Capacitor question

Discussion in 'General Electronics Chat' started by shortbus, Sep 1, 2010.

  1. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    I have another dumb question. Does it harm a capacitor to keep it static in a circuit?

    By static I mean constantly connected to both + and - voltage but only switched into the rest of the circuit when needed. Basically it is a bootstrap cap for a mosfet gate driver, and the mosfet will not be needed in the active part of the circuit. It will only be used to discharge a capacitor bank once in a while with a push button switch through a load resistor.

    Will the bootstrap cap heat up or otherwise cause a problem when used like this?

    Thank you for your answers.
  2. Nik

    Well-Known Member

    May 20, 2006
    If it is an ordinary electrolytic, it may have very slight leakage current, which may impinge on your power budget. Otherwise, IMHO, no problem. FWIW, old electrolytics needed time to 're-form' on connection to power.
  3. SgtWookie


    Jul 17, 2007
    Actually, electrolytic caps that have been sitting around for awhile need to be re-formed by charging them via a high impedance source until the leakage rate at their rated voltage is acceptable.

    If you simply apply power without limiting the current to a cap that's lost it's dielectric, expect a loud bang as it overheats and boils the electrolyte, causing the package to rupture forcefully.
  4. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    Thanks guy's for the answers. The cap I'll be using is a ceramic disc.
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
    Ceramic caps are almost indestructable and most exhibit leakages so low it can't even be measured.