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Old 27th February 2010, 11:22 PM   #1
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Default Is this heat sink OK?

I've just started building a Gainclone amp. Currently I am just experimenting with a single chip (mono) trying to get my head around ground loops etc. but my LM3875 chip is getting really warm.

I am using a 240v - 2 x 18V Toroid, and currently using a bar of aluminium 90mm x 30mm x 10mm.

I eventually want to make my own enclosures for my amps, and was originally going to just bolt the chips to the case, but maybe just plain old aluminium won't be good enough.

Would this be any good:

FISCHER ELEKTRONIK|SK 100/100 SA|HEAT SINK, 100MM, 1.5C/W | Farnell United Kingdom

It says : Thermal Resistance:1.5C/W and the calculation I did on the Overture Design Guide said for a 6 ohm load that I need 3.08C/W.

I don't understand C/W, so do I go lower or higher to be on the same side.

Or maybe this one:

http://uk.farnell.com/fischer-elektr...66?Ntt=4621566

This would make my case look better

Thanks
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Last edited by portreathbeach; 27th February 2010 at 11:32 PM.
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Old 27th February 2010, 11:32 PM   #2
space is offline space  Norway
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As long as the heat sink has equal or lower C/W number than what you need you are OK.

A heat sink with 1.5C/W will heat up half of what a heat sink with 3C/W will.


space
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Old 27th February 2010, 11:33 PM   #3
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Thanks very much for your info
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Old 28th February 2010, 03:34 AM   #4
jaycee is offline jaycee  United Kingdom
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These would work. However Farnell do a nice 160 wide, 40mm deep, 75mm long heatsink on there by Fischer, and this will adequately cool two LM3886's (i saw your other thread) perfectly
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Old 28th February 2010, 11:08 AM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by portreathbeach View Post
It says : Thermal Resistance:1.5C/W and the calculation I did on the Overture Design Guide said for a 6 ohm load that I need 3.08C/W.
I recommend that the National value be doubled, i.e. 3.08C/W becomes 1.5C/W to keep the chip cooler than absolute maximum rating.
For this the 1.5C/W would be ideal.
If you want to mount two chipamps on the same heatsink then adopt 0.7 to 0.8C/W
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Old 28th February 2010, 11:56 AM   #6
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Thanks for the advice,

I was a bit confused with the sizing of heat sinks, but at least now I know. I will obviously way oversize it, just to keep the chips cool.
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