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13

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 con-
stant. The switching frequency of Q1 is approximately 100KHz (70KHz~160KHz).
2) DC-DC Inverter Function
The DC27V as input is converted into a rectangular wave by the switching transistor Q201, then isolated and transduced by T2.
DC+15V, -15V and 3.3V are outputted by a rectification smoothing circuit composed of D401, D301, D701, C401, C301 and C702.
The +3.3V of the three outputs is PWM-controlled by IC201 to keep constant.The switching frequency of the Q2 is approx. 55 KHz.
3) Ringing signal output function
Ringing signal (20/25Hz, 75Vac from main board) is amplified in power by power amplifier circuits (including of IC501, R601~R608,
C601~C603).
Ringing signal amplified in power is transmitted to the ringing transformer through pin 4 of CN601.
4) AC Power Failure Detection
AC power failure is detected by D31~D32, R33~R41, C31, PC31.
When AC power is on, PC31 is on.
When AC power is turned off, PC31 is off.
5) 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 type. 0.4A.

AC-DC Inverter Function

This function isolates and transduces the AC input voltage to DC input and output 

of DC27V.

DC-DC Converter Function

This function outputs DC+15V, -15V and 3.3V from the inputted DC27V.

Ringing Signal Output Function

Based on the 20/25Hz sine wave signal output from KX-TES824/KX-TEM824,
this function generates ringing and supplies to the system.

AC Power Failure Detection

This function detects any cut off of the AC power supply and outputs an AC alarm
signal to the CPU.

Battery Back Up Adaptor Function

This  function  connects battery and service unit without battery adaptor, only
needs a cable connected to the battery and service unit.

14

1) Bell signal detection
2) DC loop formation circuit
3) Pulse dial transmission circuit 
4) CALL ID interface circuit 
5) COL bidirectional amplifier circuit 

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 → T2 → R5 → L1 → Ring: This cause pin4 of PC1 to change the level from High to low.

Ring 

→ L1 → R5 → T2 → C3 → PC2(1-2) → R2 → L1 → Tip: This cause pin4 of PC2 to change the level from High to low.

15

In the off hook status, PC5 is ON.
DC loop path:
Tip

→L1→D1→D2→D3→Q10(E-C)→Q1(C-E)→R9→R8→D3→L1→Ring

At this time, the output of the photo coupler PC1 changes level from High to low.
Ring

→L1→D3→R8→R9→Q1(E-C)→Q10(C-E)→D3→D2→D1→L1→Tip

At this time, the output of the photo coupler PC2 changes level from High to low.
Afterwards, G/A monitor this change (low level to high level). If the high level continues for a specified time set by system data
programming. G/A assumes that CO line has become On hook status. And the CO line circuits is restored to the idle status.

When the Off hook status, pulse dial transmission is executed by alternating On hook and Off hook. The status of On hook or Off
hook is controlled by the switching transistor Q10. 

  It is insulated by the transformer in a COL circuit, and the call ID signal inputted from outside line is transmitted to a CALLID
option card.
The flow of a CALLID signal 
Tip

→L1→R2→PC1(1-2)→C3→T2→R5→L1→Ring

Ring

→L1→R5→T2→C3→PC2(1-2)→R2→L1→Tip

16

This circuit consists of bidirectional amplifier function for communication between the extensions and COL, returns loss com-
pensation for conference, shunt function and mute function.
(Composition)
For transmitting signals from the extensions to COL, this circuit consists of R34, R35, R26, R27, R18, R29, C14, C15, C10, C16
and the operational amplifier (IC1).
For transmitting signals from the COL to extensions, this circuit consists of R24, R25, R31, R28, R37, R30, C12, C13, C17, C18,
and the operational amplifier (IC1).
COL side-tone suppression circuit which includes a balanced network BN1 consists of R22 R23, C11 and R16, R17, R20, R21.
EXT side-tone suppression circuit which includes a balanced network BN2 consists of R41, R42 and R40, R43, R38, R39.
Also extension side-tone suppression circuit which includes a balanced network BN3 consists of R45, R46 for supplementing
side-tone suppression during the conference communication.
The analog switch (IC2) is used for the following:
(1) Conference (Pin 6, 8 and 9)
(2) Shunt (Pin 12, 10 and 11)
(3) Mute (Pin 13, 1 and 2)