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PCB Layout

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The connections on a PCB should be identical to its corresponding circuit diagram, but while the circuit diagram is arranged to be readable, the PCB layout is arranged to be functional, so there is rarely any visible correlation.

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PCB layout
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Dimitri Tskhovrebadz

I am using a couple of SMPSs on a 4 layers PCB. The recommended PCB layout seems to use solid copper regions to connect the design together. So I have the following questions: Should thermal-reliefs be used on the capacitors and resistors? Does it have any effect on performance of a SMPS circuit?
Statement: This post is only the personal view of the author and does not represent the opinions of


You can leave thermal reliefs on the inductor, resistors and small signal capacitors. Layout is very critical with SMPS designs to prevent false triggering and subharmonic oscillation. Hope that helps.


The large bodied capacitors should indeed avoid thermal relief unless absolutely necessary for manufacturability -- extra parasitics are not a good idea, and you will notice that the reference layout does not include them either. Thermals on the resistors are indeed a non-concern in this case, though their function is a low-current, and the extra resistance is insignificant compared to the resistors themselves.


When ons of my professional friend review my SMPS layout, he definitely recommended I remove all the thermal reliefs on the input and output capacitors because they add inductance and degrade the performance.

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