Uses of zener diode, Electrical Engineering

Uses of Zener Diode

Zener diodes are extensively used as voltage references and like shunt regulators to regulate the voltage across small circuits. While connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts while the voltage arrives at the diode's reverse breakdown voltage. From that point on, the comparatively low impedance of the diode holds the voltage across the diode at that value.

402_Uses of Zener Diode 2.png

 In this type of circuit, a typical voltage reference or regulator, an input voltage that is denoted by UIN, is regulated down to a stable output voltage that is denoted by UOUT. The intrinsic voltage drop of diode D is stable over a broad current range and holds UOUT comparatively constant even though the input voltage might fluctuate over a fairly wide range. Due to the low impedance of the diode while operated like this, Resistor R is employed to limit current through the circuit.

180_Uses of Zener Diode 1.png

 Figure: Zener diode shown with typical packages. Reverse current - iZ is shown.

In the case of this general reference, the current flowing in the diode is determined by using Ohms law and the known voltage drop across the resistor R. IDiode = (UIN - UOUT) / RΩ

The value of R has to be satisfies two conditions:

1. R must be enough small that the current via D keeps D in reverse breakdown. The value of this current is provided in the data sheet for D. For instance, the common BZX79C5V6 device, a 5.6 V 0.5 W Zener diode, has a suggested reverse current of 5 mA. If insufficient current exists by D, then UOUT will be not regulated, and less than the nominal breakdown voltage (this varies to voltage regulator tubes in which the output voltage will be higher as compared to the nominal and could rise as high as UIN). While measuring R, allowance must be made for any current via the external load, not displayed in this diagram, connected across UOUT.

2. R must be sufficiently large that the current via D does not destroy the device. If the current through D is ID, the breakdown voltage VB of it and the maximum power of it dissipation PMAX, then IDVB < PMAX.

A load might be located across the diode in this reference circuit, and as long as the zener stays in reverse breakdown, the diode will give a stable voltage source to the load.Shunt regulators are simple, but the needs that the ballast resistor be small enough to prevent excessive voltage drop throughout worst-case operation (low input voltage concurrent with high load current) tends to leave numerous current flowing in the diode much of the time, making for a quite wasteful regulator with high quiescent power dissipation, only appropriate for smaller loads.

Zener diodes in this type of configuration are frequently employed as stable references for much more advanced voltage regulator circuits.These devices are as well encountered, usually in series with a base-emitter junction, in transistor stages in which selective choice of a device centered around the avalanche or Zener point can be employed to introduce compensating temperature co-efficient balancing of the transistor PN junction. An instance of this type of use would be a DC error amplifier employed in a regulated power supply circuit feedback loop system.

Zener diodes are as well employed in surge protectors to limit transient voltage spikes. Other notable application of the zener diode is the make use of noise caused by its avalanche breakdown in a random number generator which never repeats.

Posted Date: 1/11/2013 12:37:25 AM | Location : United States

Related Discussions:- Uses of zener diode, Assignment Help, Ask Question on Uses of zener diode, Get Answer, Expert's Help, Uses of zener diode Discussions

Write discussion on Uses of zener diode
Your posts are moderated
Related Questions
The conveyor system is driven by a 240 Volt 50 Hz AC motor requiring a continuous 1 Amp supply. The conveyor has single direction operation. The loading mechanism for the winder

i cant imagine of something called complex frequency...i find it important for laplace transformation,but i am lacking the physical explanation,please explain this to me

Q. Athree-phase, 60-Hz substation bus supplies two wye-connected loads that are connected in parallel through a three-phase feeder that has a per phase impedance of 0.5 + j2 . Loa

Q. Explain Inductorless Filters Inductorless (Active) Filters Filters (used to pass or eliminate certain frequency components of a signal) that are suitable for IC fabricati

Breifly explain abrasive jet machining in Briefly explain the following key terms in electrochemical machining (a) Electrolytes (b) ECM tooling techniques with suitable ex

The transformer of Example is supplying full load (i.e., rated load of 50 kVA) at a rated secondary voltage of 240 V and 0.8 power factor lagging. Neglecting the exciting current o

To design a VI that can be used to show how the voltage falls across a resistor in a simple CR circuit when excited by a step function. The title of the VI will be Capacitor Res

A 100-kW, 230-V shunt generator has R a = 0.05  and R f = 57.5 . If the generator operates at rated voltage, calculate the induced voltage at (a) full load, and (b) one-half fu

Define Series VAr Compensation? For very long transmission lines, the inductive reactance of the line becomes so high that not much power can be transmitted through the line, s

The observations from these experiments led to 'The Laws of Electromagnetic Induction' 1)  'If the magnetic flux threading through an electrical circuit changes, then an e.m.f.