PBL38573 Просмотр технического описания (PDF) - Ericsson

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PBL38573

Speech Circuit for constant current feeding systems

Ericsson  

PBL 385 73

Power supplies DCO and V+C.

(See fig.18)

PBL 385 73 generates its own DC

supply V+C dependent of line current with

an internal shunt regulator. This regulator

senses the line voltage VL via R3 and line

current via R6 in order to set the correct

V+C so the circuit can generate the required

DC characteristic for a given line resistance

RLine and the line feeding data of the

exchange. A decoupling capacitor is

needed between pins +C and -L. The V+C

supply changes its voltage linearly with the

line current. It can be used to feed an

electret microphone. Caution must be ta-

ken though not to drain too much current

out of this output because it will affect the

internal quick start circuit by locking itself

into active state. (max. permissible current

drain 700µA)

Care has to be taken when deci-

ding the resistance value of R3. See fig.6.

All resistances that are applied from +Line

to ground (-Line) will be in parallel, forming

the real impedance towards the line. This

will sometimes result in, that the ohmic

value of R3 is increased in order to comply

to the impedance specification towards the

line. The speech circuit sinks ≈ 1mA into

pin 4, which means that the working voltage

for the speech function V+ will decrease

with increasing R3, thus starving in the end

the circuit of its working voltage . This

dependency is often falsely taken as a sign

PBL 385 73

1.2V

+

-

15k

15k

Hook

switch

1

+Line

7

0-470Ω

DC0

6V

11

1-10M

+ 4.7-47

µF

VDC0

-Line

Figure 18. DC - supply for external load.

of that the circuit does not work down to the

low line current specified, but in fact it is the

working voltage at pin 4 that has become

too low. It is obvious that this problem is

also connected into what kind of DC-

characteristic is set. See fig. 8.

The circuit has further a temperature

and line current compensated DC supply

DC0 . DC0 is a voltage supply for supplying

diallers, can 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 pre-

vent noise entering the line, a series

resistor and a reservoir capaciotor is

recommended in for this output.The output

current given in the specification is 2 mA..

VDD

CMOS

DIALLER

MUTE

DTMF

GND

123

45 6

789

*0 #

R18

4-8M

1

R1

200Ω

C8

1µF 9

MIC.

AM

1µF 10

+

R2

C9

200Ω

DC-supply

7

65

8

PBL 385 73

AT

AR

3

2

12

11

R17

100Ω

+ C7

47µF

R16

C4

+

100µF

R12

1k

R4

18k

R15

R5

22k

C3

100nF

R7

910Ω

R6

75Ω

C5

100nF

R11

6.2k

R8

560Ω

R9

11k

C6

47nF

R10

62k

R13

11k

13

14

+4

R3

910Ω

+ C1

47µF

Hook

switch

1N4007

1N4007

15V

C2

15nF

1N4007

1N4007

Telephone

line

R14

10Ω

Figure 19. Typical standard DTMF dialling telephone application.

11

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