1. Transistor

4. BJT Transistors: NPN Transistor PNP 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 v1>0.7 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
backward
Forward

6. Transistors have three terminals:
Collector
Base
Emitter
Active: Always on
Ic=BIb
Saturation :Ic=Isaturation
On as a switch
Transistors work in 3 regions
Off :Ic=0
Off as a switch

7. Transistor as a Switch Transistors can be used as switches.1
Transistors can either
conduct or not conduct current.2
ie, transistors can either be on or off.2

8. Transistor Switching Example15
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.
LED = Off.
Cover LDR.
RLDR .
VLDR .
Transistor switches on.
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 (P=V*I).

11. Amplifier example: Example: Input Amplitude =0.2v Output amplitude=10v
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 amplitude=10v
Gain=10/0.2=50

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. The modern computer is a digital and electronic device.
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 5 5
Short Circuit
large voltage flow, but no voltage differential 5

18. Digital Switch - Transistor
Computers are constructed from transistors
Transistor are used as on-off switches (0-off, 1-on), hence binary 5 5

19. Transistor controlling the circuit5 5

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 5 5

21. NAND – Not AND
A B Out
0 0 1
0 1 1
1 0 1
1 1 0 5 A B 5 A B