Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 112

Circuit 89: constant current with FET transistor
Setup information
Install the FET transistor, the LED diode and the silicon diode as shown in Fig. 2.89. Then install the resis-
tor. The three jumper wires come next. Check the placement on the board and only then connect the bat-
tery.
Experiment
Although everything is wired correctly, nothing will happen when you connect the battery. Up to now you
still don't know the value of the LED. You can use any LED, whether red, yellow or green. Current will always
be high enough for a bright LED light. Unlike our previous experiment, this time only half the amount of
current flows through the LED. Even if battery voltage drops, the LED will always shine with the same bright-
ness.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.89.
114
Components required:
1 x J111 FET transistor,
1 x LED (see Experiment
for value), 1 x 1N4148
silicon diode, 1 x 1 kΩ
resistor, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.89: constant current
with FET transistor