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SEPIC controller recommendation

George Biner (Arrow)
Intellectual 705 points
Other Parts Discussed in Thread: UCC2801, UCC2800

 

1)  Which controller would you recommend for a SEPIC controller?  Vin 15 to 47VDC.

2)  What is the output power and output voltage limitation for a SEPIC topology?  100W? 500W? or 1kW?

  • 0 in reply to George Biner (Arrow)
    TI__Mastermind 25130 points

    George,

    You are proposing a converter that is at about the upper power limit for what i would recommend for a sepic converter.

    As for controllers I expect that any one of our single ended converters would work for your application but since you will be starting it from a rail that goes from 15 to 47 volts and then I would assume being powered off a bootstrap winding I would expect that you will want something that has a very low startup current and a fairly wide hysteresis between UVLO "ON" and "OFF".  An IC with a 13.5 volt maximum UVLO start voltage may be difficult to work with considering the 15 to 47 volt input range.

    The next question is the duty cycle limitations. Obviously the design will be with a power transformer but that still has a 3 to 1 variation in the input voltage, hence the transformed voltage. An IC that gives a 50% max duty limts the design and control loop.  

    These conditions limit the IC selection. For instance the UCC2800 has a "100%" on time and a turn on UVLO max of 7.8 volts but a minimum on/off hysteresis of 0.12 Volts Not great for boot strap operations. The UCC2801 is better with a minimum hysteresis of 1.6 volts and a turn on of 10.2 volts but a max duty cycle of 50%.

    The UCC2813 family has similar options as does the UCC28V40 family of parts..

    Regards,

    John