Buck Converter Calculator
A buck converter steps a DC voltage down. Its inductor and output capacitor decide how much the output ripples, and this shows starting sizes for the ripple level you choose.
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How it works
The duty cycle is the output voltage divided by the input voltage. The inductor value is the input minus the output, times the duty cycle, divided by the switching frequency times the ripple current. The ripple current is the ripple percent of the output current.
The output capacitor is the ripple current divided by eight times the switching frequency times the allowed ripple voltage. This is the ideal-ripple formula, so it ignores the capacitor's series resistance.
Worked example
A converter going from 12 V down to 5 V at 2 A, switching at 500 kHz, needs an inductor of about 9.7 µH. The output capacitor comes to about 3 µF.
Questions
What does the ripple setting do?
Ripple is how much the current wiggles around its average. A bigger ripple allows a smaller inductor but a noisier output. Many designs start between 20 and 40 percent.
Why does the switching frequency matter?
A higher frequency lets you use a smaller inductor and capacitor. It also adds switching losses, so the right choice depends on your parts.
Is this enough to build a converter?
It gives starting values only. The chip's datasheet has its own recommended values and layout rules, and those should win.
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