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UCC28600: Issue with Flyback Converter Simulation in TINA-TI

Atharva Patil
Prodigy 30 points
Part Number: UCC28600
Other Parts Discussed in Thread: TINA-TI, LM5023

Tool/software:

Dear Experts,

I have designed a flyback converter for an application with the following specifications:

  • Input: 120 VDC to 375 VDC
  • Output: 12 VDC at 3.75 A

For current limit protection, I selected the UCC28600 controller. However, while developing the design, I encountered a few discrepancies in the datasheet that were addressed in the forum previously. After resolving those issues, my design now closely aligns with the values calculated using the design calculator(Not exactly same). The schematic is provided below for reference.

The issue arises when simulating the converter in TINA-TI. The simulation works as expected at 120 V input, but when the input voltage is increased above 120 V, I observe the following behavior:

  • Above 200 VDC input, there is a significant spike in the primary current, reaching around 10 A.
  • This spike results in the converter shutting down.
  • Ideally, for a constant output load, the primary current should decrease with an increase in input voltage, but instead, I observe an unexpected increase.

I have attached the waveform for a 375 VDC input, which shows the spike in primary current.

To clarify:

  • The converter operates well at 120 VDC input, drawing expected currents.
  • At input voltages above 200 VDC, there is a large spike in primary current, around 10 A, followed by a shutdown of the converter.

Additionally, I would like to mention that all models used in this simulation are the same as those used in another flyback converter design that employs the LM5023, which operates correctly in the same simulation environment.

TINA schematic: https://shorturl.at/TEZCO

Waveform @ 375VDC input: https://shorturl.at/y3PRl

Could you please assist me in resolving this issue or provide guidance on why the simulation behaves in this manner?

Thank you for your time and support.

Best regards,
Atharva Patil

  • 0
    TI__Guru* 86266 points

    Hello,

     

    Your inquiry has been received and is under review.

     

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86266 points

    Hello,

     

    The LM5023 is a QR controller but does not have primary fault sensing like the UCC28600.  The following link will bring you to an application note that describes primary fault sensing, similar to what the UCC28600 uses.  The issues with this technique and how to resolve them.  I think this information will help you resolve your issue.

    https://www.ti.com/lit/pdf/sluaac5

     

    I reviewed your schematic and functionally it looks correct.

     

    I reviewed your model from waveform from your simulation and can see the current spike you mentioned.  FB is slammed high at this time demanding max current.

     

    I reviewed the block diagram for this device and see with a VREF of 5 V the maximum current sense is controlled to 1.36 V when FB is 5 V.  This actually matches your simulation which is good.

     

    What I don’t see here is your SS voltage or why there is no switching after that first current spike.  This design most likely is not starting up due to a fault.  Also, it looks like you have an issue with SS that you need to investigate.

    The simulation seems to be running which is good.  To help resolve this issue, I think you need to probe OVP and CS pins with waveforms that you have taken to see if an OVP fault is preventing you from starting up.  You also may need to decrease the time base so you can see more resolution of the waveforms to help you trouble shoot it.

    Once you have determined what fault is causing the simulation not to work you can debug it.  Application note sluaac5 will help with this if the design is fault related.

    Thank you for interest in Texas Instruments (TI) products.  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.

     

    Regards,