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PCB trace width calculation

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sabu31

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Hi

I am designing a dc-dc converter with input current of 12A. Using pcb trace calculators available online, i am getting required width of around 400mils. The the thickness of trace is 32um. I have seen that in general the current density (for inductor design etc) is 3A/mm^2. But the given value of 400mils gives about 30A/mm^2 which is very high. Is the trace width calculator wrong or is there any thing wrong in my assumption?. Thanking you.
 

Current density values and trace widths are related to acceptable conductor overtemperature, they are no magic numbers.

Heat dissipation mechanisms of PCB traces and inductor windings are completely different. You can't compare them. Trace width calculators give at least a reasonable estimation. The overall PCB heating, also considering other parts and acceptable voltage drop may require a correction of trace widths.

I would also calculate the total trace power disspation and individual voltage drops and check if it's acceptable. As a rule of thumb, 1 oz (35 µm) copper has a sheet resistance of 0.5 mohm. The value is the resistance of a square conductor element, e.g. a 400 mil wide, 4 inch long trace has a resistance of 5 mohms.
 
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    sabu31

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FvM said:
Current density values and trace widths are related to acceptable conductor overtemperature, they are no magic numbers.

Heat dissipation mechanisms of PCB traces and inductor windings are completely different. You can't compare them. Trace width calculators give at least a reasonable estimation. The overall PCB heating, also considering other parts and acceptable voltage drop may require a correction of trace widths.

I would also calculate the total trace power disspation and individual voltage drops and check if it's acceptable. As a rule of thumb, 1 oz (35 µm) copper has a sheet resistance of 0.5 mohm. The value is the resistance of a square conductor element, e.g. a 400 mil wide, 4 inch long trace has a resistance of 5 mohms.
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Thanks FVM for the reply. As the loss is rougly 1 W for 4inch long trace ,i think its acceptable for my application.
 

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