Buck Converter Boost Converter Buck - boost Converter

(LDO) Low Dropout Regulator

input Capacitor of DCDC

Converter Type	Input Cap Importance	Output Cap Importance
Buck	✅✅✅ High	✅ Moderate–High
Boost	✅ Moderate	✅✅✅ High
Buck-Boost	✅✅✅ High (both!)	✅✅✅ High

Buck Converter

• Switch is between input and inductor
• It draws pulsed current from the input cap
• Input cap must:
  • Absorb sharp switching pulses
  • Prevent VIN bounce, EMI, and ripple into the power rail
• Output is filtered through the inductor, so ripple is easier to manage ✅ Input cap is more stressed → needs low ESR, tight placement, and enough capacitance

Boost Converter

• Switch is between ground and inductor; input current is continuous
• But the output cap sees pulsed current every switch cycle
• Output cap must:
  • Absorb charge dumps from the inductor during switch-off
  • Maintain output voltage during the switch cycle ✅ Output cap is more stressed → must be carefully sized to maintain voltage and limit ripple