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UCC28881: Max Vout

Part Number: UCC28881

Hi!

What's the max Vout for the following requirements:

Vin 40-160V, I out 0.01A?

Kind regards,

Marion

  • Marion,

    Assuming this design is for a CCM flyback, there is a power limit to the device but there is also a duty cycle limit for the flyback.

    VOUT=N*(Dmax/1-Dmax)*VIN, where N is the transformer turns ratio 

    From a max output power point of view, POUT(max)=4.5 W (see table below) when 85 Vac<VIN<265 Vac (120 V<VIN<375 V). For Iout=10 mA, VOUT(max)=450 V. However, your minimum input voltage is 40 V, so the input current will be 3X higher compared to the case where VIN(min)=120 V, which would reduce VOUT(max) by 3X. For 40 V<VIN<160 V, the maximum output voltage should be limited to ~150 V (450 V/3). If you use 150 V as the max allowable output voltage, you can now determine what the transformer turns ratio (N) should be to maintain VOUT<150 V, Dmax<0.48, CCM operation.

    Regards,

    Steve M