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Need a switcher I can apply power to output

Robert Wuest94
Prodigy 20 points
Other Parts Discussed in Thread: TPS54140A

Hi,

I have a circuit board, power circuitry shown in image below, which currently uses a 7805, that may be powered from an external +5V source (P7 or P14) or from an external battery pack at 12-36V (J7).

When P16 is installed with jumpers 1-5 and 2-4,  the two buses (+5V and B5V)  are connected (there is another use of this where they use separate power).

The current draw is around 0.75A.

When the external +5V power is used, that power gets applied to the output of the voltage regulator.  The existing 7805 circuit uses a diode from its output to input to prevent excessive current, however, the power dissipation is crazy high, too high, and so I'm looking to replace it with a switcher. 

Does anyone have a recommendation on a suitable switcher to use for this?

Robert

  • 0
    TI__Guru**** 191445 points
    Is the battery still connected when you have the external power applied? In the first case, I would probably not want to use a linear regulator to convert 12 to 36 V down to 5 V. A switching regulator would be much better (maybe TPS54140A?). Then I think I would want to add an OR'ing diode:
    www.ti.com/.../overview.html
    or a load switch:
    www.ti.com/.../products.html
    to manage the power distribution of the 3 different 5 V options. Let me know what you think.
  • 0 in reply to JohnTucker
    Prodigy 20 points
    Thanks for the help John!

    The input to the regulator is disconnected when the external 5V power is used with the shorting jumper (the two parts of the board may be used without the shorting jumper and both external 5V and battery powers provided, but that's not a problem case).

    I already considered an oring diode, we use them all over the place for power supply redundancy, but ruled it out due to the Vf drop not being acceptable for part of the system. Not even a schottky diode.

    I'm not opposed to using a load switch, just have to figure out how to control it here.

    Robert