WEBENCH® Tools/LM5023: LM5023_QR Flyback Power supply

Part Number: LM5023

Tool/software: WEBENCH设计工具


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

17 Replies

  • In reply to Sonal Singh:

    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


  • In reply to chime xia:


    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.



  • In reply to Sonal Singh:

    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.

  • In reply to chime xia:

    Thank you for your support!
  • In reply to chime xia:

    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:


    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!

  • In reply to chime xia:

    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? 


  • In reply to Sonal Singh:

    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