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11.1.2. Control Section
1) AC-DC Inverter Function
The AC input voltage is rectified and smoothed by D10-13 and C5. The obtained DC voltage is converted into a rectangular wave
by the switching transistor Q1, then isolated and transduced by T1. This converted rectangular wave is rectified and smoothed by
D101 and C101 to output DC27V. The DC27V is transmitted to the primary side by PC1 and then PWM- controlled to keep
constant. The switching frequency of Q1 is approximately 60KHz.
2) DC-DC Inverter Function
The DC 27V DC is converted into a rectangular wave by control IC201, and then output as an output voltage of +15V by the
smoothing circuit which is composed of D201, L201, C201.
The 27V DC is converted into rectangular wave by control IC301 and then output as an output voltage of +3.3V by the smoothing
circuit which is composed of D301, L301, C301.
3) Battery back up function
This back up battery adaptor circuit has DC supply function, from battery (+24V) to service unit and DC charge from service unit
to battery (+24V). Charge current is typ. 0.3A.
11.2. CO INTERFACE CIRCUIT
11.2.1. Composition
This is composed of the following circuit:
1) Bell signal detection
2) DC loop formation circuit
3) Pulse dial transmission circuit
4) CALL ID interface circuit
5) COL bidirectional amplifier circuit
1) Bell signal detection
When CO line is idle, photo coupler PC1, PC2 are OFF.
When there is an incoming signal from CO line, the current flows PC1 as in the following way.
Tip → L1 → R2 → PC1(1-2) → C3 → R5 → L1 → Ring: This cause pin4 of PC1 to change the level from High to low.
Ring → L1 → R5 → C3 → PC2(1-2) → R2 → L1 → Tip: This cause pin4 of PC2 to change the level from High to low.
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KX-TEA308CE
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