Is it possible to have two power supplies, where one cuts off the other one? And if so, how?

I have a circuit which regulates a 16V supply to 3.3V and powers a microcontroller. However I would also like if the microcontroller could be powered off 5V from a USB connection, where the 5V would "overwrite" the 3.3V and turn that off, until the USB is disconnected and the 3.3V takes over.

The regulator is a TS2950 and the microcontroller is a Attiny2313, if that helps.

  • 3
    \$\begingroup\$ Yes, it's possible. \$\endgroup\$
    – jonk
    Commented Dec 11, 2021 at 22:41
  • \$\begingroup\$ But how? Diodes and transistors? \$\endgroup\$
    – jonas
    Commented Dec 11, 2021 at 22:43
  • 2
    \$\begingroup\$ Without any more information than you have given (very sparse), such as current compliance requirements for example or whether or not you would allow a short period of no power at all (I could assume, but I won't do so), it's hard to suggest anything more concrete. For example, there are connectors which include built-in mechanical switches you could use. But this would likely mean break-before-make arrangements which might mean a loss of power. Or you may require some momentary storage (caps.) How much can the voltage droop? What circuits do you have now? In these, I'm ignorant. \$\endgroup\$
    – jonk
    Commented Dec 11, 2021 at 22:50
  • \$\begingroup\$ But, for example, there are so-called 'powerpath' products like this one that may also be able to consider. \$\endgroup\$
    – jonk
    Commented Dec 11, 2021 at 22:54
  • \$\begingroup\$ You want to turn off the 3.3V output of the regulator and inject 5V into the same rail? That seems odd. \$\endgroup\$
    – Passerby
    Commented Dec 12, 2021 at 5:52

1 Answer 1


The TS2951 (in SOP-8 package) has a shutdown feature that could be used, but the TS2950 does not. If you could change to that part then the SHUTDOWN pin could be tied to the USB power (no protection needed) to disable the 3.3V regulated output when USB power is applied.

But you still need protection when both USB and the 16V supply are connected, as @jonk hinted at.


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