3-7
Figure 3-4D.—Schematic symbols for Zener diodes.
Figure 3-4E.—Schematic symbols for Zener diodes.
Zener diodes of various sorts are used for many purposes, but their most widespread use is as voltage
regulators. Once the breakdown voltage of a Zener diode is reached, the voltage across the diode remains
almost constant regardless of the supply voltage. Therefore they hold the voltage across the load at a
constant level. This characteristic makes Zener diodes ideal voltage regulators, and they are found in
almost all solid-state circuits in this capacity.
Q1. In a reverse biased PN-junction, which current carriers cause leakage current?
Q2. The action of a PN-junction during breakdown can be explained by what two theories?
Q3. Which breakdown theory explains the action that takes place in a heavily doped PN-junction with
a reverse bias of less than 5 volts?
Q4. What is the doping level of an avalanche effect diode when compared to the doping level of a
Zener-effect diode?
Q5. During avalanche effect breakdown, what limits current flow through the diode?
