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UCC28950: current doubler with MOSFET,

kwangwoon Lee
Prodigy 230 points
Part Number: UCC28950

Hello, 

We are developing a 6kW class dc/dc converter. 

Since the load max current is 200A, the secondary side is configured as a current doubler rectifier.

Currently, the primary side MOSFET continues to be damaged between approximately 60 to 90A of load current. 

The waveforms below are transformer primary voltage and current measured at load current of 30A and 60A.

The direction of the current probe was measured from the Qa, Qb leg to the transformer direction, should it be considered a normal waveform? 

The phase of voltage and current seems strange, please review.

   

30A                                                                                                                                              60A

For reference, the leakage inductance of the transformer is 20uH, and the external shim inductor uses 3uH. 

The output inductors of the current doubler rectifier are each 3.3uH.

The same applies to removing the external shim inductor, is there any way to fix it? 

There are no special heating elements.

Thank you for your help.

  • 0
    TI__Genius 9790 points

    Hi, Kwangwoon

    Thanks for your interest in TI here.  Please note the team that supports this device is in the US so they will have a delayed response due to the US holiday. Please expect a response in the week of Jan 4th.

    Yunsheng

  • 0 in reply to Yunsheng Qu
    TI__Guru* 86266 points

    Hello,

    I reviewed the current waveform of the primary and it does not look correct.  Could you double check your connections of the current probe?

    FETs are generally damaged by over current or over voltage.  Could you double check the design to make sure this is not occurring during steady state and large signal transients, such as load transients and startup, full load and no load.

    The other thing that may cause this is if the SR FETs are not connected correctly on the output.  Please double check that as well.

    You may also find the following tools helpful in checking your design.

    Webench Design Tool: 

    Excel Design Tool: 

    UCC28950 Application Note:

    The UCC28950 evaluation module, the users guide can be found at the following link.

    Regards,