PBL 385 70
The fourth DC-supply V
has an
enough the current capability can be
increased by connecting the outputs of
DC1andDC2inparallel.Thedrivingcapa-
city will increase almost to the double but
the voltage drop across the necessary
series resistor will go upp thus limiting the
useful current.
The voltage level that is common for
both of these supplies is set by DC2. DC2
isa highprecision,referencequalitysupply
that can be used to supply microphones,
optocouplersetc.Theinternallysetvoltage
canbeadjustedwithexternalresitorswhen
needed (RDC1 and RDC2).
The circuit has further two temperature
andlinecurrentcompensatedDCsupplies
DC1 and DC2. DC1 is a voltage supply for
supplying diallers, can also be used for
memory back up because it does not leak
any current back into the circuit. Typical
voltage 2.4V down to line voltage of 4.1V,
in case the line voltage is lower than 4.1V
calculate ; actual line voltage minus 1.9V.
In order to prevent noise entering the line,
aseriesresistorandareservoircapaciotor
isrecommendedinseriesatthisoutput.The
output current is given to be 2 mA in the
specification. In case this would not be
PA
advantage that it does not influence the
circuits DC characteristics even at high
current drain. The supply has a floating
ground reference in the plus line in order to
minimize RFI problems and is used to
supply the power amplifier of a handsfree
telephone(PBL3881,38811---14). These
circuits have a current controlled charging
of the supply capacitor and the control
signal is taken across the resistor R6. In
case a monitor amplifier is required where
the ground reference is hardly necessary,
it can be supplied from V
in fig. 17.
or like in alt. b
PA
Hook
switch
I
L
+Line
1
R3
RLine
+
PA
PBL 38 570
1-10M
V
V
4
Ref.
1.2V
V
+C
+
-
0-470Ω
8
+
+
-
V
DC1
DC2
V
L
T
b.
V
9
0-470Ω
15k
R
DC1
R
Feed
7
Lim
V
Mon.
ƒ
a.
15k
14
R
DC2
+
+
+
3
4.7-47
2
4.7-47
µF
µF
V
exh.
+
+
C1
R6
-Line
a. Supply arrangement for a handsfree system power amplifier. For ex. PBL 38811---14
b. Supply arrangement for a call monitor cicuit.
Figure 17. DC-supplies
1-10M
1
Hook switch
VDD
PBL 385 70
10
17
AD
AM
100Ω
CMOS
AR
AT
220Ω
MIC.
Rec.
1µF
1µF
DIALLER
MUTE 9
12
13
10n
18
4
Telephone line
DTMF 12
220Ω
DC-supply
9
+
GND
33k
14
8
7
5
6
11
3
2
15
16
10Ω
47n
100Ω
100Ω
680p
910Ω
6.2k
62k
1
4
7
2
5
8
0
3
6
9
#
100n
18k
22k
3.3n
560Ω
910Ω
*
*
Voltage
adjust
11k
10Ω
75Ω
15n
15V
+
+
*
+
11k
47µF
47µF
47µF
100n
Figure 18. Typical DTMF tone dialling telephone. 18-pin DIP package. * marked components for gain regulation.
11
ERICSSON [ ERICSSON ]
