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Original question:

UCC28070: UCC28070 design for 3Kw

UCC28070: UCC28070 design for 3Kw, 5 kW, and 300 W

Dante Mora
Prodigy 20 points
Part Number: UCC28070
Other Parts Discussed in Thread: UCC27324

Hi,

I have been trying to make my 3.7 kW prototype work. Despite the simulation results seems to do very well with the UCC28070 model for PSpice, the fact is the converter prototype does not regulate at all.
Based on some oscilloscope measurements, It seems only one leg works for a while and suddenly the other leg tries to work, some times it does with a phase shift of 180° a other times it overlaps with the other phase. As a result, the output voltage varies from the desired voltage of 400 V. 

At first sight I though the problem was the CT sensor polarity which was connected with the same that is indicated in the 300 W application in http://www.ti.com/lit/ug/sluu312b/sluu312b.pdf
However, the polarity  is different among the two legs as it is described in the 3 kW application: http://www.ti.com/lit/df/slur217/slur217.pdf . It confuses me and I do not  know the cause of the output voltage regulation problem. Do I have to use different CT sensor polarity between the 2 legs or the problem is associated to other stuff?

It is worthy to mention that all of the hints and recommended operating conditions described in the UCC data sheet were followed (I also use the ucc27324 as a driver). Then, I wonder if someone if the specialized TI team would help me with my problem.

Thanks

  • 0
    TI__Mastermind 34465 points

    Hello Dante Mora,

    The SLUU312B schematic actually shows that the sensed current in phase A (CSA) is in phase with the phase  A MOSFET current and that the sensed current in phase B (CSB) is in phase with the phase B MOSFET current .This is exactly what is required.
    I think you are confused by the dots drawn on the current transformers. The dots are for reference only and in this application the two current transformers are completely separate. I dont know why the circuit designer drew one CT with the dots reversed but I can see where your confusion arises.

    You should disconnect one gate drive, say GDB. Then check that the phase A leg is switching properly.
    Afterwards disconnect GDA and check that phase B is working.
    This will give you a better understanding of what the issue is.

    Regards

    John

  • 0 in reply to John Griffin1
    TI__Mastermind 34465 points
    Hello Dante Mora,
    I am marking this post as closed since it has been 3 weeks since the last posting.
    If you need further help please open a new thread.
    Regards
    John