All diodes are Zener diodes. For instance a 1N4148 is a 120v zener diode as this is its
reverse breakdown voltage.
And a zener diode can be used as an ordinary diode in a circuit with a voltage that is
below the zener value.
For instance, 20v zener diodes can be used in a 12v power supply as the voltage never
reaches 20v, and the zener characteristic is never reached.
Most diodes have a reverse breakdown voltage above 100v, while most zeners are
below 70v. A 24v zener can be created by using two 12v zeners in series and a normal
diode has a characteristic voltage of 0.7v. This can be used to increase the voltage of a
zener diode by 0.7v. See the diagram above. It uses 3 ordinary diodes to increase the
output voltage of a 3-terminal regulator by 2.1v.
To tests a zener diode you need a power supply about 10v higher than the zener of the
diode. Connect the zener across the supply with a 1k to 4k7 resistor and measure the
voltage across the diode. If it measures less than 1v, reverse the zener.
If the reading is high or low in both directions, the zener is damaged.
Here is a zener diode tester. The circuit will test up to 56v zeners.
ZENER DIODE TESTER
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