I have drawm up a power supply on eagle, on bread board it all works
fine, but when i did a single layer pcb it didn't. Now one thing i
noticed if i use autoroute the current doesn't seem to take the same
path as it does on breadboard, it seems to run here and there... does
this matter?
Possibly...
Schematic:
http://chrispol.ath.cx:8080/power.jpg
Board Layout:
http://chrispol.ath.cx:8080/powerboard.jpg
First, I see an error on the schematic - the AC ground should come
from pin 2 of the connector, not pin 3.
The board layout seems to have six diodes, but there are only four on
the schematic???
The board layout is poor - the capacitors at the input and output of
the regulators should be placed very close to the regulators - you
want short fat tracks between the hot side of the capacitors and the
regulator, and between the ground side of the capacitors and the
regulator. I can't see how you get from C2+ to IC2-in.
Autorouters can be useful, but they can also seriously mess up the
routing - things may be connected, but the tracks will go all over the
countryside. Strangely, they will often do a worse job on a simple
board like this than on a more complex board.
I don't know if Eagle has an auto-placer - but if so, don't bother
with it. Autoplacers were invented to appease the marketing
department, and rarely do anything useful, even on high-end CAD
systems.
I don't know what currents you expect to have on this board, but as a
matter of course, I would use .050, or even .100, tracks in a power
supply. There is lots of room on the board for Really Big tracks.
A comment on schematic drawing conventions - I consider it Bad
Practice to have 4-way junctions on a schematic - if the connection
dots go fuzzy (as they will after a few photocopies), it will be
unclear whether C1- and C5+ are just connected to each other, or if
they are also connected to ground. I would move the whole -12
regulator section right one grid position, so that you only have 3-way
connections - that would make it perfectly clear that C1- and C5+
connect to ground.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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