lab leds and zener

8/9/2019 LAB LEDs and Zener

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EECE 310L : Electric Circuits Laboratory

Experiment 7

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A m e r i c a n U n i v e r s i t y o f B e i r u t

Fall 2013

Experiment 7

LEDs and Zener Diodes


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Experiment 7

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Table of Contents

I. Objectives .................................................................................................................................. 3

II. Material and Procedure ........................................................................................................ 3

A. Light Emitting Diodes ....................................................................................................... 3

A1. LED forward characteristics ................... ...................... ..................... .................... ............ 3

A2. LED reversed characteristics .................. ...................... ..................... .................... ............ 3

A3. LED Conduction angle ..................... ..................... ..................... ..................... ..................... . 4

B. Zener Diodes ........................................................................................................................ 5

B1. Zener Forward voltage .................... ..................... ..................... ..................... ..................... . 5

B2. Zener Diode Characteristics .................... ...................... ..................... .................... ............ 5

B3. Zener Diode Characteristics Analysis ................... .................... ...................... ............... 5

B4. Zener Diode line regulation............................. ..................... .................... ..................... ..... 6

B5. Zener diode load regulation .................... ...................... ..................... .................... ............ 6

III. Outcomes ................................................................................................................................... 7

IV. Appendix: In Lab Report ....................................................................................................... 8

Exercise A-1: LED Forward Region ........................................................................................ 8

Exercise A-2: LED Reverse Region ......................................................................................... 9

Exercise A-3: LEDs Conduction Angle ................................................................................. 10

Exercise B-1: Zener Voltage ................................................................................................... 10

Exercise B-2: Zener Regions .................................................................................................. 11

Exercise B-4: Zener Line Regulation ................................................................................... 12

Exercise B-5: Zener Load Regulation .................................................................................. 12


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I. OBJECTIVES

In this experiment you will learn how to:

Investigate the characteristics of light emitting diodes (LEDs) and some of their

applications.

Investigate the characteristics of Zener diodes and calculate their voltage

regulation.

II . MATERIAL AND PROCEDURE

A. LIGHT EMITTING DIODES

Procedure

A1. LED FORWARD CHARACTERISTICS

Connect the circuit of Fig. A-1 using the red light emitting diode (LED). Starting from a

value of 0.5 V, increase VSin steps of 0.1 V and measure the LED voltage and current for

each VS. Do not exceed 30 mA of current in the diode.

Figure A-1: LED Circuit

A2. LED REVERSED CHARACTERISTICS

Repeat Part A.1 with the diode connection reversed. Plot the forward and reverse

characteristics of the LED and determine the incremental resistance of the diode in the

forward and reverse conducting regions.

Refer to in-lab 6 exercise A-1Exercise


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Experiment 7

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A3. LED CONDUCTION ANGLE

Connect the circuit of Fig. A-2 using the red LED. Carefully measure the voltage levels

and conduction angles in the forward and reverse directions, using the oscilloscope.

Figure A-2: LED Circuit using AC input

Compare the measured values with those predicted from the value of VS and the

diode characteristics.

Calculate the power dissipated in the forward and reverse directions.



Discussion on Part A

If VS = 12 V DC, choose the series resistor to give 20 mA through thered LED. Draw the load line.

In the circuit of Fig. A-2, does the power dissipated in the reverse

direction serve any useful purpose? How can it be eliminated?


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Experiment 7

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B. ZENER DIODES

B1.

ZENER FORWARD VOLTAGE

ProcedureConnect the circuit shown in Fig. B-1 and measure VZwhen VSis 15 V.

Figure B-1: Zener Diode Circuit

B2.

ZENER DIODE CHARACTERISTICS

Reduce the value of VS in steps of 0.5 V, and measure VZ and IZ. Calculate the power

dissipation in the Zener diode.

B3. ZENER DIODE CHARACTERISTICS ANALYSIS

Plot a curve of IZversus VZ.

Calculate the value of the Zener resistance rZ.

What is the minimum value of VSrequired to get Zener diode breakdown?

Take additional measurements around this minimum VSto answer the following two

questions:

What is the value of the knee Zener voltage, VZK?

