Vol. DIY Electronics Projects
Chapter 5 Discrete Semiconductor Circuit Projects

Si Lab - Zener Diode Voltage Regulator

In this hands-on semiconductor electronics experiment, build a simple DC voltage regulator circuit and learn how to use reverse-biased Zener diodes as voltage clamps.

Project Overview

Zener diodes are frequently used as voltage regulating devices because they act to clamp the voltage drop across themselves at a predetermined level. In this project, you will build and test a simple Zener diode voltage regulator, as illustrated in Figure 1, for a number of different supply voltages

 

Test setup for measuring the voltage of a Zener diode voltage regulator.

Figure 1. Test setup for measuring the voltage of a Zener diode voltage regulator.

 

Parts and Materials

  • Four 6 V batteries
  • Zener diode, 12 V—type 1N4742
  • One 10 kΩ resistor

Any low-voltage Zener diode is appropriate for this experiment. The 1N4742 model listed here (Zener voltage = 12 V) is but one suggestion. Whatever diode model you choose, I highly recommend one with a Zener voltage rating greater than the voltage of a single battery for a maximum learning experience. It is important that you see how a Zener diode functions when exposed to a voltage less than its breakdown rating.

 

Learning Objectives

  • Understand the function of Zener diodes

 

Instructions

Step 1: Build the simple circuit shown in the circuit schematic of Figure 2 and illustrated in Figure 3. 

 

Schematic diagram of a simple zener diode voltage regulator.

Figure 2. Schematic diagram of a simple zener diode voltage regulator.

 

Terminal strip implementation of a simple zener diode voltage regulator.

Figure 3. Terminal strip implementation of a simple zener diode voltage regulator.

 

Be sure to connect the Zener diode in a reverse-bias orientation (cathode positive and anode negative).

Step 2: Measure the voltage across the diode with one battery as a power source. Record this voltage drop for future reference.

Step 3: Measure and record the voltage drop across the 10 kΩ resistors.

Step 4: Modify the circuit by connecting two 6 V batteries in series for a 12 V total power source voltage.

Step 5: Re-measure the diode’s voltage drop, as well as the resistor’s voltage drop, with a voltmeter, as illustrated above in Figure 1.

Step 6: Connect three, then four, and 6 V batteries together in series, forming an 18 V and 24 V power source, respectively. Measure and record the diode and resistor’s voltage drops for each new power supply voltage. 

Questions to consider:

  • What do you notice about the diode’s voltage drop for these four different source voltages?
  • Do you see how the diode voltage never exceeds a level of 12 V?
  • What do you notice about the resistor’s voltage drop for these four different source voltage levels?

The reverse-biased Zener diode clamps the voltage drop at their breakdown voltage. Above this Zener voltage, the Zener diode conducts a lot more current so that any excess voltage supplied by the power source is dropped across the 10 kΩ series resistor.

However, it is important to note that a Zener diode cannot make up for a deficiency in source voltage (unlike some types of voltage regulators). For instance, this 12 V Zener diode does not drop 12 V when the power source is only 6 V. It is helpful to think of a Zener diode as a voltage limiter that establishes a maximum voltage drop but not a minimum voltage drop.

 

SPICE Simulation of a Zener Diode Voltage Regulator

A zener diode may be simulated in SPICE with a normal diode by setting the reverse breakdown parameter (bv = 12) to the desired zener breakdown voltage. Figure 4 is an illustration of a Zener diode circuit schematic with node numbers added for SPICE simulation.

 

Zener diode voltage regulator schematic with SPICE node numbers.

Figure 4. Zener diode voltage regulator schematic with SPICE node numbers.

 

Netlist (make a text file containing the following text, verbatim):

Zener diode 
v1 1 0 
r1 1 2 10k 
d1 0 2 mod1 
.model mod1 d bv=12 
.dc v1 18 18 1 
.print dc v(2,0) 
.end 

 

Related Content

Learn more about the fundamentals behind this project in the resources below.

 

Textbook:

 

Worksheets:

Published under the terms and conditions of the Design Science License