I have a charge & a drain circuit connected to a Li-ion cell. As only one circuit can be connected to the cell at a time, I believe I need some diodes. My questions are about when the drain circuit is on and the charge circuit is off.

(In the pic attached, charge circuit on the right, drain circuit on the left.)

As far as i can work out, I only need one diode stopping the battery current flowing back into the charger. Is this correct or are some required at the negative side too?



Generally, all that is needed is a single diode to prevent discharge back into the charge circuit when operating on battery power only. The disadvantage is that you lose a diode forward volt-drop when charging but this (generalism alert) is not normally a problem.

I would also advise that if the battery is a raw (ish) cell then under-voltage protection might be needed to prevent failure of the battery from too much discharge into the target load.

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    \$\begingroup\$ Thanks for that! Im using an arduino to measure the capacity & internal resistance so its constantly reading the voltage anyway. Once the voltage reaches certain thresholds the circuits will alternate so over-discharge (hopefully) shouldn't be an issue \$\endgroup\$ – I Used To Be Funny Feb 21 '18 at 10:16

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