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45

KX-FC268RU-T

This power supply board uses the switching regulator method.

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.

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.

Bias is applied to the Q101 gate via this circuit when the AC power is turned on and Q101 begins operating.

A-B Voltage Wave Form

C-D Voltage Wave Form

E-F

G-H Voltage Wave Form

0

0

0

Input
Circuit

AC
Input

Surge
Absorber
Circuit

G

H

4V

24V

E

IC101

D110

R104

F

9~6V

GND

Control
Circuit

Kick-on
Voltage
Circuit

Converter
Circuit

C

D

4V
Output
Circuit

24V
Output
Circuit

+

-

Rectifier
Circuit

A

B

C106

Error Detecting
Circuit

Surge
Absorber
Circuit

Q101

46

KX-FC268RU-T

The following is an overview of how the power supply unit is controlled. 
The control method of this power supply unit is pulse width modulation.

When Q

1

 is ON, the energy is charged in the transfer primary coil according to E

1

. When Q

1

 is OFF, the energy is output from

the secondary transfer as follows.
    L 

→ D

1

 

→ Load → L

Then the power is supplied to the Load. When Q

1

 is ON, power is not output from the secondary side. The output voltage is fed

back in the control IC according to the error amp rectifier. Then depending on how T

ON

 is controlled, stabilization occurs. Also,

when the current load becomes too large, in order to decrease the voltage output, the increase in 

 is controlled and the output

voltage is stabilized.
Therefore, basically the timing: Ton/Toff of Q1 controls the output voltage.

47

KX-FC268RU-T

This circuit is for absorbing surge voltage generated by the transformer.

The control circuit amplifies the output with increased voltage detected in the error detecting circuit. Then it drives the main tran-
sistor.
In this power supply, the duty ratio is defined by changing the ON period of the main transistor.
This is shown as follows.
When the output voltage of the 24V circuit increases, the current of the photo coupler PC101 increases, the pulse width of the
output control IC becomes narrower and the ON period of Q101 becomes shorter.

The highest drain current (Q101) is limited by a limiter circuit (IC101) of 24V. The 24V output is limited by this circuit.

If the 24V output increases because the error detecting circuit or control circuit is broken, IC101 will recognize this signal and
output becomes 0V.

Refer to Power Supply Board Section (P.129).

48

KX-FC268RU-T

SPEAKER

RECEIVER

MIC

CHARGE

CIRCUIT

Q4, Q9, R7

CHARGE

CONTACTS

CHARGE(+)

CHARGE(-)

CHARGE_CTRL

CHARGE

EEPROM

SCL

SDA

BATTERY

TERMINAL

D7

VBAT

J1

J2

1.8 V

Q2

1.8 V

LCD

CD

RESET

CSB

SDA

 SCL

CPU

Analog

Front

End

D/A

A/D

33

35

15

16

19

20

32

31

57

58

 36

13

43

42

63

54

55

66

ADPCM

Codec

Filter

DSP

Speech

Decoding

Speech

Encoding

BMC

Burst

Decoding

RF PA

ANT1

Burst

Encoding

RF

PLL

MOD/DEMOD

5

3

4

3

6

7

8

9

2

77

78

75

RXn

RXon

ANT1

DA801

RXp

TXp

TXn

Pon

PSEL

TXon

VDD-PADRY

9

10

XTAL

X1

10.368

MHz

BATTERY

44

ON SWITCH

KEYPAD

Charge

Pump

ROWS

COLUMNS

CP3.0 V

CP4.0 V

48, 49, 50, 51

22, 23, 24, 25, 26

BBIC

 56

LCD-BACK  LIGHT

KEY   LED

BELL  LED

52

68

73

74

80

LDO_CTRL

KX-FC268RU-T: CORDLESS HANDSET BLOCK DIAGRAM