Power calculator, part of Premium
Boost converter
Charge a coil from the input, then let it spill on top of it: more volts, fewer amps.
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The example, worked out
Given
- Input
- 3.7 V
- Output
- 12 V
- Load current
- 500 mA
- 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
- power in equals power out plus losses
- the inductor charges from the input while the switch is on
- the capacitor feeds the load alone while the switch is on
Results
The formulas
- D = 1 − η Vin / Voutthe share of the time the switch is on
- Iin = Vout × Iout / (η Vin)power in equals power out plus losses
- L = Vin × D / (f × ΔIL)the inductor charges from the input
The usual traps
- The input current is larger than the load current by the voltage ratio.
- A boost cannot turn its output off: the input reaches it through the diode.
Questions
How do I calculate the duty cycle and inductor of a boost converter?
D = 1 − η Vin / Vout: the share of the time the switch is on. Iin = Vout × Iout / (η Vin): power in equals power out plus losses. L = Vin × D / (f × ΔIL): the inductor charges from the input.
What does it give for typical values?
D 72 %, L 10 µH, C 15 µF for 3.7 V → 12 V at 500 mA. Duty cycle: 72.2 %; Inductor: 9.89 µH; Output capacitor: 14.4 µF.
What are the usual mistakes?
The input current is larger than the load current by the voltage ratio. A boost cannot turn its output off: the input reaches it through the diode.
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.
Open the calculatorOpens in the app on 1 December, with Circuit Notebook 1.0
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