This document discusses diodes and their voltage-current characteristics. It introduces the diode equation and explains the forward bias and temperature effects on diodes. It then examines three diode models: the exponential model, constant voltage model, and piecewise linear model. Applications of diodes as voltage regulators and in LED voltmeters are also covered. Key diode parameters like saturation current, thermal voltage, and dynamic resistance are defined.

1. Diode – Voltage &
Current
Yong Heui Cho @ Mokwon University
Some of slides are referred to:
[1] A. S. Sedra & K. C. Smith, Microelectronic Circuits.

2. 2
Electronic Circuits
3. Basic Circuit Theory
4. Diode – Operational Principle
5. Diode – V/I
6. Diode – Basic Applications

3. 3
Diode Equation
• Equation based on quantum mechanics



4. 4
Forward Bias
i = Is(ev/nVT – 1)
IS(T) : reverse-biased saturation current
depends on Temp. and junction area
≈ 10-15 (doubles at every 5 ºC)
VT = kT/q
V2 – V1 = 2.3nVT·log(I2/I1)
2.3VT is theoretical threshold swing : 60 mV

5. 5
Cut-in V of LED

6. 6
Temperature Effect
Reverse-bias / Breakdown regions
i = Is(ev/nVT – 1) i ≈ Is when v is negative and more than a few VT
Reverse current : doubles for every 10 ºC
Zener breakdown and avalanche breakdown

7. 7
Exponential Model
The exponential model:
ID = Isev/nVT
ID = (VDD – VD) / R
ID = Isev/nVT
Graphical Analysis

8. 8
Constant V Model
iD = 0, vD ≤ VD
iD = undefined , vD ≥ VD

9. 9
Piecewise Linear Model
iD = 0, vD ≤ VD0
iD = (vD - VD0) / rD , vD ≥ VD0

10. 10
Diode Analysis
mA
kR
V
I R
R 10
1
010




ideal diode model
constant V model
VD = 0.7V
rD = 5
mA
kR
VV
I DR
R 3.9
1
7.010






piecewise linear model
mA
krR
VV
I
D
DR
R 254.9
51
7.010








11. 11
Diode Voltage Regulator
• Diode level shifter
VS = 5V

12. 12
Analysis - Ideal Diode
VS = 5V
VD = 0V
rD = 0
VVR 000 
mA
kR
V
I
L
R
R 0
1
0






13. 13
Analysis – Constant V
VS = 5V
VD = 0.7V
rD = 0
VVR 4.17.07.0 
mA
kR
V
I
L
R
R 4.1
1
4.1






14. 14
Analysis – Piecewise Line
VS = 5V
VD = 0.7V
rD = 1
V
kmAmAVR
54.1
)1//2//50)(700100(


mA
kR
V
I
L
R
R 54.1
1
54.1






15. 15
Small Signal
rD = nVT / ID : small-signal resistance
id = IDvd/nVT = vd / rD
ID = Isev/nVT
vD(t) = VD + vd(t)
iD(t) ≈ ID(1 + vd/nVT) , vd/nVT ≪ 1
iD(t) = ID + IDvd/nVT = ID + id

23Troomat26mVVT 


16. 16
Zener Breakdown
At Bias point, ΔV = ΔI ·rZ
rZ : dynamic resistance
Almost linear i-v characteristics
VZ = VZ0 + rZ·IZ
IZK : minimum current for the operation of Zener diode

17. 17
Diode Symbols

18. 18
LED Voltmeter
• According to battery V, LED turns on one by one.
– D1: 10.6V = 9V (breakdown V) + 1.6V (LED V)