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24VDC input, adjustable 3.6 to 36VDC output switching power supply, digital adjust

David Nyce
Prodigy 180 points
Other Parts Discussed in Thread: LM5175, LM5022, TPS54061

Looking for the simplest circuit to implement a switching regulator having a digitally adjustable out put voltage.  Input = 24VDC +/- 5%.  Output = 3.6 to 36VDC at up to 80 mA, with the output voltage to be adjustable by a microcontroller.  If there is no direct way, then a digital pot could be used for the adjustment.

Thanks

  • 0
    Prodigy 5 points
    Hello David.
    To get 36V from 24Vin you must boost somehow.
    To get down to 3.6V from 24Vin you step down, ldo or buck.

    For one chip that can do both see LM5175
    www.ti.com/.../LM5175
    It can step down and step up to the voltages you need, from 24Vin.
    This document shows the concept.
    www.ti.com/.../slyy106.pdf

    Your 80mA load is not alot. However the device can do it.

    Using a DPOT on the lower resistor in the feedback divider you could adjust it.
    www.ti.com/.../digital-potentiometers-overview.page

    You could boost to 36V with one converter, then step down all the way to 3.6V.
    In this case you design a boost (Webench) for 24Vin - 36Vout 100mA
    LM5022 comes up in Webench as the first choice.

    Then a variable buck to go from 36V to 3.6V.
    TPS54061 can be used for this section.
    Again using the DPOT to control the lower resistor in the feedback divider.

    With an LDO type of step down from 36V, it would produce much heat loss.
    At 36Vin and 3.6Vout, 32.4V, and 80mA output, is 2.6Watts dissipated in the LDO.

    I hope this helps.