Team No. 1:
Sebastian Strzelak
Maciek Urbański
Experiment No. 7
The Power Amplifier
Table of data
R0 [Ω]
10
RS [Ω]
5600
βbc211
150
Class
AB
βbc313
110
Simplified schematic diagram of the circuit
+15V
UZAS(+) = +5V
I1
IB1
D1
RB1
D2
RB2
Rs = 5,6k
SIN
T1
BC211
EP
C
eS
IB2
I2
T2
BC211
R0 = 10
EP = 2.5V
-15V
1
Static characteristics of BC211 and BC313
Type
BC211
BC313
Polarization
NPN
PNP
VCEmax
40V
40V
ICmax
1A
1A
Ptot
800mW
800mW
Amplification
40min
40min
es,pp=
Block diagram of a circuit used for simultaneous observation of signals
What to do to display the transfer characteristic between any two different
points of the amplifier?
Expression for the output stage efficiency factor η looks as follows:
η=P0/Ps
P0 – power dissipated at the load
Ps – power delivered by all supply lines
2
Laboratory session
Settings:
 the output stage configuration as in the simplified scheme,
 set the feedback loop selector switch to “741”,
 observe signals es and vout,
 adjust signal generator frequency to 1kHz,
 adjust its amplitude to get an output signal vout with maximal amplitude, but
without saturation,
 note observed value of vs,pp:
vs,pp=
Can symbols es and vs be used in this case interchangeably?
Why the value obtained from measurement differs from the one calculated in
the project?
Output stage distortions:
 all observations and measurements in this section should be carried with
R0=10 [Ω], f~1kHz and for constant output peak-to-peak voltage value
vout,pp=1,6 [V]. Both oscilloscope input modes should be set to “DC”,
 set the “R7<->R8” switch for the lower Rs value,
 display and draw transfer characteristics VR0=f(V741) in one figure and the
shapes of the output voltage in the other one, for both positions of the
“AB<->C” switch,
 observed distortions are called “cross-over” distortions,
 remember to keep vout,pp=1,6 [V].
3
Figures
VR0=f(V741) characteristics for two positions
of “AB<->C” switch.
Output voltage shapes for two positions
of ”AB<->C” switch.
In what case the distortions are smaller and at what cost?
4
Class „C” output stage
 force the output stage to class „C”,
 display and draw the transfer characteristics VR0=f(V741), output voltage shape
and shape of the voltage at point B for both positions of the R7R8 switch.
Switch at position R7:
Transfer characteristics
Output voltage shape
Voltage at point B
5
Switch at position R8:
Transfer characteristics
Output voltage shape
Voltage at point B
Comments
6
Negative feedback effects
 set “R7R8” voltage to smaller value,
 adjust the signal generator to have et the output Vout,pp=1,6V at f=1kHz,
 set the feedback switch to “741”,
 draw shapes of signals at the output of the signal generator, at the point “741”
and at the output,
 measure THD level,
 switch on the main feedback loop (feedback switch at position “R0”),
 adjust the signal generator to have Vout,pp=1,6V,
 draw the shapes as before,
 measure THD level.
Figures
Signal generator output
Voltage at point „741” – feedback switch at „741”
7
Voltage at point „741” – feedback switch at „R0”
Voltage at the output – feedback switch at „741”
Voltage at point „741” – feedback switch at „R0”
THD (switch at 741) = .................... %
THD (switch at R0) = .................... %
Comments
8
Dynamic characteristics
 set output stage configuration as specified: R0=10 Ω, Rs = 560 Ohm, class AB,
feedback switch at “741”, f = 1kHz,
 measure Vout,pp, THD, Iout,av versus Vout741,pp at the output of the ua741 IC,
 calculate: output power Pout, supply power Pz and efficiency η.
Measurements and results
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3
4
5
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7
8
9
10
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15
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