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Isolated DC-DC converter design support

filids
Prodigy 70 points
Other Parts Discussed in Thread: UCC28700-Q1, UCC28700, LM5022, PMP9334

Hello,
For a new project, we have to design an isolated DC-DC power supply.

The minimum requirements for our project are:
Input: 9Vdc to 60Vdc
Output 1: 5Vdc ±5% @ 2A 
Output 2: 24Vdc ±10% @ 0.2A
Topology: Flyback
If possible, without optocoupler for the feedback.

Could you please suggest an controller IC for the above requirements?

Thanks in advance.

Regards,

Filippo D. S.

  • 0
    Genius 3295 points
    Hello Filippo,

    You can search the TI website and easily find a wide selection of flyback isolated dc dc pwm IC controllers. The UCC28700-Q1 would work very well in this application. The IC is set up for a voltage feedback from an auxilary transformer winding -no opto coupler needed. This is very wide range input design, so a variable frequency, transition mode type modulator works very well. You get high efficiency and stability since your are in DCM (No RHP zero.).
  • 0 in reply to Chuck Sampson
    Prodigy 70 points
    Hello Chuck,
    thanks for your reply.

    FDS
  • 0 in reply to Chuck Sampson
    Prodigy 70 points

    Hello Chuck,
    I checked if the UCC28700 is ok for our application, but unfortunately, it has 21V UVLO turn-on threshold and our power supply has to start-up to 9V.


    What do you think about the LM5022 controller?
    I could use a primary side regulation from an auxiliary winding with a resistor divider to the feedback pin. I found the following reference design:

    http://www.ti.com/tool/pmp9334


    Thanks for your help.


    Regards,
    Filippo D. S.

  • 0 in reply to filids
    Genius 3295 points

    Filippo,

    You're welcome, although I haven't really been of much help. Sorry about missing that UVLO spec, you're right, the chip doesn't work below 21 V. The LM5022 looks good to me. The pmp9334 design using the auxillary winding  is a good way to get feedback without using an opto-coupler. Be aware that the aux winding will have some error in the aux winding with the variation of the load. When the load increases the aux winding current increases and the voltage drop across the aux diode and damp resistor increases slightly. Also you have error due to noise and ringing in aux waveform. So you have to account for these errors in your feedback if you need a precise output voltage regulation.

    If you need better than 5% regulation, I would probably add a linear regulator to the output.

    -Chuck