What is the value of knee Zener current, IZK?

Refer to in-lab 6 exercise B-1Exercise



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B4. ZENER DIODE LINE REGULATION

Apply a VSof 3 VAC peak-to-peak with a frequency of 500 Hz, superimposed on a 12 VDC level. The resulting VSis of the form ( )Volts.

Measure VZ. What is the DC (average) value of VZ?

What is the AC component in VZ?

Find the line regulation of the Zener diode.

Note The AC component in VZ can be calculated using the voltage divider formed by rZand

the resistor R.

The line regulation is the ratio of the change in VZto the change in VS, provided that the

diode is in the Zener region.

B5. ZENER DIODE LOAD REGULATION

With VS = 12 V DC, connect a load resistor RLin parallelwith the Zener diode. Measurethe Zener voltage, Zener current, and load current for the following values of RL: 56 K,

22 K, 10 K, 4.7 K, 2.2 K, 1 K, 680 , 470 , and 220 .

For what range of load resistors does the Zener diode regulate the load voltage?

What is the load regulation of the Zener diode?

Note The load regulation is defined as the ratio of the change in VZ to the change in

ILOAD, provided that the diode is in the Zener region.




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III. OUTCOMES

By the end of Experiment VII, students:

Are familiar with LED characteristics

Are familiar with Zener characteristics

Are able to calculate the line and load regulation for a Zener diode.

Discussion on Part B

How is the maximum current in a Zener diode determined?

How is the minimum current in a Zener diode determined?

Show that for a Zener voltage regulator, the value of the resistor R

should be chosen using the equation:


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IV . AP PEND IX : IN LA B REPORT

EXERCISE A-1: LED FORWARD REGION

Connect the circuit of Figure A-1 using the red light emitting diode (LED). Starting from

a value of 0.5V, increase Vsin steps of 0.5V and measure the LED voltage and current for

each Vs. Do not exceed 30mA of current in the diode.

Vs VLED ILED LED (ON/OFF)

0.5

1

1.5

22.5

3

3.5

4

4.5

5

5.5

6

6.5

77.5

8

8.5

9

9.5

10

10.5

11

11.5

1212.5

13

13.5

14

14.5

15

15.5

16

16.5

17


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EXERCISE A-2: LED REVERSE REGION

Repeat Part A-1 with the diode connection reversed. Plot the forward and reverse

characteristics of the LED and determine the incremental resistance of the diode in the

forward and the reverse conducting regions.

Vs VLED ILED LED (ON/OFF)

0.5

1

1.5

22.5

3

3.5

4

4.5

5

5.5

6

6.5

77.5

8

8.5

9

9.5

10

10.5

11

11.5

1212.5

13

13.5

14

14.5

15

15.5

16

16.5

17


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EXERCISE A-3: LEDS CONDUCTION ANGLE

Connect the circuit of Figure A-2, measure the voltage levels (positive and negative) and

the conduction angle.

EXERCISE B-1: ZENER VOLTAGE

Connect the circuit in figure B-1, measure Vzwhen Vsis 15 Volts.

Measured values

Vz V

Vpositive(V)

Vnegative(V)

Time of Conduction (ms)

Conduction Angle (Degrees)


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EXERCISE B-2: ZENER REGIONS

Refer to circuit in figure B-1. Starting from a value of 0.5 V, increase VSin steps of 0.5 V

and measure Vzand Iz.

Vs VZ IZ

0.5

1

1.5

2

2.5

33.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

10.5

11

11.512

12.5

13

13.5

14

14.5

15


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EXERCISE B-4: ZENER LINE REGULATION

Measure Vz. What is the DC (average) value of Vz(in V)? What is the AC component in Vz(in mV)?

Measured values

Vz(DC) V

Vz(AC) mV

EXERCISE B-5: ZENER LOAD REGULATION

Connect a Load resistor RLin parallel with the Zener Diode. Measure the Zener voltage,

Zener current and Load current.

Resistor

()VZ (V) IZ (mA) ILoad (mA)

56 K22 K

10K

4.7 K

2.2 K

1 K

680

470

220

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