I've been using switchers on all my boards. EMI noise should be less
if the regulator is in a corner away from data traces. I don't know
about current consumption but the 1A regulators only get slightly
warm. With respect to PCB area, looking at a board design I did a
few years back with a 7805, I think a 7805 plus heatsink might take
more space than a switcher that does not need a heatsink.
Off board supply is a very good option. There are regulated
switching wallwarts around now that make the task trivial. Or an off
board power brick like you say.
Cheers, James
On 14/11/2010 3:17 AM, Andrew Lynch wrote:
Hi Max! Thanks! I looked into
James DRACblade power circuitry. He is using an LM2575T
for 5V
output. The part is able to produce 1A output. At
Digikey they have
many similar parts which support 5V @ 3A output like
these
LM2756
LM2676
LM2670
LM2599
LM2576
LM2585
LM2586
LM2596
LM2673
I think any of them would work. The
switching supplies all seem to need an external
inductor, Schottky diode, and a
couple of large value capacitors. The good thing about
switchers is they
are more power efficient. The bad news is they eat up
more PCB space and have
more EMI noise. The power circuit now is a power jack,
the LM323 VR, 2
small capacitors, and a protection diode which is space
efficient although heat
dissipation will be an issue I believe.
Right now the PCB is grinding away in the
trace route optimizer getting down to a reasonable
level. It is at ~496
vias and 1690 inches overall trace length which is good
progress considering it
started at >730 vias and >1730 inches overall
trace length. Still,
it has a long way to go. While it is working I will
investigate some
ideas for possible change to a switching supply
modification.
The other option is to just offload the
power circuitry to an off board supply. An off board
supply certainly
helps with the heat *and*
EMI
noise issues. That would work too since we are looking
at an off board
supply (9VDC unregulated or 5VDC regulated) in either
case. I like to
reuse those scrap laptop and printer “power bricks” that
are so
cheap on eBay. I have several scrap units laying
around.
Thanks and have a nice day!
Andrew Lynch
Hi Andrew,
James has some good success with switching regulators
on his mini board and the
DRACblade. Maybe check his schematic.
Regards,
Max
On Fri, Nov 12, 2010 at
9:06 AM, Andrew Lynch <lyn...@yahoo.com>
wrote:
Hi
John! Yes, on board voltage regulators generate
a lot of
heat even when the load is light. Driving a
heavy load really cranks out
the wattage and they can get too hot to touch
and probably should not be next
to electronics.
The good news for using an off
board 5V regulated power supply are
cheap and plentiful on ebay. Also it would
take no change from the
current PCB design. Just plug in VCC and GND
into the appropriate VR pins
and remove/don’t install the 9VDC power
connector. The two wires
feed to the power supply into the board
directly. Nice and easy!
Something
like this would be ideal
http://cgi.ebay.com/DC-5V-3A-15W-Regulated-Switching-Power-Supply-CCTV-DVR-/370454060491?pt=LH_DefaultDomain_0&hash=item5640c85dcb
Thanks
and have a nice day!
Andrew Lynch
On 11/11/2010 05:21 AM, Andrew Lynch
wrote:
2. Is using a
9VDC power supply even feasible with
this
design? The VR is able to handle 3A
but the 9VDC unregulated supply will
have to carry at least 3A input to
work. This would have to be a laptop
or printer power brick not a cheap
wall wart. The alternative is to feed
5V regulated into the board from an
off board supply. This will save some
PCB room and is next on my list for
elimination if we need more space.
My own experience with on-board linear
regulators is with S-100. They
generate a lot of unnecessary heat, in my
opinion. Small switching power
supplies can be had for under $20, and I
think that that is a better route to
take. Just use good heavy traces to
distribute power around what is a
power-hungry board.
--John
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