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Battery ---------->|----o----o MCU +VCC
Main 5V6         Diode  |      Main +5V, Backup +4.8V
                        |
                        |
Battery----------->|----'
Backup 5.5V      Diode


I guess simpler than that is impossible.
Does it solve your problem?

jaythesis wrote:
> hi!
> 
> does anyone have a circuit design on back-up power supply? like if
> the main power is cut-off, the battery automatically takes over to
> supply the MCU. can i have the design?
> 
> thanks in advance.
> 
> -jay



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