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'[EE:] - Heat sink??'
2006\11\28@141131 by Carl Denk

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subject=Re:[EE:] - Heat sink??
source= http://www.piclist.com/piclist/2006/11/23/121602a.txt?

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Thanks for all the help. Sorry, I didn't get back sooner, but I didn't
get copied on the replies.

The comments of the wall wart high voltage - probably can pick a wall
wart with a lower voltage that will provide reliable voltage above the
5VDC out of the regulator, maybe 6 or 9 VDC. That should reduce the heat
considerably.

One of the drawbacks of heatsinking the regulator to the aluminum box is
thermal expansion. The PCB (it's less than 2" x 2") also has fiber optic
transmitter and receiver on it that are threaded and double nutted
through the box wall. Probably the expansion between the board and box
won't be an issue, but reliablity long term (30 years or so) is
important. Would be nice to have a flexible pad that would conduct heat
good.
:)

2006\11\28@143437 by James Newtons Massmind

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source= http://www.piclist.com/piclist/2006/11/23/124152a.txt?

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'[EE:] - Heat sink??'
2007\01\09@101037 by Carl Denk
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subject=Re:[EE:] - Heat sink??
source= http://www.piclist.com/piclist/2006/11/23/121602a.txt?

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Here's the latest on this thread:
Found some switching 5 volt wall warts that actually under my load are
more like 5.4 volts actual. The PIC 18F1320 has 5.5 volt max. input, but
the pressure sensors have a 5.2 volt max. Think I'll return the 5 volt
wall warts to Digikey, and order a 6 volt switching or linear wall wart,
and change the on board regulator from 7805 to a LDO LM2930T. The board
is going to fabrication (quantity 3 or 4 to include spares to last a
long time) with space for the TO3 regulator and a wire hole for direct 5
volt.

Comments always appreciated. :)

2007\01\09@104743 by Bob Axtell

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Carl Denk wrote:
> subject=Re:[EE:] - Heat sink??
> source= http://www.piclist.com/piclist/2006/11/23/121602a.txt?
>
> ---
>
> http://www.piclist.com/member/cdenk-alltel-
> PIC/PICList FAQ: http://www.piclist.com
>
> Here's the latest on this thread:
> Found some switching 5 volt wall warts that actually under my load are
> more like 5.4 volts actual. The PIC 18F1320 has 5.5 volt max. input, but
> the pressure sensors have a 5.2 volt max. Think I'll return the 5 volt
> wall warts to Digikey, and order a 6 volt switching or linear wall wart,
> and change the on board regulator from 7805 to a LDO LM2930T. The board
> is going to fabrication (quantity 3 or 4 to include spares to last a
> long time) with space for the TO3 regulator and a wire hole for direct 5
> volt.
>
> Comments always appreciated. :)
>  
Why not just increase the load, using an external 25 ohm resistor would
give you a constant 200mA
load and would probably make the  wall wart switcher  fall into 5.0v
range. There would be some heat, but
would be only (P=I*V; P=.2*5) or  1 watt.

--Bob

2007\01\09@112427 by Carl Denk

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That's the problem, the little aluminum box. The power connector is
through the box wall, and the wall wart just plugs in. I need to keep
the heat inside the box to a minimum, and mounting anything outside the
box like a resistor is not possible. I'm trying to keep this as simple
as possible, and where relatively untrained people (family) can do
something like change out a board or wall wort.

Bob Axtell wrote:
{Quote hidden}

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