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SN6501: query in transformer reset

naga sahitya
Intellectual 550 points
Part Number: SN6501

In the above circuit ,  How magnetic flux of the core reset when the both the  primary switches are off . Means which path it will flow.

  • 0
    TI__Genius 17100 points

    Hi Naga,

    During the break-before-make instances of SN650x output transistors, the transformer core's applied magnetic field drops to 0 because current flow = 0. Since the inductor remains energized, a residual magnetic field remains until one of the switches turns on. This is shown in the highlighted points of the magnetic hysteresis graph below.



    For all intents and purposes, current does not flow when both primary switches are off.

    Is this the scenario you are asking about? Or during a power-off scenario?


    Thank you for your post!
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points
    Hi Naga,

    For additional insight: the time both Q1 and Q2 are open is very small - about 50ns @ Vcc = 5V operation. This means either primary switch is conducting 98% of the time and the magnetic flux will change direction during next half cycle.

    I will await your response!


    Best,
    Manuel Chavez
  • 0 in reply to Manuel Chavez
    Intellectual 550 points

    first point to note is , there is no inductor at the output side.  

    when the both switches are open , it may be 50ns  according to u , but in this case there is no path for magnetizing current to flow. this is not correct according to the inductors nature, which wont allow sudden change of currents. 

  • 0 in reply to naga sahitya
    TI__Genius 17100 points
    Hi Naga,

    Transformers, unlike inductors, continuously transfer energy with any energy storage being considered "leakage" and nonideal. This is true throughout the entire rise, hold, and fall of the Q1 and Q2 voltages. Power is transferred from primary to secondary side proportionally to the switching duty cycles and decreases to 0 as both switches open.

    All of the energy being transferred is stored in the output capacitor which provides charge to the load during the break before make moments.


    Kindly,
    Manuel Chavez