Buck Converter
Steps a higher DC input (9–18 V) down to a steady 5 V at up to 3 A, efficiently. Unlike a
linear regulator (which burns the extra voltage as heat), a buck switches the input through an
inductor, so ~85 % of the input power reaches the load.
- U1 — the switching controller. Compares the feedback voltage to an internal reference
and switches
SW to hold the output at 5 V.
- L1 — the inductor, storing and releasing energy each cycle. This is the mechanism that
makes a buck efficient.
- Cin / Cout — input bulk + output smoothing/stability.
- R1 / R2 — the feedback divider. The ratio sets the output voltage:
Vout = Vref × (1 + R1/R2) → 0.8 V × (1 + 39k/10k) ≈ 5 V.
Exposes: vin (9–18 V), vout (+5 V, 3 A), and grounds.
⚠ Cin is rated 25 V — keep the input below ~20 V or it's the first thing to let go.
switches to hold the output at 5 V
stores/releases energy each switching cycle
supplies the switcher's fast current pulses
smooths the output, keeps the loop stable
top of feedback divider — sets Vout
bottom of feedback divider
Inside the chip: Buck controller — a comparator flipping a switch
What U1 actually does, drawn out in discrete parts — the same view the editor's “break into discrete” shows.
The simplest REAL control scheme there is: hysteretic ('bang-bang') regulation. The comparator watches the feedback pin against a ~1.0 V reference — FB below the reference means the output sagged, so the switch turns ON; above it, OFF. The inductor and output cap (outside this chip) smooth the banging into a steady rail. Honest simplifications: the reference is drawn as a zener (real parts use a ~1.0 V bandgap — zeners don't come that low); production controllers use fixed-frequency PWM with an error amplifier instead of pure hysteresis, plus soft-start, current limiting, and dead-time. But hysteretic converters ship in real products — this isn't a cartoon, it's the minimum viable truth. Open the comparator for the next layer down.