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UCC28704: How to design 200VDC--800DC--->13V,4W flyback

user129038
Prodigy 10 points
Part Number: UCC28704
Other Parts Discussed in Thread: UCC28C40

Dear Sir,

I am making a flyback, the input voltage is 200VDC--800VDC, (150VDC~900VDC range will be better), output voltage is 13V, total output power is about 4W.

Can UCC28704 support this wide input voltage?

My original design is to use UCC28C40, transformer is EEL16, Npri=300,Naux=22, Lpri=8mH, it works well from 200V~800VDC input. But I need to reduce the power loss @light load. So I try to use UCC28704 with the same transformer, but it could not work normally, as the Voltage of Aux can not reach 13V, it can only reach <5V, it seems that the duty cycle has been limited, the power. I am not sure if the fault is due to transformer design or not, could you please help? If transformer problem, could you please advise the details? The WEBENCH tool doesn't support wide range input voltage.

  • 0
    TI__Guru* 86206 points

    Hello,

    A 6 to 1 input design range with the UCC28704 is possible. There is a design tool that can be found at the following link that should help with your design.

    The UCC28704 is DCM flyback controller was your UCC28C40 designed for continuous current conduction?  If it was the transformer will not work with the  UCC28704.  The excel tool should be able to tell you what the primary magnetizing inductance; as well as, what the turns ratios should be.

    For a reference point. The turns ratio aux (Na/Ns) to secondary should be set wit the following equation.

    Na/Ns = Vaux/Vsec

    Regards,

    Mike