Ece-425.-labreport-2-leynes.docx

Republic of the Philippines Batangas State University College of Engineering, Architecture and Fine Arts Mechanical Engineering Department

ECE 425 – Basic Electronics with Measurements Laboratory Report No. 2 Diode Characteristics and Configurations (Series and Parallel)

Submitted by: Leynes, Rica Meracle V. ME-4105

Submitted to: Engr. Sarah B. Tolentino Instructor

Septmber 24, 2018

Objective: To calculate, compare, draw, and measure the characteristics of a silicon and a germanium diode.

Materials: a.) DMM b.) Resistors - (1) 1-kΩ, (1) 1- MΩ c.) Diodes – (1) Silicon, (1) Germanium d.) DC power supply

Theory of Operation Digital multimeter can be used in determining the operating condition of a diode. They have a scale donated by a diode symbol that will indicate the condition of the diode in the forward and reverse bias regions. If connected to establish a forward-bias condition the meter will display the forward voltage across the diode at a current level typically in the neighborhood of 2mA. If connected to establish a reverse-bias condition an “OL” should appear on the display to support the open-circuit approximation frequently applied to this region. If the meter does not have the diode-checking capability the condition of the diode can also be checked by obtaining some measure of the resistance level in the forward and reverse-bias region. The current-volt characteristics of a silicon or germanium diode have the general shape shown in Fig.1.1. Note the change in scale for both the vertical and horizontal axes. In the reversed-biased region the reverse saturation currents and fairly constant from 0V to the Zener potential. In the forward-bias region the current increases quite rapidly with increasing diode voltage. Note that the curve is rising almost vertically at a forward-biased voltage of less than 1V. The forward-biased diode current will be limited solely by the network in which the diode is connected or by the maximum current or power rating of the diode. The “firing potential” or threshold voltage is determined by extending a straight line (dashed lines of Fig. 1.1) tangent to the curves until it hits the horizontal axis. The intersection with the V D axis will determine the threshold voltage VT at which he current begins to rise rapidly.

The DC or Static resistance of a diode at any point on the characteristics is determined by the ratio of the diode voltage at that point, divided by the diode current. The AC resistance at a particular diode current or voltage can be determined using a tangent line. The resulting voltage and current deviations can then be measured and the following equation applied.

It can be shown through the application of differential calculus that the AC resistance of a diode in the vertical-rise section of the characteristics is rD= ohms. For levels of current at and below the knee of the curve the AC resistance of a silicon diode is better approximated by rD= ohms.

Procedure: A. Diode Test Diode Testing Scale The diode testing scale of a DMM can be used to determine the operating condition of a diode. With one polarity, the DMM should provide the “firing potential” of the diode, while the reverse connections should result in an “OL” response to support the open circuit approximation. Using the connection in Fig. 1.2, the constant-current source of a about 2mA internal to the meter will forward-bias the junction, and a voltage of about 0.7V (700mV) will be obtain for silicon and 0.3 (300mV) for germanium. If the leads are reverse, an OL indication will be obtain.

If a low reading (less than 1 V) is obtained in both directions, the junction is shorted internally. If an OL indication is obtained in both directions, the junction is open. Perform the tests of Table 1.1 for the silicon and germanium diodes

Resistance Scales As indicated in the Theory of Operation section of this experiment, the condition of a diode can also be checked using the resistance scales of a volt-ohm-meter (VOM) or digital meter. Using the appropriate scales of the VOM or DMM, determine the resistance levels of the forward- and reverse-bias regions of the Si and Ge diodes. Enter the results in Table 1.2 Although the firing potential is not revealed using the resistance scales, a “good’’ diode will result in lower resistance level in the forward bias state and a much higher resistance level when reverse-biased. Based on the results of Table 1.2, are in both diodes in good condition?

B. Forward-bias Diode Characteristics In this part of the experiment we will obtain sufficient data to plot the forward-bias characteristics of the silicon and germanium diodes on Fig. 1.5. a.) Construct the network of Fig.1.4 will the supply (E) set at 0V. Record the measured value of the resistor.

b.) Increase the supply voltage until VR (not E) reads 0.1V. Then measure VD and insert its voltage in Table 1.3. Calculate the value of the corresponding current ID using the equation shown in Table 1.3. c.) Replace the silicon diode by a germanium diode and complete Table 1.4. e.) On fig.1.5, plot 𝐼𝐷 versus 𝑉𝐷 for silicon and germanium diodes. C. Reverse Bias a.) In fig 1.6 a reverse bias connection has been established. Since the reverse saturation current will be relatively small, a large resistance of 1MΩ is required if the voltage R is to be of measurable amplitude. Construct the circuit and record the measured value of R in the diagram.

b.) Measure the voltage 𝑉𝑅 . Calculate the reverse saturation current from 𝐼𝑆 =

𝑉𝑅 (𝑅𝑚𝑒𝑎𝑠 II 𝑅𝑚 )

𝑅𝑚 = 10𝑀Ω. c.) Repeat step b for the germanium diode. d.) How do the resulting level of 𝐼𝑆 for silicon and germanium compare. e.) Determine the DC resistance levels for silicon and germanium diodes using the equation 𝑅𝐷𝐶 =

𝑉𝐷 𝑉𝐷 𝐸 − 𝑉𝑅 = = 𝐼𝐷 𝐼𝑆 𝐼𝑆

use

D. DC Resistance a.) Using the Si curve of figure 1.5 determine the diode voltage at diode current levels indicated in Table 1.5. Then determine the DC Resistance at each current level. Show all calculation. b.) Repeat step a for germanium diode and complete Table 1.6 c.) Does the resistance for Si and Ge change as the diode current increase and we move up the vertical-rise section of the characterestics?

