Boost Output Capacitor

Cout = Iout · D / (fs · ΔVout)

Quick answer

This calculator solves Cout = Iout × D / (fs × ΔVout) for Output Capacitance. With Output Current 2 A, Duty Cycle 50 %, Switching Frequency 100 kHz, Output Ripple 0.6 V, the result is 16.67 µF. It solves in 5 directions, so you can enter the values you have and get the one you need.

Calculator

Output Capacitance (µF)
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Formula

Cout = Iout × D / (fs × ΔVout)

Description

In a boost converter the output capacitor alone supplies the load during the switch on-time, when the inductor is disconnected from the output. This formula sizes the capacitor for an allowed output ripple voltage. Boost outputs are inherently noisier than buck outputs because of this pulsed delivery, so the capacitor (and its ESR) dominates output ripple.

Variables

  • Cout — Output capacitance (F)
  • Iout — Output current (A)
  • D — Duty cycle (0–1)
  • fs — Switching frequency (Hz)
  • ΔVout — Allowed output ripple (V)

Practical Notes

This counts only the capacitive ripple; ESR adds ΔV = ΔIL_peak × ESR on top. Use low-ESR ceramics or parallel capacitors to meet a tight ripple spec.

Symbols and units

Symbol Meaning Default unit Accepted units
Cout Output Capacitance µF pF, nF, µF, mF, F
Iout Output Current A pA, nA, µA, mA, A, kA
D Duty Cycle — —, %
fs Switching Frequency kHz Hz, kHz, MHz, GHz
dVout Output Ripple mV pV, nV, µV, mV, V, kV

Step by step

  1. 1. What you know: Output Current 2 A, Duty Cycle 50 %, Switching Frequency 100 kHz, Output Ripple 0.6 V
  2. 2. The relation: Cout = Iout × D / (fs × ΔVout)
  3. 3. Substitute: Iout = 2 A, D = 50 %, fs = 100 kHz, dVout = 0.6 V
  4. 4. Result: Output Capacitance = 16.67 µF

Related quantities from the same inputs

  • P = V × I = 1.2 W

Nearest standard component values

Series Nearest value Error
E12 18 µF 8%
E24 16 µF 4%

Worked examples

Minimum range

Given: Output Current 2 mA, Duty Cycle 2.5 %, Switching Frequency 100 Hz, Output Ripple 10 mV

Result: Output Capacitance = 50 µF

Low range

Given: Output Current 20 mA, Duty Cycle 25 %, Switching Frequency 1 kHz, Output Ripple 100 mV

Result: Output Capacitance = 50 µF

Typical

Given: Output Current 2 A, Duty Cycle 50 %, Switching Frequency 100 kHz, Output Ripple 0.6 V

Result: Output Capacitance = 16.67 µF

High range

Given: Output Current 100 A, Duty Cycle 0.8, Switching Frequency 0.5 MHz, Output Ripple 0.9 V

Result: Output Capacitance = 0.1778 mF

Maximum range

Given: Output Current 1 kA, Duty Cycle 8, Switching Frequency 5 MHz, Output Ripple 9 V

Result: Output Capacitance = 0.1778 mF

Solving for each variable

Solve for Output Capacitance

Output Current 2 mA, Duty Cycle 2.5 %, Switching Frequency 100 Hz, Output Ripple 10 mV → 50 µF

Solve for Output Current

Output Capacitance 100 nF, Duty Cycle 2.5 %, Switching Frequency 100 Hz, Output Ripple 10 mV → 4 µA

Solve for Duty Cycle

Output Capacitance 100 nF, Output Current 2 mA, Switching Frequency 100 Hz, Output Ripple 10 mV → 0.005 %

Solve for Switching Frequency

Output Capacitance 100 nF, Output Current 2 mA, Duty Cycle 2.5 %, Output Ripple 10 mV → 50 kHz

Solve for Output Ripple

Output Capacitance 100 nF, Output Current 2 mA, Duty Cycle 2.5 %, Switching Frequency 100 Hz → 5 V

How Output Capacitance changes with Output Current

Output Current (input) Output Capacitance (result)
0.2 A 1.667 µF
0.5 A 4.167 µF
1 A 8.333 µF
1.5 A 12.5 µF
2 A 16.67 µF
3 A 25 µF
4 A 33.33 µF
8 A 66.67 µF
14 A 116.7 µF
20 A 0.1667 mF

The same result in other units

Unit Value
nF 16670
µF 16.67
mF 0.01667

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Frequently asked questions

How do you calculate Boost Output Capacitor?

Use Cout = Iout × D / (fs × ΔVout). With Output Current 2 A, Duty Cycle 50 %, Switching Frequency 100 kHz, Output Ripple 0.6 V, Output Capacitance works out to 16.67 µF.

What is the formula for Boost Output Capacitor?

The formula is Cout = Iout × D / (fs × ΔVout). In a boost converter the output capacitor alone supplies the load during the switch on-time, when the inductor is disconnected from the output.

How do you find Output Current when you know the other values?

Rearrange for Output Current: with Output Capacitance 100 nF, Duty Cycle 2.5 %, Switching Frequency 100 Hz, Output Ripple 10 mV, Output Current is 4 µA.

How do you find Duty Cycle when you know the other values?

Rearrange for Duty Cycle: with Output Capacitance 100 nF, Output Current 2 mA, Switching Frequency 100 Hz, Output Ripple 10 mV, Duty Cycle is 0.005 %.

What units does Boost Output Capacitor use?

Output Capacitance is shown in nF, µF, mF. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

Related Concepts

All Power & Efficiency formulas →
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