Calculate ripple current, inductance, switching frequency, or input/output voltage for an ideal continuous-conduction buck converter. Select the value to solve; ripple means peak-to-peak inductor current.

Ideal buck converter in continuous conduction: 0 < output voltage < input voltage. Ripple is peak-to-peak inductor current, not capacitor RMS current.

Ripple Current Formula

The following ideal buck-converter formula estimates peak-to-peak inductor ripple current with 0 < Vo < Vi. It excludes losses, discontinuous conduction and controller limits. Solving for output voltage can give two solutions; both are shown.

Iripple = Vo / Vi × (Vi - Vo) / (Fs × L)
  • Where Iripple is the Ripple Current (amps)
  • Vo is the output voltage (volts) 
  • Vi is the input voltage (volts) 
  • Fs is the switching frequency (Hz) 
  • L is the inductance (H)

How to Calculate Ripple Current?

The following example problems outline how to calculate Ripple Current.

Example Problem #1

  1. First, determine the output voltage (volts). In this example, the output voltage (volts) is determined to be 10.
  2. Next, determine the input voltage (volts). For this problem, the input voltage (volts) is measured to be 50.
  3. Next, determine the switching frequency (Hz). In this case, the switching frequency (Hz) is found to be 2.
  4. Next, determine the inductance. In this case, this is 4H.
  5. Finally, calculate the Ripple Current using the formula above: 

Iripple = Vo / Vi * (Vi-Vo)/ (Fs*L)

Inserting the values from above and solving yields: 

Iripple = 10 / 50 * (50-10)/ (2*4) = 1 (amps)

Example Problem #2

Using the same method as above, determine the variables required by the formula. For this example problem, these are:

output voltage (volts) = 4

input voltage (volts) = 23

switching frequency (Hz) = 5

inductance (H) = 3

Entering these given values into the calculator or the formula above yields: 

Iripple = 4 / 23 * (23-4)/ (5*3) = .2203 (amps)