ESP8266 Community Forum

- Sun May 17, 2015 5:24 am #17634 Hi,

Got to say, love the PCB and well done ArnieO for the technical calculations. Great little device presented with this little mosfet. It seems to me that the PCB track thickness has been missed in current calculations here. I would not want to sink 5 amps of current through a PCB track this size. A calculation as follows would be required to ensure PCB track is capable of supplying required current:

The trace width is calculated as follows:

First, the Area is calculated:

Area[mils^2] = (Current[Amps]/(k*(Temp_Rise[deg. C])^b))^(1/c)

Then, the Width is calculated:

Width[mils] = Area[mils^2]/(Thickness[oz]*1.378[mils/oz])

For IPC-2221 internal layers: k = 0.024, b = 0.44, c = 0.725

For IPC-2221 external layers: k = 0.048, b = 0.44, c = 0.725

where k, b, and c are constants resulting from curve fitting to the IPC-2221 curves

It works out for a track of 1 inch in length, 2 oz copper thickness fr4 laminate the width would need to be 1.38mm

Another question I want to ask, is why was the dc module used instead of a 3.3v LDO regulator?

Nice work again well done.

- Sun May 17, 2015 6:48 am #17645 That's a very good point danbicks, thanks! The traces in the current design are 0.67mm wide, which according to http://www.4pcb.com/trace-width-calculator.html would cause a 32.4 degrees Celsius increase in temperature for a 3 Amp load.

I think it's safe to say we should consider 3A to be a good upper limit for this design. I'm thinking of doing a small redesign to take your advice into account, making those traces 2.54mm wide. That would make the traces capable of doing 7.5A comfortably.

- Sun May 17, 2015 10:09 am #17660 Hi Clement,

A pleasure. Making many high current PSU's over the years does help

Why did you use a module for the PSU 3.3v? Was it simply a case of allows wider input voltages?

Really like your work, keep up it up. Look forward to seeing the new board.

Regards

Dans

- Mon May 18, 2015 4:53 am #17730 The converter module instead of a linear regulator is purely to have a smaller power footprint. This module uses a switching transistor to regulate the output voltage instead of dissipating it as heat, so it uses considerably less power.

That is, unless I've completely missed out on some LDO regulator that performs comparably to a switching one?

Thanks for your feedback, it's great to see that there are people excited about this project!