Switch Mode Power Supply
A 120V → 8V switch mode power supply designed from scratch in PSpice and built for an Electronics course.
A switch mode power supply (SMPS) designed from scratch as a semester project for Electronics I, stepping down 120V AC wall power to a regulated 8V DC output.
Design
The circuit uses an LM555 timer IC as the switching element, driving the converter at a set frequency. The 120V AC input passes through a transformer to step it down before rectification and filtering.
Key stages:
- Transformer — steps down 120V AC
- Rectifier — converts AC to pulsating DC
- LM555 switching circuit — chops DC at high frequency
- LC filter — smooths the output to a steady 8V DC
The full design was simulated in PSpice before being built on a breadboard, which let me verify waveforms and iron out component values before soldering anything.
What I Learned
Designing a power supply from first principles — rather than reaching for a module — forces you to understand energy storage, switching losses, and filter design. The gap between a simulation that works and a physical circuit that doesn’t smoke is humbling.