Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 127

Circuit 104: Discharge circuit for AA batteries
Setup information
Install the transistor, the two diodes and the two resistors as shown in Fig. 2.104. 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. We already
came across this circuit several times in connection with supplying power to LEDs. You should however,
fully discharge NiMH batteries every now and then. That is why a discharge circuit is very useful. Constant
discharge current of about 20 mA is flowing in our circuit here.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.104.
Components required:
1 x 2N3904 transistor,
2 x 1N4148 silicon diodes,
1 x 22 Ω resistor, 1 x 4.7 kΩ
resistor, 1 x breadboard,
1 x 9V battery with clip
connector, 1 x AA battery
holder
Fig. 2.104: Discharge circuit for
AA batteries
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