View
167
Download
0
Category
Tags:
Preview:
DESCRIPTION
23.transistor
Citation preview
Author : Khairi
TRANSISTOR
Transistor is made of semiconductor material
Transistor is produced by attaching n-type semiconductor and p-type semiconductor
Transistor is used as electronic switching or current amplifier
There two types of transistor ; npn transistor and pnp transistor
Author : Khairi
TRANSISTOR
n p n attachment
n p n
p n p attachment
p n p
npn transistor
pnp transistor
PRODUCING A TRANSISTOR
Author : Khairi
TERMINALS OF TRANSISTOR
n p n
npn transistor
collector,C
base,B
emitter,E
SYMBOLC
B
E
TRANSISTOR
Author : Khairi
p n p
pnp transistor
collector,C
base,B
emitter,E
SYMBOLC
B
E
TRANSISTOR
TERMINALS OF TRANSISTOR
Author : Khairi
AMPLIFIER
Amplifier is used to amplified current
Amplifier is widely used as audio amplifier such as in radio and television
Transistor is used to build an amplifier
TRANSISTOR
Author : Khairi
Connection of npn transistor as an amplifier
RB
Base circuit
BE junctionForward biased
B
E
Collector circuitBC junction
Reverse biased
C
TRANSISTOR
C ----- +
B ----- +
- --- E --- -
Author : Khairi
RBB
E
C
When base current ,IB flows
IB
Collector current, IC flows through transistor
IC
Emitter current,IE is produced
IE
IE = IB + IC
A bigger magnitude of current produced
TRANSISTOR
Connection of npn transistor as an amplifier
Author : Khairi
There are 2 types of automatic controlled switch :
1. Light controlled automatic switch
e.g. Street lights will be switched on at night and will be switched off at daytime automatically
2. Heat controlled automatic switch
e.g. Fire alarm will sound automatically when the fire occurs
AUTOMATIC SWITCH
Author : Khairi
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
Vi
R1
R2VB
VB = ViR1 + R2
R2
Value of VB (potential difference across R2) is very important in determining whether the transistoris activated(turn on) or not activated(turn off)Value of VB is depending on R2 and R1
AUTOMATIC SWITCH
Author : Khairi
VB = ViR1 + R2
R2
If R2 is high - VB becomes high - transistor is activated
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
Vi
R1
R2
VB
Author : Khairi
VB = ViR1 + R2
R2
If R2 is high - VB becomes high - transistor is activated
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
Vi
R1
R2
VB
Author : Khairi
VB = ViR1 + R2
R2
If R2 is low - VB becomes low – transistor is not activated
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
Vi
R1
R2
VB
Author : Khairi
LIGHT CONTROLLED AUTOMATIC SWITCH
LDR
Light controlled automatic switch uses light dependent resistor (LDR)
Resistance of LDR is high in the darknessand low in bright light
Dark --- R highLight ---- R low
AUTOMATIC SWITCH
Author : Khairi
LDR
Light bulb
RB
R1
R2
AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH
Author : Khairi
LDR
Lightbulb
RB
R1
R2
In bright light Resistance of LDR is low
Potential difference of VB is low
VB
Based current,IB is smallIB
Transistor is not activated
IC does not flow
Light bulb does not light up
VB = ViR1 + R2
R2
AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH
Author : Khairi
LDR
Lightbulb
RB
R1
R2
In the darkness
Resistance of LDR is high
Potential difference of VB is high
VB
Base current,IB is bigIB
Transistor is activated
IC flows through transistor
IC
Light bulb lights up
VB = ViR1 + R2
R2
AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH
Author : Khairi
EXERCISE
LDR Lightbulb
RB
R1
R2
Explain what happen in the darkness and bright light situation
VB = ViR1 + R2
R2
Bright light, R1 low, VB high,
IC flows through transistor and light bulb lights up
IB big, transistor is activated,
AUTOMATIC SWITCH
Author : Khairi
LDR Lightbulb
RB
R1
R2
VB = ViR1 + R2
R2
Dark, R1 high, VB low,
IC does not flow through transistor and light bulb does not light up
IB small, transistor is not activated,
AUTOMATIC SWITCH
EXERCISE
Explain what happen in the darkness and bright light situation
Author : Khairi
HEAT CONTROLLED AUTOMATIC SWITCH
thermistorHeat controlled automatic switch uses thermistor
Resistance of thermistor is low when the temperature is highResistance of thermistor is high when the temperature is low
AUTOMATIC SWITCH
Author : Khairi
thermistor
RB
R1
R2
siren
AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH
Author : Khairi
thermistor
RB
R1
R2
siren
VB = ViR1 + R2
R2
High temperature
Resistance of thermistor is low
R1 low
VB big
VB IB big
IB
Transistor is activated
IC flows through transistor
IC
Siren sounds
AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH
Author : Khairi
thermistor
RB
R1
R2
siren
VB = ViR1 + R2
R2
Low temperature
Resistance of thermistor is high
R1 high
VB small
VB IB small
IB
Transistor is not activated
IC does not flow
Siren does not sound
AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH
Author : Khairi
EXERCISE
thermistor
RB
R1
R2
siren
Vi = 6.0 V
10 kΩ
Siren is set to make a sound when the potential difference across R2 is 4.0 V.
