Voltage drop detection and battery backup switch

[ChrisGreece52]

Hello i have a pretty basic questions but i do not know how to search for a solution.
The circuit is basically a reference crystal with a high frequency that gets divided and then decade counters just count up ms , seconds , minutes , hours , etc. The data gets fed to CD4543 BCD decoder ics that are connected to 7 segment displays for output.

Problem is that when the power goes out i want the oscillator and the crystals keep going with the help of a battery and have the decoder ics and 7 segment displays shut down.
First questions is : Would a comparator circuit work for this aplication ?
2) Can it operate fast enough so the circuit does not lose track of counting
3) Will there be a problem in controlling the power delivery of the 7 segment displays and the decoders through a mosfet.

Thank you. (if you need more information i would be more than happy to provide it)

[danadak]

If you operate offline on a battery you just use diode
steering to handle this -

https://www.allaboutcircuits.com/projects/battery-backup-power-supplies/


http://www.instructables.com/id/Simple-5v-battery-backup-circuit/


Regards, Dana.

[ChrisGreece52]

I think that should do it.
The clock will be wall powered and with this circuit , a big capacitor to smooth the transition and keep the counter running till the battery kicks in i think i should be fine.
Thank you.