Hello, I have made a simple circuit using the LM311N comparator to switch a single cell lithium battery from being charged by a solar cell charge controller to powering the load. I have set the hysteresis thresholds for the comparator between 3.4V and 4V and the switch used is a P channel MOSFET. Would this circuit work?

 

Should work; but simulation shows you get closer to your 3.4V and 4V targets if R2=2k7 and R3=6k8.

 

Should work; but simulation shows you get closer to your 3.4V and 4V targets if R2=2k7 and R3=6k8.

Thank you. For the MOSFET selection would something like the IRFP9140N be suitable? Maximum load current for the design is ~8A.

 

The trip points are ratiometric to the 6V supply. How stable is it?

 

The trip points are ratiometric to the 6V supply. How stable is it?

From testing it seems stable, the supply is from the REGN pin of the BQ24650 charge controller IC.

 

would something like the IRFP9140N be suitable?

I wouldn't use that one; its Rds(on) is rather high (0.117Ω), so it would dissipate > 7W at 8A load current, requiring a large heatsink.

 

Ok it looks like the FDS6575 is a better option with an Rds(on) of 13mΩ