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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS66 heatsink Q.
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Bodega



Joined: Nov 02, 2008
Posts: 75
Location: Montreal

PostPosted: Tue Sep 29, 2009 8:12 pm    Post subject: CGS66 heatsink Q. Reply with quote  Mark this post and the followings unread

Hi wonderful ElectroMusic people,

I'm having a bit of a mental block here regarding the LM337/LM317 and heatsink set for the CGS66 I'm making.

Here it says it should be a TOP-3 heatsink:

http://www.cgs.synth.net/modules/cgs66_psu.html

Problem is that I can't seem to find a matching LM337/317 amongst the bazillions on Mouser. Everything seems to be TO-[something else].

Maybe I'm misunderstanding this whole thing - this is the first time I've ordered both heatsinks AND LM337s - but shouldn't they be the same format?

Any help much appreciated!

Matthew

ps. if anyone has a suggestion for LEDs on Mouser... again, there's just so many to choose from, it's a bit bewildering!
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Adam-V



Joined: Jan 29, 2007
Posts: 300
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PostPosted: Wed Sep 30, 2009 3:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think that's actually a typo on Kens page, it should be TO-3

Cheers,
Adam-V

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zthee



Joined: Feb 20, 2008
Posts: 413
Location: Stockholm

PostPosted: Thu Oct 01, 2009 6:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Is there any recommended size for the heatsinks? Like 4°C/W or something?

The ones I'm using now are running bacon hot, which might not be so good in the long run...

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Bodega



Joined: Nov 02, 2008
Posts: 75
Location: Montreal

PostPosted: Thu Oct 01, 2009 3:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cheers for the reply, Adam-V. I ended up ordering myself some TO-220s based on a recommendation that they would do the trick the same as a TO-3.

In hindsight, I wonder if that will fit....
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Adam-V



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PostPosted: Thu Oct 01, 2009 3:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

zthee wrote:
Is there any recommended size for the heatsinks? Like 4°C/W or something?

The ones I'm using now are running bacon hot, which might not be so good in the long run...


From Ken's site:

"Another factor limiting the maximum current that can be drawn from the unit is the size of the heatsink. With 600ma being drawn, each regulator can easily be dissipating 6 watts, and will require a heatsink with a rating of 12°C/W or better to operate in an ambient of 25°C. As heat in an enclosed space may well be greater than this, I'd recommend going for the best heatsink of the correct profile you can get. Hobby shops in Australia have them available at 8.5°C/W (50 mm) and 11°C/W (40 mm), depending on the shop, though I have used 63 mm heatsinks I salvaged from old switch-mode power supplies. "

Cheers,
Adam-V

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Adam-V



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PostPosted: Thu Oct 01, 2009 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Bodega wrote:
Cheers for the reply, Adam-V. I ended up ordering myself some TO-220s based on a recommendation that they would do the trick the same as a TO-3.

In hindsight, I wonder if that will fit....


If the regulators you used are in TO-3 packages (a large rounded diamond shape) then they won't work. If they are TO-220 packages (a small rectangle with 3 legs at the bottom and a metal tag at the top) then they will work.

The following show the differences between the two packages:
TO-3 Package
TO-220 Package

Cheers,
Adam-V

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zthee



Joined: Feb 20, 2008
Posts: 413
Location: Stockholm

PostPosted: Fri Oct 02, 2009 3:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Adam-V wrote:
zthee wrote:
Is there any recommended size for the heatsinks? Like 4°C/W or something?

The ones I'm using now are running bacon hot, which might not be so good in the long run...


From Ken's site:

"Another factor limiting the maximum current that can be drawn from the unit is the size of the heatsink. With 600ma being drawn, each regulator can easily be dissipating 6 watts, and will require a heatsink with a rating of 12°C/W or better to operate in an ambient of 25°C. As heat in an enclosed space may well be greater than this, I'd recommend going for the best heatsink of the correct profile you can get. Hobby shops in Australia have them available at 8.5°C/W (50 mm) and 11°C/W (40 mm), depending on the shop, though I have used 63 mm heatsinks I salvaged from old switch-mode power supplies. "

Cheers,
Adam-V


Thanks!

Was so long ago I checked that page I forgot about it!

Cheers,

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Bodega



Joined: Nov 02, 2008
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PostPosted: Fri Oct 02, 2009 8:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Adam-V wrote:
If the regulators you used are in TO-3 packages (a large rounded diamond shape) then they won't work. If they are TO-220 packages (a small rectangle with 3 legs at the bottom and a metal tag at the top) then they will work.

The following show the differences between the two packages:
TO-3 Package
TO-220 Package

Cheers,
Adam-V


Thanks Adam - that does make things more clear! My order should - knock on wood - arrive today with the heat sinks and I can see for myself.

[snip]
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Bodega



Joined: Nov 02, 2008
Posts: 75
Location: Montreal

PostPosted: Sat Oct 03, 2009 3:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Everything fits! I did have to widen the holes a touch, but no biggie.

