with only isolation pads and thermal paste if necessary.
Adding intervening thermal interfaces, greatly reduces the effectiveness of the sink,
making your junction temperatures higher.
Many builders make the heat sink serve as the side of the chassis all by itself.
https://vikash.info/audio/chipamp-lm3886/
Adding intervening thermal interfaces, greatly reduces the effectiveness of the sink,
making your junction temperatures higher.
Many builders make the heat sink serve as the side of the chassis all by itself.
https://vikash.info/audio/chipamp-lm3886/
Internal heatsinks are fine. Make sure that the fins are vertical and the enclosure has ventilation both above and below the heatsinks.
Ed
Ed
Nice, I'll go for that then. This is my first "test" amp build so I will consider a heat sink side panel for my next build.
@rayma: I can't quote your message. Yes 2x LM1875 and 1x LM4780TA. Usually listening to low volume so not a lot at all.
Ok, just ensure good vents top and bottom, aligned with the fins.
Also use high feet, an inch or more.
Also use high feet, an inch or more.
@catcream Have you read the datasheet?" The calculations for determining the heatsink requirements are pretty straightforward. A moderate supply voltage used exclusively at lower levels won't need an overly large sink.
I have a pair of lm3886's bolted directly to the back panel of an old fire alarm can and the chips run ~40°C - 42°C at higher volumes. The PS is +/-30Vv.
The can is 14ga steel so it's heavy... they don't make em like that anymore.
The 3886 bridged/parallel application note shows a HS that's somewhere around 3" x 5" x 1.25" and assumes adequate airflow. I think the document is AN 1192
I have a pair of lm3886's bolted directly to the back panel of an old fire alarm can and the chips run ~40°C - 42°C at higher volumes. The PS is +/-30Vv.
The can is 14ga steel so it's heavy... they don't make em like that anymore.
The 3886 bridged/parallel application note shows a HS that's somewhere around 3" x 5" x 1.25" and assumes adequate airflow. I think the document is AN 1192
IF the back panel is aluminum it's acceptable to "sandwich", specially if naked or anodized.
Using proper heatsink paste between all surfaces.
More than metal added, most problematic is the inevitable air film between surfaces.
If back panel is iron, instead of aluminum, it will be painted, and typically in a cabinet, thick grainy surface Epoxy paint or "industrial" type will be used.
PA and musical instrument amplifiers have cutouts, so active devices mount straight to heatsink.
Outside heatsinks are way better than internal ones.
They are acceptable in HiFi/Home use which is lighter duty.
Using proper heatsink paste between all surfaces.
More than metal added, most problematic is the inevitable air film between surfaces.
If back panel is iron, instead of aluminum, it will be painted, and typically in a cabinet, thick grainy surface Epoxy paint or "industrial" type will be used.
PA and musical instrument amplifiers have cutouts, so active devices mount straight to heatsink.
Outside heatsinks are way better than internal ones.
They are acceptable in HiFi/Home use which is lighter duty.
Nope, I will take a look, thanks. Pretty surprised it dissipates 25W for 2.5W output at +-30V.
This is also useful
@JMFahey: Alright, the side panels are anodized aluminum so should be okay then. Maybe scraping off coating gives even better result?
"Front and back cover are made from anodized aluminum. Top and Bottom cover are made from steel with anti-scratch paint. These materials allow the housing to be robust and light which can be used for professionnal use."
Also re cut outs, do you mean cutting out a hole for the whole heat sink or just a hole for the IC? A bit concerned about the angle of the mount if just for the IC.
(this but more).
"Front and back cover are made from anodized aluminum. Top and Bottom cover are made from steel with anti-scratch paint. These materials allow the housing to be robust and light which can be used for professionnal use."
Also re cut outs, do you mean cutting out a hole for the whole heat sink or just a hole for the IC? A bit concerned about the angle of the mount if just for the IC.
Anodizing is incredibly thin so it does not hurt at all.
And as Rayman mentioned, sanding, scratching, etc, will make surface rougher, so not recommended.
Windows cut/punched do not need to be full heatsink size , if anything for mounting reasons, but of course should be somewhat larger than semiconductor case.
Say 10mm extra around all edges?