Diode and Zeners

Diode
The function of a diode is to let electrical current flow only in one direction, in a circuit is to stop electrical current from flowing in the wrong direction. Thus diode can be put in place to protect other component from back emf happening.



IMPORTANT: As you can see in the graph below, too much forward current and the diode may be damaged and conduct in both directions. Too much reverse voltage will damage the diode and cause it to conduct in the wrong direction.

If you look closely at VF the diode doesn't start conducting until 0.6-0.7v this is known as the knee voltage, so when calculating voltage after the diode, voltage suplied(vs) - (vd) voltage diode 12-0.7=11.3v

Data Sheet infomation
what to look for so you dont blow the diode
Peak Inverse Voltage: This represents the maximum reverse voltage that can be
applied before the diode breaks down.
Maximum DC forward Current:This is the maximum recommend forward current, if the current exceed the rating it will destroy the diode.

What is a Zener diode
A zener diode is  a  special kind of diode that if voltage is apply in the reverse bias it acts as a voltage regulator, so input might be 12v but the output of the end result would be eg 9.1v if you use 9v1


zener diodes are typically available in the following voltages: 2.4, 2.7, 3, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, 10, 11, 12, 13, 15, 18, 20, 22..., and in 300mW, 500mW, 1.3W, 2W, 3.25W, and 5W rated packages.

How to use
To use the zener diode, the diode has to be in parallel with the zener as above in the picture



To work out Zener diode resistor

If Vs=10, Vz=5v1, Iz max= 0.06, RL=470
I=V/R
Rs=Vs min-Vz/Iz min

I=5/470=0.01063A
Rs=(10-5)/0.01063=470



Breakdown voltage
 Breakdown voltage of a zener is  the maximum reverse voltage the zener can handle until it stops working like it should. eg 9.1v  but only a small amount of current can be pass through it eg 1A a resistor is put in series to prevent this.
This is why we use a zener diode for, so that no more than eg 9.1v can be pass through in the reverse bias to protect components 

Forward bias region
This is the region voltage is passing through the zener diode in forward bias anode to cathode.this work just like a normal diode.

Knee voltage

This is the region in the forward bias before it reaches the working voltage of 0.7V.