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270Vdc isolated flyback, Multiple outputs using TPS40210.

Keith Pant
Intellectual 265 points
Other Parts Discussed in Thread: TPS40210

270Vdc isolated flyback, Multiple outputs using TPS40210.

The problem is the gate drive output pulses go from 8V high pulses to 6V high pulses at about 200Vdc input.

Has anyone seen this problem?

 

  • 0
    TI__Mastermind 35165 points

    Hi Keith,

    I haven't seen this before. Could you share the schematic with the FET part number?

    Thanks,
    Anthony

  • 0 in reply to Anthony F
    TI__Mastermind 35165 points

    A couple things you could also check. My first theory would be that the VBP voltage is also dropping with the 200V input. If it is we will have to track down the cause of this.

    1. Does the VBP voltage also drop with the 200V input? If it does, is this due to the VDD voltage dropping?
    2. Is there somehow a heavier load on the VBP or GDRV when the input voltage drops to 200V?
  • 0 in reply to Anthony F
    Intellectual 265 points

    Do to company policy, I cannot show you the schematic on a public website. The FET is a 950V with a Qg=40nC.

    The VBP doesn't drop and the Vcc voltage stays at 17Vdc. No components are attached to the VBP in except the 1uF cap that is recommended. The GDRV is connected to the gate of the FET thru a 3 ohm resistor.

    What appears to be happening is the duty cycle is going very small (less than 2%) so it appears not to go to 8V. I placed a 1A load on the feedback supply. The GDRV voltage goes to 8V and the duty cycle goes to approximatly 10%. It should be 40 to 50% with this load. I am puzzled by this.

    FYI. I have a 130Vdc power supply of the same design, except fro transformer, works fine.

     

  • 0 in reply to Keith Pant
    TI__Mastermind 35165 points

    I sent you a friend request so you could send the schematic to me. Based on the transformer comment, could you double check the transformer design to make sure the spec is right and everything is wired up correctly? I'm wondering if something was wrong with the orientation of one of the windings or the turns ratio.

  • 0 in reply to Anthony F
    Intellectual 265 points

    I accepted the friend request. It will take me a few days to get export control clearence to send the data.

    I have checked the turns ratios and they are correct to the specifications. All the outputs are showing the correct voltages. I will need to isolate the transformer pins on the board to verify winding orientation, with respect to the primary.

  • 0 in reply to Keith Pant
    TI__Mastermind 35165 points

    Ok, thanks Keith. For now, could you share the feed supply voltage and turns ratio? Also if the design is operating in CCM or DCM?