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device recommendation for wide input range isolated dc-dc

Mattias Moritz
Prodigy 60 points
Other Parts Discussed in Thread: UCC28600, LM5021, LM5022, TL431, PMP9334

Hi,

i want to design an isolated dc-dc converter with a wide range input of

18V-150V (DC) => output voltage of 5V @2.5A.

Which device would you suggest ?

Is a adaption of an e.g. UCC28600 (AC-DC design) possible ?

Is a flyback topology the best ?  

(probably the transformer is a non standard type, the isolation voltage should be 2.5kV)

Thanks for your reply

  • 0
    TI__Genius 9130 points

    For this very wide input range, it does sound like a flyback is probably a good choice. However, the design will be challenged, since the currents at 18 V input will be large, yet the max input voltage of 150 Vdc will require a MOSFET rated for at least 300 V or more. (standard rated parts means that a 500 V part is probably required, not many available between 250 V & 500 V).

     

    In order to make the right choice, what are the key specs and features for the design?

     

    - Is integrated startup from the line required? If so, most parts target either the lower DC range for telecoms (up to 60 or 80 Vdc), or else the higher range for universal AC-DC (80-264 Vac).

    - What is the eff target?

    - Can the load go down to zero?

    - Is the no-load/standby power important?

    - Is the efficiency at light load important?

    - Is fixed PWM freq required, or can it be variable?

    - Does the design require PWM freq dithering for EMC reduction?

    - Is quasi-resonant or valley-switching required/preferred (=> variable freq)?

     

    For a very brief review of available EVM's & reference designs, this one may be a possible first starting point:

    http://www.ti.com/tool/lm3464-120v24w

     

    This is targetted at LED applications, but the front-end uses LM5021 for 90-132 Vrms (up to 186 Vdc), with 48 V output at 25 W. This can probably be adapted for your application. The LM5021 should start at low input voltages too, as low as 8 V.

     

    Hope this helps get you started.

     

    Thanks,

    Bernard

  • 0 in reply to Bernard Keogh
    TI__Genius 9130 points

    The LM5022 also lists several wide input range designs:

    http://www.ti.com/product/LM5022/toolssoftware?keyMatch=pmp7958&tisearch=Search-EN

     

    This one is close at 30-300 V:

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

    This regulates on the primary bias rail, but a secondary side TL431+opto should be added to get imporved regulation for a 5 V output.

     

     

     

     

  • 0 in reply to Bernard Keogh
    Prodigy 60 points

    Thanks for the device recommendation.

    I'll start with the pmp9334 reference design. The efficiency is not a critical parameter for the design.

    So, first i'll try to shift the minimum voltage from 30V down to 18V.

    Regards

    Mattias