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Author Topic: Power Supply Heat Sink Question  (Read 6124 times)
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w8khk
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« on: April 23, 2017, 11:50:53 PM »

I bought a power supply kit from the far east, which did not include any instructions.  Here is a link to the product:

https://www.banggood.com/DIY-USB-Boost-Single-Turn-Dual-Power-Module-Linear-Regulators-Multiple-Output-Power-Kit-p-1022517.html

I will attach a few pictures to clarify my question. 

The power supply uses a switcher to provide positive and negative voltages to a series of linear regulators: 78M05, 78M12, 1117-3.3, 79M12, and 79M05.  The switcher is an XLSEMI XL6008.  The regulators and switcher are all tab surface mount devices. 

The power supply works as designed, but I do not know the correct method to mount the heat sinks.  There are six finned aluminum sinks, which appear to have double-sided tape for mounting.  I would assume the sinks mount on the bottom side of the board, and heat is conducted from the solder tab through the board. 

But, is it possible I am wrong, and the sinks should be applied to the top of each device?  Someone reading this must know the correct method.  Thanks for your help!

 


* BoardTop.jpg (1345.53 KB, 2592x1944 - viewed 278 times.)

* BoardBottom.jpg (800.17 KB, 2592x1944 - viewed 282 times.)

* SinksAndChips.jpg (1177.92 KB, 2592x1944 - viewed 309 times.)
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Rick / W8KHK  ex WB2HKX, WB4GNR
"Both politicians and diapers need to be changed often and for the same reason.”   Ronald Reagan

My smart?phone voicetext screws up homophones, but they are crystal clear from my 75 meter plate-modulated AM transmitter
WD5JKO
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« Reply #1 on: April 24, 2017, 07:34:01 AM »



It does appear they mount to the back side. The thermal impedance through the board and the 3 plated thru holes is likely pretty high. Then the thermal impedance added with double sided sticky makes the thermal path to the tiny heatsink even higher. Still, the total output in watts is 10W.

One change I might consider to try. If the double sided sticky can be removed (try with razor blade), then super glue the heat sinks to the back.

One poster had a -12v problem, and found that -12v cannot be loaded unless the +12v is also loaded.

Jim
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w8khk
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« Reply #2 on: April 24, 2017, 11:01:30 AM »

Thanks for the suggestions, Jim.

I will clean the sinks and mount them with super glue.  I had the same concerns about the thermal impedance through the board, but I will be loading it lightly, only using +5, +12, and -12 for a digital function generator.  I tried loading each output individually and all seems ok on my unit.

A related question about sil-pads.  Are they used without thermal compound, or is the thermal grease required?  I am currently building a 16 fet class E amplifier for 75M and PDM modulator ala QIX design.  I have used mica insulators in the past, but never tried sil-pads. 

Thanks again and 73
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Rick / W8KHK  ex WB2HKX, WB4GNR
"Both politicians and diapers need to be changed often and for the same reason.”   Ronald Reagan

My smart?phone voicetext screws up homophones, but they are crystal clear from my 75 meter plate-modulated AM transmitter
WD5JKO
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« Reply #3 on: April 24, 2017, 05:14:45 PM »


Rick,

    This thermal stuff is full of pitfalls. The K7DYY SS Class D rig uses plastic insulated FET's so they don't need an insulator. The compromise there is the convenience of not having an insulator is replaced with a much higher thermal impedance junction to heatsink.

     Then there are some GAN FET's and possibly some SIC Fet's which make the FET case the source instead of the drain. They should all be made that way!

      The TO-220 package is subject to mechanical cocking from the screw tightening, so the area getting hot might not be clamped very well. The insulator can get pinched too from this effect on the tab side.

      Then the thermal greases made are NOT the same. Most are now ROHS compliant, and therefore pretty useless, but still better than air.

      Jim
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w8khk
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« Reply #4 on: April 24, 2017, 05:29:58 PM »

Thanks, Jim.  I am planning to use sixteen FQA11N90 fets.  I believe they are similar to the TO220 tabs, albeit a bit larger.  Wondering if you would use sil-pads, or would mica be better?

I am not up on the various heat sink compound qualities.  I bought a small tub of HALNZIYE HY400 thermal grease, wondering if that is any good for this application, and whether I should use it with mica, or with sil-pads, or just sil-pads.

I am open to other suggestions and do not mind spending a bit more to protect my investment thus far.   I will be using the overload/shutdown circuits and protecting the rig as much as possible....
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Rick / W8KHK  ex WB2HKX, WB4GNR
"Both politicians and diapers need to be changed often and for the same reason.”   Ronald Reagan

My smart?phone voicetext screws up homophones, but they are crystal clear from my 75 meter plate-modulated AM transmitter
KD6VXI
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« Reply #5 on: April 24, 2017, 07:47:51 PM »

I only use sil pads now.  Unless it's something I have a mica insulator for.

AFAIK, sil pads do NOT use any heat sink compound.  I've never used any, fwiw.

My CNC controller has the same types of sinks on each channel (I have a 4 axis control).  Each ic has a sil pad that had adhesive on both sides.

Remove adhesive, apply to ic.  Remove adhesive on top, apply heat sink to the chip.

