Boost Output Capacitor RMS Ripple
Icout = Iout · √(D / (1 − D))
Quick answer
This calculator solves Icout(rms) = Iout × √(D / (1 − D)) for Output Cap RMS Ripple. With Output Current 2 A, Duty Cycle 50 %, the result is 2 A. It solves in 2 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
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.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| Icout | Output Cap RMS Ripple | mA | pA, nA, µA, mA, A, kA |
| Iout | Output Current | A | pA, nA, µA, mA, A, kA |
| D | Duty Cycle | — | —, % |
Step by step
- 1. What you know: Output Current 2 A, Duty Cycle 50 %
- 2. The relation: Icout(rms) = Iout × √(D / (1 − D))
- 3. Substitute: Iout = 2 A, D = 50 %
- 4. Result: Output Cap RMS Ripple = 2 A
Worked examples
Minimum range
Given: Output Current 2 mA, Duty Cycle 2.5 %
Result: Output Cap RMS Ripple = 0.3203 mA
Low range
Given: Output Current 20 mA, Duty Cycle 25 %
Result: Output Cap RMS Ripple = 11.55 mA
Typical
Given: Output Current 2 A, Duty Cycle 50 %
Result: Output Cap RMS Ripple = 2 A
High range
Given: Output Current 100 A, Duty Cycle 0.8
Result: Output Cap RMS Ripple = 0.2 kA
Maximum range
Given: Output Current 1 A, Duty Cycle 0.8 %
Result: Output Cap RMS Ripple = 89.8 mA
Solving for each variable
Solve for Output Cap RMS Ripple
Output Current 2 mA, Duty Cycle 2.5 % → 0.3203 mA
Solve for Output Current
Output Cap RMS Ripple 100 µA, Duty Cycle 2.5 % → 0.6245 mA
How Output Cap RMS Ripple changes with Output Current
| Output Current (input) | Output Cap RMS Ripple (result) |
|---|---|
| 0.2 A | 0.2 A |
| 0.5 A | 0.5 A |
| 1 A | 1 A |
| 1.5 A | 1.5 A |
| 2 A | 2 A |
| 3 A | 3 A |
| 4 A | 4 A |
| 8 A | 8 A |
| 14 A | 14 A |
| 20 A | 20 A |
The same result in other units
| Unit | Value |
|---|---|
| µA | 2000000 |
| mA | 2000 |
| A | 2 |
| kA | 0.002 |
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<p><a href="https://vbatpower.com/formulas/output-cap-rms-ripple-boost/">Boost Output Capacitor RMS Ripple</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Boost Output Capacitor RMS Ripple?
Use Icout(rms) = Iout × √(D / (1 − D)). With Output Current 2 A, Duty Cycle 50 %, Output Cap RMS Ripple works out to 2 A.
What is the formula for Boost Output Capacitor RMS Ripple?
The formula is 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.
How do you find Output Current when you know the other values?
Rearrange for Output Current: with Output Cap RMS Ripple 100 µA, Duty Cycle 2.5 %, Output Current is 0.6245 mA.
What units does Boost Output Capacitor RMS Ripple use?
Output Cap RMS Ripple is shown in µA, mA, A, kA. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
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