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UCC2895: Peculiar behavior while using it for 3 level converter.

SANJAY BOLE
Prodigy 10 points
Part Number: UCC2895
Other Parts Discussed in Thread: UCC3895

Tool/software:

Hello,

UCC2895 is used for 3 level converter design in voltage mode control. When the current signal is connected to CS pin, it is observed that at the startup converter/ at transformer primary is facing full duty-cycle for 10 to 20 cycles before entering into the soft start mode. If it is removed, it starts up in the soft start. Is there any limitation with the controller when used in 3 level conversion with CS pin connected to current signal.

  • 0
    TI__Genius 12795 points

    Sanjay,

    We need the waveform and schematic to better assist you.

  • 0 in reply to Ning Tan
    Prodigy 10 points

    Dear Ning Tan,

    Thanks for immediate response. Attached is control & power schematic for your reference. The drive is through pulse transformer. The delays observed are around 400 nS for switching frequency of 100 kHz. Attached video is the capture at the time of turn ON at transformer primary at lower input DC voltage. Once it turns ON the converter works normally. There were random failures observed at field of either Q1 or Q4. DC Bus Voltage +/- 350VDC 

    Sanjay Bole

  • 0 in reply to SANJAY BOLE
    TI__Genius 12795 points

    Sanjay,

    You waveforms are not viewable. Please make sure you attached the right format.

    Thanks,

    Ning

  • 0 in reply to Ning Tan
    Prodigy 10 points

    IMG_5651.zip

    Added in .ZIP, can be downloaded & check. This is start up checked at lower input. 

  • 0 in reply to SANJAY BOLE
    Prodigy 10 points

    Tested at 680 VDC input, 1 kW output.

  • 0 in reply to SANJAY BOLE
    TI__Guru* 86266 points

    Hello,

     

    I can see that you are not using the UCC2895 in a phase shifted full bridge but you are using it in a 3-level converter.  I searched the TI data base and can find any reference design material on how to use a PSFB control for 3 level design.

    So, there are no know waveforms to compare the UCC2895 in a 3 level design to use as a reference, also there is no design information on ti.com.  So I will not be able to offer advice on to use the UCC2895 or any other phase shifted full bridge converter in your design.

    I did find a reference using a C2000 digital control at the following link.  It might be easier to use this controller for your design rather than the UCC2895.  This may eliminate the issue that you are seeing.

    https://www.ti.com/lit/ug/tiduez0a/tiduez0a.pdf

     

    Regards,

  • 0 in reply to Mike O'
    Prodigy 10 points

    Thanks for the reply. Attaching the application notes for your information for use of PMFB controller for 3 level converter application. It is widely used for the 3 level converter topology. I am not facing the Issue with the topological constraint. Issue is at the start up in voltage mode control for UCC3895 & current signal is connected for protection against transient load. Once it is connected at the start-up, the controller starts up with full duty cycle for some cycles before it resumes the soft start. This is not seen if it works without current signal. What is the phenomenon when the current signal is connected? Is there any issue with internal architecture or something to do with the schematic? Or is there any way to protect the device from transient loading. 

    01epe-froehleke-schniedermann (1).pdfThree level converter.pdf

  • 0 in reply to SANJAY BOLE
    TI__Guru* 86266 points

    Hello,

     

    I cannot see the misbehaved waveform.  Could you repost it in another format so we can see it?

     

    Regards and thanks,