Cell Protection: under-voltage cutoff with hysteresis

by VladM

14 parts

Drag the "cell" pot: it sets the cell voltage from 2.02 to 3.58V (E1 buffers it, so the load cannot pull it down). U1 compares the cell with a 2.5 V reference through R1, R2 and R3, and drives Q1, the load switch. The load turns off at 2.500V and comes back only at 2.802V. The 0.302V gap is hysteresis: a real cell's voltage springs back once its load is removed, and without the gap the cutoff would chatter on and off. Real cells: lithium iron phosphate cells (3.2–3.3V nominal) are typically cut off between 2.0 and 2.5V.