[time-nuts] Regulator choices
Hal Murray
hmurray at megapathdsl.net
Sun Jun 30 20:48:34 UTC 2013
bob at evoria.net said:
> The one thing that is missing is how to quantify the heat sink needs for a
> linear regulator. Any thoughts? IOW, is there some way to project how many
> square inches of heat sink needed for X watts to dissipate?
In the simple minded case, you can add up the (series) resistance. The units
are degrees/watt. Chips and heat sinks will have a parameter in the data
sheet: often Theta something-or-other.
Mumble, round up for the connection between the chip and heat sink.
With fins-to-air, it depends on the velocity of air. With a fan, that might
be a constant. If you are depending upon convection, it gets messy, aka
nonlinear. (I think, but don't have a good URL.)
If you are using the PC board rather than a heat sink, the key factor is the
size of the copper plane that the chip is soldered to. National had several
app-notes with numbers for various chunks of copper. With typical (digital)
multilayer boards, you can also help a lot by using many vias to connect the
small surface copper planelet to the ground plane(s) internal to the PCB.
--
These are my opinions. I hate spam.
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