Circuit Q1 constitutes a constant voltage output, Q2 constitutes a constant current output circuit, and Q3 is an adjustable constant current output circuit;
Adjusting W2 can make current flow through Q1 and Q2, the voltage. The drop generated across R4 is sufficient to turn on Q3, so the charging current to the battery is the sum of the currents flowing through Q2 and Q3. Therefore, by adjusting W2, the whole circuit can have the maximum load current output.
When the battery voltage exceeds the base voltage of Q2, Q2 will enter the saturation region and the output current of Q2 will begin to decrease, causing a corresponding decrease in the voltage generated on R4 and the output current. of Q3 will also It begins to decrease until Q3 stops first, leaving only Q2 still producing low current. Finally, Q2 also cuts off and charging is completed;