Instructables

DIY Heatsink for Small Transistors

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Here's a little mini-instructable:

Want to squeeze a bit more current through those inexpensive TO-92 package transistors? Then add a small metal heatsink.

I made this for a PWM DC motor driver, as some 2N2222 bi-polar transistors were handy. It worked OK, but the 2N2222 was getting very hot (too hot to touch.)

This will work with any TO-92 device--but the device must have a flat part to contact the sink (as TO-92 cases do.)

It's not entirely crazy; commercial heatsinks are available for this package. And the 2N2222 specs include two power dissipation ratings, Tamb <= 25 C (500-800mW) and Tcase <= 25 C (1.2-1.8 mW) (being ambient air temperature and case temperature.) Keep the case at 25 C or below, and the current rating more than doubles.
 
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Step 2: Cut out the Heatsink

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The nibbler tool is a great way to cut shapes from any sheet metal material, even steel.

The heatsink should be large enough to soak up excess heat, but can be almost any shape. However, it must have a "tab," slightly wider and taller than the transistor.

It can contain a hole for attaching to a circuit board, if that's desired.

Step 3: Fine-tune the Shape

In order that it doesn't fall right off, the heatsink should be shaped by adding a few notches or a narrower "throat" at the top of the tab.

This prevents the "tab" from sliding out of the heat shrink tubing, and off the transistor.

Note: to be honest, tapering the "throat" at the top of the tab seems to work better....the drawing illustrates this alternate method (which I used on the prototype.)
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mgingerich2 years ago
Great little instructable. This should keep my CNC controller from melting itself :)
Electorials2 years ago
epic!
I've never seen anything like this before,

5 stars ^^
gmoon (author)  Electorials2 years ago
Thanks!
comodore6 years ago
How can I make a heatsink for a big transistor like this one in the pictures?
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Just find an old computer, rip out the CPU heatsink and fan, and get some thermal paste. Apply the thermal paste to the transistor and stick the heatsink and fan assembly to that. From there, if you really want to, you could wire the fan up to some sort of power supply and that would solve your problem.
How big of a transistor is that?? New cpu heatsinks are designed to dissipate a LOT of heat.
gmoon (author)  comodore6 years ago
Those TO-3 packages are meant to be bolted to an aluminum heatsink, and those are pretty common. Thermal compound is a good idea here, too.

Here's a link with a nice visual...
beehard44 gmoon4 years ago
well, i salvaged a lotta devices wid heatsinks, and some use thermal mat or some sort. instead of thermal paste, that is used. It is like rubber, but not rubber

comodore gmoon6 years ago
Thank you!
You can buy heat sinks for these.  All they are is a square with sides bent up like this:

l___l 

*If the picture above doesn't work this should:

l......l

All the way around.  Then cut down the sides every .6cm or so and drill 2 holes for the pins and 2 more for screws and the collector connection and that's it.


Nvm both pictures work...
Jodex comodore4 years ago
Stupid question comes here, but I have to ask because I'm not sure. Is the casing of that transistor its base or something? Thanks for the answer.
Drill a hole in a big metal plate and screw it in.
Nah, that is to easy... ;D
Not if it's six inches of steel and you use a handpowered drill it isn't.
Well... :D
I will soon add a instructable on how to do so (with a CPU fan and it heat sink)
OK. Thank you!
beehard443 years ago
lol nice idea
finally i can use my lm317l to give me 1A
Good idea. I have used aluminum tape before, but it gets bent out of shape easily. 
Capt. Howdy5 years ago
Nice. I'm gonna use this on an upcoming project.
Koil_15 years ago
On this same kind of transistor I usually just cut the heat sink with a tab that wraps around the IC. I can definitely see how this would work pretty well. I like the heat transfer from a crimped on heat sing a little better. It can easily get out of hand though, if you crimp it to hard. If you do, it breaks the chip which is considerably bad if you still want to use it. Kudos on the innovation. It's a much safer way to apply a heatsink to a small chip without a mounting hole.
Prometheus6 years ago
I like the project, but I suggest that the heatsink actually wraps around the casing to improve heat-transfer to it. Aluminum is best for this, and I can suggest using a soda can for scrap aluminum that is sufficient for this task. Also, keep in mind that thicker heatsinks are for handling surg3es, thinner ones are for more continuous duty. There is no such thing as a heatsink too big. Employ as much surface area as you can, and you can see results far beyond expectations until you actually start burning-out junctions. Crazy as it may sound, heatsinking the leads themselves can actually help too. Solder copper foil to the pins over the surface-mpount, and even more power can be pushed through, just make sure they don't touch.
gmoon (author)  Prometheus6 years ago
Yes, only the prototype was copper. The heatsink in the 'ible build was aluminum. These are all excellent points. Thanks!
flagbuff6 years ago
Very Clever! thank you!
gmoon (author)  flagbuff6 years ago
Yup. :-)
acaz936 years ago
Very useful , specially if you have to switch some motors , Cool pictures Btw
gmoon (author)  acaz936 years ago
You might think that little guy couldn't drive a 12V motor. But it does pretty well. Thanks.
acaz93 gmoon6 years ago
im using it for controlling a Relay actually , it heats up quickly since it's hardcore Fast switching!

BTW:have you seen(*)The Solenoid Concert ? (8)
1up acaz936 years ago
Dude! That is awesome! I should do that using a parallel port...
gmoon (author)  acaz936 years ago
No, I hadn't see that. It's great!
Maxx16 years ago
I feel bad for that poor transistor. I understand when your in a pinch for a part but I would rather get a part that is more rated for the task.. Good instructable tho....
gmoon (author)  Maxx16 years ago
Yes, of course-- it's always best to use the correct part. But "heatsinking" is a primary way of extending the power dissipation of any semiconductor, so this isn't a radical technique.

Besides, it's fun to test components to failure (and to be surprised when they don't fail.) Especially if you've got 20 or 30 of 'em, and they were $0.10 a piece....
rc jedi gmoon6 years ago
Testing to failure? that's what i do to my cars!
charper gmoon6 years ago
I also couldn't help but thinking "poor breadboard". Excessive current can be very destructive to them too.
gmoon (author)  charper6 years ago
No doubt. That wouldn't be an issue here: drawing about 230 mA of pulsed 12V, and it's never at 100% duty cycle.
Awesome Instructable! Pictures are great too.
gmoon (author)  GorillazMiko6 years ago
:-)
c0redump6 years ago
Just thinking about the last photo, where it shows the heatsink held on with heat-shrink sleeving. Now, if the thing gets REALLY hot, the sleeving will melt and the heatsink will fall off, making a bad situation much worse. Could you hold the heatsink on the transistor with metal, somehow, so it would never fall off?
gmoon (author)  c0redump6 years ago
You could adapt this to your needs, for sure. A twisted wire, to hold everything together might work (I'm pretty sure the transistor would fail before the plastic melts--I'm not even sure heat shrink tubing will melt, it might just crumble and burn.)

There are other options, too. Arctic Silver makes a thermal adhesive, essentially a thermally-conductive epoxy. I used what was handy...
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