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Original question:

UCC28740: About DESIGN CALCULATOR TOOL

UCC28740: About Cbulk

Kenji Ohno1
Genius 5095 points
Part Number: UCC28740

Hi Team,

My customers are designing using TI's design sheet.

The application is a servomotor amplifier.

Because Cbulk is designed as a motor drive power supply and a common power supply, we are studying 3000 μF instead of 5.4 μF obtained by the calculation result.

Below, my customers would like to know.

1) Is there a problem even if Cbulk = 5.4uF → 3000uF?

2) How does Cbulk affect Np (primary winding number)? What calculation method?

3) Is there a recommended protection circuit assuming that a surge of 1000 V is applied to the VH pin?

Best Regards,

Kenji

  • 0
    TI__Mastermind 27135 points
    Hi Kenji,

    1. this will result in less ripple voltage on Cbulk and the minimum valley voltage on Cbulk will be larger. This is ok but keep in mind that the ripple current in Cbulk will be larger if Cbulk is bigger

    2. The minimum valley on Cbulk will be larger so this will affect the turns ratio calculation. I would recommend using the UCC28740 calculator to calculate the appropriate turns ratio. You can find the calculator at the bottom of this page: www.ti.com/.../toolssoftware

    3. Please keep in mind that the HV pin is rated to 700V only. It depends on how much time the 1kV surge lasts but a MOV connected from HV to gnd might be sufficient.

    Best Regards,
    Ben Lough