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Flyback Control using UC3844

User: "Altair Forum User"
Altair Employee
Updated by Altair Forum User

Hi All,

I am trying to control Flyback Control using UC 3844. I am using app note for the same. However, when simulating the circuit. The sytem only works fine if both the input and output are on same ground. How can we simulate with different grounds since Flyback converter is supposed to give isolated output

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    User: "Altair Forum User"
    Altair Employee
    OP
    Updated by Altair Forum User

    Please post your schematic. It is likely that something odd is happening. It could be that you are using the "node to ground" voltage probes instead of the node to node probes when your secondary is isolated.  image  .

    If you are using the node to ground then you will get garbage waveforms when the secondary is isolated.

    User: "Altair Forum User"
    Altair Employee
    OP
    Updated by Altair Forum User
     
     
    image

    I have attached the schematic. The system is operating fine if both output and input grounds are same. But if i remove ground of output side to make it as an isolated supply , it doesnt work.

    User: "Altair Forum User"
    Altair Employee
    OP
    Updated by Altair Forum User
    image

    if you remove this ground your voltage feedback is no longer referenced properly and it won't work. You need to use the isolating voltage sense element. 

     

    image

    Does that make sense?

    User: "Altair Forum User"
    Altair Employee
    OP
    Updated by Altair Forum User

    Hi…I'm attempting to utilize UC3844 to plan a flyback converter. I read datasheet of UC3844. Also, in this paper, I see the reference plan. However, I don't comprehend the Error Amplifier how can it work. Also, how can it work in blend with current sense?

    User: "Altair Forum User"
    Altair Employee
    OP
    Updated by Altair Forum User
    image