DC-DC converter (buck, boost) inductor calculator
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KEY POINTS
A buck converter's inductance is L = (Vin − Vout)·D / (fsw·ΔI), with ripple current usually set to 20 to 40% of output current. Making 3.3 V at 5 A from 12 V at 500 kHz with 30% ripple needs about 3.5 µH. Both the inductor and the output capacitor shrink in inverse proportion to frequency, so higher frequencies with devices such as GaN make power supplies smaller.
Inputs
Ideal equations for continuous conduction mode (CCM). Choose an inductor whose saturation current has 20 to 30% margin over the peak current, and remember that ceramic capacitors lose much of their effective capacitance under DC bias.
Switching frequency, inductance and ripple
| Frequency | Required L | Ripple from capacitance |
|---|---|---|
| 100 kHz | 17.72 µH | 18.8 mV |
| 250 kHz | 7.09 µH | 7.5 mV |
| 500 kHz | 3.54 µH | 3.75 mV |
| 1000 kHz | 1.77 µH | 1.88 mV |
| 2000 kHz | 0.89 µH | 0.938 mV |
Higher frequency means smaller components
A DC-DC converter sets its output voltage by varying the fraction of time the switch applies voltage to the inductor (the duty cycle). Both inductance and capacitance can shrink in inverse proportion to switching frequency, so a higher frequency makes the power stage smaller. Switching loss rises in proportion to frequency, however, so the frequency is a balance between loss and component size.
GaN power transistors have very low switching loss and stay efficient above 1 MHz, which is why they spread through compact laptop adapters. Data center power for GPUs uses multiphase buck converters that step 48 V down to below 1 V at very high currents, where the performance of power semiconductors and inductors governs power efficiency.
FAQ
What inductor ripple ratio should I choose?
20 to 40% of the output current is common. Lower ripple needs a larger inductor; higher ripple increases peak current and output capacitor ripple.
Why does the output capacitance shrink at higher frequency?
The ripple charge the capacitor must absorb in each cycle falls in proportion to the switching period, so the same ripple voltage needs less capacitance.
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Last updated: October 23, 2026