SPICE-ing Up KiCad

Use simulation to reduce risks in electronic design

- By Andrew Malcolm

Designing a power supply can be an interesting yet dangerous engineering task. You can reduce some of the inherent risk by building a model and running simulations with SPICE in KiCad.

I was recently tasked with designing a small mains power supply with an output of 5V at 1A. As the design would eventually have to pass stringent safety and compliance approvals, an off-the-shelf supply was not an option. Instead, I set out to discover how to do this design with as many standard components and with as few design iterations as possible.

Classic low output voltage power supplies use a transformer to reduce the AC mains voltage to a much lower AC voltage that is then rectified, smoothed, and regulated to produce usable DC output. However, such transformers that operate at a main frequency of 50/60Hz are bulky and inefficient, and they often generate stray magnetic fields that can be troublesome to nearby sensitive circuitry.

Switched Mode

Almost all current power supplies and voltage converters are switched mode power supplies (SMPS). This term covers all manner of power conversion devices, but what they have in common is converting a DC voltage into a pulsed signal that is then fed to some type of inductor that is in turn used to convert those pulses into pulses at a different voltage for subsequent conversion back to DC.