← Block library
⎏

LDO voltage regulator

@electrace/ldo-regulator@1.0.0 · CC-BY-4.0
vin 4.5–12 Vvout 3.3 Viout_max 0.5 Adropout 0.3 V
REG
The actual schematic inside this block — every part is explained below.

LDO Regulator

A low-dropout linear regulator that holds the output at a fixed 3.3 V. Unlike a buck, it doesn't switch — it acts like a smart variable resistor, burning the excess voltage as heat. That makes it quiet and cheap, but inefficient when the input is much higher than the output.

  • U1 — the regulator. Senses its own output and adjusts the pass element to keep 3.3 V.
  • Cin / Cout — required decoupling. Cout in particular sets the control-loop stability; most LDOs specify a minimum value and ESR range.

Exposes: vin (4.5–12 V), vout (3.3 V, up to 0.5 A), and gnd.

Efficiency ≈ Vout / Vin — so at 12 V in, only ~28 % of the power reaches the load and the rest is heat: P_heat ≈ (Vin − Vout) × Iout. Great for low currents from a near rail, wasteful for big steps — reach for the buck instead.

Exposed nets

●vinin · power · 4.5–12 V
●gndin · gnd
●voutout · rail · 3.3 V

Inside this block

U1
ldo-3v3
linear pass element — drops the input to a clean, low-noise 3.3 V
Cin
1uF
input stability / local charge
Cout
10uF
output stability — most LDOs require a minimum output cap

Inside the chip: Linear regulator — discrete series-pass

What U1 actually does, drawn out in discrete parts — the same view the editor's “break into discrete” shows.

The IC, drawn out: a zener sets a fixed reference and an NPN emitter-follower passes the load current, so the output sits one Vbe below the reference (Vout ≈ Vz − 0.6 V). That's the whole idea of a linear regulator — a reference plus a pass element. A real LDO integrates these with an error amplifier for tighter regulation and lower dropout; this is the teaching equivalent, not a production-optimal part.

Limits & gotchas

⚠vin.max 15V — Regulator abs-max is ~15 V in; beyond that the pass device overheats. Linear means it burns (Vin−Vout)·Iout as heat — mind the dissipation.
Use this block in a real design
Drop it on a canvas, wire it up, and watch the live checks — free, no card.
Start designing →
✦This page is generated from the block's source — the same content powers the editor's explanations and live checks.