1 Zener Breakdown and Forward Bias a 3 points Calculate Rz T

1. Zener Breakdown and Forward Bias

a. (3 points) Calculate Rz. The givens; the Zener begins to breakdown at precisely 4.85V. The current at this point is so small, it is immeasurable. You may consider the current at this point 0mA. Assuming the reference point is the anode side of the diode, the current through the Zener, when the cathode has a voltage potential of 5.52V, is a positive 955mA towards ground.

b1. (1 point) In a few sentences, what would the voltage potential be across a diode if the diode was perfectly ideal.

b2. (1 point) In a few sentences, answer this question. We all know forward bias, typically, happens at 0.7V, what can you say about a diode when forward bias starts to happen at 2.3V?

2. (10 points) The source you need to work from is the transformer we used for Lab 3. S1, S2 and Center Tap (CT) are at your disposal. You do not need to use all three source points, but feel free to use them all if your design requires it. Design a 10VDC signal.

3. Draw your design from question 2 using a SPICE program (PSPICE, B2SPICE, LTSPICE, etc.). Must be a SPICE program.

a. (5 points) This is not hand drawn. Provide your schematic from the SPICE program.

b. (5 points) Simulate and verify a 10VDC (Hint: At t=0s and the immediate moments after t=0s, will, typically, show an unstable signal. If designed correctly, the output signal will steady to the output you want over time).

Solution

a) Rz = (5.52-4.85)/955mA = 0.7 ohms

b1) If the diode is in forward bias then the vltage across an ideal zener or normal diode is zero.

If a diode is in reverse bias then the voltage across the diode is the applied reverse voltage and if its the zener diode then the voltage acroos the diode is the breakdown voltage.

b2) If the forward voltage is 2.3V then one can make out the the material used to make diode has huge bandgap.