Forward converter design

Discussion in 'General Electronics Chat' started by rochak.chadha, May 3, 2012.

  1. rochak.chadha

    Thread Starter New Member

    Mar 17, 2012
    7
    0
    Hi everyone,

    I am working on a maximum power point tracker application in which I wish to use a forward converter. I used an application note by ON Semiconductor
    the link to which is PDF"]http://www.onsemi.cn/pub_link/Collateral/NCP1216AFORWGEVB_MANUAL.PDF[/URL].

    I simulated the circuit in Psim and it worked fine and then I made a schematic and printed the PCB. However, the PCB doesnt work at all. The MOSFET gets too hot and the output is no more than 0.4-0.5V at a load 0f 82 ohm.

    I have attached my schematic. I would appreciate if any one can provide me any insights as to what might be wrong.

    Thank you,

    Rochak
     
  2. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    polarity of coils?
     
  3. rochak.chadha

    Thread Starter New Member

    Mar 17, 2012
    7
    0
    Even I discovered later that the reset winding has to be out of phase with the primary winding. I corrected that and the circuit performs better, however the MOSFET still heats up at low voltages (~16 V) when the duty cycle is about 28%.
    Any other thing that you feel could be wrong ?

    Thanks for your input though, really appreciate it.
     
  4. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Check for transformer core saturation.
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    So this was the reason?

    I did not understand the dephts of the design,
    however, this is common from the effect you listed,
    like a short, or nearly a short.

    How much is VDC??
     
    Last edited: May 4, 2012
  6. rochak.chadha

    Thread Starter New Member

    Mar 17, 2012
    7
    0
    How can I do that on the actual hardware ? sorry I am new to this


    @takao21203: The VDC is used to drive the MOSFET, its about 10V.

    I corrected the polarity of coils, the output voltage is atleast more than 1v now without actually burning the MOSFET. But the circuit is not performing the way I want it to perform.
    Another question that I have is that "should the secondary coils be out of phase with primary windings ? Also, since I am using a bifilar winding primary coil, the magnetizing inductance between the coils may be too small, could this be a reason for high current through the reset winding ?
     
  7. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    One way would be to put a scope probe on the drain of U4. As long as the coil isn't saturated, the voltage should be a ramp. If the voltage goes all the way to the Vin rail, you might have a problem. Your coil might be saturated or shorted. The voltage will ramp until the coil is saturated or the Vin rail is reached. If the voltage ramps to Vin, then the pulse is too long.
     
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