--Shane
KD6VXI
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w8khk
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« Reply #6 on: April 25, 2017, 12:05:05 PM »

Shane, Thanks for the clarification.  I will go with the sil pads.  I have a very large aluminum sink, and hope to get away without running a fan on the Class E amplifier and the PDM deck.  73....
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Rick / W8KHK  ex WB2HKX, WB4GNR
"Both politicians and diapers need to be changed often and for the same reason.”   Ronald Reagan

My smart?phone voicetext screws up homophones, but they are crystal clear from my 75 meter plate-modulated AM transmitter
KD6VXI
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« Reply #7 on: April 26, 2017, 11:30:42 AM »

No problem Rick.

I had a similar question  and then I had the first board come complete for the cnc.  And the silpads where as described.

I'll snap a pic tonight, if I remember.  This new motorcycle is taking a lot of my time :-)

--Shane
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w8khk
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« Reply #8 on: April 26, 2017, 12:33:09 PM »

Thanks, Shane, I look forward to seeing the photo. No apologies for the motorcycle taking up your time, that is as it should be.  I have two, a Honda Shadow 600 and a Yamaha V-Star 950.  It is finally warm enough to ride again!
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Rick / W8KHK  ex WB2HKX, WB4GNR
"Both politicians and diapers need to be changed often and for the same reason.”   Ronald Reagan

My smart?phone voicetext screws up homophones, but they are crystal clear from my 75 meter plate-modulated AM transmitter
WD5JKO
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« Reply #9 on: April 26, 2017, 01:37:29 PM »


I have attached some info on mounting these transistors. They show the thermal resistance versus screw torque, and there is a sweet spot...too tight is as bad as too loose.

Jim
Wd5JKO

* AN101_TO220_Guidelines.pdf (680.65 KB - downloaded 655 times.)
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w8khk
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« Reply #10 on: April 26, 2017, 02:00:44 PM »

That is all interesting reading, including lead bending techniques and soldering practice.  Thank you for sharing the document.  I have disassembled many boards that included the metal clips that apply pressure to the device body, and I think I will use those for the FETs, and a torque limiting tool to carefully tighten the mounting hardware.
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Rick / W8KHK  ex WB2HKX, WB4GNR
"Both politicians and diapers need to be changed often and for the same reason.”   Ronald Reagan

My smart?phone voicetext screws up homophones, but they are crystal clear from my 75 meter plate-modulated AM transmitter
KD6VXI
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« Reply #11 on: April 26, 2017, 11:54:05 PM »

Rick,

I already put the silpads and sinks on the new controller, but I'll include a pic of the original controller, which never worked, but utilizes the same plug in stepper controller boards.

I believe it will be self explanatory lol.

Incidentally, I was given a largish square of the silpad material for these, and didn't like this method.  I wasn't able to exactly trim it, since it has two slippery silicon(ish) layers to protect the adhesive surfaces.

Hope it helps!

--Shane
KD6VXI


* 14932648783801013785683.jpg (2393.02 KB, 2304x4096 - viewed 251 times.)

* 1493264934815257475464.jpg (2105.69 KB, 2304x4096 - viewed 265 times.)

* 1493265081117582870633.jpg (3213.89 KB, 2304x4096 - viewed 240 times.)
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KD6VXI
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« Reply #12 on: April 27, 2017, 12:02:27 AM »

As to the bike, it was time.  I bought an Suzuki Intruder 1400.  Fits my son and I great, he's 12, but just south of 6 foot.  I'm. 6'4", fruit didn't fall far from the tree.

My son and I walked to the city bus, rode it to the Greyhound.  Greyhound from Bakersfield to Los Angeles.  Coworker out of Los Angeles office from LA to Riverside.  Bought the bike, took a 2 day cruise home (we got it at 8 pm, so first night was about a hundred miles).

Interestingly enough, the LAST time I got on a bike, I took a ride into a concrete barricade at 130.  Wide open throttle on a bike w a turbo. 

I knew, if we had no other way to get back home, I'd 'man up'.  Had walked into a dealership twice here and walked out.

Anyway, feels great.  It was time.  15 minutes into the ride, my son says 'Dad, this is something EVERY kid should experience'.  I agree.

Didn't mean to derail the thread....

--Shane
KD6VXI
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w8khk
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« Reply #13 on: April 27, 2017, 09:11:35 PM »

Thanks for sharing the photos.  Looks like a very compact CNC controller, with the little Arduino Nano.  Would like to see links to the rest of your CNC project.

Thanks for all the info on the sil pads. As stated previously, I will go with sil pads and clips to provide even torque on the chips to minimize thermal impedance.

No worries about  a thread hijack, good to hear about your new bike.  I looked it up, a classy sleek machine!  I bet your son loves it!  That was quite a ride back to Bakersfield.  Of course better than riding the bus!  One of the problems with riding here in the east this time of year is the constant outbreak of thunderstorms.  I don't like to ride in the rain or after dark.  But I do have quite a bit of luggage space on both my bikes so I can go for several days.
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Rick / W8KHK  ex WB2HKX, WB4GNR
"Both politicians and diapers need to be changed often and for the same reason.”   Ronald Reagan

My smart?phone voicetext screws up homophones, but they are crystal clear from my 75 meter plate-modulated AM transmitter
KD6VXI
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« Reply #14 on: April 27, 2017, 10:45:32 PM »

I'll start a thread on the cnc sometime.

My source for pc boards went back to school, and I was tired of playing games.  This one will do 6 inches by 9 inches and will engrave and drill into soft metals (copper and aluminum) as well as all plastics, wood, etc.

The laseraxe controller is supposed to be good.  Mine didn't work out of the box.

My son is hooked.  He's already decided he will be riding the bike when he gets his license (yeah, right)....  Lol

--Shane
KD6VXI
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