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6.2. THE LINE INTERFACE SECTION
6.2.1. INTRODUCTION
This section consists of the telephone line interface, bell detector, hookswitch, pulse dialing circuits, audio circuits, DC mask & line
impedance circuits, power supplies, and battery charger circuits.
impedance circuits, power supplies, and battery charger circuits.
6.2.2. TELEPHONE LINE INTERFACE (SEE Fig. 21)
The telephone line is connected (via 2 or 3 jumpers selected for country of destination) to a bridge rectifier D8. Surge suppressor
SA3 protects against excessive line voltages. Test points are TP14 (A), TP13 (B). Bridge rectifier D8 provides for lines of either
polarity. The output of D8 is “Line +” (TP50) and “Line -” which is ground.
SA3 protects against excessive line voltages. Test points are TP14 (A), TP13 (B). Bridge rectifier D8 provides for lines of either
polarity. The output of D8 is “Line +” (TP50) and “Line -” which is ground.
6.2.3. BELL DETECTOR (SEE Fig. 21)
The AC ringing signal is detected by optocoupler IC2, using its internal diode in conjunction with D4. DC from the line is blocked
by C2. The other components D2, D3, and R3 reduce current and increase the circuit impedance in line with national requirements.
When ringing is detected IC2 will turn on, and the RING line (TP76) will be dragged to a low voltage.
by C2. The other components D2, D3, and R3 reduce current and increase the circuit impedance in line with national requirements.
When ringing is detected IC2 will turn on, and the RING line (TP76) will be dragged to a low voltage.
Circuit Diagram
Fig. 21
6.2.4. CLIP CIRCUITS (SEE Fig. 21)
The caller ID signal is detected by IC4.
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KX-TCD958RUC
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