Diode – Voltage & Current

Yong Heui Cho @ Mokwon University

Some of slides are referred to:[1] A. S. Sedra & K. C. Smith, Microelectronic Circuits.

2

Electronic Circuits

3. Basic Circuit Theory

4. Diode – Operational Principle5. Diode – V/I

6. Diode – Basic Applications

3

Diode Equation• Equation based on quantum mechan-

ics

4

Forward Biasi = 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

Cut-in V of LED

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

Exponential Model

The exponential model:ID = Isev/nVT

ID = (VDD – VD) / R

ID = Isev/nVT

Graphical Analysis

8

Constant V Model

iD = 0, vD ≤ VD

iD = undefined , vD ≥ VD

9

Piecewise Linear Model

iD = 0, vD ≤ VD0

iD = (vD - VD0) / rD , vD ≥ VD0

10

Diode Analysis

mAkR

VI RR 10

1010

ideal diode model

constant V model

VD = 0.7VrD = 5

mAkR

VVI DRR 3.9

17.010

piecewise linear model

mAkrR

VVID

DRR 254.9

517.010

11

Diode Voltage Regulator• Diode level shifter

VS = 5V

12

Analysis - Ideal Diode

VS = 5V

VD = 0VrD = 0

VVR 000

mAkR

VIL

RR 0

10

13

Analysis – Constant V

VS = 5V

VD = 0.7VrD = 0

VVR 4.17.07.0

mAkR

VIL

RR 4.1

14.1

14

Analysis – Piecewise Line

VS = 5V

VD = 0.7VrD = 1

VkmAmAVR

54.1)1//2//50)(700100(

mAkR

VIL

RR 54.1

154.1

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

23 T roomat 26mVVT

16

Zener BreakdownAt 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

Diode Symbols

18

LED Voltmeter• According to battery V, LED turns on one by one.

– D1: 10.6V = 9V (breakdown V) + 1.6V (LED V)