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UCC28950's diode questions

Jacob Kim
Prodigy 250 points
Other Parts Discussed in Thread: UCC28950, UCC28950EVM-442

Hello there

One of my customer designed UCC28950 for OBC(On Board Charger) and he refered our UCC28950's EVM schematics which is ucc28950evm-442.

He asked few question and has some issue with below schematics.

1. Reveiw below customer schematics

2. What's purpose for Db, Dc

3. If he removes Db & Dc, is there any sideeffect or some problem?

If you have any question, feel free to contact me.

  • 0
    TI__Mastermind 25570 points

    There is a potential for high voltage ringing on the secondary rectifiers, caused by the difference in current between the transformer and the shim inductor when the transformer comes out of freewheeling. Diodes DB and DCprovide a path for this current and prevent any ringing by clamping the transformer primary to the primary side power rails. Normally these diodes do not dissipate much power but they should be sized to carry the full primary current. The worse case power dissipated in these diodes is:  0.5 * Lshim * (Ipri_RMS^)2 * Fsw. This equation is quite conservative.

    The diodes should be ultra fast types and rated for the input voltage of the converter – VIN (410 VDC in this case)

    Regards
    Colin