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Old 20th November 2015, 12:11 AM   #61
Ezcl is offline Ezcl  United States
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Join Date: Nov 2015
Location: Oregon, USA
Scratch my previous post (why can't I edit my post?), I have better questions.

I got bored and so I've started a SMD layout. The biggest question I have is: Should the MOSFETs be as far apart as possible, or is it okay if they're somewhat close together? I currently have the N-channel devices and P-channel devices on opposite sides of the board, 2cm from each other and about 8cm from the other type of device. Since the 4U chassis heatsinks are so massive, I think it would be okay with them bunched closer together, but I want to make sure.

Or, instead of having them arranged as they are (think SOT-6 package), maybe I should angle the ones in the corners of the boards so they are arranged in more of a circle. That might look cooler too.

Any input would be much appreciated.
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Old 20th November 2015, 06:47 AM   #62
sangram is offline sangram  India
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Join Date: Sep 2002
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Distance is always better, but you can run them very close together if your dissipation targets per device are more modest. Look at pictures of the Pass XA 30.5 for example, lots of device pairs packed tight together but each runs around 8-10 watts (I guess).

I have tried MOSFETs just next to each other (you can see some pictures I posted and got flamed for) in a very dense layout and it is still capable of decent level of bias. I saw 1.6A per amp PCB without the sinks hitting 50 degrees, but it is a massive sink with a 4x10 copper heatspreader to suck the heat from the devices. The device packages measure 50 degrees and the sinks 45. The usual wisdom is that if your sinks are large, you should spread devices as far as possible and if they are small (for example assisted by water or forced cooling) then a denser packaging helps more devices avail the benefits of the cooler surface.

I implemented SMD on a recent layout with 3 pairs per channel. Not built yet, but frees up a ton of space for the more important stuff and really simplifies routing by being able to use both sides of the board. You have to watch the dissipation on a few parts. We are using MELF resistors by Beyschlag for the build, better tempco and cheaper than the Dale RN55D we get here.
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Old 21st November 2015, 06:56 PM   #63
Ezcl is offline Ezcl  United States
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Join Date: Nov 2015
Location: Oregon, USA
Thanks for the information sangram.

My first version for this layout is done, I'd love some input:
Imgur: The most awesome images on the Internet
(Credit to Nelson Pass is on bottom silk, hidden for this picture)

I am using Stackpole's RNCP line of 1/4W resistors, which are rated for 200V, 400V overvoltage, in the 0805 package. Also rated to 155C.

The 3W resistors are rated for 500V and a ridiculous 200C temperature.

Let me know if things look too close or otherwise wrong. Thanks!
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Old 6th August 2016, 03:32 AM   #64
anystereo is offline anystereo  United States
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Join Date: Apr 2005
Location: Watertown, MA USA
I just come across some real nice heavy duty mil spec 32 v regulated power supplies good for 10 amps at 41 deg c. and I am thinking about finally building the turbos v2. From what i can tell the ps's should handle at least 50watts a channel with plenty of headroom. Has anyone experimented with a regulated supply for the turbo's or have advice for such?
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