What is the formula for Boost Output Capacitor RMS Ripple?

The Boost Output Capacitor RMS Ripple formula is Icout(rms) = Iout × √(D / (1 − D)), where Icout—Output-capacitor RMS ripple current (A); Iout—Output current (A); D—Duty cycle (0–1).

What does Icout mean in the Boost Output Capacitor RMS Ripple formula?

Icout is Output-capacitor RMS ripple current (A).

Boost Output Capacitor RMS Ripple

Q: How do you calculate Boost Output Capacitor RMS Ripple?

Use the formula Icout(rms) = Iout × √(D / (1 − D)). A boost converter’s output capacitor carries heavy pulsed current because it supplies the full load whenever the switch is on. Enter the values you know in the calculator above and it solves for the remaining variable.

Icout = Iout · √(D / (1 − D))

Calculator

Output Cap RMS Ripple

Output Current

Duty Cycle

Result

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Formula

Icout(rms) = Iout × √(D / (1 − D))

Description

A boost converter’s output capacitor carries heavy pulsed current because it supplies the full load whenever the switch is on. The RMS ripple current grows rapidly with duty cycle, so high step-up ratios place severe ripple-current demands on the output capacitor. This rating, not capacitance alone, usually determines how many capacitors are needed.

Variables

Icout — Output-capacitor RMS ripple current (A)
Iout — Output current (A)
D — Duty cycle (0–1)

Practical Notes

At D = 0.5 the ripple equals Iout; at D = 0.8 it is twice Iout. Parallel low-ESR ceramics to share the ripple current and reduce ESR-driven ripple voltage.

Related Concepts

All Power Distribution formulas →

Decoupling Capacitor Impedance Capacitor Ripple Current (Buck) Bulk Capacitor Hold-Up Energy Buck Input Capacitor RMS Ripple Boost Output Capacitor RMS Ripple

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