Abu Dhabi University Collage of Engineering& Computer Science

Course: Electronic Devices & Circuits Course ID: CEN304

Course Lecturer: Dr.Montasir Qasymeh

Lab 1: DC& ACCharacteristics of Diodes

Prepared by: Eng. Ahmed Sweleh Date: 20/9/2012
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Objectives:
This lab aims to educate the student in the following:1. 2. 3. 4. Putting the diodein reverse bias and forward bias. Measuring forward current (IF) and reverse current (IR). Observing the AC characteristics of a diode. Plotting the characteristic curve of a diode.

Tools:
For this lab the following tools will be used:1. 2. 3. 4. 5. 6. 7. 8. 9. Breadboard Digital Multi Meter DC Power Supply Function Generator Oscilloscope Breadboard Cables Crocodile Clip Cables Resistors Silicon Diode1n4148

Introduction
Diodes can be characterized interims of their doping material or application. An example of doping material we have:  Silicon diodes (VF = 0.7v).

An example on application we have the light emitting diode (LED). In theory you toke that a diode consists of two sides:   Positive “+” side (P-type or Anode) Negative “-“ side (N-type or Cathode)

As we can see in Figure 1(C), we can tell which side of the diode in real life is the cathode by looking for the stripe mark on the diode. In case of LEDs the short leg is the cathode.

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Figure 1

Procedure:
1. Putting the diode in reverse biasand forward bias. Measure the voltage across the diode when it’s in forward and reveres bias in this experiment. Connect your circuit and site the voltage to 5V as shown in Figure 2 and write down your results in Table 1 .
XMM1 XMM2 R2 1kΩ Vr

2 V1 5V

R1 1kΩ Vf

1 D2 DIODE_VIRTUAL 0

4 V2 5V

3 D1 DIODE_VIRTUAL 0

Forward biase

Reverse biase

Figure 2 Table 1 silicon Forward voltage (v) Reverse voltage (v)

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2. Measuring forward current (IF) and reverse current (IR). Measure IF and IR for just the silicon diode. To do that first disconnect the red probe from the (HzVΩ) terminal of your multi meter and connect it to the multi meter’s (mAuA) terminal of your multi meter and move the dial to the (mA) sign an fallow the coming steps: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Connect the circuit shown in Figure 3-A. Turn on the circuit. Connect the multi meter’s terminal (mAuA) to diodes “-“terminal. Connect the multi meter’s terminal (COM) to ground terminal from the power supply. Now move the voltage curser slowly from 0V to 10V. Write down the value of current that the multi meter displays at the voltage value shown in Table 2. Turn off the circuit. Connect the circuit shown in Figure 3-B by simply reversing the diodes connections Turn on the circuit. Now move the voltage curser slowly from 10V to 0V. Write down the value of current that the multi meter displays at the voltage value shown in Table 2. Turn off the circuit.
2 V1 10 V 0 XMM1 5 Forward biase A Reverse biase B 6 R1 1kΩ Vf 1 D2 DIODE_VIRTUAL 4 V2 10 V 0 XMM2 R2 1kΩ Vr 3 D1 DIODE_VIRTUAL

Figure 3

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Table 2

Forward bias Voltage(v) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 3 4 7 8 9 10

IF

Reverse bias Voltage(v) -0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9 -1 -2 -3 -4 -7 -8 -9 -10

IR

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3. Observing the AC characteristics of a diode. To observe the AC characteristics of the diode, do the following steps: 1. 2. 3. 4. 5. 6. 7. 8. 9. Disconnect your DC power supply from the circuit. Connect your function generator’s output to CH1 of your oscilloscope. Set your function generators output sin wave, 2VP and 10 KHz Connect the function generator’s output and the oscilloscope, CH1 & CH2 as shown in Figure 4. Set the oscilloscope’s to display both CH1 & CH2 at the same time and with a scale of 1V/DIV for the minimum of two cycles. Position both signals in the center of the oscilloscope screen to compare them together. Save your output screen. Reverse the diode and check what changes this has on the oscilloscope’s output. Keep the connections as they are because you will need them in the next part.
XSC1
Tektronix

XFG1
P G 1 2 3 4 T

CH1 R1 1kΩ D1 1N4148 CH2

Figure 4 4. Plotting the characteristic curve of a diode The characteristic curve of the diode can be obtained using the oscilloscope through the following steps: 1. 2. 3. 4. On the oscilloscope’s panel press the “Horizontal Menu” button. Select XY plotting by pressing on F5 (next to the oscilloscope’s screen) Center the plot in the middle of the screen using CH1 & CH2 positioning nobs. Save your output screen.

Now using the data you have collected in Table 2 to plot the characteristic curve of our diode using MATLAB’s plot command& compare it with the one you obtained from the. Is there any deference between them and why 6