Diode Unit

band gap

energy needed for electron to move fro valence to conduction band

overlap=conductor

space=insulator

fermi level

energy 1/2 between valence and conduction bands

silicon

Si, nonconductive, 4 electrons

doping

adding impurities to silicon to increase carriers

N-type

extra electrons that allows for conductivity

(cathode)

P-type

more silicon, positive charge, insulator (anode)

charge carriers

extra electrons creating N-type

holes

decrease electrons, leaving holes creating P-type

PN junction

depletion region with no charge (prevents I from flowing) 0.7V

diode conduction

when V applied is greater than barrier V

nonlinear curve

forward bias

conducts, closed switch, 1st quad

reverse bias

open switch, 3rd quad

breakdown

excessive reverse, 3rd quad

leakage I = current flow in reverse bias, supported by minority carriers

minority carrier

P=type = neg charge

N-type= pos charge

majority carrier

P-type = pos charge

N-type = neg charge

series resistor

stops excessive heat, need in series in forward direction to limit I

Vf

Io

Vr

P

forward V drop

avg forward I

peak reverse V

max P dissapation

heat sink

zener diode, removes excessive heat

limiter/clipper circuits

removes peaks from input signal

zener diode

allows I in forward and reverse bias (if V is larger than breakdown V)

zener forward

P to +ve, N to -ve

zener reverse

zener has breakdown rating and I increases sharply when Vbreakdown (Vz) is reached

com zener V ranges (Vz)

com tolerance

3.3-75V

5 and 10%

common applications

regulator, comparator, limiter, power supplies