Battery Charger - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.44 Battery charger

Circuit 101: Charge circuit for AA batteries
Setup information
Install the transistor, the three diodes and the two resistors as shown in Fig. 2.101. Then install the three
jumper wires. Finally connect the AA battery holder. Check the placement on the board again and only then
connect the battery.
Experiment
This experiment shows where else you could deploy a constant current source in a meaningful way. We
already came across this circuit several times in connection with supplying power to LEDs. But charging a
NiMH-AA battery using a 9V battery does not really make sense. If needed, you could power the circuit by a
9V DC power adapter. Constant charging current of about 40 mA is flowing in our circuit here. A continuous
operation is not recommended; the transistor would quickly die of heat death.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.101.
126
Components required:
1 x 2N3904 transis-
tor, 2 x 1N4148 silicon
diodes, 1 x BAT85
Schottky diode,
1 x 10 kΩ resistor,
1 x 4.7 kΩ resistor,
1 x breadboard, 1 x 9V
battery with clip con-
nector, 1 x AA battery
holder
Fig. 2.101: Charge circuit for
AA batteries