124
Circuit 99:
Constant current supply for LEDs
Setup information
Install the transistor, the diode and the two resistors as shown in
Fig. 2.99.
Then install the three jumper
wires. Check the placement on the board again and only then connect the battery.
Components required:
1 x 2N3904 transis-
tor, 2 x 1N4148 silicon
diodes, 1 x LED (see
Experiment for value),
1 x 220
Ω
resistor,
1 x 10 k
Ω
resistor,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.99:
Constant current
power supply for LEDs
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. Only half the amount of current flows through the LED com-
pared to the previous experiment. 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. 3.99.
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...
