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UCC28950 Vdd power options

Matthew Graney
Prodigy 130 points
Other Parts Discussed in Thread: UCC28950, UCC3895

Hello,

I am creating an isolated full bridge DC/DC converter using the UCC28950. It will have a large input voltage range of 300V-650V. My question is how to power the UCC28950 itself. I am thinking one option is to design a small wide-input flyback converter to power the UCC28950 and the gate drivers. I also saw the PMP5410 design example which shows the UCC28950 powered from a non-isolated buck regulator. However, the feedback must be opto-isolated. It seems like the main difference is whether the UCC28950 is referenced to the input or the output. I am wondering which method is better? My biggest concern is size and weight. Cost is not the biggest concern. Thanks for any help!

  • 0
    Intellectual 385 points

    I am using flyback for my designs but with 650V input its not  possible  to implement the supply  with an integrated flyback IC like tny 268 or so.

    I suggest an auxilliary winding on your main transformer to make a 15 to 30v dc and then regulate with a linear regulator like 7812.(and of course a  3W start up resistor)

    personally I used two switch fly back for my  3 phase 380v  input  10kw converter with ucc3895 but for weight and volume sensitive design its not recommended.

    by the way the   power integration website  has an app. note for using their  ICs on higher input voltage that you can find it easily.

  • 0 in reply to Ali Mansoori
    Prodigy 130 points

    Hi Ali,

    Thanks for the advice. I am thinking about using the Power Integrations LNK606 with the "StackFET" configuration for higher voltage like you mentioned.

    I am curious about the 3W start-up resistor idea. Would this be a supply derived from the input voltage? If so, would it always be dissipating 3W during operation?

    Thanks, Matt

  • 0 in reply to Matthew Graney
    Intellectual 385 points

    No it won't dissipate 3w but for 650v input you have to use 4 x1/4w or 3 x1/2w or 2x 1w resistor in series to withstand the voltage.

    1/4 resistors are rated for 250v and 1/2 for 350v and 1w for 500v ....

    with a 0.5 mA startup and 650v, there is just 325mw power dissipation.

    if you need this power supply just for your controller and its very low power, auxiliary winding is a better option.(unless you want the circuit work in short circuit condition and there is an error indicator or so)