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Old 12th Oct 2019, 5:58 pm   #1
G6Tanuki
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Default LM380 cooling.

The LM380 is one of my go-to chips when I need an 'indestructible' audio amp with a couple of Watts output - but it's just a straightforward 14DIL package with no facilities for a heatsink so it tends to run rather warm.

In some designs I've seen extended areas of copper PCB material left around the centre 3 pins on each side (these all being earth) in the hope it will conduct the heat away but I doubt it's really that efficient, specially since it's on the underside of the PCB where air circulation is minimal.

I've got some 1.5mm-thick copper sheet here and was planning to make up some 'wings' to solder to the central sets-of-pins in the hope of improving cooling; I was wondering if anyone else has done this sort of thing in the past and how successful it was?
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Old 12th Oct 2019, 6:26 pm   #2
Ambientnoise
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Default Re: LM380 cooling.

Yes it does work. This chip is thermally connected to the 3 pins on each side for this purpose so an area of the pcb or “wings” soldered on can be used. One version of the data sheet outlines such wings.

Ken
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Old 12th Oct 2019, 7:05 pm   #3
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Default Re: LM380 cooling.

It's good to know my idea isn't crazy! I feel some research and experimentation coming on.

Current idea: take a square of this copper I've got, slice it diagonally to give 2 pyramids, then slice the 'tops' off the pyramids to produce a straight bit to solder to the central 3 pins on each side. I'm thinking of drilling a hole through the centre of each pyramid too, so I can use a 6BA nut/bolt/spacer-tube to join them and so give added support.
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Old 12th Oct 2019, 8:25 pm   #4
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Default Re: LM380 cooling.

If i understand you correctly, the pieces of copper would be better described as "triangles" wouldn't they? Triangles are essentially two-dimensional, but pyramids are three-dimensional...
Colin.
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Old 12th Oct 2019, 8:33 pm   #5
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Default Re: LM380 cooling.

Yes, triangles with the apexes cut-off.
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Old 13th Oct 2019, 12:44 am   #6
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Default Re: LM380 cooling.

From the National datasheet for the LM380
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Old 13th Oct 2019, 3:09 pm   #7
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Default Re: LM380 cooling.

You could also solder on some lengths of solid copper wire from a bit of T+E.
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Old 13th Oct 2019, 3:46 pm   #8
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Default Re: LM380 cooling.

Quote:
Originally Posted by paulsherwin View Post
You could also solder on some lengths of solid copper wire from a bit of T+E.
I think my proposed copper 'wings' will be more efficient and elegant. Alas it's on-hold since I just broke my last junior-hacksaw blade!
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Old 13th Oct 2019, 4:03 pm   #9
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Default Re: LM380 cooling.

G6- a few posts to ponder
https://www.diystompboxes.com/smffor...topic=121981.0
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Old 13th Oct 2019, 10:12 pm   #10
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Default Re: LM380 cooling.

Quote:
Originally Posted by Oldcodger View Post
OOh! Thanks for this!!
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Old 16th Oct 2019, 7:29 pm   #11
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Default Re: LM380 cooling.

I've made up "flags" - see below - and having soldered them to the 'middle' pins each side of my LM380 amps they're working well-enough that they no longer go into thermal-shutdown when playing 80s high-level bands like Simple Minds/The Chameleons.

I consider this a success!
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Old 20th Nov 2019, 1:36 am   #12
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Default Re: LM380 cooling.

Hi G6Tanuki,

Oh no your idea is certainly NOT crazy, when I built my mono record player amplifiers using a TBA800 IC I used 2.5 flat, 15 amp grey power cable, stripped down for the copper. The copper was then cut into 7mm lengths, and laid side by side against the heatsink, on the underside of the PCB and soldered in place, of course all that being done first before the chip was inserted.

I dare not say the things I experimented with before I had that perticular brain wave, I have tried very old copper pennies soldered to the heatsink of the TBA800 with the heatsink bent upwards, and have also used old copper piping flatened out and cut to size just like your picture.

