7Transistor

By:Md. Al Imran BhuyanNazmul HasanSabuj MandalRukaiya Binte FaridNasif Hossain

What is a transistor?

Who invented transistor?

P

P

P

N

N

N

Types of Transistor:

IB(µA) IB(µA)

Ic(mA)

IE(mA) IE(mA)

IC(mA)

N

P

NThe collector is lightly doped. C

The base is thin and is lightly doped.

B

The emitter is heavily doped. E

NPN Transistor Structure

The C-B junction is reverse biased.

N

P

N

NPN Transistor Bias

C

B

E

No current flows.

The B-E junction is forward biased.

N

P

N

NPN Transistor Bias

C

B

E

Current flows.

When both junctionsare biased....

N

P

N

NPN Transistor Bias

C

B

E

Current flowseverywhere.

Note that IB is smallerthan IE or IC.

IC

IB

IE

N

P

N C

B

E

Although IB is smallerit controls IE and IC.

IC

IB

IE

Note: when the switch opens, all

currents go to zero.

Gain is something smallcontrolling something large

(IB is small).

N

P

C

B

E

IC = 99 mA

IB = 1 mA

IE = 100 mA

b = IC

IB

The current gain frombase to collector

is called b.

99 mA

1 mA= 99

N

P

C

B

E

IC = 99 mA

IB = 1 mA

IE = 100 mA

IE = IB + IC

99 mA= 1 mA +

= 100 mA

Kirchhoff’scurrent law:

C

B

E

IC = 99 mA

IB = 1 mA

IE = 100 mA

In a PNP transistor,holes flow from

emitter to collector.

Notice the PNPbias voltages.

Emitter

Base

Collector

Memory aid: NPNmeans Not Pointing iN.

EBC

NPN Schematic Symbol

Collector

Base

Emitter

EBC

PNP Schematic Symbol

Memory aid: NPNmeans Pointing iN Properly.