Diode and transistor

semoconductor

1. Semiconductor
Diode
NURUL FADHILAH BINTI ALIAS | MRSMALOR GAJAH

2. MRSMPARIT 2
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This Photoby Unknown Author is licensed under CC BY-SA

3. Semiconductor diode
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4. p-n junction (Semiconductor diode)
4
p-type n-type
Positive hole Negative
electron
Symbol
p-n junction
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5. Diode in Forward-biased
5
p-type of the diode is connected
to ………………….
n-type is connected to the
…………………… of the
battery.
Electron moves across the p-n
junction
Current flow through the circuit
Diode is forward biased
+ -
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6. Diode in Reverse-biased
p-type of the diode is connected to
………………….
n-type is connected to the
…………………… of the battery.
Electrons and holes pulled away from
the p-n junction
No Current flow through the circuit
Diode is reverse biased
6
- +
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7. Diode allows current flow in one direction
only

8. Graph : current vsvoltage
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9. Diode as rectifier
A.C to D.C.
Rectification is a processto convert an alternating current into
a direct currentby using a diode.
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10. Half-wave rectifier
10
•First half –cycle, diode is forward biased
•Current flow through the circuit
•Second half-cycle, diode is reversed biased
•No current flow
•Diode as half-wave rectifier
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12. Full -wave rectifier
12
•First half –cycle, diode ____________are forward biased
•Current flow through the circuit
•Second half-cycle, diode ___________are forward biased
•Current flow through the circuit
•Diode as full -wave rectifier
To CRO
a
.
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15. Capacitor
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16. MRSMAG #AGNO1 16

17. Capacitor smoothing
17
Acts as a current regulatoror smoother
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18. storethe electricalenergyand
give thisenergyagain to the circuit when necessary.
In other words, it charges and discharges the electric charge stored in it.
Other functions of a capacitor are as follows:
◦It blocks the flow of DC and
◦permits the flow of AC.
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Capacitor:

19. 19
To CRO
a
To CRO
a.
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As the output voltage increases, the capacitor is charged,
When the output voltage falls back to zero, the capacitor releases its
charge (discharge current)
Steady output voltage is maintained across a resistor

20. Transistor
NURUL FADHILAH BINTI ALIAS | MRSMALOR GAJAH

22. TRANSISTOR
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24. extra
The arrow in thesymbolindicates the direction of flow of
conventional current in the emitter with forward biasing
applied to the emitter-base junction.
Definition:The transistor is asemiconductor devicewhich
transfers a weak signal from low resistance circuit to high
resistance circuit. The wordstransmeantransfer
propertyandistormeanresistance property offered to the
junctions.In other words, it is a switching device which
regulates and amplify the electrical signal likes voltage or
current.
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25. TRANSISTOR
I
Base
current, ᶙA
Collector
current,
mA
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27. I
B in
ᶙA and
I
cin mA

30. Sound amplifier system
I
B
I
c
Talk
(slow
sound)
Loud
sound
heard
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31. Current Amplifier
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!"#$%&'(=
*
!
*
"
=
= 1000
I
c= 1000I
B
Collector
current, I
c/ mA
Base current , I
B /ᶙA
1×10
#$
1
%
10
#&

32. Current Amplifier
Collector current = 1000 x base current
I
c= 1000 x I
B
Slow sound amplified by transistor –
become louder sound that spread out
Through the loudspeaker.
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33. When the switch is open, bulb L
1does not light up as the circuit
is _______________
the base current, I
Bis ____________.
Bulb L
2does not light up although the collector circuit is
complete because the transistor is ___________________ on
and the collector current, Icis zero.
Close the switch, bulb L
1is dim ∵ R
Bhas a high resistance
The base current, I
Bis very small.
L
2lights up brightly ∵the collector current, Icis larger than I
B.
A small I
B can produce a minimum base voltage, V
BEto turn
onthe collector circuit.
The I
Bcan control the flow of the Ic.
This enables the transistor to act as a switch.
The resistance at the base circuit, R
Bis large to limit the I
B
So that the transistor will not become too hot and burn.

37. Light-dependent resistor (LDR) is a type of resistor.
Its resistance changes with the ________________ of light.
The LDR resistance value is ______________ when the light
intensity is low and vice versa.
In the dark, LDR resistance is very ____________________.

40. A thermistor is a resistor.
Its whose resistance changes with its surrounding _______________.
The resistance is ________________ under room temperature conditions
(low temperature).
As the surrounding temperature increases, the resistance becomes
____________ and voltage across the thermistor ________________.

41. Transistor
as a switch
To make the bulb lights up at night,
you have to interchange the position of
LDR and resistor 10 kΩ
Because, at night, resistance of LDR
increases
Then no base current, I
B =0 , no I
B flow
to transistor
Therefore , no collector current , I
c =0 ,
no I
cflow to transistor also
Transistor is off

42. Transistor
as a switch
Example :
1. transistor is used as a switch for
streetlamp –
At night , the streetlamps turn on
Daytime, the streetlamps turn off
2. transistor also can be used to
activate fire alarm. Discuss
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