KX-TDE6101RU - Panasonic PBX Service Manual (repair manual). Page 14

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• POWER block (BLOCK 13)

This consists of DC/DC converter circuit and various regulators.
Configuration:
IC1901 ( 3.3V, 2.5V DC/DC converter ), IC1902 ( 1.25 DC/DC converter ), IC1908 (1.8V regulator), IC1907 (1.2V regulator),
IC1903 (Comparator), Q1901, Q1902, Q1903 (FET, transistor), B1901, IP1901 (circuit protection device) and so on.
Function:
+15V_CON input is stepped down to +3.3VD and +2.5VD by DC/DC converter circuit which consists of IC1901, Q1901 and
Q1902 and is supplied to each IC power. 
Q1901 and Q1902 and is supplied to each IC power. 
+3.3VD is generated by the DC/DC converter is converted to +1.25VD and supplied to IC101 core power.
+2.5VD is generated by the DC/DC converter is converted to +1.8VD and supplied to IC1101 core power.
+2.5VD is generated by the DC/DC converter is converted to +1.2VD and supplied to IC801 core power.
BAT1901, which is a lithium battery for backup, is connected to the power supply of IC1301 (SRAM) and IC802 (RTC) via D1904,
D1905.
IC1903 compares B1901 output voltage to the reference voltage (about +2.7V) and drives LED (BATT ALARM) that indicates
dropping of backup voltage.

• TDA600_CON block (BLOCK 14)

This provides the control interface between IPCEMPR Card and BUS-M Card.
Configuration: CN2001 (Connector for BUS-M ),IC2001-IC2001(buffer) and so on.
Function:
Control interface between IPCEMPR Card and BUS-M Card.

• SVM_VOX block (BLOCK 15)

It is VOX detection circuit.
Configuration: IC2201, IC2202 (CODEC), IC2203, IC2204 (OP Amp), IC2205, IC2206 (Comparator) and so on.
Function:
The SVM voice data are made D/A conversion in IC2201, IC2202 amd IC804 (SVM DSP). After these are amplified with the
amplifier, the sound is detected with the comparator.