Zener Diode Meter - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.19 Zener diode meter

Circuit 45: Meters for 4.7 V Zener diodes and higher
Setup information
Install the two transistors and the three resistors as shown in Fig. 2.45. The seven 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
The Zener diode meter shows the Zener voltage of a properly functioning Zener diode by means of the
moving-coil meter. Please note: Zener diodes are connected in the reverse direction!
Look for Zener diodes in your crafting box. If you find one within the voltage range of 4.7V to 7.5V, you could
test them now. The Zener diode is faulty, if it shows either no or full-scale deflection when operated reverse-
biased as well as forward-biased.
If you cannot find a proper Zener diode, you could get around it with the following: Get a red, a green and a
yellow LED and connect in series. Place this pseudo Zener diode into the meter in forward-bias. The sum of
the threshold voltages will be displayed.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.45.
70
Components required:
2 x 2N3904 transistors,
1 x 100 Ω resistor,
1 x 2.2 kΩ resistor,
1 x 4.7 kΩ resistor,
1 x moving-coil instru-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.45: Meters for 4.7 V
Zener diodes and higher