115
Circuit 90:
Constant current with bipolar transistor
Setup information
Install the two transistors, the LED diode and the silicon diode as shown in
Fig. 2.90.
Then install the resis-
tor. The seven jumper wires come next. Check the placement on the board and only then connect the bat-
tery.
Components required:
1 x J111 FET transistor,
1 x 2N3904 transistor,
1 x LED (see Experiment
for value), 1 x 1N4148
silicon diode, 1 x 1 k
Ω
resistor, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.90:
Constant current
power source with bipolar
transistor
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 to deliver a bright LED light. Substantial current flows through the LED in our circuit. Even if
battery voltage drops, the LED will always shine with the same brightness.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.90.
Summary of Contents for ELECTRONICS EXPERIMENTS BOX
Page 4: ......
Page 265: ...267 Fig 3 56 Cir cuit 56 Audio limiter Fig 3 57 Circuit 57 Amplifier for a storm detector...
Page 269: ...271 Fig 3 64 Circuit 64 Stabilizer for 1 9 V Fig 3 65 Circuit 65 Stabilizer for 2 5 V...
Page 275: ...277 Fig 3 80 Circuit 80 Quiztimer 30 seconds Fig 3 81 Circuit 81 Handy diode tester...
Page 315: ...317 Fig 3 179 Circuit 179 HF generator 150 kHz Fig 3 180 Circuit 180 HF generator 420 kHz...
