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PMP7763: 24V output from a 30V input with 8:1 transformer ratio

Danilo A.
Mastermind 24715 points

Part Number: PMP7763

Hi Team,

The PMP7763 reference design shows that it can operate from 30V-800VDC input supply. The datasheet of the T100 transformer shows that it's turns ratio is 8:1 which translates into 30V/8 = 3.75V output from a 30V input. A customer wants to know how it is possible to output 24V from a 30V input if the transformer turns ratio is 8:1?

Regards,

Danilo

  • 0
    TI__Guru 68675 points

    Hi Danilo,

    Thank you for posting. It is a flyback circuit, and the duty cycle satisfy the following equation:

    D(Vin) = (Vo +VF) / (Vo + VF + Vin/ktr)

    Where ktr is the transformer turns ratio, which is 9 in this case.  

    Vo=24V, and VF=0.7V (diode drop).  Then when you plug the Vin=30V and 800V, you get a duty cycle of 0.87 and 0.19, respectively, which are within the LM5022's operating range.  

    Thanks,

    Youhao Xi, Applications Engineering