Diode Curve Tracer ROCHESTER INSTITUTE OF TECHNOLOGY ELECTRICAL & MICROELECTRONIC ENGINEERING

Transcription

1 ROCHESTER INSTITUTE OF TECHNOLOGY ELECTRICAL & MICROELECTRONIC ENGINEERING Diode Curve Tracer Using Digilent Analog Discovery Module, Adam Wardas Webpage: Electrical and 82 Lomb Memorial Drive Rochester, NY Tel (585) DiodeCurveTracer.ppt Page 1

2 INTRODUCTION The Analog Discovery module is used with your computer and the free WaveForms software to turn your computer into a two channel oscilloscope, curve tracer, 16 channel logic analyzer, arbitrary waveform generator, 16 channel digital pattern generator, power supplies and voltmeters, network analyzer, spectrum analyzer and more. The module connects to your USB port. Find more information on line at Academic price ~$159 Page 2

3 ANALOG DISCOVERY PIN-OUT Page 3

4 THEORY The equations on the next two pages should be familiar to you from your basic course in semiconductor devices. The ideal diode equation used to model the current-voltage characteristics of a diode in forward and reverse bias. The second page gives the equations for the space charge layer within a uniformly doped pn junction. Including build in voltage, width of space charge layer, maximum electric field, and junction capacitance. These equations are use in the Excel spread sheet that follows. You can download this Excel file from Dr. Fuller s web page. Page 4

5 THEORY - CURRENTS IN PN JUNCTIONS V RB = reverse breakdown voltage Is Id Forward Bias Reverse Bias Id = Is [EXP (q VD/KT) -1] Id p n + V D - Ideal diode equation V D Vbi = turn on voltage ~ 0.7 volts for Si Is = qa (Dp/(LpNd) +Dn/(LnNa))ni 2 Is = CT 2 exp (-qe g /KT) Page 5

6 THEORY - UNIFORMLY DOPED PN JUNCTION Built in Voltage: = KT/q ln (N A N D /ni 2 ) ni = 1.45E10 cm -3 Width of Space Charge Layer, W: with reverse bias of V R volts W W 1 W 2 = [ (2 q +V R ) (1/N A 1/N D )] 1/2 W 1 width on p-side W 2 width on n-side Maximum Electric Field: W 1 = W [N D /(N A N D )] W 2 = W [N A /(N A N D )] = - [(2q/ +V R ) (N A N D /(N A N D ))] 1/2 Junction Capacitance per unit area: C j r W = r [(2 q +V R ) (1/N A 1/N D )] 1/2 o r = 8.85E -12 (11.7) F/m = 8.85E -14 (11.7) F/cm Page 6

7 THEORY pn JUNCTION CALCULATOR To use this spread sheet change the values in the white boxes. Results are given in the purple boxes and the I-V plot is updated. You can investigate effects of doping, temperature and photocurrent, determine reverse breakdown and junction capacitance. Enjoy! Page 7

8 COMPONENTS USED FOR THIS LAB 100 ohm resistor 1N4448 Diode Vishay BPW46 Photodiode LED any color 9 Volt Battery and connector 47 ohm ¼ watt resistor (used as heater) Protoboard Diode 1N4448 Photodiode LEDs Resistors Page 8

9 SCREEN CAPTURE OF DIGILENT SETUP AND DATA Page 9

10 CIRCUIT SCHEMATIC FOR DIODE I-V CURVE volt peak triangle wave 100 hz + - I p n + R V R - + Vd - Scope ch2+ Scope ch2- Scope ch1+ Scope ch1- I = V R /R Page 10

11 PHOTO OF SET UP FOR DIODE I-V CHARACTERISTICS 100 ohm resistor in series with 1N4448 diode. I = V R /R Page 11

12 WAVEFORM GENERATOR SETUP Page 12

13 OSCILLOSCOPE SET UP R=100 ohm I = V R /R or 10mA/volt Page 13

14 SCREEN CAPTURE OF DIGILENT SETUP AND DATA R=100 ohm I = V R /R or 10mA/volt Page 14

15 DATA IS ALSO AVAILABLE ~ -2 V ~ 0 V ~ +0.2 V ~ +0.6 V ~ V ~ V 10,000 data points are measured. Some are shown here. Page 15

16 CIRCUIT SCHEMATIC FOR DIODE I-V CURVE volt peak triangle wave 100 hz + - I = V R /R I + Vd - Scope ch2+ + R V R - Scope ch2- Scope ch1+ 47 ohm heater V+ = 9V On/Off Scope ch1- Page 16

17 PROTOBOARD FOR TEMPERATURE EFFECT A 47 ohm resistor under the diode is used as a heater and is connected to 9V battery. I will get hot and the diode curve will shift to the left. Theory predicts a ~ -2.2 mv/ C Caution: don t let the 9V wires touch wires going to Analog Discovery module Page 17

18 DIODE I-V AT ROOM TEMPERATURE I = ~ -200 uaat Room T ~25 C Page 18

19 DIODE I-V HEATED Shift ~.05 volts Temperature ~100 C above ambient Page 19

20 CIRCUIT SCHEMATIC FOR DIODE I-V CURVE volt peak triangle wave 100 hz + - I = V R /R I + Vd - Scope ch2+ + R V R - Scope ch2- Scope ch1+ LED 120 ohm V+ = 5V On/Off Scope ch1- Page 20

21 PROTOBOARD FOR PHOTODIODE I-V Triangle wave from the waveform generator and 100 ohm resistor in series with 1N4448 diode. Plus 5 volt power supply and 120 ohm resistor in series with LED. Page 21

22 LED IS OFF V+ OFF I = ~ 0 Page 22

23 LED IS ON V+ IS ON I = ~ -200 ua Page 23

24 SUMMARY We were able to investigate diode I-V characteristics. We observed the effect of light on the I-V characteristics. We observed the effect of heat on the I-V characteristics. The diode I-V characteristics were compared to theoretical calculations. Page 24

25 HOMEWORK DIODE CURVE TRACER 1. Use the excel spread sheet to investigate diode I-V characteristics. 2. What happens to the I-V characteristic when a diode is heated? 3. What happens to the I-V characteristic when a diode is exposed to light? Bonus: Modify the excel spreadsheet to include ideality factor (n) and internal series resistance (RS). Page 25