Of course all that was whilst I was experimenting and perfecting everything, and also before I got skillful enough to cut the slits in the PCB to allow the heatsink of the IC to remain downwards on the board. I soon discovered that bending the heatsink upwards was damaging some of the IC's (but not all of them) so I settled on not bending them at all, and using the extra copper underneath, turned out far more reliable and neater.

Paul
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Old 20th Nov 2019, 12:03 pm   #13
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Default Re: LM380 cooling.

I've found a lot of modern consumer electronics (routers, PVRs, PCs) found in the WEE bin will contain very useful heatsinks which would fit a 14-pin DIL chip like that with minimal modification. The kind I'm thinking of are simply bonded to the IC with some kind of glue, and can be removed with a sharp twist in my experience, then repurposed.
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Old 20th Nov 2019, 12:24 pm   #14
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Default Re: LM380 cooling.

Yes. Though a power IC like the LM380 might have too much thermal resistance for the sort of heat that the chip generates, for bonding a heatsink to the epoxy package (though it will certainly help). The 'heatsink pins' on this IC have a specially-designed direct thermal path to the chip itself.
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Old 20th Nov 2019, 3:02 pm   #15
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Default Re: LM380 cooling.

Maybe its because I live in Australia and the ambient temperature can hit 40 Deg C, or maybe its just a plain silly idea to try to squeeze powers like 2 watts out of an IC (or transistors) in an epoxy package without a proper heat flag.

Power output transistors , at least TO-5 and T0-220 etc, the transistor die is thermally bonded to the metal case/flag. That way the thermal resistance is much lower. To expect a great result trying to extract heat via IC pins from small junctions in the IC body to me is a somewhat optimistic bodge, especially considering the geometry and cross sectional area of the pins.

Sure, you can get it to work, but I would never label it elegant, the junction temperatures of the output devices in the IC will run in the high range and depending on your ambient temp, it can push them very hard. It all equates to a shorter life for the IC.

It became the fashion for example that the vertical scan amplifier stages were built into one IC in many latter day video monitors. These amplifiers are very much like their audio amp counterparts. Seemed like a good idea for the manufacturers, but as the years have past these IC's are dropping off like flies.

The situation can be a little improved if the IC is a type with a metal top where you can thermally bond it to a good heat sink.

My advice for an amp over a couple of watts, get one with an IC with an integral heat flag that you can screw to a decent heat sink, of make it out of discrete components, with output transistors you can screw to a heat sink.
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Old 20th Nov 2019, 4:07 pm   #16
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Default Re: LM380 cooling.

I've seen TDA1170s with their wings straightened so that the device could sit in a slot in the middle of an extruded heatsink with the wings screwed to the heatsink. As Argus alludes, it struck me as an attempt to glitz a sow's ear.
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Old 20th Nov 2019, 4:14 pm   #17
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Default Re: LM380 cooling.

My "finned" LM380 seems to be working just fine: it's in a Roberts R707 that had 'come back' to me three times with failed output-transistors despite me replacing pretty much every component in the original ouput-stage the first time round!

Yes, a 380 isn't really _that_ serious as an audio-amp - I've got similar-era TBA810AS here if I need something that can be driven a bit harder - but the LM380 results in a compact amplifier that works well [it has overheat- and short-circuit shutdown as part of the design, and in my experience it tends to survive mistreatment well].
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Old 20th Nov 2019, 5:08 pm   #18
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Default Re: LM380 cooling.

LM380 is a National Semiconductor design.

I don't think Nat Semi (Bob Pease, Robert Widlar, and others) ever produced a bad linear IC.
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Old 20th Nov 2019, 6:49 pm   #19
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Default Re: LM380 cooling.

I saw a 14( or possibly 16) pin DIL package used in an electronic organ amplifier. That had a reasonable sized heat sink attached-presumably bonded. It worked very well for many years after being re-purposed in an old radio cabinet as a bench amplifier.
So heatsinks for DIL are/were available.
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