Transcript Document

Electronics - Revision
1. Copy and complete the three blocks which make up an electronic
system.
2. In electronics, it is the voltage that is important. Draw voltage time
graphs for analogue and digital systems.
3. Draw a block diagram for a public address system.
4. Why do we need an amplifier in the system ?
5. What is the voltage gain of an amplifier ?
6. What is the gain of an amplifier which has input voltage of 2V and
output voltage of 8V ?
7. What does an amplifier do to the frequency of the signal ?
Tutorial Questions page 72 Qu 1 to 6
Operational amplifiers (op amps) are multistage amplifiers and can
give high gain with very little distortion. Fortunately we don’t have
to know how they operate – just how they can be used.
Circuit symbol
Inverting input
_
Non-inverting input
+
output
Connecting the power supply
2 x 9V
batteries
Vout
Adjust the offset control until Vout = 0 this balances the batteries
The Op Amp
– Inverting Mode, d.c.
Vo
V1
+Vsupply
Rf
Feedback
resistor
R1
-
V1
0V
+
Vo
The Op Amp
– Inverting Mode, d.c.
Vo
V1
V1(V) VO(V) Vgain Rf/R1
R1()
Rf ()
100k
100k
0.5
10k
100k
0.5
100k
10k
0.5
100k
1M
0.5
1M
100k
0.5
10k
1M
0.5
Op Amp in inverting mode
Vo = - Rf V1
R1
Tutorial Questions page 74 Qu 9
Revision Ex 5.1
Uses of an op amp in inverting mode
Inverting (changing +/-)
Multiplication (amplifying)
Addition
Binary/digital converter
Making square waves
Tutorial question p73 Qu 8, 10 to15
Revision Ex 5.2 and 5.3
Try the experiments
showing these.
Op Amp Differential Mode
R1
Rf
V
out
R2
+Vsupply
Rf
+Vsupply
R1
-
V2
V1 R2
+
R3
Vo
R1 = R2 = R3 = Rf = 10k
V1
V2
Vo
0.6
0.4
- 0.2
1.0
0.4
-0.6
0.3
1.0
0.7
0.6
1.0
0.4
1.8
0.6
-1.2
Vo = V2 – V1
R1 = R2 = 10k
Rf = R3 = 100k
V1
V2
1.0
1.1
2.0
2.2
0.6
0.8
0.7
0.5
Vo
Op amp in the differential mode.
For higher Rf R3
Vo = (V2 – V1) Rf
R1
R2
R1
The op amp finds the difference between the two inputs ie subtracts
them. It then amplifies this difference.
Tutorial questions p 76 Qus 16 to 21
Rev Qus Ex 5.4 and 5.6
b
NPN transistor
c connected
to +Vs
I
+0.7 V
e at 0V
b base
c collector
e emmitter
PNP Transistor
c connected to
- Vs
b
I
- 0.7V
e at 0V