Portable emergency light with automatic stop function

After the power is turned on, press SW1 once, and the charging indicator LED lights up. At this time, due to the low battery, the voltage of the "e" pole of Q1 is lower than the voltage of the "b" pole, so Q1 is cut off, Q2 is also cut off, Q3 is turned on to attract the relay, J1-1 is closed and self-locked, and charging begins; when the battery voltage is charged to 7.5V, Q1 turns from cutoff to on, Q2 is also turned on, Q3 loses the base voltage and cuts off, J1 loses power and releases, the power is disconnected, charging stops, and the charging indicator LED goes out. In the figure, D1 is an isolation diode, which can prevent the battery from discharging in reverse, and adjusting RW1 can make the circuit charge batteries of different voltages.