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Original question:

UCC28C44: Looking for alternative PWM controller

UCC28C44: 1500VDC output Application consult

Lin_Charles
Expert 4260 points
Part Number: UCC28C44

Hi team,

It is nice to know you here. My customer want to realize below application,

VIN=85-265VAC, Vo=adjust from 30V to 1500V DC, Po=50W, switching frequency is 100kHz. Do you find any risk to such application?

If so, how to choose turn ratio, inductance and frequency? Thanks.

  • 0
    TI__Mastermind 31580 points

    Hi Charles,

    The risk here is the large variation in output voltage, its a 1:50 ratio, which means that if we have a max duty cycle of say 90%, the minimum duty cycle will have to be 1.8% which is not realistic.

    To eliminate the variation in input voltage I suggest you use a flyback to boost the voltage to say 1500V, you can then design a high voltage buck to buck down the output voltage. It may not be possible to regulate down to 30V but you may be able to get to say 5% duty cycle, 100V.

    Since this a very niche application TI has no reference designs in this space, but you can use the powerstage designer tool to help with the design.

    Regards

    Peter

  • 0 in reply to Peter Meaney
    TI__Expert 4260 points

    Hi Peter,

    I also want to recommend customer to design this with flyback topology, the customer wants to design this with switching frequency100kHz. I want to know the minimum on-time of this device to eliminate the risk. Please help assess it. Thanks. 

  • 0 in reply to Lin_Charles
    TI__Mastermind 31580 points

    Hi Charles,

    At 100kHz switching frequency the period is 10us, once the duty cycle drop below 500ns then there may be some jitter in the PWM duty cycle due to noise in the system and lower control signal levels which effectively reduce the signal to noise ration of the controller.

    If the duty cycle drops to approximately 100ns to 200ns then the controller may start to drop gate drive pulses as it tries to maintain regulation. This is most likely to happen at high input voltage and very light load or no-load condition.

    Regards

    Peter

  • 0 in reply to Peter Meaney
    TI__Mastermind 31580 points

    Hi Charles,

    I hope there has been some progress on your side, since there has been no reply to my post for awhile now, I am going to close this post. please open a new post if you have more questions.

    Regards

    Peter