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TPS92314 driver IC

ANNIE POULOSE KALAPPARAMBATH
Prodigy 30 points
Other Parts Discussed in Thread: PMP

I have an 18W isolated design. O/P voltage is 35V and current 500mA. Design is based on PMP 8011. Winding changed  to suit o/p requirement. Circuit diagram is attached. Turs ratio of P to S is 7.5.  R1 and R2  are 0.25W. Actually, it requires minimum 0.5W. After few hours, R1, R2 , Mosfet and current sense resistors will burn. R1 and R2  are burning due to insufficient wattage.  Mosfet used is 2.5A, 800V. Gate resistor is not used. Is that the reason for failure? For inrush current limit, Can I use 0.5W , 3.3  ohm resistor alone  or 3.3 ohm resistor in parallel with 2.2mH inductor? What might be the reason for burning?

Led Driver schematics.pdf

  • 0
    TI__Expert 3495 points
    Annie:
    The MOSFET burned first and caused R1, R1 and Rsense to burn. The possible reasons for the MOSFET to burn are overheating, drain to source tun off voltage spike higher than the rating. You need to check the MOSFET voltage spike and make sure it is lower than 800V.
    You also need to monitor the temperature of the MOSFET. If it is too hot, use a heat sink.
    David Zhang
  • 0
    TI__Expert 3495 points
    Annie:
    You can use 3.3 ohm 0.5W resistor alone for inrush current limit. The inductors are for EMI.
    David Zhang
  • 0 in reply to David Zhang
    Prodigy 30 points

    Dear David,

    Thank for the reply.  The failure happened when I used a winding which was not correct. Now, I am using correct winding.

    I am asking these questions to ensure the design is correct. MOSFET temperature is 61C.  Few more clarifications.

    1.  I am using 500mA fuse.

    2. Is the inrush current limiter is a must?

    3. By mistake, I used 680K across O/P electrolytic capacitor. It takes  more  time for discharge. Will it create any other issues?

    4. For 7.5  p/s turns ratio and o/p 35V, what value o/p diode is required?

    Thank you .

    Regards,

    Annie

  • 0 in reply to David Zhang
    Prodigy 30 points
    Dear David,
    In the wrong winding, I selected 65KHz frequency . Now, I selected 100KHz and the core used is E19/8/5.
    Now, Max. drain to source voltage will be 695 V as per calculation.
  • 0 in reply to ANNIE POULOSE KALAPPARAMBATH
    TI__Expert 3495 points
    Annie:
    I am glad you got it fixed. The inrush current limit is not important for this design because the total input capacitance is less than 1uF. 680K resistor across output cap does not create any problem. Don't worry about that. The output diode needs to be rated at least 100V. It is better to use 150V or 200V diode to have some margin. Here is the calculation of the voltage across output diode.
    V_diode = Vin_peak/7.5 + Vout = 264*1.414/7.5+35 = 85V. 61C MOSFET temperature is good.
    David Zhang
  • 0 in reply to ANNIE POULOSE KALAPPARAMBATH
    TI__Expert 3495 points
    Annie:
    I suggest you using bigger core. E19/8/5 is to small and is hard to pass safety. Usually you need either margin tape for using triple insulated wire to meet the safety requriement. Increasing swithing frequency makes transformer smaller but it is harder to pass EMI with higher switching frequency. It is a trade off.
    David Zhang