Transcript automatic switch

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
PRODUCING A TRANSISTOR
n p n attachment
n
p
n
npn transistor
n
p
pnp transistor
p n p attachment
p
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TRANSISTOR
TERMINALS OF TRANSISTOR
npn transistor
collector,C
n
p
n
emitter,E
C
SYMBOL
base,B
B
E
Author : Khairi
TRANSISTOR
TERMINALS OF TRANSISTOR
pnp transistor
collector,C
p
n
p
emitter,E
SYMBOL
C
base,B
B
E
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TRANSISTOR
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
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TRANSISTOR
Connection of npn transistor as an amplifier
C ----- +
Collector circuit
B ----- +
RB
BC junction
Reverse biased
C
B
Base circuit
E
BE junction - --- E --- Forward biased
Author : Khairi
TRANSISTOR
Connection of npn transistor as an amplifier
IC
C
RB
B
IB
E
IE
When base current ,IB flows
Collector current, IC flows through transistor
Emitter current,IE is produced
IE = IB + IC
A bigger magnitude of current produced
Author : Khairi
AUTOMATIC SWITCH
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
Author : Khairi
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
R1
Vi
R2
VB
VB = Vi
R2
R1 + R2
Value of VB (potential difference across R2) is very important in
determining whether the transistor
is activated(turn on) or not activated(turn off)
Value of VB is depending on R2 and R1
Author : Khairi
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
R1
Vi
R2
VB
VB = Vi
R2
R1 + R2
If R2 is high - VB becomes high - transistor is activated
Author : Khairi
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
R1
Vi
R2
VB
VB = Vi
R2
R1 + R2
If R2 is high - VB becomes high - transistor is activated
Author : Khairi
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
R1
Vi
R2
VB
VB = Vi
R2
R1 + R2
If R2 is low - VB becomes low – transistor is not activated
Author : Khairi
AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH
Light controlled automatic switch uses light dependent resistor (LDR)
Resistance of LDR is high in the darkness
and low in bright light
LDR
Dark --- R high
Light ---- R low
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AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH
Light bulb
R1
RB
R2
LDR
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AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH
In bright light
Light
bulb
R1
RB
R2
LDR
IB
 Resistance of LDR is low
 Potential difference of VB is low
 Based current,IB is small
 Transistor is not activated
VB
 IC does not flow
 Light bulb does not light up
VB = Vi
R2
R1 + R2
Author : Khairi
AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH
In the darkness
IC
R1
RB
R2
LDR
IB
Light
bulb
 Resistance of LDR is high
 Potential difference of VB is high
 Base current,IB is big
 Transistor is activated
VB
 IC flows through transistor
 Light bulb lights up
VB = Vi
R2
R1 + R2
Author : Khairi
AUTOMATIC SWITCH
EXERCISE
R1
Light
bulb
LDR
VB = Vi
RB
R2
R1 + R2
R2
Explain what happen in the darkness and bright light situation
Bright light,
R1 low, VB high, IB big, transistor is activated,
IC flows through transistor and light bulb lights up
Author : Khairi
AUTOMATIC SWITCH
EXERCISE
R1
Light
bulb
LDR
VB = Vi
RB
R2
R1 + R2
R2
Explain what happen in the darkness and bright light situation
Dark, R1 high, VB low,
IB small, transistor is not activated,
IC does not flow through transistor and light bulb does not light up
Author : Khairi
AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH
Heat controlled automatic switch uses thermistor
thermistor
Resistance of thermistor is low when the temperature is high
Resistance of thermistor is high when the temperature is low
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AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH
R1
siren
thermistor
RB
R2
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AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH
High temperature
IC
R1
thermistor
RB
R2
siren
 Resistance of thermistor is low
 R1 low
IB
 VB big
 IB big
VB
 Transistor is activated
 IC flows through transistor
VB = Vi
R2
 Siren sounds
R1 + R2
Author : Khairi
AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH
Low temperature
R1
RB
R2
siren
thermistor
 Resistance of thermistor is high
 R1 high
IB
 VB small
 IB small
VB
 Transistor is not activated
 IC does not flow
VB = Vi
R2
 Siren does not sound
R1 + R2
Author : Khairi
AUTOMATIC SWITCH
EXERCISE
R1
thermistor
RB
siren
Vi = 6.0 V
R2
10 kW
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
Author : Khairi
AUTOMATIC SWITCH
EXERCISE
R1
thermistor
RB
siren
Vi = 6.0 V
R2
10 kW
Siren is set to make a sound when the potential difference across R2
is 4.0 V.
VB = Vi
R2
R1 + R2
4 = 6 [10 000/(R1 + 10 000)]
4 = 60 000/(R1 + 10 000)
R1 + 10 000 = 60 000/4
R1 = 5 kW
Author : Khairi
AUTOMATIC SWITCH
EXERCISE
R1
VB = Vi
R2
R1 + R2
siren
thermistor
RB
Vi = 6.0 V
R2
10 kW
Siren is set to make a sound when the potential difference across R2
is 2.0 V.If in a fire,the resistance of thermistor becomes 20 kW.
Will the siren sound ?
VB = 6 [10 000/(20 000 + 10 000)]
VB = 2 V
VB = 2.0 V
Siren sounds
Author : Khairi
AUTOMATIC SWITCH
EXERCISE
siren
R1
Vi = 6.0 V
R2
thermistor
Modify the circuit to control a fan which turn on when temperature is high.
Explain how your circuit works.
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AUTOMATIC SWITCH
EXERCISE
R2
thermistor
fan
Vi = 6.0 V
240 V
ac
R1
Thermistor is interchange with R1
Siren is replaced with relay
Relay is connected to fan and 240 V ac power supply
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AUTOMATIC SWITCH
EXERCISE
R2
thermistor
fan
Vi = 6.0 V
240 V
ac
R1
 When temperature is high,the resistance of thermistor becomes low.
 Potential difference across R1 becomes high.
 IB flows and transistor is activated.
 IC flows and relay is turned on.
 Relay switches on the secondary circuit of 240 V ac and fan.
Author : Khairi
PAST YEARS QUESTION
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
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PAST YEARS QUESTION
In which circuit does the bulb light up ?
Rules
C --- +
B --- +
- --- E --- -
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PAST YEARS QUESTION
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
Author : Khairi
PAST YEARS QUESTION
Which circuit will the light-emitting diode (LED) light up when the
switch is on ?
A.
B.
C.
D.
Rules
C --- +
B --- +
- --- E --- Author : Khairi
PAST YEARS QUESTION
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
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PAST YEARS QUESTION
c. What is the function of relay,R in the circuit ?
To switch on the secondary circuit
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PAST YEARS QUESTION
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
Author : Khairi
PAST YEARS QUESTION
Modify the circuit in the diagram to enable a fan to switch on
automatically when the room is hot.Explain your modification.
Author : Khairi
PAST YEARS QUESTION
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.
Author : Khairi