Buck

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A step-down (buck) DC–DC converter switching at a fixed duty cycle.

Buck converter: a PWM-gated IGBT (duty $D=0.5$) chops the 12 V input at the switch node $V_{\mathrm{m}}$; the freewheeling diode plus the L-C filter average it down to a smoother $V_{\mathrm{out}}$ across the 20 Ω load.

An IGBT chops the input voltage while a freewheeling diode and an LC output filter average it down to a lower, smoother DC level; a PWM block driven by a constant duty-cycle reference gates the switch. The plots show the chopped switch-node waveform next to the filtered output, so you can see the ripple shrink across the inductor and capacitor.

The switch node V_m is a square wave that snaps between 12 V (IGBT on) and 0 V (diode freewheeling). Its average is D · Vin = 0.5 × 12 = 6 V, and that is what the L-C filter passes to V_out — the inductor smooths the current, the capacitor smooths the voltage, so V_out settles near 6 V with only a small triangular ripple. The run uses a 1 µs step over 30 ms so both the fast switching edges and the slow output settling are visible. Change the duty reference and V_out tracks it linearly; that proportional relationship is the whole point of a buck.