Physical Electronics(ECE3540) The PN junction Diodesblogs.cae.tntech.edu/...Junction-Diodes-Group-131.pdf · Physical Electronics(ECE3540) The PN junction Diodes ... The zener diode

Physical Electronics(ECE3540)

The PN junction Diodes

ennessee Technological University, Fall 2013

Group (13)

N junction

p–n junction is a boundary or

terface between two types of

emiconductor material, p‐type

nd n‐type, inside a single crystal

f semiconductor.

he total charge on each side of

he junction must be equal and

pposite to maintain a neutral

harge condition around the

nction.

N junction Diode

p–n junction diode is made of a crystal

f semiconductor. Impurities are added

o it to create a region on one side that

ontains negative charge carriers

lectrons), called n‐type semiconductor,

nd a region on the other side that

ontains positive charge carriers (holes),

alled p‐type semiconductor.

Typical diode packages in same alignmendiode symbol. Thin bar depicts the cathod

N junction Distance

N‐type material has lost electrons and

ype has lost holes, the N‐type material

come positive with respect to the P‐type.

N junction Distance

s electric field created by the diffusion process has created a "built‐in potential

erence" across the junction with an open‐circuit (zero bias) potential of:

ere:

s the zero bias junction voltage

s the intrinsic concentration.

the thermal voltage of 26mV at room temperature

and NA are the impurity concentrations

ow Current Diodes

hese diodes body is about 3mm long can

arry maximum forward current of about

00mA and withstand a reverse voltage of

5V without breaking down.

edium current Diodes

hese diodes can pass a forward current of

bout 500 mA and can withstand a reverse

oltage of 250 V.

gh Current Diode

hese current diodes or power diodes can carry a

orward current of many amperes and can

ithstand several hundred volts of reverse

oltage.

ener Diode

is basically the same as the

tandard PN junction diode but

re specially designed to have a

w pre-determined Reverse

reakdown Voltage that takes

dvantage of this high reverse

oltage. The zener diode is the

mplest types of voltage regulator

nd the point at which a zener

ode breaks down or conducts is

alled the "Zener Voltage" ( Vz ). Electronic symbol

ener Diode I‐V Characteristics

he diodes anode connects to the negative

upply. From the I‐V characteristics curve

bove, we can see that the zener diode has

region in its reverse bias characteristics of

most a constant negative voltage

egardless of the value of the current

owing through the diode and remains

early constant even with large changes in

urrent as long as the zener diodes current

emains between the breakdown current

Z(min) and the maximum current rating

Zener Diode I‐V Characteristics

ercise

5.0V stabilised power supply is required to be produced from a

2V DC power supply input source. The maximum power rating

f the zener diode is 2W. Using the zener regulator circuit above

alculate:

olution for ( a , b )

e maximum current flowing through the zener diode.

e minimum value of the series resistor, RS

olution for ( c, d )

e load current IL if a load resistor of 1kΩ is connected across the Z

.

he zener current IZ at full load.

unnel Diode

tunnel diode or Esaki diode is a type of

emiconductor that is capable of very fast

peration, well into the microwave

equency region, made possible by the use

f the quantum mechanical effect called

unneling.

p

There are 3 possible biasing conditions:

1. Zero Bias No external voltage is applied to the

PN‐junction.

2. Reverse Bias effect of Increasing the PN‐junction width.

3. Forward Bias effect of Decreasing the PN‐junction width.

ro biased junction diode

n a diode is Zero Biased, no external energy source is applied and a natural Potent

er is developed across a depletion layer which is approximately 0.5 to 0.7v for silic

es and approximately 0.3 of a volt for germanium diodes.

hen a junction diode is Reverse Biased, the thickness of the depletion region

creases and the diode acts like an open circuit blocking any current flow, (only

very small leakage current).

Reverse resistance of a diode ranges from 5MΩ to 1000MΩ

junction diode is Forward Biased, the thickness of the depletion region reduces

de acts like a short circuit allowing full current to flow.

p

Forward Biased Diode Reverse Biased Diode

the junction temperature increases the de's characteristic shifts to the left.

oth, Silicon and Germanium this shift isabout 0.25mV/°C

an increase in the temperature causes ain saturation current (leakage)

Every increase of 10°C in junction temresults in approximate doubling of this

e generates heat and if the ambient temperature is high, this heat may not be diss

gh and will change the diode's parameters (characteristics).

• Reverse Bias the diode is reverse‐biased, a very small drift current due to thermal excitation fl the junction. This current (reverse saturation current,I0) is given, according to themann equation, by the formula

K0 is a constant depending on the pn junction geometry and V0 is the built‐in of the diode (see chapter “Semiconductor Materials: pn junction”)

Forward Bias

e diode is forward‐biased through a voltage V, a small drift current flows againe junction. In that case, however, there is an additional component, the diffusionVd, given by the formula:

eo link: e P‐N junction – How diodes work?

• http://www.youtube.com/watch?v=JBtEckh3L9Q

eference

orr, Wayne. "The PN Junction." PN Junction Theory for Semiconductor Diodes.

ayne Storr, 1999. Web. 31 Oct. 2013.

chey, Jason. "P–n Junction." Wikipedia. Wikimedia Foundation, 28 Oct. 2013.

eb. 31 Oct. 2013.