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Buck converter

D 42 %, L 10 µH, C 3.3 µF for 12 V → 5 V at 2 A

The switch chops the input; the coil and the capacitor smooth it into a steady output.

Opens in the app on 1 December, with Circuit Notebook 1.0 See it worked out

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The example, worked out

Given

Input: 12 V
Output: 5 V
Load current: 2 A
Switching frequency: 500 kHz
Inductor ripple: 30 %
Output ripple allowed: 50 mV
Efficiency expected: 90 %

Working

the share of the time the switch is on
the inductor that keeps the ripple to what you asked
the capacitor that absorbs the ripple current
the saturation current to look for

Results

Duty cycle41.7 %

Inductor9.72 µH

Output capacitor3 µF

Peak inductor current2.3 A

Inductor ripple600 mA

Inductor rms current2.01 A

Input current926 mA

Input capacitor rms986 mA

Loss (at the efficiency given)1.11 W

Continuous down to300 mA

Switch and diode see12 V

The formulas

D = Vout / Vinthe share of the time the switch is on
L = (Vin − Vout) × D / (f × ΔIL)the inductor for a ripple
Cout = ΔIL / (8 f ΔV)the capacitor that absorbs the ripple

The usual traps

An inductor that saturates at the peak current, not the average.
The ESR of the output capacitor sets the ripple more than its capacitance.

Questions

How do I choose the inductor and capacitor of a buck converter?

D = Vout / Vin: the share of the time the switch is on. L = (Vin − Vout) × D / (f × ΔIL): the inductor for a ripple. Cout = ΔIL / (8 f ΔV): the capacitor that absorbs the ripple.

What does it give for typical values?

D 42 %, L 10 µH, C 3.3 µF for 12 V → 5 V at 2 A. Duty cycle: 41.7 %; Inductor: 9.72 µH; Output capacitor: 3 µF.

What are the usual mistakes?

An inductor that saturates at the peak current, not the average. The ESR of the output capacitor sets the ripple more than its capacitance.

In the app

Your circuit, drawn live

Change a value: the schematic redraws with your numbers on the parts.

The part you can buy

Results rounded to standard values (E12, E24, E96) and power ratings.

The working, shown

Every step written out. Try it first by hand, then check.

Into your notebook

One click puts the circuit on a sheet of your project.

Opens in the app on 1 December, with Circuit Notebook 1.0

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