LAB 5

LIGHT EMITTING DIODE

MUHAMMAD HILMI BIN OTHMAN 51210210360 20 OCTOBER 2010

ABSTRACT

This experiment is set to study the principles and the properties of the diode. This experiment helps us to know how to differentiate between forward-biased circuits with the forward-biased circuit. We also use to determine the I-V characteristics of the diode. By plotting the graph, we know what relationship V-I of the diode in the circuit. This experiment also is aim to test diode application. By using normal circuit of diode and the rectification of diode circuit, we be able to test the application based on our data result.

INTRODUCTION

A diode is made up by combining the p-type material and n-type material on the same crystal base. The pn junction is formed results of the combination. When it is formed, a barrier potential is created to prevent further current flow without external voltage source. If dc voltage source is connected to the diode, the polarity of the connection has the effect of either increasing or decreasing the barrier potential. This effect is ensuring the diode to allow current to flow in one direction only. The diode is forward biased when the anode is more positive than the diode is reversed biased when the cathode is more positive than anode.

The full wave rectifier circuit is makes use of the entire waveform, both positive and negative half-cycles, of the AC source voltage in powering the DC load. As a result, there is less "ripple" voltage seen at the load. The RMS (Root-Mean-Square) value of the rectifier’s output is also greater for this circuit than for the half-wave rectifier.

Procedure

Task 1 (biasing diode)

i. The forward and reverse resistance of the diode is measured by reversing the multimeter leads across the diode. The diode passes the test if the resistance is significantly different between the two measurements. The data then is recorded.

ii. The circuit as the figure 1 is constructed on the breadboard by using R1 value of 330Ω.

iii. V1 = 0V value is set, and then LED condition is observed, type of circuit is determined and the LED is removed back from the circuit.

iv. The supply voltage is increased and the data result is recorded in the table.v. The current then is calculated by applying Ohm’s Law to R1 and the data result is

recorded.vi. The graph of V against I is plotted.

vii. The circuit then is named.viii. The same procedure for the circuit in figure 2 is repeated like figure 1.

Task 2 (diode application)

i. The circuit in figure 3 is constructed on the breadboard.ii. The value of V1 is set to 8 Vp and the oscilloscope is connected to the output, (Vrl) of

the circuit.iii. The output waveform of the circuit is sketched.iv. The output voltage, Vrl is measured in dc voltage and the data result is recorded in

the table.v. The procedure for the circuit is repeated for figure 4.

Figure 1

330 R1

+ V1

D1DIODE

R1330

+ V1

D1DIODE

Figure 2

+

-

V1R110k

D1DIODE

Figure 3

Rl10k

+

-

Vs1

D1BRIDGE

Figure 4

RESULT & DISCUSSIONTask 1

Component Measured valueD1

Forward Resistance139.5 kΩ

D1Reverse Resistance

Unable to detect

In forward resistance, the LED is lightening up due to polarity of the diode is same with voltage supply. Hence, it is forward-biased circuit.

In reverse resistance, the LED is not lightening up due to different polarity of the diode with voltage supply. Hence, it is reverse-biased circuit.

Vsupply (V1)

Vd figure 1(V)

Vd figure 2(V)

Vrl figure 1(V)

Vrl figure 2(V)

I figure 1(V)

I figure 2(A)

0.3 0.216 0.22 0.0001 0 0.3μ 0/10k = 0A0.5 0.405 0.44 0.015 0 45.4 μ 0/10k = 0A0.6 0.463 0.53 0.075 0 227 μ 0/10k = 0A0.7 0.487 0.68 0.132 0 400 μ 0/10k = 0A0.8 0.51 0.73 0.224 0 678.8 μ 0/10k = 0A0.9 0.527 0.89 0.32 0 969.7 μ 0/10k = 0A.3 0.535 1.0 0.371 0 1.12m 0/10k = 0A

1.5 0.577 1.45 0.832 0 2.52m 0/10k = 0A 2.0 0.603 1.98 1.306 0 3.96m 0/10k = 0A2.5 0.623 2.52 1.832 0 5.55m 0/10k = 0A3.0 0.635 2.94 2.26 0 6.85m 0/10k = 0A

From this results data, the current and the voltage drop across the resistance does not flowing in the circuit if it is reversed biased circuit. Meanwhile, in forward biased circuit, the current across the resistance increase as the voltage supply through the circuit increases.

Figure shows the stimulation of diode circuit using MultiSim. In forward bias, the stimulation shows the value of resistance of the diode is 92.45 kOhm and reverse bias is unable to read.

From the graph also, we can see that as voltage supply is increases, the current flows across the resistance also is increases. So, the circuit is obeys the Ohm’s law.

TASK 2

Circuit VRL

Figure 3 2.3 VFigure 4 4.2 V

This figure shows the stimulation of half rectifier circuit using MultiSim.The value of voltage peak from this stimulation is 7.4 V.

figure shows the stimulation of full rectifier diode circuit using MultiSim.The value of voltage peak from this stimulation is 7.4 V.

CONCLUSION

In this experiment, the experimental approach is differing slightly with the stimulation using MultiSim. This is due to some errors in this lab. In this lab, we knew that in forward bias diode circuit, there are current flowing through the circuit, meanwhile in reverse bias diode circuit, there is no current flows across the circuit. We also knew how to stimulate diode circuit using MultiSim.

REFFERENCE.

1. Note lecture from electronic device.2. Task sheet from Coursework.

The picture shows the output waveforms for the circuit in figure 3.Voltage peak that we got is

2.6 x 2 x 1 = 7.2 V.This is differing with value simulated by MultiSim which is 7.4 V.The error value is (7.2-7.4)/7.4 x 100 =2.7 %This is due to inaccurate value of voltage supply that we set up.

The picture below shows the output waveforms for the circuit in figure 4.

The voltage peak value that we got is 3.4 x 2 x 1 = 6.8

This is differing with the simulation value from the MultiSim which is 7.4 V.

Thus, the percentage error is

(7.4 – 6.8)/ 7.4 x 100 =8.1%

The error may come from the inaccurate adjustment of voltage supply.