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1.27mm wide pcb trace carrys 1.2Amps RMS

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pcb trace resistance

i am laying out double layer 10w smps (12v in).

I have a 1.27mm trace which is taking 1.2 Amps rms for about 2cm......it is on the top layer and is decoupled either end.

my bottom layer is ground plane .

i want to make this 1.27mm trace thicker but i am told that i should not do so, but instead should fill the area around it with more ground fill.

i feel this trace should be thicker, it runs from the input emc LC filter to the power switch loop capacitor of a boost converter.

should i make it thicker to dissipate heat. or should i fill around it with ground and leave it at 1.27mm?
 

power pcb v1.2

I would definitely make it thicker.

Given that its carrying switching currents, its power dissipation can easily be higher than you might expect (P = I^2 x R remember).

Any power it's dissipating is appearing as ripple voltage, so thickening it, reducing it's resistance, will also help with ripple.

My philosophy is, why make thicker ground planes to handle more power, if I don't need to generate that much heat to begin with?


Frank.
https://www.frankvh.com
 

current capacity pcb trace

There are at least two aspects: Maximum current capacity of a trace respectively overtemperature and acceptable resistance respectively voltage drop. In low voltage circuits, the second is usually defining the trace widths.

I suggest to calculate the trace resistances. In your example it's already 8 mohm with a 1 oz (35 µm) copper PCB, quite a lot to my opinion.

As a another point, the melting integral ∫I²dt of the trace should be suficiently higher than of the fuse protecting the circuit.
 

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