Capacitor Ripple Current (Buck)

Irms = Iload × √(D×(1−D))

Quick answer

This calculator solves Irms = Iload × √(D × (1 − D)) for RMS Ripple Current. With Load Current 4.4 A, Duty Cycle 50 %, the result is 2.2 A. It solves in 2 directions, so you can enter the values you have and get the one you need.

Calculator

RMS Ripple Current (A)
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Formula

Irms = Iload × √(D × (1 − D))

Description

The input capacitor of a buck converter must handle significant RMS ripple current because it supplies pulsed current during the switch-on time. The ripple current is maximum at 50% duty cycle where it equals half the load current. Insufficient ripple current rating causes capacitor heating, reduced lifespan, and increased ESR over time. Ceramic capacitors handle ripple current well, while electrolytic capacitors have strict ripple current limits that must be observed to prevent premature failure or even catastrophic venting.

Variables

  • Irms — RMS ripple current in the input capacitor (A)
  • Iload — DC load current (A)
  • D — Converter duty cycle (0 to 1)

Practical Notes

Output capacitor ripple current is typically much lower, approximately equal to the inductor ripple current divided by √12. Always check capacitor datasheets for ripple current ratings at the operating frequency and temperature. Ceramic capacitors lose capacitance with applied DC bias (voltage derating), which effectively increases ripple.

Symbols and units

Symbol Meaning Default unit Accepted units
Irms RMS Ripple Current A pA, nA, µA, mA, A, kA
Iload Load Current A pA, nA, µA, mA, A, kA
D Duty Cycle — —, %

Step by step

  1. 1. What you know: Load Current 4.4 A, Duty Cycle 50 %
  2. 2. The relation: Irms = Iload × √(D × (1 − D))
  3. 3. Substitute: Iload = 4.4 A, D = 50 %
  4. 4. Result: RMS Ripple Current = 2.2 A

Worked examples

Minimum range

Given: Load Current 4.4 mA, Duty Cycle 2.5 %

Result: RMS Ripple Current = 0.6869 mA

Low range

Given: Load Current 44 mA, Duty Cycle 25 %

Result: RMS Ripple Current = 19.05 mA

Typical

Given: Load Current 4.4 A, Duty Cycle 50 %

Result: RMS Ripple Current = 2.2 A

High range

Given: Load Current 0.22 kA, Duty Cycle 0.8

Result: RMS Ripple Current = 88 A

Maximum range

Given: Load Current 2.2 A, Duty Cycle 0.8 %

Result: RMS Ripple Current = 0.196 A

Solving for each variable

Solve for RMS Ripple Current

Load Current 4.4 mA, Duty Cycle 2.5 % → 0.6869 mA

Solve for Load Current

RMS Ripple Current 2 mA, Duty Cycle 2.5 % → 12.81 mA

How RMS Ripple Current changes with Load Current

Load Current (input) RMS Ripple Current (result)
0.44 A 0.22 A
1.1 A 0.55 A
2.2 A 1.1 A
3.3 A 1.65 A
4.4 A 2.2 A
6.6 A 3.3 A
8.8 A 4.4 A
17.6 A 8.8 A
30.8 A 15.4 A
44 A 22 A

The same result in other units

Unit Value
µA 2200000
mA 2200
A 2.2
kA 0.0022

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Frequently asked questions

How do you calculate Capacitor Ripple Current (Buck)?

Use Irms = Iload × √(D × (1 − D)). With Load Current 4.4 A, Duty Cycle 50 %, RMS Ripple Current works out to 2.2 A.

What is the formula for Capacitor Ripple Current (Buck)?

The formula is Irms = Iload × √(D × (1 − D)). The input capacitor of a buck converter must handle significant RMS ripple current because it supplies pulsed current during the switch-on time.

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

Rearrange for Load Current: with RMS Ripple Current 2 mA, Duty Cycle 2.5 %, Load Current is 12.81 mA.

What units does Capacitor Ripple Current (Buck) use?

RMS Ripple Current is shown in µA, mA, A, kA. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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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