TF EIMLab8 Writeup

Lab 8 The Diode Objective: Measure the current-voltage curve of a silicon diode.

Reverse current

1.) Construct the circuit below using a DC power supply, a diode.

2.) attach an Oscilloscope set to 1M[math]\Omega[/math] input impedence so the probe is located at point B. The oscilloscope's internal resistance will serve as a Resistor (R) to measure the voltage across the diode and calculate the current.

3.) Calculate the value of R needed to observe the current without burning up the diode. What is the max reverse voltage you will have.

3.) Measure the diode reverse current [math]I_r \lt 1 \mu A[/math] as a function of the DC supply voltage. (30 pnts)

IN5230-B-T (4.7 Volt Zener Diode), The other diode is the IN5238B

Data sheet =>

V_Z	Z_Z (I_Z)	I_R (V_R)
4.7	19\Omega (20 mA)	2\mu A (1 Volt)

Bias Volts	V_{scope} (1 M\Omega)(mV)	Current (V/R)	Power
-2.5\pm 0.05	5 \pm 7	5/50 = 0 \pm 0.02 mA
-4.4\pm 0.05	59\pm 10 mV	2.18 \pm 0.06 mA
-4.70 \pm 0.05	220 \pm 10 mV	16.48 \pm 0.2 mA	449 mW
-5.03 \pm 0.05	1050 \pm 15	37.2 \pm 0.2 mA
-5.22 \pm 0.05	2280 \pm 50	77.6 \pm 0.2 mA	too much power

Bias Volts	V_{scope} (1 M\Omega)(mV)	Current (V/R)	Power
2.50 \pm 0.05	24 \pm 1	24/50 = 0.5 \pm 0.02 mA	125
3.14 \pm 0.05	31.1 \pm 2	0.62 \pm 0.064 mA
4.07\pm 0.05	109 \pm 03 mV	2.18 \pm 0.06 mA
4.46 \pm 0.05	274 \pm 3 mV	5.4 \pm 0.06 mA
4.74 \pm 0.05	824 \pm 10 mV	16.48 \pm 0.2 mA	449 mW
4.89 \pm 0.05	1860 \pm 10	37.2 \pm 0.2 mA
5.02 \pm 0.05	3880 \pm 10	77.6 \pm 0.2 mA

Bias Volts	V_{scope} (1 M\Omega)(mV)	Keithley ammeter
0.6 \pm 0.001	2 \pm 1	1.24 \pm 0.01
0.9 \pm 0.001	10 \pm 1	8.69 \pm 0.01 nA
1.05 \pm 0.005	22 \pm 0.5 mV	24.3 \pm 0.05 nA
1.16 \pm 0.005	40 \pm 1 mV	49.4 \pm 0.05 nA
1.23 \pm 0.005	56 \pm 1 mV	78.6 \pm 0.05 nA
1.27\pm 0.005	68 \pm 1 mV	98.2 \pm 0.005 nA
1.30\pm 0.005	75 \pm 1	118.2 \pm 0.5
1.35 \pm 0.005	93 \pm 1	158.2 \pm 0.5
1.4 \pm 0.005	112 \pm 1	213.0 \pm 0.1
1.45 \pm 0.005	132 \pm 1	279.1 \pm 0.1 nA
1.50 \pm 0.005	155 \pm 1	366 \pm 0.5 nA
1.55 \pm 0.005	182 \pm 1	474 \pm 0.5
2.53 \pm 0.01	902 \pm 4	24 \pm .5 \times 10^{3} nA
2.95 \pm 0.05	290 \pm 9	10 \pm 1 \times 10^{4} nA
3.85 \pm 0.05	2240 \pm 20	83 \pm 1 \times 10^{4}
4.62\pm 0.05	2900 \pm 6	8.0 \pm 0.5 \times 10^{6}
5.5 \pm 0.05	3740 \pm 30	NA
6.4 \pm 0.05	4760 \pm 23
7.4 \pm 0.05	5700 \pm 33
9.84 \pm 0.05	8.04 \pm 30

4.) Fill in the blank. The reverse biased diode act as a constant _______________ source. (5 pnts)

Forward Current

1. now swap the diode direction and repeat the measurement in the previous section.

IN5230-B-T (4.7 Volt Zener Diode)

Bias Volts	V_{scope} (1 M\Omega)(mV)	Keithley ammeter
0.922 \pm 0.005	1780 \pm 40	1740/50 = 34.8 mA
0.953 \pm 0.005	2800 \pm 40
1.00 \pm 0.005	4280\pm 50

Bias Volts	V_{scope} (1 M\Omega)(mV)	Keithley ammeter
0.850 \pm 0.005	1740 \pm 20	1740/50 = 34.8 mA
0.872 \pm 0.005	3090 \pm 20
0.883 \pm 0.005	4230\pm 35

Graph

1. make the same measurements in parts 1 and 2 above for a germanium diode.
2. Plot the diode current (on the ordinate) versus the diode voltage (on the abscissa)for both diodes on the same graph. (50 pnts)

Questions

1. The reverse biased diode acts like a constant ____________. (10 pnts)
2. The forward biased diode has a very __________ resistance. A reverse biased diode has a very ____________ resistance.(10 pnts)
3. The approximate DC forward resistance for diode #___________ is _________ when the forward current is _______________.(10 pnts)
4. The approximate DC reverse resistance for diode #___________ is _________ when the forward current is _______________.(10 pnts)
5. The silicon diode #___________ has an approximate turn on voltage of ___________.(10 pnts)

Forest_Electronic_Instrumentation_and_Measurement