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2.20 Variable Zener diode
Circuit 47: Discreet 2.2V Zener diode
Setup information
Install the two transistors and the six resistors as shown in Fig. 2.47. The ten jumper wires come next. Last
but not least connect the moving-coil instrument. Check the placement on the board again and only then
connect the battery.
Experiment
This circuit delivers constant voltage at the output – where the moving-coil instrument is connected – even
at fluctuating battery voltage. It behaves just like a connected Zener diode. Basically, Zener voltage is
defined by the value of the R2. In our case here, we have an output voltage of 2.2 V. The battery voltage may
fluctuate between 5V and 9V.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.47.
72
Components required:
1 x 2N3904 transistor,
1 x 2N3906 transistor,
2 x 1 kΩ resistors,
2 x 2.2 kΩ resistors,
1 x 10 kΩ resistor,
1 x 22 kΩ resistor,
1 x moving-coil instru-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.47: Discreet 2.2V Zener
diode
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