Determine the resistance of thermistor that enable the siren to sound
AUTOMATIC SWITCH
Author : Khairi
thermistor
RB
R1
R2
siren
Vi = 6.0 V
10 kΩ
VB = ViR1 + R2
R2 4 = 6 [10 000/(R1 + 10 000)] 4 = 60 000/(R1 + 10 000) R1 + 10 000 = 60 000/4 R1 = 5 kΩ
AUTOMATIC SWITCH
Siren is set to make a sound when the potential difference across R2 is 4.0 V.
EXERCISE
Author : Khairi
thermistor
RB
R1
R2
siren
Vi = 6.0 V
10 kΩSiren is set to make a sound when the potential difference across R2is 2.0 V.If in a fire,the resistance of thermistor becomes 20 kΩ.Will the siren sound ?
VB = ViR1 + R2
R2
VB = 6 [10 000/(20 000 + 10 000)]
VB = 2 V VB = 2.0 VSiren sounds
AUTOMATIC SWITCH
EXERCISE
Author : Khairi
thermistor
R1
R2
siren
Vi = 6.0 V
Modify the circuit to control a fan which turn on when temperature is high.Explain how your circuit works.
AUTOMATIC SWITCH
EXERCISE
Author : Khairi
thermistorR2
R1
Vi = 6.0 V
AUTOMATIC SWITCH
EXERCISE
Thermistor is interchange with R1
Siren is replaced with relay
Relay is connected to fan and 240 V ac power supply
fan
240 Vac
Author : Khairi
thermistorR2
R1
Vi = 6.0 V
AUTOMATIC SWITCH
EXERCISE
When temperature is high,the resistance of thermistor becomes low.
Potential difference across R1 becomes high.
IC flows and relay is turned on.
fan
240 Vac
IB flows and transistor is activated.
Relay switches on the secondary circuit of 240 V ac and fan.
Author : Khairi
Which of the following is correct about the transistor ?
Electrode P Type of transistor
A. Emitter pnp
B. collector pnp
C. Emitter npn
D. Collector npn
PAST YEARS QUESTIONPAST YEARS QUESTION
Author : Khairi
In which circuit does the bulb light up ?
RulesC --- +B --- +
- --- E --- -
PAST YEARS QUESTIONPAST YEARS QUESTION
Author : Khairi
What change should be done to light up the bulb during the day time ?
A. Reverse the terminal of battery
B. Interchange R1 and R2
C. Replace the npn transistor with a pnp transistor
D. Replace resistor R3 with a resistor of lower resistance
PAST YEARS QUESTIONPAST YEARS QUESTION
Author : Khairi
Which circuit will the light-emitting diode (LED) light up when the switch is on ?
A. B. C. D.
RulesC --- +B --- +
- --- E --- -
PAST YEARS QUESTIONPAST YEARS QUESTION
Author : Khairi
a. State the relationship between resistance and intensity of light received by the light dependent resistor
Resistance is inversely proportional to intensity of light
b. Complete the diagram,if the motor works when there is light
PAST YEARS QUESTIONPAST YEARS QUESTION
Author : Khairi
c. What is the function of relay,R in the circuit ?
To switch on the secondary circuit
PAST YEARS QUESTIONPAST YEARS QUESTION
Author : Khairi
d. Explain how the circuit works.
1. When there is light,resistance of LDR is low
2. Base voltage become high
3. Base current flows and transistor is activated
4. Collector current flows and relay function
5. Relay switch on the secondary circuit
PAST YEARS QUESTIONPAST YEARS QUESTION
Author : Khairi
Modify the circuit in the diagram to enable a fan to switch on automatically when the room is hot.Explain your modification.
PAST YEARS QUESTIONPAST YEARS QUESTION
Author : Khairi
Modified circuit as shown in the diagram.
1. When temperature increases,the resistance of thermistor decreased.
2. Potential across R1 becomes high.
3. Base current flows and transistor is activated.
4. Collector current flows and relay switch on the secondary circuit which contain high voltage power supply and fan connected in series.
PAST YEARS QUESTIONPAST YEARS QUESTION
Recommended