TABLE OF CONTENTS Although Zener diodes may sound different then silicon-controlled rectifiers (SCRs), they are both found where voltages must be controlled or regulated. This chapter describes how Zener diodes operate and what their typical applications are. The behavior of SCRs and triode alternating current switches (TRIACs) is discussed as are their typical applications. These are important subjects because these devices are found everywhere in modern electronic circuitry that involves power and power applications.
A Zener diode is a diode designed to be operated in its reverse-bias condition. Normally, when you exceed a diode's peak inverse voltage (PIV) rating, the diode is ruined. However, by doping a diode's junction in a particular manner a diode is developed, which, though it will operate in its forward-bias mode, is intended to operate at its designed PIV or Zener voltage.
Why would someone want to do this? Because within the dissipation rating of the diode, the diode will conduct any amount of current (above a minimum current) while maintaining the same drop across the diode. The diode in a forward direction requires about a 0.7-volt (silicon) drop to conduct and will maintain that drop until saturated (that is, until there is no further increase in emitter current for an increase in voltage across the emitter base junction). In the same way, the Zener will maintain the Zener voltage until the current is so great that the heat generated destroys the diode.
The Zener diode is ideal for use as a voltage reference or as...
