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UCC21520: UCC21520

Shahamat Shahzad
Prodigy 20 points
Part Number: UCC21520
Other Parts Discussed in Thread: UCC21330, UCC21551, SN6501

Hi TI.

I am looking for a driver solution that is specific to a type of cycloconverter. I have already successfully utilized UCC21520 for the development of a Dual active bridge (DAB) prototype, but for my new project, I need to use a hybrid DAB design with an active full bridge on the primary side and a cycloconverter on the secondary side which is connected to a grid. The cycloconverter uses two sets of back to back N-channel Mosfet (working as two bidirectional switches) connected in the common source configuration.     

S1 and S3 are high frequency switches while S2 and S4 operate at grid frequency and are used for current unfolding. The primary side is a full bridge. Below is the functional diagram for UCC21520 which I am using for the primary side. The primary side also requires a bootstrap circuitry for the high side switch.

For the secondary side I could use the same driver in the configuration given below, where I could drive S1 and S2 using OUTA and OUTB. Use as single 15V supply for VDDA and VDDB and combine VSSA and VSSB to the common source point of the higher bidirectional switch. A similar configuration can be used for the lower side bidirectional switch consisting of S3 and S4. 

I think this is not an optimal solution and I could use any other non isolated general purpose gate driver but my questions are 

1. Weather there are any cost effective specific solution from the vast TI library to this configuration?

2. Weather I would need any bootstrap circuitry in this configuration?

3. Can I use a single 15V supply to power gate driver circuit for the upper and lower bidirectional switch?

Thanks in advance.

    

  • 0
    TI__Genius 17136 points

    Hi Shahamat,

    That sounds like a working idea to me. Can you explain "current unfolding"? Why is there a higher frequency for S1 and S3?

    It sounds like it will save space to use a dual channel driver, and there is not a channel spacing requirement.

    There are less expensive drivers, such as UCC21551 and UCC21330 that are also dual channel.

    Best regards,

    Sean

  • 0 in reply to Sean Cashin
    Prodigy 20 points

    Hi Sean.

    Thank you for the response. To be more illustrative, S1 and S3 operate at high frequency and S2 and S4 operate at the low grid frequency when the grid voltage is positive, while S2 and S4 operate at high frequency and S1 and S3 operate at grid frequency when the grid voltage is negative. The high frequency switches on the secondary side are phase shifted from the primary bridge to transfer the required power to the grid.

    Getting to my main question.

    Do I need t use two different 15 volt gate driver supplies for the higher and the lower bidirectional switch.What actually I had in my mind was something like below.

                                              

    But I am not sure if I could use the same 15V supply for the upper and lower bidirectional switch. It will make the point A and B at the same potential.

    So, do I need 2 isolated 15V power supplies for the upper and lower switch with 2 independent grounds.

    Regards

    Shahamat

  • 0 in reply to Shahamat Shahzad
    TI__Genius 17136 points

    You would need 2 isolated supplies for these 4 channels. That is, 2 independent "grounds"

  • 0 in reply to Sean Cashin
    Prodigy 20 points

    Thank you Sean.

    My second question is about the Boot strap circuitry. Since both, the mosfet in a single bidirectional switch have same ground, we do not need to use a bootstrap circuitry. right?

    and any suggestion on low cost auxiliary 15 volt supply that we can use with each driver for the bidirectional switches.

    Regards

  • 0 in reply to Shahamat Shahzad
    TI__Genius 17136 points

    Hi Shahamat,

    For these 2 supplies, you could either use 2 isolated supplies, or one isolated supply with a bootstrap circuit for the high-side.

    One recommendation for an isolated supply is to use the SN6501 with a small push-pull transformer. 

    Best regards,

    Sean