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Programmable controller for active clamp forward/ flyback converters

Anindya Dasgupta61
Prodigy 60 points
Other Parts Discussed in Thread: TL431, UCC2897A, LM5021

Hi,

I am looking for programmable voltage mode controllers for Active clamp (high side clamped) forward and flyback topologies. By "programmable" the following offline features are meant:

(i) Controller coefficients (eg Kp , Ki , Kd ) for linear controllers,

(ii) Dead time between turning on/off of main and auxiliary switch,

- these features should be configurable off line via appropriate external Resistance/ Capacitance.

For my application: Input voltage range is 24 to 42 V, the switching frequency should atleast be 400 kHz.

Could anyone please suggest a suitable part?

Thank you in advance,

Anindya

  • 0
    TI__Mastermind 27145 points
    Hi Anindya,

    Thanks for your interest in active clamp forwward and flyback. Does the active clamp forward and flyback need to be isolated? Typically the control loop for isolated topologies uses an external error amplifier such as TL431 with type II or type III compensation. You can tune the compensation components which will move the poles and zeros accordingly but is not the same as discretely adjusting Kp, Ki or Kd independent of each other. This resource provides some tips for compensation of isolated topologies: training.ti.com/power-tips-compensating-isolated-power-supplies

    For active clamp forward, you could consider UCC2897A. Dead time is configurable by the RTDEL pin through a resistor to ground. If I could get a little bit more information about your design requirements (output power, size requirements, minimum efficiency, etc), I can provide a suggestion for the flyback controller.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 60 points

    Hi Ben,

    Thanks so much for responding and trying to help. Yes, my application needs isolation. I would look at your suggestions. Controllable  poles, zeros placement should be fine. I had looked at UCC2897A earlier, but could not spot this feature. Does it provide such an option?  I will look at it again and revert.

    My output power is 10 W and 20 W. Desirable efficiency over 75 % . The dynamic performance (settling time, voltage dip etc) and emi requirements are stringent. Here, we would like to have controller ICs that would allow us to realize the designed controllers.

    Regards,

    Anindya Dasgupta

  • 0 in reply to Anindya Dasgupta61
    TI__Mastermind 27145 points
    Hi Anindya,

    Yes, UCC2897A does have configurable dead time. Figure 15 of the UCC2897A datasheet provides a graph of delay time vs delay resistance:www.ti.com/.../ucc2897a.pdf

    The dead time in a flyback is important primarily for designs using synchronous rectification which replaces the diode on the secondary side with a MOSFET and SR driver to get higher efficiency. If you're design does not need synchronous rectification, then you would just need to select a diode with low enough reverse recovery charge to prevent shoot through. I think a current mode flyback such as LM5021 could work well here.

    Best Regards,

    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 60 points
    Hi Ben,

    I meant to ask whether UCC2897A provides the option of programming my controller (PID etc My 1st query in the original post )? I understand that it has a configurable dead time.

    Thanks,
    Anindya
  • 0 in reply to Anindya Dasgupta61
    TI__Mastermind 27145 points
    Hi Anindya,

    UCC2897A itself does not set the compensation components but you can set these in your feedback circuitry on the secondary side . This would also allow you to adjust compensation settings through resistance/capacitance values.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 60 points

    Dear Ben,

    Could you please provide a technical/application note that explains how to use TL431 to set up feedback (compensator) circuitry on the secondary side.

    Thanks,

    Anindya

  • 0 in reply to Anindya Dasgupta61
    TI__Mastermind 27145 points

    Hi Anindya,

    This link is helpful for understanding how to configure your compensation network:.

    Best Regards,

    Ben Lough