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Isolated flyback multiple outputs - PSR?

ctw
Prodigy 20 points
Other Parts Discussed in Thread: UCC28911, UCC28710, UCC28700

Hi, my design spec is 6W, 15Vin -> 2 separately isolated 15V outputs with reasonably loose regulation requirements i.e. +-0.5V would be fine.

Output 1 - 15V, 300mA

Output 2 - 15V, 100mA

Isolation pri->sec 4kV, sec->sec 4kV

I'm thinking this could be a candidate for PSR flyback to achieve a cheap design, given that output 2 is lightly loaded and will stop conducting long before output 1.
 Reading the datasheet for UCC28911 (figure 48) it seems that some implementations of PSR would handle this pretty well.

Can anyone shed any light on whether this would be a good idea, and whether there is a integrated switch IC more appropriate to the voltage/power level that would work doing PSR in this situation?

http://www.ti.com/product/UCC28911/datasheet/applications_and_implementation

Thanks

  • 0
    TI__Mastermind 34465 points
    The PSR controllers with integrated power switch like the UCC2910 family and the PSR controllers with high voltage start up like the UCC28710 family all require a minimum of 35V input in order to start.
    The UCC28700 PSR controller does not have an integrated switch but has a 21V under-voltage lockout on VDD.
    This is an issue with your 15V input voltage
    I suggest that you consider using the a member of the UCC3845 family
    www.ti.com/.../ucc38c42.pdf
    You should be able to achieve the required regulation if you use the transformer bias winding as the feedback
    and there will be no need for an optocoupler.