Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 114

Circuit 91: Constant current with bipolar transistor
Setup information
Install the two transistors and the three resistors and the LED diodes as shown in Fig. 2.91. The six jumper
wires are next. Check the placement on the board again and only then connect the battery.
Experiment
If everything is wired correctly, current will always be high enough for the LEDs to shine bright – even if bat-
tery voltage has dropped.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.91.
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Components required:
1 x J111 FET transistor,
1 x 2N3904 transistor,
1 x red LED, 1 x green
LED, 1 x yellow LED,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.91: Constant current with
bipolar transistor