Boost Converter Calculator
Duty cycle, inductor, output capacitor and switch current for a step-up converter.
What it does
A boost converter steps a DC voltage up. The calculator gives the duty cycle, inductor, output capacitor and the larger input current the converter draws.
Where it's used
Running 5 V or 12 V circuits from a single Li-ion cell, LED drivers and USB power banks.
How to use it
- Enter input and output voltage and output current.
- Enter the switching frequency.
- Choose the inductor ripple and the output ripple voltage.
- Check the inductor and switch current ratings.
The formula explained
- D
- 1 − Vin·η / Vout
- I_L
- average inductor (input) current = Iout / (1 − D)
- L
- inductance for the chosen ripple
- Cout
- output capacitance for the chosen ripple voltage
Worked example
A Li-ion cell boosted to 5 V at 1 A.
Inputs:
- Input voltage: 3.7 V
- Output voltage: 5 V
- Output current: 1 A
- Switching frequency: 1M Hz
- Inductor ripple (ΔI/I_L): 30 %
- Output voltage ripple: 50m V
- Efficiency estimate: 90 %
The calculator gives:
- Duty cycle D: 33.4 %
- Minimum inductance: 2.743 µH
- Minimum output capacitance: 6.68 µF
Tips and common mistakes
- The input current is always larger than the output current — size the battery and wiring for it.
- A basic boost cannot output less than its input voltage.
- Very high duty cycles (above about 85 %) are inefficient and hard to stabilise.
Questions people ask
How is the duty cycle worked out?
D = 1 − (Vin × efficiency) / Vout. From a 3.7 V cell to 5 V at 90 % efficiency that is 1 − 3.33 / 5 ≈ 33 %.
How much current does it take from the battery?
Power in equals power out divided by efficiency: Iin = Vout × Iout / (Vin × η). For 5 V at 1 A from 3.7 V at 90 %, the cell supplies about 1.5 A — size the battery, connector and wiring for that, not for 1 A.
Can a boost converter switch its output off?
Not a basic one. Even when it stops switching, current flows from the input through the inductor and diode, so the output sits at about the input voltage. Use a converter with true load disconnect, or add a load switch, if the output must go to 0 V.
Reference: CCM
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Enter your values to get the result with the formula, substituted values and an explanation of each step.