Author Topic: Where to locate TO-220 transistor on a rectangular heatsink  (Read 1169 times)

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Offline vr6Topic starter

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Where to locate TO-220 transistor on a rectangular heatsink
« on: April 04, 2019, 05:56:40 pm »
I have a rectangular Fisher SK 485 heatsink (160mm x 60mm) and I want to attach a TO-220 transistor to it. What is the best location to mount it? Is it near the bottom edge or right in the middle?
Thanks in advance
 

Offline helius

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Re: Where to locate TO-220 transistor on a rectangular heatsink
« Reply #1 on: April 04, 2019, 06:35:42 pm »
I think you're asking if there is any difference in thermal performance? There isn't any difference.
Mounting location depends on the mechanical design of the unit and the mounting method. Common mounting methods are machine screws with nuts and nylon insulators, specially made clips, or in some cases sheet metal screws.
The TO-220 device can be electrically insulated from the heat sink with silicone pads or mica.
 
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Offline vr6Topic starter

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Re: Where to locate TO-220 transistor on a rectangular heatsink
« Reply #2 on: April 04, 2019, 06:46:08 pm »
Thanks that's what I wanted to know.
 

Offline alex.martinez

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Re: Where to locate TO-220 transistor on a rectangular heatsink
« Reply #3 on: April 04, 2019, 07:01:57 pm »
If the heat soruce is near the dissipation region, you will have no difference on where you locate it, for t --> inf.
 

Offline helius

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Re: Where to locate TO-220 transistor on a rectangular heatsink
« Reply #4 on: April 04, 2019, 07:10:08 pm »
Really?
The practical power for a TO-220 is around 30W. Mounting the device at the edge or in the center doesn't make much difference at such a flow rate. Much more important is controlling the mounting pressure.
 

Offline Mechatrommer

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Re: Where to locate TO-220 transistor on a rectangular heatsink
« Reply #5 on: April 04, 2019, 07:12:13 pm »
i always like in the middle if possible. heat will spread in heatsink and dissipated to air more evenly. i believe putting it on the edge will make higher case temp due to uneven temp gradient on the heatsink, but havent made a math on that, ymmv.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline alex.martinez

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Re: Where to locate TO-220 transistor on a rectangular heatsink
« Reply #6 on: April 04, 2019, 11:01:54 pm »
i always like in the middle if possible. heat will spread in heatsink and dissipated to air more evenly. i believe putting it on the edge will make higher case temp due to uneven temp gradient on the heatsink, but havent made a math on that, ymmv.

This is true before you reach steady state (a couple of minutes) since the heat must spread to the cooling region. Once it starts flowing, there is not much difference.
 


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