Boost Converter Calculator
Calculate duty cycle, inductor, and output capacitor for a step-up (boost) DC-DC converter.
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How the Boost Converter Calculator Works
A boost converter steps up voltage from a lower input to a higher output using an inductor, switch, diode, and capacitor. The energy stored in the inductor during the ON phase is released to the output during the OFF phase, raising the voltage.
Duty Cycle
D = 1 − Vin / Vout
Converting 12V to 48V gives D = 1 − 12/48 = 0.75 (75%). The switch is ON for 75% of each cycle. Note that high duty cycles (above 0.85) are generally avoided due to efficiency and control loop stability concerns.
Input Current
Iin = Iout × Vout / Vin (assuming 100% efficiency)
The input current is much higher than the output current. For a 12V-to-48V, 0.5A output design, the input draws ~2A. Size the input capacitor and trace width accordingly.
Inductor and Output Capacitor
L = Vin × D / (f × ΔIL) Co = Iout × D / (f × ΔVout)
The output capacitor in a boost converter must handle a large discontinuous current (the diode current). Use low-ESR capacitors and verify the RMS current rating against the datasheet.
Design Example: 12V to 48V, 0.5A, 200kHz
- D = 1 − 12/48 = 0.75
- Iin = 0.5 × 48/12 = 2.0A
- With 20% ripple → ΔIL = 0.4A
- L = 12 × 0.75 / (200e3 × 0.4) = 112.5 μH
- With 100mV ripple → Co = 0.5 × 0.75 / (200e3 × 0.1) = 18.75 μF
Frequently Asked Questions
Why is the boost converter input current so high?
Power conservation: Pin = Pout (ignoring losses). If Vin is much lower than Vout, the input current must be correspondingly higher. Always size your input components — traces, connectors, capacitors — for the input current, not the output current.
What is the maximum practical duty cycle for a boost converter?
Most boost converter ICs limit the maximum duty cycle to 80–92% to ensure the inductor can fully transfer energy and to maintain control loop stability. Designs requiring D > 0.85 often use a cascade or SEPIC topology instead.