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Using UC2825 in two switch forward converter in AC DC Power supply

Al Baruch
Prodigy 10 points

Hi,

I am having problem starting the power supply with a resistive load.  The power starts fine with an active load.

What maximum capacitor can I use at Soft start pin of this device?

Thanks

  • 0
    TI__Expert 4015 points

    I suspect the difference in performance is because your electronic load has a minimum turn on voltage in Constant current mode and a lower minimum turn on voltage or no minimum turn on voltage in constant resistance mode.
    There isn't a limit on the capactiance you can put on the soft start pin but in an offline application where your bias rail may be a multiple/fraction of your output voltage the unit needs to start fast enough that the bias winding is higher than the Vcc UV threshold before the Vcc cap is depleted down to the this threshold.