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DIY Bench Power Supply #8 – Mounting Transistors on the Heatsink

DIY Bench Power Supply #8 - Mounting Transistors on the Heatsink

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In this video I go through the process of mounting the 2N3055 (TO-3) and the BD140 (TO-126) transistors to a heatsink. This is in preparation for testing the power supply under load.

Some parts for this project from my Amazon Store:

* How to mount transistors to a heatsink.
* How to mount transistors on a heatsink.
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Tags: transistors

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  1. Date: March 19, 2015 at 14:35
    Author: Aaron Meade

    Hi Martin,

    Thanks for doing these video's they're great! I was just wondering if the design is going to remain the same or if you will be revisiting it later.

    I plan on building this PSU and was wondering if you'll be covering PCB design also and whether at that stage some components may change.



  2. Date: March 19, 2015 at 14:53
    Author: Frank Nielsen

    Hmm is that the newer Metrix mtx i see on your bench!
    Are you working on a review for it ? ( what model you got? )
    I really liked to buy the old model like you have but never could get the money together for it now i am dreaming of the new model 🙂
    But of curse it depends if its just as good with the features.

  3. Date: March 19, 2015 at 15:50
    Author: USS Liberty

    Hi Martin, where can I get your final power supply schematic ?

  4. Date: March 19, 2015 at 17:55
    Author: Kris Ankers

    Is there a reason you didn't put the to220 on the inside of the heat sink. 

  5. Date: March 19, 2015 at 18:00
    Author: T Woody

    realy shouldnt use both a heat sink and pads. you want as little material between your heat sink and heat sources. youll get better transfer of heat 🙂 basicaly More is NOT better 🙂

  6. Date: March 19, 2015 at 18:13

    Martin thank you for this episode. I always enjoy power electronics.

    Where did you get that heat-sink? its huge!! looks like a 800watt heat-sink. I agree those TO-3 packages are always a mission to mount (but they very rugged devices) .Do look at using using a Sil-Pad for TO-3 packages, they serve as mechanical "cookie cutter" for outlying mechanical drilling as well. (Apart from their primary purpose, which is isolation)

    Would be a good idea to calculate the heat-sink size, Dave Jones did a good video on calculating heat sink thermal resistance.

  7. Date: March 19, 2015 at 18:54
    Author: Hi'gak Iya

    What I did when I'm mounting a TO-3 package like what you did is first I make a template out of a damage TO-3 transistor. I removed the top cover and after exposing the die I then remove the pins of the Base and Emitter leaving a hole where in you can mark the heat sink to be drilled. By doing this,you can exactly align the transistor pins without having to worry of a misaligned hole. You can also make a TO-3 template out of a cardboard.

  8. Date: March 19, 2015 at 20:33
    Author: seephor

    Martin, Good video… However, I do think sometimes you make things a bigger deal than they really are. Drilling 4 holes in soft aluminum really doesn't require this much preparation and discussion. If this was an aircraft part with high levels of precision, I would understand but you're just mounting a transistor on a heatsink… Just my two cents…

  9. Date: March 19, 2015 at 21:48
    Author: zx8401ztv

    Sticky parcel labels, good for marking out holes with a pencil and drilling through.
    Then peel the label off, no marks left behind. 🙂

  10. Date: March 19, 2015 at 23:16
    Author: Ni5ei

    The hole for the BD140 wires isn't that close, you just should've kept the heat shrink shorter. They could've been a quarter of the length.

  11. Date: March 20, 2015 at 02:22
    Author: logikgr

    Thank you for this series of high-quality videos!

  12. Date: March 20, 2015 at 22:35
    Author: Ju00Ls

    Hi, nice progress on the power supply project, very enjoyable to watch!

  13. Date: March 22, 2015 at 08:04

    Hello Martin. Thanks for the video's. Do you plan to make PCB's available for this at some point? I really want to build this so I hope you finish it soon.

  14. Date: March 23, 2015 at 13:58
    Author: MrLikerBiker

    Martin, I think that your use of thermal paste and the the thermal pad is incorrect. The best thermal contact is metal to metal. However the microscopic profile of the two metal surfaces will be very rough. Think of it as pressing together two mountain ranges (one will be inverted). The gaps that exist will contain air which is a very good insulator. This is why thermal paste is used. Although it is not as good a conductor of heat as metal, it is better than air. When applying, only use a very small amount (wipe on wipe off) since you don't want the paste getting in the way of a genuine metal to metal contact.

  15. Date: March 27, 2015 at 03:36
    Author: tbbw

    Can't wait for episode 9… project series like these are actualy realy entertaining to follow 😛

  16. Date: April 9, 2015 at 16:59
    Author: Sudheer Gautam

    im a mechanical engineer, i never understood electronics. I starterted understanding by learning from your videos.
    Me being a begineer, can you please advice what instruments to buy which power supply, multimeter etc

  17. Date: May 4, 2015 at 00:42
    Author: KEATH POLYAK

    Martin, I enjoy all your episodes…still working through your vast library.  I have learned a lot from your videos

    The imperial screw numbers may confuse people, here is some help.  

    A number 0 (zero) screw is 0.060" in diameter, and each number after that, is 0.013" larger. So a 6-32 screw in theory is 0.138" in diameter & has 32 TPI (threads per inch), and a 10-24 screw has a Ø 0.190" and has 24TPI.  Number 12 is the last as fractional threads follow.

    One more thing that may be helpful is finding tap drill sizes.  If you have to tap an M6 x 1.0 thread you will drill a hole 5mm (Ø – pitch).  This works for metric and for inch sizes as well.  This will get you into the ball park.  

    With imperial threads you will have to deal with fractional drills, number drills, & letter drills, to get the tap drill size.  Usually it is one closest size larger. ***always use a test block to confirm before using on your project.

    Thoughts from a machinist :o)

  18. Date: November 26, 2015 at 15:36
    Author: Robert Langford

    A rubber grommet would protect the leads passing through the heatsink better than passing them through the bare metal.

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