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

On 6/9/2012 4:37 PM, 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

 

You can override the default trace width using the Change -> Width tool.

    This will allow you to manually specify segment by segment the width

of a trace.

Jim

On 6/9/2012 4:37 PM, 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

 

You can override the default trace width using the Change -> Width tool.

    This will allow you to manually specify segment by segment the width

of a trace.

Jim