E. AC Resistance a.) Using equation 𝑟𝑑 =

∆𝐶 ∆𝐼

, determine the AC resistance of the silicon diode at 𝐼𝐷 = 9 𝑚𝐴 using

the curve of Fig. 1.5. Show all work. 𝑟𝑑(𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑) =______________________ b.) Determine the AC resistance at at 𝐼𝐷 = 9 𝑚𝐴 using the equation 𝑟𝑑 =

26 𝑚𝑉 𝐼𝐷

for silicon diode.

𝑟𝑑(𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑) =______________________ How do the result of a and b compare? c.) Repeat step a for 𝐼𝐷 = 2 𝑚𝐴 for the silicon diode. 𝑟𝑑(𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑) =______________________ d.) Repeat step b for 𝐼𝐷 = 2 𝑚𝐴 using the silicon diode. 𝑟𝑑(𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑) =______________________ How do the result of c and d compare?

F. Firing Potential Graphically determine the firing potential (threshold voltage) of each diode from its characterestics as defined in the Theory Operation. 𝑽𝑻(𝒔𝒊𝒍𝒊𝒄𝒐𝒏) =________________ 𝑽𝑻(𝒈𝒆𝒓𝒎𝒂𝒏𝒊𝒖𝒎) =________________

RESULT AND FINDINGS:

Table 1.1 Si 0.557 V 0V

Test Forward Reverse

Ge 0.250 V 0V

Table 1.2 Test Forward Reverse

Si 0.673 MΩ 0

Ge 1.120 KΩ 4.739 MΩ

DMM DMM

Table 1.3 SILICON DIODE

(using DMM)

(using Multisim)

𝑽𝑹 (V)

𝑽𝑫(V)

𝑰𝑫 (mA)

𝑽𝑫(V)

𝑰𝑫 (mA)

0.1

0.566

0.1013171226

0.417563

0.1000618382

0.2

0.573

0.2026342452

0.452748

0.2001236764

0.3

0.577

0.3039513678

0.473417

0.3001855146

0.4

0.582

0.4052684904

0.488254

0.4002473529

0.5

0.587

0.506585613

0.499615

0.5003091911

0.6

0.591

0.6079027356

0.509088

0.6003710293

0.7

0.597

0.7092198582

0.517195

0.7004328675

0.8

0.600

0.8105369807

0.523966

0.8004947057

0.9

0.604

0.9118541033

0.536161

0.9005565439

1

0.607

1.013171226

0.72066

1.000618382

2

0.626

2.026342452

0.592494

2.001236764

3

0.644

3.039513678

0.6087832

3.001855146

4

0.654

4.052684904

0.619193

4.002473529

5

0.663

5.06585613

0.628533

5.003091911

6

0.672

6.079027356

0.636391

6.003710293

7

0.678

7.092198582

0.643358

7.004328675

8

0.683

8.105369807

0.644354

8.004947057

9

0.689

9.118541033

0.649453

9.005565439

10

0.693

10.13171226

0.654969

10.00618382

Table 1.4 GERMANIUM DIODE

(using DMM)

(using Multisim)

𝑽𝑹 (V0

𝑽𝑫(V)

𝑰𝑫 (mA)

𝑽𝑫(V)

0.1

0.229

0.1013171226

0.2

0.232

0.2026342452

0.3

0.234

0.3039513678

0.4

0.237

0.4052684904

0.5

0.238

0.506585613

0.6

0.241

0.6079027356

0.7

0.242

0.7092198582

0.8

0.244

0.8105369807

0.9

0.245

0.9118541033

1

0.247

1.013171226

2

0.258

2.026342452

3

0.267

3.039513678

4

0.274

4.052684904

5

0.279

5.06585613

6

0.285

6.079027356

7

0.288

7.092198582

8

0.293

8.105369807

9

0.295

9.118541033

10

0.300

10.13171226

0.462106 V 0.488597 V 0.504394 V 0.515692 V 0.524503 V 0.531739 V 0.537751 V 0.543051 V 0.547665 V 0.551814 V 0.57917 V 0.595151 V 0.606521 V 0.615351 V 0.622528 V 0.628606 V 0.633878 V 0.638531 V 0.642692 V

𝑰𝑫 (mA) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 3 4 5 6 7 8 9 10

For Fig. 1.6. (reverse bias) Silicon Diode 𝑹𝒎 = 10 𝑀Ω; 𝑹𝒎𝒆𝒂𝒔 = 1.005 𝑀Ω 𝑽𝑅 = 0.995 𝑉

Germanium Diode 𝑹𝒎 = 10 𝑀Ω; 𝑹𝒎𝒆𝒂𝒔 = 1.005 𝑀Ω 𝑽𝑅 = 0.492 𝑉

𝑰𝑺 = 1.089549751

𝑰𝑺 = 0.5387522388

𝑅𝐷𝐶 =

15𝑉−0.995 𝑉

𝑉𝐷 𝑉𝐷 𝐸 − 𝑉𝑅 = = 𝐼𝐷 𝐼𝑆 𝐼𝑆 15𝑉−0.492 𝑉

𝑅𝐷𝐶 = 1.089549751

𝑅𝐷𝐶 = 0.5387522388

𝑅𝐷𝐶(𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑) = 12.85393346

𝑅𝐷𝐶(𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑) = 26.92889042

Table 1.5 𝑰𝑫 (mA)

𝑽𝑫

𝑹𝑫𝑪

0.2 1 5 10

Table 1.6 𝑰𝑫 (mA)

0.2 1 5 10

Sumarry:

Conclusion:

𝑽𝑫

𝑹𝑫𝑪