Day 2 - Experiment No.3 and 4 Zener diode

Theory
Zener diode conduct like normal diode in the forward direction. In the reverse direction, it conduct like normal diode, blocking current. When the reverse voltage rises above a certain value, the zener diode breaks down in a nondestructive manner and conducts.
Zener diode dissipates power as heat so it is rated in watts.

Zener diode is used for providing a stable voltage reference in many circuits.(e.g power supplies and regulators)

Markings

 The band on a zener diode indicates the cathode.




Experiment No.3 Zener diode

For R= 100Ω and RL= 100Ω, Vs= 12 V
What is the value of Vz? 4.98V

Vary Vs from 10V to 15 V

What is the value of Vz

VS(10V) - VZ(4.81V)
VS(12V) - VZ(4.98V)
VS(15V) - VZ(5.09V)

Explain what is happening here
Even though the power source voltage varies between 10 and 15 volts, we get a constant output zener voltage which is around 5.1 volts.

What could this circuit be used for?

This circuit could be used for a voltage regulation or protection circuits.

Reverse the polarity of the zener diode.

What is the value of Vz? Make a short comment why you had that reading.

Vz = 0.86V

From the point of forward biased region, zener diode has the same characteristics as a standard diode. Therefore the voltage drop of zener diode(Vz) is approx 0.7 volts.

Experiment No.4

                                        10 Volts                                                                   15 Volts

Volt drop V₁:                   4.67V                                                                      4.82V

Volt drop V₂:                   0.67V                                                                      0.70V

Volt drop V₃:                   5.34V                                                                      5.52V

Volt drop V₄:                   5.19V                                                                      10.07V

Calculated current A:   (10-.34)/1000=4.66mA           (15-5.52)/1000=9.48mA                                       

Describe what is happening and why you are getting these readings:
V1: when reversed biased, the reverse biased voltage of zener diode is approx 5.1 volts.
      (refers to datasheet)
V2: when forward biased, if the voltage of a diode exceeds 0.6 volts, the current will flow.
V3: the sum of zener diode reverse biased voltage and forward biased diode voltage
      (because it is the series circuit)
V4: gets different measurement from the calculation, V4 should be 4.66 volts which is (Vs-V3).