Battery switching circuit.

Thread Starter

Bod

Joined Sep 18, 2016
317
I was thinking is there a way to make it so when a battery goes below a certain voltage it switches to a backup battery. For instance, in my remote control car I want to make a modification so you can have two batteries plugged in at once. The second battery will not be supplying any power to the car until the first battery goes below, let's say, 4V.

EDIT: I've looked through the other post about battery switching circuits - They aren't really what I need.

Thanks,
Bod.
 
Last edited:

crutschow

Joined Mar 14, 2008
34,285
Below is the LTspice simulation of a switchover circuit using the common LM339 or LM393 comparator and the TL431 voltage reference.
U3 generates a stable 2.5V reference voltage.
The circuit switches from battery V1 to V2 when V1 drops to 4V (as set by pot U4).

Note the opposite orientation of the two MOSFETs.
That's to block V2 when V1 is connected, and to block current back into V1 when the output is higher than V1's voltage due to V2 supplying power to the load.
(That's to avoid reverse conduction through the MOSFET's substrate diode).

The P-MOSFETs can be any logic-level devices that will handle the load current with a maximum Vgs(th) of about 2V or less.

upload_2017-8-14_11-23-18.png
 

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But the quiescent current might kill the design compared to the 6700 series. There are dual (with mixes of rising/falling covered) and single comparators again with rising/falling covered. all as separate p/n's.
 
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