Inrush current in ultracaps

Discussion in 'General Electronics Chat' started by Varkatzas, Nov 13, 2012.

  1. Varkatzas

    Thread Starter New Member

    Oct 22, 2012
    Hi all,

    I want to know how to calculate the inrush current due a ultracaps bank. This is because i'm designing a DC DC converter and i don't want to break the semiconductors. Is there a way to calculate it knowing the capacitance, ESR, voltages (ΔV) and switching frequency? Does the same procedure applies for normal capacitors?

    Thanks a lot.
  2. tshuck

    Well-Known Member

    Oct 18, 2012
    It would appear that you could use the ESR to do this... if my understanding from a quick Wikipedia( :D ) search is correct, the current will be the voltage/ESR...
  3. JDT

    Well-Known Member

    Feb 12, 2009
    It depends on the ESR of the capacitors, the resistance of the connections and the rate of rise of the applied voltage.

    You will need to soft-start your DC to DC. Or have some kind of active current limiting.
  4. Varkatzas

    Thread Starter New Member

    Oct 22, 2012
    Does the inrush current apply only to a capacitor in t=0 with Vc=0? If the cap is pre-charged to at least 1/4 of its rated voltage and then the voltage is increased, an inrush current is expected?

  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    The design has to incorporate current limiting or soft-start which protects the converter during charge up or it won't survive. The best type is pulse-to-pulse limiting as used in a current mode converter.