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UCC2897A: UCC2897A active clamp forward topology, output synchronous rectifier, why the total burning synchronous rectifier?

user5187796
Intellectual 265 points
Part Number: UCC2897A

Ask: why do you always burn synchronous rectifiers? Customer SCHEMATIC_3712-5A.pdfafter the use of returned bad products always burn Q1_ax or Q2 ax. after replacement measurement waveforms are normal, I do not know why?

  • 0
    TI__Mastermind 34465 points
    Hello chime xia,
    I suspect there is some timing issue relating to the synchronous rectifiers and you need to get some scope waveforms that show the switching on both of these parts.
    Your output node is labelled batt_3V+. Does this mean the output is connected to 3V battery.
    In other words does this circuit start up into a 3V output ?
    The UCC2897A with synchronous rectifiers will not be able to do this because as soon as either Q1_ax or Q2_ax turns on it will short out the battery.
    If this is so you need to replace these parts with diodes .
    Regards
    John
  • 0 in reply to John Griffin1
    Intellectual 265 points

     hello John Griffin,

    The project is used to charge the 3V battery. The output is directly attached to the 3V battery. 

    Do you have any good advice? Because using rectifier diode efficiency will be low.

    thanks!

    chime xia

  • 0 in reply to user5187796
    TI__Mastermind 34465 points
    Hi chime xia,
    It is not possible to use synchronous rectification with the UCC2897A and with a pre-biased load on the output.
    With a battery connected directly to the output the synchronous rectifier freewheeling switch (Q1-ax in your schematic) will short out the battery when Q1_ax turns on. This will happen at startup when the output voltage is higher than the secondary voltage. The recommended solution is to use rectifier diodes to prevent the converter from drawing power from the battery.
    Regards
    John
  • 0 in reply to John Griffin1
    Intellectual 265 points

    HI John,

    Thank you very much for your reply!

    Is there a good proposal to recommend?

    My requirements are:

    input: 2.5~5v DC;

    input current: 2A;

    output voltage: 58V DC;

    I / O isolation: isolation;

    efficiency: 75% min