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UCC25600: wide range output

Expert 2875 points

Replies: 18

Views: 615

Part Number: UCC25600

Dear All,

i selected the UCC25600 for a 400 W resonant converter.

the problem is that i need to adjust the output voltage of a resonant converter when it works.

the output voltage has a wide range from 0 to 400 V.

the input voltage is 400 V ( form UCC28019A PFC stage ).

the maximum current is 1 A and the load is a  resistance ( variable resistance 400 W ).

please see the bellow schematics ( form data sheet ):

can i adjust the voltage by change the Vs?

or can i adjust the voltage by changing the upper resistance in the divider?

or is there any other methods to do that?

Regards,

Ras

  • Ras

    To adjust the output voltage of UCC25600, the reference voltage out the outer voltage loop needs to be adjusted. In the typical schematic the reference is set by the TL431, which has an internal voltage reference. In order to turn this fixed reference to a variable voltage the feedback needs to be modified. A common implementation technique is to use an op amp as the following app note shows www.ti.com/.../slva662.pdf. Note that the Vref in Figure 1 of this app note is the control voltage that will determine what the output voltage will be.

    I'd like to highlight that the performance of UCC25600 will be very limited with such a wide output voltage range. Resonant LLC converters generally do not work well with wide input or output voltage ranges, so a large range of 400V will be very challenging to meet and will have limited performance. A Phase Shift Full Bridge with UCC28951 would be a better topology to use since it does not have the same voltage range limitation. You can adjust the output voltage of this controller/topology using the same scheme that's described earlier.

    Best Regards,
    Eric
  • In reply to Eric Faraci:

    Hi Eric Faraci,

    thank you for the explanation.

    i have two problems:

    1) in the case of UCC25600, in the PMP5967 reference design, the input/output voltage ratio is approximately 32 ( ie 380/12 ). the performance of the design seems high.

    2) in your answer, do you consider adjusting output voltage, when converter works or in the develop stage?

    Regards,

    Ras

  • In reply to Ras Sharif50:

    Ras

    To answer your questions

    1. Since the resonant LLC topology has a transformer, the input to output voltage range is not an issue since the turns ratio can enable any ratio desired. The issue is when the input voltage range or output voltage range is wide. The following two PSDS papers provide more details about this and LLC operation www.ti.com/.../slup263.pdf and www.ti.com/.../slup306.pdf.

    2. This can adjust the output voltage when the converter is operating.

    Best Regards,
    Eric
  • In reply to Eric Faraci:

    Dear Eric Faraci,
    thank you very much.
    would you please explain the differences between UCC2895, UCC28950, UCC28951?


    Best Regards, Ras
  • In reply to Ras Sharif50:

    Hello Ras

    The UCC2895, UCC28950 and UCC28951 are Phase Shift Full Bridge controllers.

    The UCC2895 does not have SR control outputs and is mainly intended for use on the primary side of the isolation barrier.

    The UCC28950 and UCC28951 do have SR control outputs so if you they are the better choice if you want to use SRs in your design. But, even if you are going to use diode retification th They also offer easier synchronisation than the UCC2855 and include a better control in burst mode. They are also easier to use in Peak Current Mode control than the UCC2895 - they have a dedicated pin to select Voltage Mode control or Current Mode control. they have been designed to be used as secondary side controllers but have been successfully used as primary side controllers.

    The UCC28951 will operate better at wide duty cycles while in current limit than the UCC28950 and is normally the better choice

    Hope this helps - please re-post with if you have any more questions.

    Regards
    Colin
  • In reply to Colin Gillmor:

    Dear Colin Gillmor,
    thank you for that useful and valuable information.
    can you guide me how can i gather/receive this information of a product as genetal? for example how can i understand that UCC28951 will operate better at wide duty cycles.

    Bets Regards, Ras
  • In reply to Eric Faraci:

    Dear Eric Faraci,
    please verify if i think true;
    it is not possible to adjust voltage for UCC2813 as for UCC28950 since the error amplifier of UCC2813 is internal.

    best Regards,
    Ras
  • In reply to Ras Sharif50:

    Hello Ras

    The application note linked in the UCC28951 datasheet shows how to choose between the UCC28951-Q1 and UCC28950-Q1 devices. The note is valid for the UCC28950 / UCC28951 devices too. You can find it at www.ti.com/.../slua853.pdf

    In general, I would suggest that you use the UCC28951.

    Regards
    Colin
  • In reply to Colin Gillmor:

    Ras

    For your question on UCC2813, the internal error amplifier and reference can be bypassed. PMP2187 (schematic: www.ti.com/.../slur196.pdf) is a good example of it configured with an external error amplifier and reference. The same techniques discussed earlier can be used to adjust the voltage.

    Best Regards,
    Eric
  • In reply to Eric Faraci:

    Dear Eric Faraci,
    thank you for the reply.
    is there a design procedure/guide for the technique?

    Best Regards,
    Ras

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