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TPS92314: Single stage flyback protection (microseconds surge)

Egor Markov
Prodigy 180 points
Part Number: TPS92314
Other Parts Discussed in Thread: TPS92210,

Hello, everybody!

How to protect single-stage flyback with PFC (like TPS92314, TPS92210 or similar) in accordance with IEC61000-4-5, 1kV surge line to neutral?

Which size and voltage rating of varistor (230V line)?

Which current and speed rating of fuse I need?

Maybe you know any type of additional protection? 

  • 0
    TI__Mastermind 28655 points

    Hello,

    Since this is safety related I will only make recommendations to try/figure out what you need to look at:

    The MOV needs to be able to handle the surge energy, be high enough in voltage rating to not conduct and clamp well enough to protect the flyback MOSFET and other components from excessive voltage.  The flyback MOSFET will see the input voltage plus the output voltage reflected back through the turn ratio of the transformer plus and leakage overshoot.  If the MOV cannot clamp well enough to prevent the MOSFET from avalanching a higher VDS rated part should be used or different MOV.

    A fuse is a safety device and needs to be picked appropriately to prevent safety issues but also not fail in normal operation.  The fuse is part of the design process and the rest of your design.  I^2*t is important since turn on will have an inrush energy on your circuit and line surge.  But this is something that the designer needs to figure out in their design knowing what the safety tests and surge tests will be.  It's best to review the safety requirements to pick a fuse.

    The EMI filter can also absorb some of the surge but again, that is dependent on your design.  PFC flyback tends to be the more susceptible to surge due to low line capacitance.

    You can look at some of the EVMs and TI designs to see if they have information on surge and testing.  Some have been tested but again, they are only starting points/recommendations since every design is different.

    Regards,