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Flyback Convertor Question

  • 20-11-2011 01:18PM
    #1
    reliability
    Closed Accounts Posts: 2 ✭


    In a flyback convertor, why does the polarity of v2 on the secondary winding change compared to a normal transformer circuit as shown in the picture attached?

    If the voltage and current, v1 and I1 in the primary winding are flowing in the same direction in both circuits shouldn't the polarity of the induced voltage and current v2 and I2 be the same polarity in both circuits?


Comments

  • #2
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    In these circuits you have to think when is the energy transferring from the input to the output. In this case it's during the "fly back" period when the switch is open.

    Switch closes puts energy into the core, switch opens, but inductance of the winding wants to keep current flowing. So inductor goes from having a volt drop on it, to being a voltage source and delivering power to the output.

    The polarity of the windings is key. I normally think of them in terms of voltage drops and rises. I draw + & - symbols, which flip around during the fly back period.


  • #3
    reliability
    Closed Accounts Posts: 2 ✭reliability


    Is the direction of the voltage and current in the secondary just due to the way the wire has been wrapped around the transformer core as I have drawn in the picture attached?


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