• State TI Thinks Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 294 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC28251: The synchronous tube was broken down as soon as it was powered on.

shaowei cui
Intellectual 550 points
Part Number: UCC28251

Hi TI Engineers,

I am a graduate student in school, want to use UCC28251 to make a full bridge hard switching module power supply, read the manual of the chip, there is a problem is when the light load inductance current interrupted, synchronous rectifier tube is still open, then there will be reverse current into the rectifier tube causing burnout, how is your company consider it in this regard?  

The synchronous rectifier tube of the power supply is damaged when it is powered on.

Excuse me, is this the breakdown reason, how to solve it?

Regars

shaowei

  • 0
    TI__Genius 13660 points
    Hi shaowei,

    Thank you for your question, I have asked one of my colleagues to answer this question.

    Regards,
    Teng
  • 0
    TI__Intellectual 1390 points

    Hi Shaowei,

    UCC28251 employs close loop control of SR tube to reduce the negative current during the startup with a Pre-bias output voltage. Secondary side control is recommended to getter better Pre-bias startup waveform and smaller negative current. Please refer to section 9.1.2.1 on page 30 for more detail.

     

    Regards

    Frank

  • 0 in reply to Frank TANG
    Intellectual 550 points
    Hi Frank,
    Is there no other way?
    The voltage of the VSENSE pin I set is 1.1 times that of the EA-pin, which uses the pre-biased start-up function, but the tube still burnout.
    best regars,
    shaowei
  • 0 in reply to shaowei cui
    TI__Intellectual 1390 points
    Hi Shaowei,
    The simplest way is to discharge the output voltage before the soft-start or reduce the output cap. In other words, I am proposing to remove the pre-bias condition during the startup.

    Regards
    Frank
  • 0 in reply to Frank TANG
    Intellectual 550 points
    Hi Frank,
    Do you recommend using or not using pre-biasing?
    Regars
    shaowei
  • 0 in reply to shaowei cui
    TI__Intellectual 1390 points
    Hi Shaowei,
    I am proposing to discharge the pre-bias voltage on the output capacitor before UCC28251 enter into soft-start. Without pre-bias voltage on the output capacitor, it naturally remove the risk of enormous negative current through SR.
    Another proposal is to enlarge the output inductance by referring to AP under
    www.ti.com/.../slaa477.pdf

    Regards
    Frank
  • 0 in reply to Frank TANG
    Intellectual 550 points
    Hi Frank,
    Can you give me your contact information, such as QQ, Wechat, for discussion?
    Because UCC28251 has no reverse current protection function, I wonder if it can be used as a synchronous rectifier module power supply.
    Best regars,
    shaowei
  • 0 in reply to shaowei cui
    TI__Intellectual 1390 points

    Hi Shaowei,

    Reverse current protection is not an ideal way to deal with reverse current. It is because that the protection needs to turn off SR after reverse current had appeared. It removes the reverse current circulating loop and causes the avalanche breakdown of SR and sometimes may damage SR if the energy associated with reverse current is big enough.

    With proper design, UCC28251 solution is able to keep the instant reverse current pretty small even under pre-bias startup condition. Considering that MOSFET can stand very high peak current, I doubt whether your PSU failure is really from the reverse current. Could you capture the current, gate to source voltage and the drain to source voltage of SR to prove your suspicion?   

    If you have more questions, you can send the waveforms and question to my email box Frank-tang@ti.com.

    Regards,

    Frank