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UCC28951-Q1: UCC28951-Q1

Rajashekar Koutla
Intellectual 590 points
Part Number: UCC28951-Q1
Other Parts Discussed in Thread: UCC28950

Hello

1) How to decide the components D4,D6 in the figure 56. of UCC28951-Q1 datasheet? and their type of diode ( schottky or fast or ultrafast ) ? what should be the current ,voltage,and power rating of those components and how to calculate the values ?

2) what is the use of  D5,D11 in the same figure56 of UCC28951-Q1 DS .? and how to decide the component of what rating and their type of diode?

Please help.

Thanks

  • 0
    TI__Mastermind 25570 points
    Hello Rajashekar

    D4 and D6 form part of a snubber network to clamp the peak voltages on the synchronous rectifiers. These parts should be fast or ultra-fast types. They will experience a reverse voltage equal to the voltage across C1 so their reverse voltage rating should be about 1.2 times this.
    They will experience a current pulse on each switching cycle but the average current will be low. The peak current will be set by the impedance in the loop from the diode through C1 and back through the SR. The ES3BB diode shown has a 25ns reverse recovery time, a 100V reverse voltage and a 100A (non-repetitive) peak forward current. Unfortunately I can't really give you more information than this because snubber design is very dependent on the details of the circuit involved.

    The diodes D5 and D11 clamp the primary of the transformer at Vin and GND and prevent an oscillation which could overvoltage the SRs. They see a reverse voltage equal to Vin so need a reverse voltage rating which is about 1.2 times this. They also need to be ultra fast types. the forward current is difficult to predict so normally they are chosen to be able to carry the full primary current. Section 8.2.2.5 in the UCC28950 data sheet has some more details.

    Regards
    Colin