AN6077 INTERSIL [Intersil Corporation], AN6077 Datasheet - Page 5

• Manufacturer Part Number: AN6077
• Description: An IC Operational Transconductance Amplifier With Power Capability
• Manufacturer: INTERSIL [Intersil Corporation]

Power Amplifier Using the CA3094
A complete power amplifier using the CA3094 and three
additional transistors is shown schematically in Figure 14.
The amplifier is shown in a single-channel configuration, but
power supply values are designed to support a minimum of
two channels. The output section comprises Q
complementary epitaxial units connected in the familiar
“bootstrap” arrangement. Capacitor C
drive for Q
circuit can be operated from a single power supply as well as
from a split supply as shown in Figure 15. The changes
required for 14.4V operation with a 3.2 speaker are also
indicated in the diagram.
The amplifier may also be modified to accept input from
ceramic phonograph cartridges. For standard inputs
(equalizer preamplifiers, tuners, etc.) C
250k , and R
inputs, C
C
Output Biasing
Instead of the usual two-diode arrangement for establishing
idling currents in Q
used. This method of biasing establishes the voltage between
the base of Q
base to emitter voltage of a single transistor while maintaining a
low variational impedance between its collector and emitter
(see Appendix A). If transistor Q
thermal contact with the output units, the operating temperature
of the heat sink forces the V
with heat-sink temperature. The voltage bias between the
bases of Q
and tends to keep the idling current in Q
2
is removed.
FIGURE 13. A SYSTEM IN WHICH TONE CONTROLS ARE IMPLICIT IN THE FEEDBACK CIRCUIT OF THE POWER AMPLIFIER
E
SIG
PICKUP
E
PICKUP
1
SIG
=1mV
1
1
is 0.0047 F, R
E
and Q
during positive excursions of the output. The
=1mV
N
1
2
AT INPUT = 1 x 10
and the base of Q
and C
A
EQUALIZER
REF
FIGURE 12. BLOCK DIAGRAM OF A SYSTEM USING A “LOSSER” TYPE TONE CONTROL CIRCUIT
1
2
varies inversely with heat sink temperature
and Q
= 32dB
2
are omitted. For ceramic-cartridge
1
2
E
, a “V
be
is 2.5M , and the jumper across
N
4-5
AT INPUT = 1 x 10
-6
of Q
E
A
EQUALIZER
3
N
REF
be
2
is mounted in intimate
= 40 x 10
E
at a constant multiple of the
3
Multiplier”, transistor Q
SIG
= 32dB
up and down inversely
3
= 40mV
1
1
provides added base
-6
and Q
is 0.047 F, R
CONTROLS
-6
E
N
TONE
-20dB
2
1
= 40 x 10
constant.
E
TOTAL GAIN = 72dB
and Q
SIG
Application Note 6077
E
= 40mV
N
1
= 4 x 10
2
-6
E
,
is
SIG
3
, is
CONTROLS
= 4mV
VOLUME
-6
CONTROLS
VOLUME
E
N
= 40 x 10
E
A bias arrangement that can be accomplished at lower cost
than those already described replaces the V
1N5391 diode in series with an 8.2 resistor. This arrangement
does not provide the degree of bias stability of the V
multiplier, but is adequate for many applications.
Tone-Controls
The tone controls, the essential elements of the feedback
system, are located in two sets of parallel paths. The bass
network includes R
from the feedback network so that the DC gain from input to the
feedback takeoff point is unity. The residual DC output voltage
at the speaker terminals is then
where R
then
The treble network consists of R
and C
and boost, respectively. The boost limit is useful in curtailing
heating due to finite turn-off time in the output units. The limit is
also desirable when there are tape recorders nearby. The cut
limit aids the stability of the amplifier by cutting the loop gain at
higher frequencies where phase shifts become significant.
In cases in which absolute stability under all load conditions is
required, it may be necessary to insert a small inductor in the
output lead to isolate the circuit from capacitive loads. A 3 H
inductor (1A) in parallel with a 22 resistor is adequate. The
derivation of circuit constants is shown in Appendix B. Curves
of control action versus electrical rotation are also given
I
------------ -
E
ABC
SIG
R
2
N
1
= 4 x 10
R
-------------------------- - I
E
= 40mV
SIG
11
10
=
-6
R
+
–
. Resistors R
12
= 4mV
1
--------------------------------- -
BACK TONE CONTROLS
R
AMPLIFIER WITH FEED-
-6
V
is the source resistance. The input bias current is
12
CC
E
E
E
E
E
E
2 R
E
A
N
O
O
N
N
N
N
E
TOTAL
–
ABC
= 4mV AT MIN VOL
= 0.5mV AT MIN VOL
N
BUFFER STAGE
AT INPUT = 5 x 10
=
V
=
6
= 5 x 10
BE
3
6.23 x 10
4.03 x 10
, R
= 60dB
7
4
and R
4
4
A
, R
-6
TOTAL
-3
-3
5
E
, C
= 990 AT MAX VOL
9
= 640 AT MAX VOL
N
= 60dB
limit the maximum available cut
= 4.03 x 10
4
-6
7
, and C
, R
E
O
8
, R
= 4V
POWER
5
AMP
9
-3
. C
, R
E
N
6
be
10
= 6.23 x 10
blocks the DC
, C
multiplier with a
E
O
7
SPEAKER
, C
= 4V
be
8
8
-3
, C
.
9
,