Zener diode as voltage regulator lab experiment

Electronics Lab: Voltage Regulators (MultiSim)

ELEC 161 Electronics II

Module 8 Lab: Voltage Regulators

Introduction.- This laboratory exercise explores circuits for voltage regulation. The goal of voltage regulators is double: First, they attempt to maintain a constant voltage at the output, independently of the current drawn by the load. Secondly, they attempt to maintain a constant voltage at the output independently of variations in the input voltage, either DC variations or AC variations (ripple voltage)

Procedure

1.- Series Regulator Circuit

Although the Series Regulator circuit is the most basic attempt to provide voltage regulation, it is often used when the specifications are not very stringent or we can ensure that the current will not exceed a specified value during normal operation.

1.1 Build the circuit shown in Figure 8-1. The Transistor can be found in the NPN family of Transistors. The Zener Diode can be found in the Zener Subgroup from the Diode family.

Figure 8- 1: Basic Series Regulator

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1.2 Verify that the circuit is working correctly by measuring the voltage across the Zener and the Voltage across Base-Emitter. The voltage across the Zener should be around 5 V while the voltage across B-E should be around 0.7 V.

1.3 Our first experiment will be to measure the change in output voltage for a given change in the current through the load. Again, the goal is for the voltage to change as little as possible. We will simulate the load with a potentiometer as shown in Figure 8-2.

Figure 8- 2: Circuit to measure Voltage Regulation

1.4 Set the Potentiometer value to 100%. This means that the load is 100% of 10 kΩ.

1.5 Connect one DMM to measure the voltage across the load resistor (potentiometer). Connect another DMM to measure the current that flows through the load. Remember that to measure current the DMM must be in series with the load. Record these values.

1.6 Change the value of the potentiometer down by 5%. Again, measure voltage and current and record the values.

1.7 Repeat the process all the way to 5%. Do not use 0% as this is a short circuit

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1.8 Plot Voltage (Y-axis) versus Current (X-axis). Make sure that the Y-axis runs all the way from zero to Vout. Ideally, the line should be as flat as possible. Calculate percentage of change in voltage. This is a parameter of quality for the regulator.

1.9 To investigate the ripple, we will return the potentiometer to 100%. In addition, we will add an AC signal at 60 Hz (line voltage) in series with the DC source. This will simulate any unfiltered voltage from the voltage supply. The circuit we will use is shown in Figure 8-3.

Figure 8- 3: Circuit to measure ripple

1.10 Connect Channel 1 of the oscilloscope at Node Vin (after the DC source) and Channel B at Node Vout. Run the simulation. You will have to set the coupling for both channels in AC.

1.11 Measure the peak voltage in both channels (It should be 1 Vp for Channel A). Calculate the Ripple voltage at the input and at the output of the circuit and comment on your results. Use the DC value measured in 1.8

Use: Ripple = (Vrms/Vdc ) x 100

1.12 Comment on your results.

1.13 The ripple voltage, however, is also dependent on the current through the load. The value we have calculated is with a very large load. To measure the ripple with a full load, change down the value of the potentiometer to 5% and repeat the measurements from Section 1.11

1.14 What is the new ripple factor? Has it changed much?

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2. Series Regulator with Operational Amplifier

In the Improved Series Regulator shown in Figure 8-4, that the Operational Amplifier tries to maintain the same voltage across its two input terminals. This forces a voltage value in the voltage divider made by R5 and R6.. An advantage is that the regulated output voltage can be changed by changing the ratio of R5 to R6.

Figure 8- 4: Improved Series Regulator

2.1 Build the circuit shown in Figure 8.4

2.2 Using the same technique as in Section 1, plot Vout versus the current through the load. Calculate the percentage of change in Vout.

2.3 Connect the same AC source as in Section 1 and measure the ripple voltage with the load at 100% and at 5%

2.4 Compare the results obtained for both Series Regulator (normal and improved). What are their benefits and drawbacks?

2.5 Modify R5 and R6, so the Vout at full load is equal to 7.5 V. Verify your results.

Laboratory Report Create a laboratory report using Word or another word processing software that contains at least these elements:

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- Introduction: what is the purpose of this laboratory experiment?

- Results for each section : Measured and calculated values, calculations, etc. following the outline. Include screenshots for the circuits and waveforms as necessary -- You can press Alt + Print_Screen inside Multisim or if using Windows 7, you can use the “Snipping tool”. Either way, you can paste these figures into your Word processor. Also include here the charts and graphs that you have created with the data you have collected.

- Conclusion : What area(s) you had difficulties with in the lab; what did you lean in this experiment; how it applies to your coursework and any other comments.