safety capacitor

Discussion in 'General Electronics Chat' started by m.majid, Dec 24, 2008.

  1. m.majid

    Thread Starter Active Member

    May 28, 2008
    39
    0
    hi everyone

    I am designing a switching powersupply using TNY268 to convert AC220v to DC5v

    the datasheet says to use a safety capacitor bitween +HV (primary) and GND (secondary) pins of bobbin in order to satisfy EMI standard.

    but I am confused, it sounds to be dangerous bacause the DC5v would be no longer isolated. :confused:

    could anyone clarify me?
    what would happen if I dont use this capacitor?
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    This is not my field of work but searching on the NET I do find this piece of article telling you why it is needed in the circuit. More information is presented in the source.

    Source for image below: primary-secondary bridging capacitor

    It is there to block/reduce capacitive coupled switching noise from primary to secondary.

    [​IMG]
     
  3. m.majid

    Thread Starter Active Member

    May 28, 2008
    39
    0
    Dear L.Chung

    I get all info I needed about bridging capacitor from your attachment. :)

    thanks so much
     
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