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Old 28th August 2012, 02:37 AM   #1
Einric is offline Einric  United States
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Default Heatsink For LM4780

I have a rather small heatsink for my LM4780's.
Each chip is running in a parallel setup and I'm limited on space.
Because of this I am building a detached power supply.
My heatsink is vertical fin 3.5" wide, 3.75" High & 1.5" fins with a .3875" thick base, there are 16 smooth fins.
I have another heatsink that I was thinking about using as the pressure plate to hold the chip to the heatsink.

What do you think?
The heatsink pressure plate should assist in thermal dissipation.
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Old 28th August 2012, 10:49 AM   #2
AndrewT is offline AndrewT  Scotland
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The clamp does not get much heat.
The thermal resistance of the plastic package is too high. Yes you clamp the package not the tab.
The sink looks big enough, if it is mounted in free air with the fins & backplate standing vertical.
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Old 28th August 2012, 01:25 PM   #3
Einric is offline Einric  United States
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OK, great the fins will be external with one on each side of the enclosure.
For the external power supply, what would be the best for shielding? Just Aluminum or Stainless Steel, mesh....ect.?
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Old 28th August 2012, 01:53 PM   #4
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Not quite the tool you're looking for -- here's Aavid Thermalloy's bonded fin heat sink thermal impedance calculator:

- heatsink design tools
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Old 28th August 2012, 02:48 PM   #5
macboy is offline macboy  Canada
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Quote:
Originally Posted by jackinnj View Post
Not quite the tool you're looking for -- here's Aavid Thermalloy's bonded fin heat sink thermal impedance calculator:

- heatsink design tools
Not at all.
The heatsinks above are clearly extruded, not bonded fin; they are completely different beasts.
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Old 28th August 2012, 03:26 PM   #6
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They are different in that you can fit more fins in a bonded fin heatsink, for a given amount of space they are much more efficient than extrusions.

Here's another calculator:
Cold Plates, Heat Sinks, Peltier Coolers, Heat Spreaders
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Old 28th August 2012, 04:00 PM   #7
AndrewT is offline AndrewT  Scotland
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Jack,
what are you suggesting?
That he blow the fins with a fan?
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Old 28th August 2012, 05:03 PM   #8
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Quote:
Originally Posted by AndrewT View Post
Jack,
what are you suggesting?
That he blow the fins with a fan?
As Lauren Bacall said to Humphrey Bogart: "Just pucker up and blow". As soon as the heat sink starts hotting up air starts moving -- obviously not like a fan at 200 LFM, but at some low tens of LFM.
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Old 29th August 2012, 01:59 AM   #9
Einric is offline Einric  United States
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I have found these, what do you think?
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Old 29th August 2012, 01:38 PM   #10
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Don't know if you've tapped heat sinks before -- it helps to have the taps for "blind hole" -- unless you're going all the way through (which isn't pretty). McMaster sells a set of 3 taps for each screw size, one being a "bottoming tap". I use the 4-40's.
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