Inductor smooths current, capacitor smooths voltage. Together, the output is clean DC. This is the Buck converter.
In the previous two lessons we saw: capacitors smooth voltage but cause current spikes; inductors smooth current but leave voltage ripple. What if we combine them?
The inductor at the switch output limits the current slew rate, shaping square-wave current into triangular; the capacitor across the load integrates/filters the triangular current, further suppressing residual voltage ripple.
This is a classic LC low-pass filter! Its cutoff frequency fc = 1/(2π√(LC)). As long as the switching frequency is much higher than fc, the output is very smooth DC.
With this, a complete Buck converter is formed: DC source → switch (PWM controlled) → inductor → output capacitor → load. The diode provides inductor freewheeling.
Vout ≈ D × VIN. By changing duty cycle D, you adjust the output voltage. Efficiency is high (ideally near 100%) and the output is clean. This is the fundamental topology used from phone chargers to server power supplies.
L=1mH, C=100μF. Output≈6V, minimal ripple. This is the Buck converter!
After reading this section, run the simulation and observe the waveforms. To explore further, open the example in a standalone page.