Experiment No.3 and 4 - Zener diode

A Zener diode is a normal diode which lets current flow from positive to negative(conventional) in forward direction. In reverse, pn layer is created so that current is restricted but when there is sufficient voltage pushing through the boundary then the zener diode limits the current by trying to keep the voltage at a certain level.
Experiment No.3

Take a look at what we did to justify the operation of the zener diode:
  The Zener is a 5V1 400mW, so basically the advertise tells us that this zener will limit the voltage drop through it by 5V. To test this, we wired it in the diagram above, then use the Voltmeter to check the zener. As we expected the Vd turned to be 5V even if we vary the supply between 10V and 15V.
  Then we try to put the zener in forward, it flows just like a normal diode, Vz is recorded as 0.848, a fairly low Vd for a forward diode, so it mean there is good flow with little difficulty.
   Normally, when a zener is reversed, a resistor also needs to be wired in series, there should be no flow across it with just low supply voltage. In our case our "zener" voltage is 5V, so when the supply reaches 5V it will start to flow in little through the zener. So it means that a zener with a "avalanche" voltage can be in range of various voltage value, for different voltage regulating purpose.

Experiment No.4

Both V1 are 5V indicating that the zener diode breaks down @ 5V in reverse and will continue to keep the voltage across it to 5V. V2 are almost the same 0.758 to 0.78 tells us that normal rectifying diode regulates a much smaller voltage drop and will vary slightly due to Voltage supply changes( 10 to 15V). As Vs increase from 10 to 15, the two diodes keep to their own voltage drops, hence the resistor obtain all the voltage drop to its own power.


"In the reverse direction, no current will flow until the voltage impressed across it is equal to the zener voltage. At this point, a current will flow and an extremely small increase in voltage will cause a large increase in current."

(Read more: http://wiki.answers.com/Q/Why_does_a_zener_diode_work_in_reverse_bias#ixzz1VHCzbmv6

 This statement relating to the voltage-current break down graph of a diode: We an see that @ the point of Vz, a modest increase in Voltage(reversed) can cause a huge climb in current, as nearly as similar to the exponential behavior of a forward bias!!! This means that after break-down point a diode if not to be broken down in a destructive way like low voltage normal diode, then break-down voltage is a substantial way to regulate a much larger voltage without having to add many small Vd diodes in forward - So this is the way they came up with a zener didode, operational when available voltage towards it reaches it's own BREAKDOWN voltage, by modifying the layers in p-n junction that would enable the diode not to self-destruct @ breakdown voltage like normal rectifying diode.
If voltage available for the zener is lower than its breakdown voltage, it won't breakdown and conduct any current. Vice versa, if avalanche current is too high that according to P=IV that exceeds the power dissipation limit of the zener, it will self-destruct from the reversed voltage breakdown regulating behavior.