91
2.27 Schmitt-Trigger
Circuit 66:
Schmitt trigger circuit with 4V hysteresis.
Setup information
Install the three transistors, the LED and the six resistors as shown in
Fig. 2.66
. Next are the 11 jumper
wires. Check the placement on the board again and only then connect the battery.
Components required:
2 x 2N3904 transistors,
1 x 2N3906 transistor,
1 x red LED, 1 x 100
Ω
resistor, 3 x 1 k
Ω
resis-
tors, 2 x 2.2 k
Ω
resistors,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.66:
Schmitt trigger with
4V hysteresis
Experiment
With this circuit we accomplish a threshold value switch with hysteresis, namely the
Schmitt trigger
, is a
basic circuit widely used in analogue electronics. The Schmitt trigger responses at a certain voltage (in our
case that is 8 V) and switches through; the red LED turns on. If the voltage at the input drops, the Schmitt
trigger will switch off again at a defined voltage value that is below the switch-on voltage. The difference of
the switch-on voltage minus the switch-off voltage is called
hysteresis
. The hysteresis of our circuit here (about 4V) is basically defined by the value of resistor R3.
Try connecting a low-power variable power supply to the input and run your experiment. You should be
able to set the voltage range between 1V and about 9V. This is a simple and vivid way to study the effect of
the switching hysteresis.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.66.
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...
