Circuit to use backup batteries only when main DC power is cut off

Thread Starter

c5462855

Joined Oct 18, 2019
1
Hello, I need the following to be achieved:
1) Have a device being powered by the main 5V DC power supply.
2) If that power supply is interrupted, the device will immediately (without any interruption in actual power supply) start drawing power from a set of backup AA or AAA batteries (classic non-rechargeable batteries).
3) When the function of the main 5V power supply is resumed, the device will automatically start drawing power from the main power supply (without any interruption in actual power supply).

I know that the above is possible to achieve, because I can see that my camera trap works exactly like that. (It has about a dozen backup AA batteries, that have not been used at all during the past two years [all of them are still at 100%] because the device has been plugged into a DC power supply without any interruption.)

I've searched the internet to find such a "gadget" that would allow me to connect (1) the device, (2) the main power supply, and (3) the battery pack, in a way to achieve the above, but found nothing.

Could anyone built such a circuit for me for a one-time fee? Just one exemplar, where it absolutely does not matter how it looks. The only thing I need is for it to function reliably.

Thank you.
Best regards,
David
 

Marc Sugrue

Joined Jan 19, 2018
147
Hello, I need the following to be achieved:
1) Have a device being powered by the main 5V DC power supply.
2) If that power supply is interrupted, the device will immediately (without any interruption in actual power supply) start drawing power from a set of backup AA or AAA batteries (classic non-rechargeable batteries).
3) When the function of the main 5V power supply is resumed, the device will automatically start drawing power from the main power supply (without any interruption in actual power supply).

I know that the above is possible to achieve, because I can see that my camera trap works exactly like that. (It has about a dozen backup AA batteries, that have not been used at all during the past two years [all of them are still at 100%] because the device has been plugged into a DC power supply without any interruption.)

I've searched the internet to find such a "gadget" that would allow me to connect (1) the device, (2) the main power supply, and (3) the battery pack, in a way to achieve the above, but found nothing.

Could anyone built such a circuit for me for a one-time fee? Just one exemplar, where it absolutely does not matter how it looks. The only thing I need is for it to function reliably.

Thank you.
Best regards,
David
If currents are low you could always diode OR the 5V supply with a slightly lower voltage battery pack

https://electronics.stackexchange.com/questions/287496/why-are-or-gates-using-transistors-different-from-or-gates-using-diodes

If the 5V PSU drops the battery will take over. If the supply is above the battery Voltage the batteries do nothing.
 
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