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EXPERIMENT 8- ZENER DIODE

FADHLINA MAZRAH BT MOHAMMAD NAJIBAP080126

1) Measure and plot the forward and reverse characteristics of a typical Zener diode using digital multimeter.

2) Demonstrate the forward and reverse characteristics of a typical Zener diode using oscilloscope.

OBJECTIVES

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EQUIPMENTS

1) Power Source 0-10Vac

2) Power Source 0-40Vdc

3) Digital Multimeter

4) Oscilloscope

5) R1-470 Ω

6) R2-10 Ω

7) VR1-Zener Diode

8) Project board with connecting wires

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PROCEDURES FOR OBJECTIVE 1

FIGURE 2

1. a)The circuit shown in Figure 2. Series resistor R1 limits the maximum diode current to approximately 80mAdc. The digital multimeter was set to a low dc volt range.

b)The dc source voltage Es was slowly increase until the forward diode voltage,VF, indicated by the digital multimeter, is 0.2 Vdc.

c)The forward diode current, IF were measure and record in table 1.

d)For each of the forward voltages listed in the Table was repeated.

e)The voltage was return to zero.

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Forward volts, VF (Vdc) ±0.01 Forward current, IF (mAdc) ±0.01

0.20 0.00

0.40 0.00

0.50 0.00

0.55 0.00

0.60 0.07

0.65 0. 10

0.70 0.35

0.75 1 .71

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RESULT (TABLE 1)

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0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.800.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

Forward Current vs Forward Voltage

Forward Current, IF (mAdc)

Forward Voltage (Vdc)

For

war

d C

urr

ent

(mA

dc)

2.a)The forward current measurements from table 1 was plot on the graph.

b)A smooth curve through all of plotted points was draw.

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3. a)The circuit was change to that shown in Figure 4, by reversing the Zener diode connection.

b)The dc source voltage,Es was slowly increase until the reverse voltage,VR indicated by the digital multimeter, is 2Vdc.

C)The reverse diode current, IR were measure and record in Table 2.

d)The measurement were repeated for each of the reverse voltage listed in the table.

e)The voltage was return to zero.

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Reverse voltage,VR (Vdc) ±0.01 Reverse diode current, IR (mAdc)

±0.012.0 0.00

3.0 0.00

4.0 0.00

5.0 0.00

6.0 0.00

7.0 0.00

8.0 0.00

9.0 0.00

10.0 0.00

11.0 0.05

12.0 0.1 0

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RESULT (TABLE 2)

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-14.0 -12.0 -10.0 -8.0 -6.0 -4.0 -2.0 0.0

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

Reverse Current vs Reverse Voltage

Reverse Current, IF (mAdc)

Reverse Voltage (Vdc)

Reverse Current(mAdc)

4. a)The reverse current measurements from Table 2 were plot on the graph. The lower left hand (reverse volts) portion of the graph was use

b)A smooth curve was draw through all plotted point.

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PROCEDURES FOR OBJECTIVE 2

5. a)The test circuit in Figure 5 was examine. The Zener diode is tested by applying a controlled ac voltage across the anode and cathode through current limiting resistor R1 and R2. The ac voltage was set to a value above the Zener voltage, alternately biased the diode in forward and reverse direction, this would cause both forward and reverse diode current to low through R1 and R2. The voltage drop across R2 is applied to the vertical input of the oscilloscope and cause the spot to move up and down. Vertical deflection is proportional to current. The vertical scale divisions was converted directly to current since the value of R2 is 10 Ω.

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b)The oscilloscope was calibrate. The vertical deflection for 0.05V/cm was calibrate and the horizontal SWEEP TIME/CM was set to EXT. The spot was center by adjusting the horizontal and vertical positioning controls. The intensity was reduce to prevent damage to the CRT.

c)The output of the variable ac power source was connect between the EXT SYN/HOR input and GDN of the oscilloscope.

d)The digital multimeter was set to 15Vac range and was connect across the output of the ac power source.

