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transformer secondary ringing

Discussion in 'Electronic Design' started by Jamie Morken, Dec 14, 2008.

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  1. Jamie Morken

    Jamie Morken Guest


    I am using a fullbridge SMPS, and when I scope the secondary of the
    transformer I am noticing a lot of voltage ringing which is approaching
    the breakdown voltage of the diodes (600VDC). I have RC snubbers across
    the primary coils, but none yet across the secondary. LTspice shows
    that if I remove the primary RC snubber the output ringing is reduced,
    what other methods are there to reduce output ringing or to protect the
    diodes besides using an RC snubber?

  2. MooseFET

    MooseFET Guest

    Depending on the circuit type:

    You can load the secondary with enough capacitance to keep the ringing
    amplitude low enough. The current spike on the primary side can be
    prevented with a circuit like this:

    --+----))))----+---- To primary switches
    ! !
    --- === C1
    ^ D1 !
    ! ! L2
    ------------+--))))--- GND

    L1 is a lowish valued high current inductor. It causes the voltage on
    the switches to dip when the current tries to spike up.

    C1 is a modest value highish current capacitor. It must be able to
    handle the ripple current caused by the energy the is circling around
    in this circuit.

    L2 is a largish valued lowish current one. It just prevents there
    from being any spikes in the current here.

    D1 returns the energy in the current spike back onto the power rail.
  3. Eeyore

    Eeyore Guest

    Since so much depends on the mutual and leakage inductance of the
    transformer, it's hard to give much advice.

    Who designed the transformer ? What are the details ?

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