Transistor

1
Transistor
2
(No Transcript)
3
(No Transcript)
4
BJT Transistors
NPN Transistor
Sandwiching a P-type layer between two n-type
layers.
                                               
                            
PNP Transistor
Sandwiching a N-type layer between two p-type
layers.
5
How a NPN Transistor works?
                                         
The base-emitter diode (forward) acts as a
switch. when v1gt0.7 it lets the electrons flow
toward collector. so we can control our output
current (Ic) with the input current (Ib) by using
transistors.
E
C
B
Forward
backward
6
Transistors have three terminals
Collector
Base
Emitter
Active Always on IcBIb
Saturation IcIsaturation On as a switch
Transistors work in 3 regions
Off Ic0 Off as a switch
7
Transistor as a Switch

• Transistors can be used as switches.1

Transistor
Switch

• Transistors can either
• conduct or not conduct current.2

• ie, transistors can either be on or off.2

8
Transistor Switching Example15
X
12V
Variable Voltage Supply

• When VBE is less than 0.7V the transistor is off
• and the lamp does not light.

• When VBE is greater than 0.7V the transistor is
  on
• and the lamp lights.

9
Transistor Circuit Light-Controlled Circuit

• This transistor circuit contains
• a Light-Dependent Resistor.

• Because of the LDR, this circuit is dependent on
  light.

• The purpose of this circuit is to turn on the LED
  when the light reaches a certain intensity.

1. LED Off.
2. Cover LDR.
3. RLDR ?.
4. VLDR ?.
5. Transistor switches on.
6. LED On.

Input Voltage Divider Process
Transistor Output LED
10
Transistor as an amplifier
Transistors are often used as amplifiers to
increase input signal in radios, televisions and
some other applications .The circuit may be
designed to increase the current or voltage
level. The power gain is the product of current
gain and voltage gain (PVI).
11
Amplifier example
As you see, the transistor is biased to be always
on. The input signal is amplified by this
circuit. The frequency of output is the same as
its input, but the polarity of the signal is
inverted.
The measure of amplification is the gain of
transistor.
Example Input Amplitude 0.2v Output
amplitude10v Gain10/0.250
12
Field Effect Transistors
JFET
MOSFET
CMOS
13
How a JFET transistor works?
When the gate is negative ,it repels the electron
in the N-channel. So there is no way for
electrons to flow from source to drain.
When the negative voltage is removed from Gate
,the electrons can flow freely from source to
drain .so the transistor is on.
14
How a MOSFET Transistor works?
In MosFET, the Gate is insulated from p-channel
or n-channel. This prevents gate current from
flowing, reducing power usage.
When the Gate is positive voltage ,it allows
electrons to flow from drain to source .In this
case transistor is on.
15
How a CMOS transistor works?
N-channel P-channel MOSFETs can be combined in
pairs with a common gate .
When Gate (input) is high ,electrons can flow in
N-channel easily . So output becomes low.
(opposite of input)
When Gate (input) is low ,holes can flow in
P-channel easily. So output becomes high.
(opposite of input)
16
SWITCHING

• The modern computer is a digital and electronic
  device.
• Runs on flow of electrons - movement of electrons
  from outer valence shells on atoms
• Requires force/energy to pull an electron out of
  a shell - Electro-motive force (EMF) - Voltage
• How tightly the electrons are held determines how
  much voltage is needed and is quantified as
  resistance
• Number of Electrons flowing is quantified as
  Amperes

17

• Computers are electronic switching devices
• Voltage source (battery)
• Meter to detect voltage differential

0
5
Short Circuit large voltage flow, but no voltage
differential
18
Digital Switch - Transistor

• Computers are constructed from transistors
• Transistor are used as on-off switches (0-off,
  1-on), hence binary

0
5
19
Transistor controlling the circuit
20
Measuring Output before the transistor

• Acts as an invertor
• No voltage on the input causes the meter to read
  5 volts
• A voltage on the input causes the meter to read
  zero

0
5
21
NAND Not AND

• A B Out
• 0 0 1
• 0 1 1
• 1 0 1
• 1 1 0