The actual schematic inside this block — every part is explained below.
Boost Converter
Makes a higher voltage from a lower one — 12 V from a 3–5 V supply — by storing energy
in an inductor and releasing it above the input. The buck's mirror image.
Each switching cycle has two beats:
Charge: U1 pulls the SW node to ground. Current ramps up through L1 from the
input — the inductor is being "wound up."
Release: U1 lets go. An inductor's current can't stop instantly, so the SW node
voltage flies up until something conducts — that something is D1, dumping the
energy into Cout at 12 V.
R1 / R2 — the feedback divider. U1 adjusts its switching to hold
Vout = Vref × (1 + R1/R2) → 0.975 V × (1 + 113k/10k) ≈ 12 V.
D1 is a Schottky — it switches fast and drops ~0.3 V instead of 0.7, which matters
when it carries the full output current thousands of times a millisecond.
Cin matters more than intuition says: a boost draws its big pulsed current from the
input side.
The number that surprises everyone: power in ≈ power out, so the input current is
bigger than the output current by the boost ratio. 12 V × 0.8 A out ≈ 10 W → at 3 V in,
that's ~4 A from the source. Size the input path for it.
⚠ A boost has no off switch on its output: even with U1 disabled, the path
vin → L1 → D1 → vout conducts. Your "off" output sits at Vin − 0.3 V. If the load must
be truly disconnectable, put a switch in front.
Exposed nets
●vinin · power · 2.7–5.5 V
●gndin · gnd
●voutout · rail · 12 V
Inside this block
U1
boost-controller
switches the low side of L1 to pump energy into the output; the FB pin holds it at 12 V
L1
4.7uH
the energy store — charged from the input each cycle, discharged into the output above it
D1
schottky-20v
lets the inductor dump into the output but blocks the output from draining back; Schottky for low drop at high frequency
Cin
22uF
feeds the big pulsed input current so the source only sees the average
Cout
22uF
smooths the chopped diode current into clean DC — boosts have inherently choppier outputs than bucks
R1
113k
top of the feedback divider — with R2 it sets Vout = Vref × (1 + R1/R2)
R2
10k
bottom of the feedback divider
Inside the chip: Boost controller — the same comparator trick, low side
What U1 actually does, drawn out in discrete parts — the same view the editor's “break into discrete” shows.
Identical philosophy to the buck's hysteretic control, mirrored for a boost: the comparator watches FB against a ~1.0 V reference, and when the output sags it turns the LOW-SIDE N-FET on — charging the inductor against ground. Release the switch and the inductor's current has nowhere to go but UP through the diode into the output. Same honest simplifications as the buck: bandgap drawn as a zener, real parts use fixed-frequency PWM with slope compensation, current limits, and soft-start around this exact core.
Limits & gotchas
⚠iin.max 4.5A — A boost STEPS UP voltage by stepping up input current: 12 V at 0.8 A out means ~4 A in at 3 V. The input wiring, inductor, and source all have to carry that — the most common boost mistake is sizing for the output current.
⚠vout.min 5.5V — A boost can only go UP. If you set Vout below Vin, D1 simply conducts and the output sits at Vin minus a diode drop — unregulated.
Use this block in a real design
Drop it on a canvas, wire it up, and watch the live checks — free, no card.