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e)The output of the ac power source was adjust for 7.07Vrms (20 volts peak-to-peak) as indicated on the digital multimeter. The oscilloscope VARIABLE/HOR GAIN control was adjust until the horizontal trace covers 10cm. The horizontal input was calibrated for 2 volts per cm.

f)The voltage was return to zero. The oscilloscope and digital multimeter was disconnect. The oscilloscope were leave horizontal and vertical gain controls set at their calibrated position.

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g)The circuit was connect as shown in Figure 5. The anode of VR1 was connect to the EXT SYNC/HOR input and the cathode to the vertical input of the oscilloscope. The oscilloscope was connect to the ground to test circuit ground.

h)The output voltage of the power supply was gradually increase to 20 volts peak-to-peak, as indicated by the digital multimeter, while observing the oscilloscope screen.

i)The current-voltage values against the values as plotted on the graph paper was compare.

j)The voltage was return to zero.

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DISCUSSION

DISCUSSION FOR OBJECTIVE 1

1)The voltage of Zener diode forward biased,VF is 0.60Vdc.

2)Comparison of forward characteristics between the Zener diode and the convensional Silicon diode.

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Zener diode

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Silicon diode

3) The Zener( avalanche) action occur when Voltage drop,VZ equal to 12.0V. Current did not flow through the diode until it reachesthe knee voltage.

4) A conventional silicon operated in the reverse breakdown region of its operating curve is normally destroy. But ,The Zener diode is specially designed to have a greatly reduced breakdown voltage and always keep voltage always higher than breakdown. A Zener diode is doped more heavily than other diodes. This doping allows the Zener diode to hold a specific voltage despite fluctuations in electrical current when the Zener diode is reverse-biased.

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1) The voltage breakdown from A is 12V and voltage breakdown from B is 8.36 V. This result differ because the resist 10 Ω was adding in Experiment B. Addition of this resistor cause the current change. Therefore the result of Experiment A and B are different.

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DISCUSSION FOR OBJECTIVE 2

Demonstrate the forward and reverse characteristics of a typical Zener using an oscilloscope.

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QUIZ

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•Zener diode is a special kind of diode which permits current to flow in the forward direction as normal and also allow it to flow in the reverse direction when the voltage is above certain value which is breakdown voltage known as Zener voltage. •A convensional silicon diode will not allow the significant if it reverse biased below its reverse breakdown voltage.

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1 ) A Zener diode differs from a conventional silicon diode?

•Since the voltage dropped across a Zener diode is a known and fixed value, Zener diode used to regulate the voltage in electric circuit. Zener diode are widely used as voltage reference and regulate the voltage across a small circuit.

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2) A Zener diode can be use as what?

•The Zener diodes maintain a fixed voltage in an electrical circuit. They are designed so that when a certain voltage is reached, the diode breaks down without damaging the circuit.

•When the Zener diode are connected in parellel with variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diodes reverse breakdown voltage.

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3) What is Zener diode voltage?

4) A Zener diode is normally connected?

•V=IR•R=V/I

= 12.0 = 120.0 kΩ

0. 1 x 10-3

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5)What is the resistance of the Zener diode in the breakdown region?

Maximum Current = Power/ Voltage, Power = I2R , I=V/R

1 = 1 + 1

R 470 Ω 10 Ω

1 = 243

R 235

R = 9.79 Ω

I = V/R

= 6.8V/9.79 Ω

=0.69 A

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6) A Zener diode is rated at 6.8V. What is the maximum Zener current the diode can safely

handle at room temperature?

CONCLUSION

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•The voltage current characteristics of Zener diode are similar to conventional silicon diode when the Zener diode is biased forward. But in reverse biased, the Zener diode act same as conventional silicon diode, until the reverse breakdown voltage value is reach. At this point, conventional silicon is normally destroy but Zener diode have a greatly reduced breakdown voltage and always keep voltage always higher than breakdown.

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THANK YOU . . .

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