Objectives Describe the introduction of a zener diode briefly Explain how a zener diode works Importance of Zener diode and its applications How Zener diode is used in voltage regulation Zener Limiting

Introduction The basic function of zener diode is to maintain a specific voltage across its terminals within given limits of line or load change. Typically it is used for providing a stable reference voltage for use in power supplies and other equipment. Fig. 3-9 Simple zener diode reg. circuit & label zener terminals This particular zener circuit will work to maintain 10 V across the load.

Zener Diodes A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but also permits it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage", "Zener voltage", "avalanche point", or "peak inverse voltage" Fig 3-2 b zener curve

Zener Diodes The zener diode’s breakdown characteristics are determined by the doping process. Low voltage zeners less than 5V operate in the zener breakdown range. Those designed to operate more than 5 V operate mostly in avalanche breakdown range. Zeners are available with voltage breakdowns of 1.8 V to 200 V. Zz= Fig 3-3 This curve illustrates the minimum and maximum ranges of current operation that the zener can effectively maintain its voltage.

Zener Diode Applications Regulation In this simple illustration of zener regulation circuit, the zener diode will “adjust” its impedance based on varying input voltages and loads (RL) to be able to maintain its designated zener voltage. Zener current will increase or decrease directly with voltage input changes. The zener current will increase or decrease inversely with varying loads. Again, the zener has a finite range of operation. Fig. 3-12 Zener Reg.

Zener Limiting Zener diodes can used for limiting just as normal diodes. Recall in previous chapter studies about limiters. The difference to consider for a zener limiter is its zener breakdown characteristics. Fig 3-16a,b,&c

In the automobile, the Zener diode plays an important role in two major areas. The generator uses a Zener regulator to regulate the charging voltage for the battery and electrical system. Inside the vehicles computers there are 5-volt regulators, since much of the internal circuitry of the computers operate an 5 volts.

Overvoltage protection is done by using Zener diodes because there is current flowing through the diode after the reverse bias voltage exceeds a certain value. This circuit provides safety for the equipment connected at the terminals. Normally the current should not exceed normal valve but if due to any fault in the circuit the current exceeds the maximum allowable limit, the equipment of the system can be damaged permanently.

Summary The zener diode operates in reverse breakdown. A zener diode maintains a nearly constant voltage across its terminals over a specified range of currents. Line regulation is the maintenance of a specific voltage with changing input voltages. Load regulation is the maintenance of a specific voltage for different loads.