Capacitor voltage question

Discussion in 'The Projects Forum' started by eblc1388, Jan 10, 2010.

  1. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008

    I'm building a high voltage output amplifier and thus require to generate positive and negative high voltage rails from a step up transformer feeds from 12V AC, as shown in the image. The high voltage amplifier output is about 6VA.

    Normally I would have chosen smoothing capacitor rated for higher working voltage but due to size constraint, I have to choose between either 470u200V or 220u350V capacitors.

    I know that rated capacitor voltages are working voltage(WV) but would a 200V capacitor suffice in this case?

    Some capacitor data sheets did mention 200V WV and 250V surge but unfortunately the data sheet of the type of capacitor I'm using says nothing about surge voltage.

  2. JDT

    Well-Known Member

    Feb 12, 2009
    The capacitors will charge up to the peak voltage of 115VAC
    = 1.414 x 115 = 162.6
    Less the diode drop, but this is insignificant.
    Then add a safety margin.

    In this case 200V is OK.
  3. mik3

    Senior Member

    Feb 4, 2008
    If the 350V capacitors are sutable use them because they will last longer than the 200V ones. The less the applied voltage than the rated the more they last.
  4. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008

    Thanks for your inputs.

    200WV is a bit low but only if I can get hold of a 250V WV one then that definitely won't be a concern.

    I think I'll go for longer life and better safety margin with the 350V capacitor as mik3 has suggested.