Enter all but one of the variables (C, I, ΔV, f) into the calculator to determine the value of the bypass capacitor; this calculator can also evaluate any of the variables given the others are known. (This uses the sinusoidal AC capacitor relationship I = 2π f C ΔV, using consistent peak or RMS values for I and ΔV.)

Bypass Capacitor Calculator

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Bypass Capacitor Formula

The following formula is used to calculate the value of a bypass capacitor (modeling the ripple/noise as a sinusoid):

C = \frac{I}{2\pi f\,\Delta V}

Variables:

  • C is the required bypass capacitance (F)
  • I is the magnitude of the AC/ripple current to be bypassed (A)
  • ΔV is the allowable magnitude of AC/ripple voltage across the capacitor (V)
  • f is the frequency of the ripple/noise (Hz)

To calculate the required bypass capacitance, divide the ripple current magnitude by 2π times the ripple frequency and the allowable ripple voltage magnitude (use consistent peak or RMS values for I and ΔV).

What is a Bypass Capacitor?

A bypass capacitor (often called a decoupling capacitor) is an electronic component used to provide a low-impedance path for unwanted AC noise/transients, typically shunting them to ground (or between two supply rails). It is commonly placed close to an IC’s power pin(s) to help keep the local supply voltage stable during fast load-current changes. A capacitor does not pass DC in steady state; instead, it blocks DC while offering progressively lower impedance to higher-frequency AC content, helping reduce noise and interference on the supply node.

How to Calculate Bypass Capacitor?

The following steps outline how to calculate the Bypass Capacitor.

  1. First, determine the ripple/noise frequency (f) in hertz (Hz).
  2. Next, determine the magnitude of the AC/ripple current to be bypassed (I) in amperes (A).
  3. Next, determine the allowable magnitude of the AC/ripple voltage across the capacitor (ΔV) in volts (V).
  4. Next, ensure your values are consistent (use either peak values for both I and ΔV, or RMS values for both).
  5. Next, gather the formula from above = C = I / (2π f ΔV).
  6. Finally, calculate the Bypass Capacitance (C) and convert units if needed (F, μF, nF).
  7. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

AC/ripple current magnitude (I) = 50 mA

allowable AC/ripple voltage magnitude (ΔV) = 100 mV

ripple/noise frequency (f) = 1 kHz

calculated capacitance (C) ≈ 79.6 μF