Low-Dropout CC/CV 12V Lead-Acid Battery Charger With Auto Trickle-Charge 2018-03-11

For proper charging of lead-acid batteries a simple, two-stage technique is to start with a constant-current until the battery reaches a specific voltage, indicating it is near a full charge (≈90%), and then revert to a constant-voltage trickle-charge mode at a lower voltage to avoid over-charge while topping off and then maintaining the battery charge.

Below is the LTspice simulation of a relatively simple circuit to do that.
M1 and Q2 initially act as a constant-current circuit that...

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