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  • EEVblog #105 – Electronics Thermal Heatsink Design Tutorial

    Posted on August 15th, 2010 EEVblog 21 comments

    A follow on from some of the recent blogs that have involved basic thermal heatsink calculation. This time around Dave takes you though the basic theory of thermal design and how heatsink calculations work. Then there are some real world temperature measurements to see how close to the theory we get.

    How do you read a heatsink thermal response graph? What is emissivity? It’s all here in thermal design 101.

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    • Cheshyr

      Great blog. It’s so easy to get lost in the complicated thermal calculations. This is a great reminder that rough calculations can carry you a long way, and there was a lot of good info for hobbyists in there.

      Also, that is an awesome shirt.

    • Joost

      Great tutorial!
      “If you double your component temperature, it will get 4 times less reliable as before”
      Are you talking about temperatures in degrees Celsius or in degrees Kelvin? That makes a big difference.

      • Manu

        @joost :-) The most ironic or the most stupid (and pretentious) commment I’ve ever read. I’m afraid it’s the second option.

    • http://www.brianhoskins.co.uk Brian Hoskins

      Hi Dave, great blog.

      Regarding your comments about the radiation properties of black objects, it’s funny you should mention that actually because just the other day I was explaining the very same thing to my better half. We’ve just bought a house and we’re in the process of redecorating it all, and while choosing the paint at our local store I was trying to convince her that although from an asthetics point of view it makes sense to paint the radiators white, it doesn’t actually make sense from an efficiency point of view because white bodies radiate heat poorly. If we want to maximise the efficiency of our heating system then we should really be painting them all black!!!

      Needless to say she wasn’t having any of that. She puts up with my geek T-Shirts, my hours and hours spent tinkering in the lab, my silly experiments around the house, and she even pretends to enjoy the electronic valentines stuff I give her every year. But she draws the line at painting the radiators black. I think I’ve found the boundaries!!! ;-)

      Brian

    • Mike

      It may be worth mentioning for some that in most transistor applications, the loss would not be that great for the values used . This You generally calculate the loss by multiplying the Rds ON by the drain current squared (for a MOSFET), and the Vce(sat) by the collector current (for a BJT), to achieve the heat dissipation in watts.

      • Karl (not that Karl, the other Karl)

        I reality it doesn’t matter. It even hardly matters with electronic heat think design. The black heat sinks just look better, they don’t work much better than blank aluminum. Black heat sinks working so much better is a myth.

        Heat sinks and radiators don’t reach the temperatures where thermal radiation really matters. They work by heat conduction and convection.

        • http://www.brianhoskins.co.uk Brian Hoskins

          Hi Karl,

          That’s an interesting suggestion! It should be quite easy to test that out. If I can find some time between work, my degree and decorating the house I just might!

          Cheers,

          Brian

          • Clint Lawrence

            @Brain, @Karl Paint vs unpainted makes a big difference, but the colour does not.

            We’ve been doing exactly this experiment recently at work. The emissivity of common metals varies a lot, but is typically 0.1 to 0.2. Most paints are up around 0.9. If you google you can quickly find some tables of values.

            Also radiation can make a significant contribution to the heat transfer of the heat sink, but it is important to consider the incident radiation the heat sink is subject too. For example, two heat sinks are sitting facing each other, they are just going to radiate at each other and therefore no benefit from the radiation.

      • http://www.eevblog.com EEVblog

        It doesn’t matter how you get or calculate the dissipated power, that’s not the point. It only matter how much power a device is dissipating. It also doesn’t matter if it’s a transistor, voltage regulator, power diode, audio amp IC or whatever. A TO-220 device dissipating 10W is not uncommon.

    • Mark

      Wow, another great vid Dave. Keep up the awesome work.

    • http://starlino.com/ starlino

      Dave, this is one the most useful blogs you ever made . Please, please – more content like this !

    • Arnold

      I’m an economist, I love it when you come with theory! It’s much more educative for amateurs than the rants/reviews.

    • Mike

      Thanks Dave, I really enjoy your blog!!! – Have you considered doing something on function generators, or a beginners guide to create your own PCB ?

    • http://www.crystalfontz.com John

      I’ve seen bad heat sinking design ruin a board. At work, one of our design engineers did a nice layout for a demo board to show off our ~1″ graphical LCDs. It used a small leadless buck-boost chip (which was a real pain in the ass to solder) and the whole circuit drew about 400 mA with all 5 LCD backlights on. The PTC on the board kept throwing and killing power to the board, and it turned out that the buck-boost was trying to dissipate heat, and the pad underneath it wasn’t hooked to the ground fill, so it would go into thermal shutdown.

      Anyways, long story short, thermal design is pretty damn important!

    • Jay

      Good Job, Dave!

    • Jo

      Very good presentation, simple and clear!

    • wpastega

      fantastic blog, entertaining, informative and bloody Australian

    • walter delbono

      awesome…

      :)

      • Karl (not that Karl, the other Karl)

        You know what one of the stupids words on the Internet is? “awesome”.

        Everything is fucking “awesome”. I can’t here it any more. Someone writes an “instructable” (yet another fucking stupid word) how to shit in a toilet, and I bet there is at least one dude commenting “awesome”.

    • http://mathewsmith.co.nz Mathew Smith

      Hi Dave,

      Great Blog, and the fact that you mentioned electrolytics being susceptible to heat, brilliant, I recently fixed a Philips plasma tv which had a dud power supply simply because two caps above the heatsink for the bridge rectifier and power transistors had dried up.
      They measured with in tolerance for their capacitance, but their esr was through the roof.

    • heel

      Look at the bottom of the page for two links, they are to thermal load simulator and design evaluation :
      http://www.pa-international.com.au/index.php?option=com_content&view=article&id=129&Itemid=174