After my initial question about switching regulators I had decided on trying to use an LM2678 for an adjustable/variable voltage form 5-24V and 5A max with an input of ~30VDC.
The application will be a stepper motor tester for varying motors, hence the adjustable voltage.
In the datasheet, they mention that the PCB layout is very important for this device:
They also give this layout pattern which I admit to not fully understand:
I made this schematic here with the following PCB layout.
Please note:
The heatsink might change, but the actual Schottky diode and the LM2678 have the tab connected to ground, so I would like to share the heatsink.
J1/J2 pin headers are just for demo, in real design they will get replaced by beefier screw terminals of course.
RV1 will actually be replaced by a front panel potentiometer and not be on the board; it's for reference here only.
And once again, with the zones filled (but harder to see silkscreen):
My questions would be:
The bold traces from the design are all very small and copper pours are used for ground and L1 to C3. Other track widths are 2mm. I tried moving the feedback wiring far from the inductor. Would this layout seem acceptable?
Is there some trace/part (I'm sure!) that could be improved?
They say prototype etc, but I only need to make two or so of those boards so I'd like to get this right and obviously on a breadboard this cannot be much tested layout-wise, so what other guidelines would there be to follow, or is this a bit of a tall order without tinkering on a real PCB?
neither the actual Schottky diode nor the LM2678 have the tab connected
How? Schottky diodes in 2-terminal TO-220 (except TO-220FP which is completely insulated) packages have the tab connected to the cathode (and thus to the GND). And the regulator's tab too is connected to GND. If you are using insulators, don't. They reduce the heat transfer capability. \$\endgroup\$ – Rohat Kılıç May 7 '20 at 6:41