
Semiconductor Components
283
When the reverse bias reaches a certain value,
called zener voltage
V
, again we have a signi-
cant increase of the current, but at the same
time we have a great reduction of the dynamic
resistance value, which goes down to a just a few
Ohms. The voltage value for which this happens
is practically independent from the current value.
This property makes the zener diode a useful
device as a voltage reference. In fact, its voltage-
current characteristic in reverse bias has a prac-
tically constant voltage value in correspondence
with a big interval of current variation, as shown
in Figure 8.32.
The phenomenon of breakdown ...