KX-TDA0103X, KX-TDA0103XJ, KX-TDA0104X, KX-TDA0104XJ, ETX1KM753MB, ETX1KM752MB - Panasonic PBX Service Manual (repair manual). Page 10

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This section converts the high DC voltage in the primary side to DC low voltage (41V) at the secondary side

1. Isolation switching transformer.

T001: provide isolation of the hazardous high voltage Primary to the SELV secondary.

2. Main switching MOSFET

Q003, Q006 : Main switching MOSFETs 

3. Main switch control circuit

Provide the switching PWM control to ensure regulated DC 41V output
IC001 : PWM IC
PC004 : photocoupler provides feedback from secondary side to primary side.
Peripheral circuit provides control and bias voltage for PWM Vcc and PFC IC Vcc
TS001 : shut down the PWM during abnormal over heating on the Primary side
PC002 : shutdown the PWM during abnormal output voltages and over current of 15V
PC003 : shutdown the PWM when the Battery reverse connection is detected.

4. Convertor 41V Output circuit

Convert the switching DC voltage to regulated DC voltage
D104, D105 : Rectifies the switched transformer secondary to DC voltage
C107, C112 : DC output smoothing capacitors
C115, L109 : Ripple filter components