Panasonic KX-TDA0103XJ Service Manual page 48

KX-TDA0103XJ / KX-TDA0104XJ / KX-TDA0108XJ / KX-TDA0103X / KX-TDA0104X / KX-TDA0108X
8.3.1.2. Main Converter
This section mainly explains about the operation of main converter circuit which converts PFC output voltage to 41V (TYP.)
output and also about the latch circuit and discharge circuit.
1) Switching Circuit
This circuit uses Self-excited Pseudo Resonance Type Converter.This system supplies DC voltage through the following
process: The DC voltage provided from the Rectifier and Smoothing Circuit is converted into RF pulse by switching ON/OFF
MOS FET Q601 repeatedly. While Q601 is switched ON, the energy is charged in the primary of T601, and it will be discharged
to the secondary of T601 while Q601 is OFF.
Sub switch Q620 turns ON while Q601 is OFF. The pseudo resonance circuit consisting of film capacitor C620 and main
winding of transformer T601 prevents surge voltage from occurring between drain and source while Q601 is OFF. Constant
voltage is controlled by giving feedback to the control circuit from the output through photo coupler PC601. The main switch
Q601 is controlled by the circuit centering on transistor Q602. The sub switch Q620 is controlled by the circuit centering on
transistor Q622.
Refer to Fig.2 (A), (B), (C), (D).
2) Main Converter Output Circuit
T601 output voltage is rectified by D652, D659 and smoothed by capacitors C651, C401, C402 and C403. And then it is
controlled by three-terminal voltage regulator IC651 to get the constant output voltage as the main converter output (41V TYP.).
Refer to Fig. 2 (G)
3) Latch Circuit
When secondary side protection circuit (Refer to Protection Circuit (P.59)) works at abnormal state, the signal is sent to
primary side through PC4. Then the main converter latch circuit works to stop switching operation of Q601. Consequently the
main converter operation is stopped. The latch circuit of main converter consists of thyristors Q603 and Q604.
Refer to Fig. 2 (E)
4) Discharge Circuit
In case that the unit is turned ON after the latch circuit worked at abnormal condition, it is impossible to boot the unit unless the
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