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WEBENCH® Tools/LM5023: LM5023_QR Flyback Power supply

Part Number: LM5023
Other Parts Discussed in Thread: TL431

Tool/software: WEBENCH设计工具

Hi!

I use LM5023 to develop a boost power supply, VCC auxiliary supply voltage is 24 V, power MOSFET voltage is 3 V. Request to raise 3V to 36V, there are problems in debugging, special help support, thank you!

The current problem is that the output voltage can only be adjusted to 13V can not be raised, transformer parameters for PQ2016, primary use 3TSs, auxiliary winding is 4TSs, output winding is 18TS.LP:2.8uH.

This is a two-way DC/DC converter.24VTO5V5A_1030.pdf

  • Hi Chime xia,

    We will get back to you on this soon.

    Thanks and Regards,
    Atul
  • Thank you, Atul Kulkarni23!

    Today I have a new development in debugging, the converter can rise to 17 V, and will run in blocking mode. But not with load.

    I did this by debugging the Optocoupler resistor in charge of the resistor and the voltage divider of the TL431, but when the output voltage continues to increase by adjusting the divider resistance, the output voltage reaches 17V and goes into blocking mode. I think it should have a lot to do with the feedback loop design.

    Thanks again! I need your support now!

    Chime xia

  • Hi Chime ,

    Could you please share the input/output conditions of the designs. You can also share the design using public share link.
    Also please let us know if the design is done using Webench.

    Thanks and Regards,
    Atul
  • Thank you very much!

    My design requirements:

    1. Input voltage: dc 2.7 V to  3.3 V, current 5 A;

    2. Output voltage DC 36 V.Output current is not required, as long as the efficiency is over 82%.;

    3. Require isolation;

    4. Efficiency 82% min;

    The design has been modified with reference to WEBENCH.

    The schematic diagram has been attached, please refer to it.

    Thank you for your reply, I will continue to look forward to your reply!

    Thank you !

    Chime xia

  • In addition, forget to explain,I didn't find a boost topology on WEBENCH, only a step-down topology.
  • Hi Atul,

    Do you have any comments on this issue?

    Here I also attached the layout, thank you.

    24VTO5V5A.pdf

  • Hi Atul,

    Help to see if the boost topology circuit designed(3V->36V) is feasible?

    Thank you
    Jerry
  • Hello Chime Xia,

    I think the 17V on the output is actually your reflected voltage from the primary ie: 3Vin*Nps this is because the controller is not turning ON. The reason for that is the Vcc turn-ON of LM5023 is 12.5V and with the givenm turns ratio Npa the Vaux is only 4V.
    Please plot Vcc, Vout, OUT to examine this, you will see VCC is sitting @ 4V and OUT is doing nothing.

    Regards,
    Sonal
  • Hi Sonal,
    Thank you for your reply!
    I think negative-VAUX is 4V, but Vaux is 36V * Nsa when it works, and my Nsa is 0.33, so VCC=36*0.33=11.3V; actually has a VCC greater than 11.3V when it's no load.

    thank you
    Chime Xia
  • Hi Chime,

    May you please plot OUT, VCC and VSD pin waveforms to look into this, I would like to understand the power demand from the controller during load conditions.

    Regards,

    Sonal

  • Today I set to 36 V, but I can't start again after the voltage is set to 36 V. The output voltage is adjusted to 20 V, and then the output voltage is 36 V by adjusting R 24.  CH1:OUT; CH2 Vout; CH4:Vcs.VCC=13V

    ch1:OUT;

  • Hello,

    I am a bit confused now because the waveforms you have attached is producing the DRV pulses.

    Also, the ref voltage @ regulation on TL431 is 2.5V, you will have to redo the divider calculation to make sure the Vout is set to 22V.

    Regards,

    Sonal

  • Hello, Sonal

    I now change the TL431, partial resistance of 1.25 V to 51 K / 2 K respectively. I also tried to change the divider resistance to 33 K / 2 K, but the effect was the same.

    In addition, the DRV is achieved by adjusting R 4 at 20 V. But when the voltage is turned on, it won't startup.

    See the final19V启动时的电压.docx video attached.

  • hi,Sonal
    Thank you for your support!
  • Hi, Sonal

    The Vsd, was measured as required by the Sonal but not detected. After thinking about it at night, I feel that the Vsd is always high after the probe is hung at the Vsd point, and the VCC should be high. Because Cvcc has been charging. Test today to see what Vcc is.

    strange! The Vsd voltage can be measured again today. Below:

    Ch1:out;ch2:Vcc;ch3:Vout;ch4:Vsd.

    The VCC voltage is not enough to measure the waveform, and has been jumping between Vcc_on and Vcc_off. My analysis shows that the output voltage is only 16 V. But if you turn the voltage up, you can't start-up it again!

  • Hello Chime,

    This is expected behavior for VSD pin, this pin is connected to the MOSFET for external high voltage startup. Once the VCC voltage has crossed the VCCON threshold this pin should be pulled low to disable that external FET.

    My thought for VCC fluctuation is did you see the same behavior when you supplied VCC through a constant DC supply? 

    Sonal

  • Hello Sonal,
    I think VCC is normal. I also pass through a constant VCC, but still can't start after 20 V.
    thank you!
    Chime xia