High Current Traces

On 6/9/2012 2:59 PM, Dave Wills wrote:

Hi,

 

I'm a new Eagle user, but I suspect this is actually a more complicated question.

 

I have traces that will carry up to 2 amps.  Those traces also control various FETs and other signals.  If I set that net node to the trace width for the high current, all of the net gets set to that width and I don't have room to route my board.  I've already re-arranged all my components so that the wide traces are short and the pins near each other.  I've even gone from 4 layers to 6 layers.  (The board routes just fine with 4 layers by 7 mil traces.)

 

I don't see a way to set the width of signals before routing, and after routing is too late.  One idea is to isolate the low current part of the net from the high current with a 0 ohm resistor, then after routing fill in will a trace.  But even that seems a little clumsy.

 

I'm considering going to thicker copper layers so that I can reduce the trace width, but I haven't tried that yet.

 

Does anyone have any ideas on how I might solve this problem?

 

Thanks,

 

Dave

 

Help -> Net Class

You can create net classes with all the traces in the same class having

various common properties including width and clearance from other

conductive elements.    Good for high(er) current and also high voltage.

Jim

Hi Jim,

I've done that.  I have a separate net class for the high current traces.  The problem is one net goes to a few high current nodes (output of high current supply, connector, resistor, FET) but it also goes to a bunch of places that are not high current (but still the same node).  So the high current pins on the node need to be connected with wide traces, but the signal level pins do not.  If I allow all of the pins to be high current traces, I can't get it to route.

That's why I said I could split the high current and signal level pins on the net with a 0 ohm resistor.  Then Eagle wouldn't automatically make all the traces high current traces.  But that sounds like a clumsy solution.  Seems better to make the copper thicker then make all the traces less wide.

Thanks for the suggestion.

Dave

Dave Wills wrote:

Hi Jim,

 

I've done that. I have a separate net class for the high current

traces. The problem is one net goes to a few high current nodes

(output of high current supply, connector, resistor, FET) but it also

goes to a bunch of places that are not high current (but still the

same node). So the high current pins on the node need to be connected

with wide traces, but the signal level pins do not. If I allow all of

the pins to be high current traces, I can't get it to route.

 

That's why I said I could split the high current and signal level

pins on the net with a 0 ohm resistor. Then Eagle wouldn't

automatically make all the traces high current traces. But that

sounds like a clumsy solution. Seems better to make the copper

thicker then make all the traces less wide.

 

Thanks for the suggestion.

 

Dave

If you have organised the positions of the high current points then you

should manually route them with the desired width and then let the auto

router do the remaining unrouted nets narrower.

Using the autorouter entirely, you could route with the setting you mention.

At this point all you wide traces are complete. Then ripup every thing

except the wide net name. Then ripup any remaining wide traces that should

be narrow. Next change the class width to narrow and run the autorouter

again

HTH

Warren

--

Viewed / responded via the newsgroup at

news.cadsoft.de

Hi Ivan,

Thanks for the suggestions.  Yes, that's pretty much what I thought

needed to be done.  But as my initial report said, I'm a new user so

I'm still learning a lot.  One thing that stops me from manually

routing is I ran into a roadblock adding vias.  I couldn't figure out

how to make the corresponding hole in the ground plane to run the via through.

In the meantime, I figure I can go to 2 oz copper and thinner

traces.  I'm pretty close in routing everything (3 wires out of 350),

so figure I can get there with some care.

Not sure about some manual routing.  I don't know enough about Eagle yet.

Thanks again!!!

Dave

Hi Ivan,

Thanks for the suggestions.  Yes, that's pretty much what I thought

needed to be done.  But as my initial report said, I'm a new user so

I'm still learning a lot.  One thing that stops me from manually

routing is I ran into a roadblock adding vias.  I couldn't figure out

how to make the corresponding hole in the ground plane to run the via through.

In the meantime, I figure I can go to 2 oz copper and thinner

traces.  I'm pretty close in routing everything (3 wires out of 350),

so figure I can get there with some care.

Not sure about some manual routing.  I don't know enough about Eagle yet.

Thanks again!!!

Dave