GND on two layers

In general, if they are to transmit high current, heat or digital

switching transients between the two ground conductors, you should place

alot of them. If the conductors are to be AC, or thermally, isolated,

only one. Not a simple topic, but most hobbyist circuits- doesn't really

matter.

Is there a package that one can calculate the voltage drop on a layer that

uses a polygon with or without via's?

"Gary Gofstein" <nospam@use.forum.net> schreef in bericht

news:hkvea1$h1m$1@cheetah.cadsoft.de...

In general, if they are to transmit high current, heat or digital

switching transients between the two ground conductors, you should place

alot of them. If the conductors are to be AC, or thermally, isolated, only

one. Not a simple topic, but most hobbyist circuits- doesn't really

matter.

No. You would need to know the distribution of the current for DC. For

AC currents in the RF range you need to know the shape of the pulse and

solve the wave equation to know where the current will flow and what

skin depth it will flow in. Nobody does that.

For "normal circuits", it's seldom an issue. How much current are we

talking about here anyway? DC, audio or RF current?

To get a comparison for DC currents you can look at trace temp rise vs

size charts for ordinary traces. You will see that unless you use super

thin "digital" traces, it's usually okay. I always use the biggest

traces I can fit anyway. There's a ULP that calculates temperature rise

on traces for DC currents; you'll see that your plane is likely to be

much bigger than necessary. You don't need to know how many vias to add,

because you should just add as many as you can to get the best

performance. You can estimate the temperature rise of a via by thinking

of it as  a wire, figure out the equivalent wire guage, consult a

current vs temp rise site or chart to get the temp rise. You should

specify your vias to be solder filled for best DC and thermal

conductance. If you will never solder to them, you don't need thermals

on vias (EAGLE default anyway). Actually, it's possible to tack solder a

wire even on a via with no thermal, so it's rare to need a thermal on a

via. All this applies only to DC currents, RF/pulse currents are a whole

nother story...

Oh yeah, if you are thinking that knowing the voltage drop is important,

it may not be. If you plan on using that ground plane as a voltage

reference you should just run parallel ground traces that don't carry

current to anyplace that needs to know ground voltage (like an opamp

input or voltage regulator). These are separate from the plane returning

current to ground potential and generating voltage drops.

The plane should carry a current of approx. 3A at 18V DC

"Gary Gofstein" <nospam@use.forum.net> schreef in bericht

news:hl1u5s$8mk$1@cheetah.cadsoft.de...

No. You would need to know the distribution of the current for DC. For AC

currents in the RF range you need to know the shape of the pulse and solve

the wave equation to know where the current will flow and what skin depth

it will flow in. Nobody does that.

 

For "normal circuits", it's seldom an issue. How much current are we

talking about here anyway? DC, audio or RF current?

 

To get a comparison for DC currents you can look at trace temp rise vs

size charts for ordinary traces. You will see that unless you use super

thin "digital" traces, it's usually okay. I always use the biggest traces

I can fit anyway. There's a ULP that calculates temperature rise on traces

for DC currents; you'll see that your plane is likely to be much bigger

than necessary. You don't need to know how many vias to add, because you

should just add as many as you can to get the best performance. You can

estimate the temperature rise of a via by thinking of it as  a wire,

figure out the equivalent wire guage, consult a current vs temp rise site

or chart to get the temp rise. You should specify your vias to be solder

filled for best DC and thermal conductance. If you will never solder to

them, you don't need thermals on vias (EAGLE default anyway). Actually,

it's possible to tack solder a wire even on a via with no thermal, so it's

rare to need a thermal on a via. All this applies only to DC currents,

RF/pulse currents are a whole nother story...