Comparing Ripple Voltage Differences by Capacitor Type | Ask an FAE

Ripple Voltage Comparison Demo

Thursday, March 16th, 2017

Comparing Ripple Voltage Differences by Capacitor Type

Determining the output capacitor when designing a buck regulator or boost converter needs more consideration than just the capacitance value. However, something that might get overlooked is the amount of ESR different capacitor types contribute. This Electronica demonstration compares various capacitor types on the same DC to DC converter. Even though each bank is the same capacitance, the output ripple varies.

dc-to-dc converter block diagram

The load for the circuit is electronic DC load, providing about a 2-ohm impedance. The scope measurements show that the Tantalum MnO2 had the highest ripple. Tantalum MnO2 capacitors have a large ESR, which is going to create a large ripple voltage.

impulse response

Aluminum Polymer (AO-CAP), Polymer KO-CAP, and Ceramic X7R all have a similar amount of ripple. The interesting comparison is that it took four ceramics, four KO-CAPs, but only a single AO-CAP.

If space is at a premium, AO-CAP or KO-CAP provides your best option. If you have plenty of space on your board, then a ceramic solution is another option.

Episode Key Points

  • ESR and ESL are important to consider
  • X7R Ceramic provided lowest ripple
  • AO-CAP had the lowest part count

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