I had one more question for you wonderfully helpful people:

Can anyone point me in the direction of a simple how-to for mounting the regs to a heatsink?

I seem to remember that the two should be isolated electrically, if obviously not thermally, with a certain kind of screw.

And you also put some kind of paste in between the two, right? Is it that white stuff that looks suspiciously like toothpaste?

I've been googling it and searching this board for a good hour with no luck - I must be using the wrong search terms, cause it seems like this would be a common question.
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Adam-V



Joined: Jan 29, 2007
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PostPosted: Sat Oct 03, 2009 4:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yep, the heatsink should be electrically isolated from the device but thermally coupled to it.

This is achieved with either mica or silicon insulators, plastic bushes and heatsink compound.

Have a look at these:

Insulating kits:
http://www.jaycar.com.au/productView.asp?ID=HP1172&keywords=heatsink&form=KEYWORD
http://www.jaycar.com.au/productView.asp?ID=HP1176&keywords=heatsink&form=KEYWORD

Heatsink compound
http://www.jaycar.com.au/productView.asp?ID=NM2010&keywords=heatsink&form=KEYWORD


Cheers,
Adam-V

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Bodega



Joined: Nov 02, 2008
Posts: 75
Location: Montreal

PostPosted: Wed Oct 07, 2009 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice one - thanks Adam-V!
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Adam-V



Joined: Jan 29, 2007
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PostPosted: Wed Oct 07, 2009 4:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

You're welcome.

Cheers,
Adam-V

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active



Joined: Jan 21, 2011
Posts: 25
Location: Brooklyn, NY

PostPosted: Tue Feb 08, 2011 11:01 am    Post subject: Reply with quote  Mark this post and the followings unread

i'm bombarding the cgs forum right now!

so i don't know much about heatsinks and am a little confused by the whole process, hence me trying to DIY route, trying to learn in a hands on manner.

so first thing, just simply soldering a heatsink onto the CGS066 is not properly isolating it from the device, correct? there needs to be some sort of insulation between the bottom of the heatsink to the board, right? And they connect to the circuit purely through the leads.

and then ratings and c/w stuff also has my head in a bit of a swarm. i'm hoping to run this unit at +/-12V. So would something like this guy work, or am i totally lost?

http://www.mouser.com/ProductDetail/Ohmite/EV-T220-64E/?qs=sGAEpiMZZMttgyDkZ5WiunankxlM5/VpbGFCQNy7vzA%3d


thanks for all your help!
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magman



Joined: Feb 04, 2009
Posts: 361
Location: Liverpool, UK

PostPosted: Thu Feb 10, 2011 8:54 am    Post subject: Reply with quote  Mark this post and the followings unread

active,

You don't have to worry about insulating the heatsink from the board, in fact it the pads it is soldered to on the CGS66 PCB shouldn't be connected to anything else anyway (If they are, there is a PCB short that should be removed).

You should have an insulting washer though, between the LM3XX devices and the heatsink, similar the the items Adam-V posted links for above. You also need an insulating washer between the screw that fixes the LM3XX devices to the heatsink. Heatsink compound is also a good addition, spread on both sides of the insulating washer.

As regards the heatsink itself, I'm afraid the size of the heatsink depends.

It depends on the voltage of your transformer and the amount of power you want to use on the PSU.

In simple terms the °C/W rating of a heatsink means how many degrees C will the temperature of the heatsink rise above the ambient temperature for each Watt of power dissipated by the heatsink.

As an example, lets say you pick a heatsink with a 10°C/W rating and want to fully load the PSU to 600mA with the transformer of 15V AC. The effective DC voltage of the rectified transformer voltage is a little over 21V. You want to use 12V, so this means the Regulator IC has to "lose" 9V, which it will do virtually all of in heat. With a 600mA load, this would equate to 5.4W.

Now with a heatsink at 10°C/W rating, this means the temperature would raise by 5.4 x 10°C or 54°C above ambient or 74°C in an average room, or in other words uncomfortably hot.

If you are using an 18V AC transformer, the temperature goes up by another 4.5°C/W (another 27°C in this example, to 101°C Shocked). If you are using less power the temperature goes down. If the heatsink is in an enclosed space, without any ventilation, the temperature goes up.

As regards the heatsink you linked to at Mouser, the detail page on Mouser states this as a 10°C/W, whereas the data sheet states this is as at least 7.4°C/W. For most applications, this will be fine as long as you don't try to take the maximum power out of the PSU and you are using a 15V AC transformer.

I think I've got these figures right, but please shout out if I've made any obvious errors.

All the best

Magman

Last edited by magman on Thu Feb 10, 2011 10:17 am; edited 1 time in total
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active



Joined: Jan 21, 2011
Posts: 25
Location: Brooklyn, NY

PostPosted: Thu Feb 10, 2011 9:40 am    Post subject: Reply with quote  Mark this post and the followings unread

@magman

thank you sooooo much! it makes a lot of sense. i still need to read a bit more to fully grasp it, but i thank you for all your help.
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