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3v3 to 40v switcher

Yukio Kato
Prodigy 20 points
Other Parts Discussed in Thread: LM3478

Hi,

I am looking to design following switcher/boost circuit/DC-DC booster with following specs:

input: 3v3

output voltage:40v

output current: less than 1mA is okay The current is typically around 1uA

I am getting error when using calculated duty cycle exceeded limit. Any idea how to fix/design such circuit? My design parameters are obviously weird, but these are for very specific and real parameters in certain application.

  • 0
    TI__Mastermind 39210 points
    Kato-san,

    Since the current is so low, I increased the Iout to 10mA and got a solution with LM3478. It is shown below. Will this work for your needs?

    webench.ti.com/.../SDP.cgi
  • 0 in reply to Nikhil Gupta (Product Folder Models)
    Prodigy 20 points

    Thank you very much Nikhil!

    I think this is perfect solution for my purpose.

    Just a one additional question about this design, the output current is 10mA, that is the maximum current, right? If my highly resistive load takes much less current (~1-100uA tested with external supply), the circuit will not forcefully regulate 10mA output current?

    Is there a minimum current spec for circuitry to maintain 40v output voltage?

  • 0 in reply to Yukio Kato
    TI__Intellectual 2405 points

    Hi Kato-san,

    The output current of 10mA in the design suggested by Nikhil, is indeed the maximum current output of the circuit. Since your application circuit load is drawing much less than that, the design should work properly without any issues. The circuit in itself will NOT forcefully regulate to 10mA output current unless load demands it. Also there is no minimum current limit constraint at the output.

    Please check it out at prototype level before finalizing the design. Hope this information helps. Kindly let us know if you face any issues.

    Thanks!!

    Best Regards,

    Mahavir Jain.