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UCC28742: UCC28742 and transformer connection

HECTOR
Intellectual 536 points
Part Number: UCC28742

Hello 

I am desiging a  non isolated capacitor charger circuit usings UCC28742 controller; 

so in our design notes of our old design i saw the transformer is conencted in  diffirent ways ; could you explain why ? and what is the diffirence please ; 

Thank you in advanced 1526.pwr.PDF

  • 0
    TI__Guru* 85616 points

    Hello,

    TR1 is incorrect and TR2 seems to be correct.  TR2 is the same as the data sheet and is correct.

    The TR1 circuit will not work correctly.

    Regards, 

  • 0 in reply to Mike O'
    Intellectual 536 points

    Thank you for answer; but in our old designed its always used in TR1; so  I asked what is the diffirence? why TR1 is prefered sometimes?

  • 0 in reply to HECTOR
    TI__Guru* 85616 points

    Hello,

    When I look at your circuit when Q15 is on both TR1 10 and 6/7/8 are shored to ground when the transformer is being energized.  When Q15 is turned off and energy is being delivered to the secondary the body diode of Q15 is should conduct.  This is because the energy being deliver to the secondary will go through TR1 pins 10, 15 and D69 and return through Q15.

    If this is the case how does the switch node ring above the input?  Unless D69's return is connected directly to pin 10.  This would cause the output rectifier voltage D69 to be greater than Vin.  This is not a configuration that I have seen before.

    Regards,