LM4780 Heatsinking

jackinnj · 5th January 2005, 05:17 PM

When you mount the LM4780 on the heat sink it's a good idea to use a small piece of aluminum stock to secure the chip onto the heatsink -- the picture below is a proto using 1/8" stock -- please excuse the fact that the screws don't match!

The LM4780 is two LM3886's but with a smaller surface area for contact with the heat sink. Thus the thermal connection is even more important than for the LM3875 and LM3886. I milled a bit of the stock away so that the chip is pulled tightly to the sink-- you could use a file to do the same thing.

I found that the amplifier would cycle in out with the SPIKE protection, until I put a girdle on the darned thing.

btw, the heat sink is around 1.6 C/W.

Mr Evil · 5th January 2005, 05:38 PM

Looks like a good idea. Perhaps it would be even better if the aluminium was bevelled very slightly to ensure most pressure is applied to the centre of the package (I assume that's where the most heat is generated - I've never opened one up to look)?

jackinnj · 5th January 2005, 05:42 PM

you can't see it from this angle, but I milled off enough so that it snugs up tight.

ingrast · 5th January 2005, 06:00 PM

I do the same with the LM3886 to better spread screw pressure on the tab.
For rigidity, I prefer a "L" profile (abt. 7x7 mm, 1.5 mm width). For the LM4780 it should be a good idea to extend the piece length in order to complete the screw holes.

Rodolfo

5th January 2005, 05:17 PM	#1
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	LM4780 Heatsinking When you mount the LM4780 on the heat sink it's a good idea to use a small piece of aluminum stock to secure the chip onto the heatsink -- the picture below is a proto using 1/8" stock -- please excuse the fact that the screws don't match! The LM4780 is two LM3886's but with a smaller surface area for contact with the heat sink. Thus the thermal connection is even more important than for the LM3875 and LM3886. I milled a bit of the stock away so that the chip is pulled tightly to the sink-- you could use a file to do the same thing. I found that the amplifier would cycle in out with the SPIKE protection, until I put a girdle on the darned thing. btw, the heat sink is around 1.6 C/W.

5th January 2005, 05:38 PM	#2
Mr Evil diyAudio Member Join Date: Aug 2004 Location: Behind you	Looks like a good idea. Perhaps it would be even better if the aluminium was bevelled very slightly to ensure most pressure is applied to the centre of the package (I assume that's where the most heat is generated - I've never opened one up to look)? __________________ https://mrevil.asvachin.eu/

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5th January 2005, 05:42 PM	#3
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	you can't see it from this angle, but I milled off enough so that it snugs up tight.

5th January 2005, 06:00 PM	#4
ingrast diyAudio Member Join Date: Sep 2004 Location: Montevideo	I do the same with the LM3886 to better spread screw pressure on the tab. For rigidity, I prefer a "L" profile (abt. 7x7 mm, 1.5 mm width). For the LM4780 it should be a good idea to extend the piece length in order to complete the screw holes. Rodolfo

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