Explain the purpose of a zener diode in a power supply to stabalise the output voltage? 10 points of course

Question

Generally interested in this=)

Any links to sueful websites, or diagrams would be appreciated

10 points for ebst answser of course

Answer 1

A zener diode is designed to "break down" at a certain voltage or current. Depending on the junction, it can become a "reverse" diode. In your application, it can be used to approach a certain voltage level and maintain the output voltage. There will be some fluxuation in the voltage output due to the diode and current never maintaining a "true" level.

Another application of a zener diode is such that with the application of sufficient reverse voltage, a p-n junction will experience a rapid avalanche breakdown and conduct current in the reverse direction. Valence electrons which break free under the influence of the applied electric field can be accelerated enough that they can knock loose other electrons and the subsequent collisions quickly become an avalanche. When this process is taking place, very small changes in voltage can cause very large changes in current. The breakdown process depends upon the applied electric field, so by changing the thickness of the layer to which the voltage is applied, zener diodes can be formed which break down at voltages from about 4 volts to several hundred volts.

Answer 2

4 uses at least.

In a very simple regulator, a resistor and a zener can produce a (more or less) fixed voltage, but with limited current capability.

Resistor in series with zener, other end of resistor to unregulated supply, output voltage across zener.

Second type adds a power transistor, with the base connected to the zener and the collector to the unregulated supply, the emitter is the output. This multiplies the output current of type 1, but still only a fixed voltage. Regulation not too great.

Third type adds a potentiometer across the zener and the slider of the pot to the transistor base.  This gets you an adjustable output voltage, but the regulation not too good.

Fourth type is a real regulated supply with output transistors, and an opamp to provide the feedback and improve the regulation. The opamp compares the output voltage with that generated by a high quality zener diode. A potentiometer provides adjustability.

type 1:

http://en.wikipedia.org/wiki/Zener_diode

type 2, figure 1:

http://www.electronics-tutorials.com/bas...

Answer 3

http://www.bcae1.com/diodes.htm

http://www.st-andrews.ac.uk/~www_pa/Scot...

Answer 4

diode is an electrical device that can be compare to  a check valve as used in water system at home .its purpose is to let only incoming but not outgoing from the water source.like in a power supply that converts ac source to dc source in which ac produces voltage that is alternating meaning terminal polarity is sometimes positive and sometimes negative, the duration depending on the cycle or frequency of the source,therefore output  voltage can be somewhat unstable.to be able to somewhat stabilized voltage(wherein diode is not the only device responsible but is one  out of several other devices such as capacitors, resistors and etc. that is needed to really produce stable voltage output), we need to connect a diode right after the ac voltage source,where the current coming from and then passing thru it , cannot turn back to where it came from ,or to the source.

Answer 5

Your question answers itself.

The purpose of a zener is to stabilise (up to a point), or limit, a voltage.  

A short discussion on using l.e.ds, http://www.davidbridgen.com/leds.htm, is relevant.