Panasonic KX-FT21RS - Manual (Page 137)

6.12. POWER SUPPLY BOARD SECTION
This power supply board uses the switching regulator method.
[Input Circuit]
The input current goes into the input rectifier circuit through the filter circuit. The filter circuit decreases the noise voltage and the
noise electric field strength.
[Rectifier Circuit]
The input current is rectified by D101,D102,D103 and D104 and charges C106 to make DC voltage. Then it supplies power to the
converter circuit.
[Kick-on voltage circuit]
Bias is applied to the Q101 gate via this circuit when the AC power is turned on and Q101 begins operating.
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KX-FT21RS