Zener regulator

A non-ideal voltage source can be modeled by a series combination of an ideal DC voltage source, a resistance, and a small-signal voltage source. The small-signal source is included to represent the noise inherent in the source. This model is illustrated in the figure below:

In practice, connecting the non-ideal voltage source to a load may result in undesirable effects due to the noise voltage vo appearing across the load.

This problem studies such effects and how a Zener diode may be used to ameliorate the problem. Assume that VI=9.5 V, RIN=1 kΩ , and vi=50.0 mV.

In the figure above, calculate the DC output voltage VO , and the output noise voltage vo for two values of the load resistance.

1.For RL=2 kΩ , the value of VO (in Volts) is:

2.and the value of vo (in Volts, to at least 3 decimal places) is:

3.For RL=4 kΩ the value of VO (in Volts) is:

4.and the value of vo (in Volts, to at least 3 decimal places) is:

Now, we can insert a Zener diode into the circuit, as shown below. The Zener diode is a nonlinear device and a piecewise-linear approximation to its i-v characteristic is shown graphically below.

Again, we calculate vo (i.e. output noise) and VO (i.e. DC output voltage) for RL =2k Ω and RL =4k Ω for this new circuit.

Hint: Your first job here is to determine which of the three regions of the piecewise-linear characteristic of the Zener is the one containing the operating point: we suggest you sketch a load line, but be very careful about the signs. Once you have determined where the operating point is, you can model the Zener in the circuit with a series combination of an independent voltage source and a resistor.

5.For RL=2 kΩ the value of VO (in Volts) is:

6.And the value of vo (in Volts, to at least 5 decimal places) is:

7.For RL=4 kΩ the value of VO (in Volts) is:

8.And the value of vo (in Volts, to at least 5 decimal places) is:

9.What is the minimum value of RL , in Ohms, that guarantees that the circuit will operate this way?

by servomotor
July 28, 2020

We don't have the I-V curve approx. for the Zener diode. It probably give its Vz (at 1 mA in reverse) and the resistance value for that almost perpendicular segment which may be essential to solve the problem. Furthermore, that looks like a homework problem. Can't you sketch the circuit with the circuitlab simulator? You have a problem doing exactly that?

by vanderghast
July 28, 2020

I agree completely with @vanderghast's comment :)

What have you tried already? Where exactly are you stuck?

by mrobbins
July 28, 2020
Add comment...

Please sign in or create an account to comment.

No Answers

No answers yet. Contribute your answer below!

Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account

Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers

Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.

About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.